1 00:00:09,390 --> 00:00:12,810 Michael Büker: Yes, alright, thank you very much, okay. I’m glad 2 00:00:12,810 --> 00:00:16,510 that you all found your way here and it’s been mentioned already, 3 00:00:16,510 --> 00:00:19,920 this is Comic Sans, which as you know is the official type-font 4 00:00:19,920 --> 00:00:23,930 of awesome particle physics stuff. *laughter* 5 00:00:23,930 --> 00:00:27,990 But in the interest of our mental sanity, I will keep it to other fonts. 6 00:00:27,990 --> 00:00:32,500 So from here on Comic Sans is just a bad memory. 7 00:00:32,500 --> 00:00:36,100 Okay, two things: First the title, Breaking Baryons, 8 00:00:36,100 --> 00:00:39,100 which of course is an allusion to Breaking Bad, was inspired 9 00:00:39,100 --> 00:00:44,520 by the wonderful talk from last year which was called “How I Met Your Pointer”. 10 00:00:44,520 --> 00:00:48,150 And which was also very successful and you can check out that talk, 11 00:00:48,150 --> 00:00:51,919 I got the link there. And this talk goes especially well 12 00:00:51,919 --> 00:00:56,090 with another talk that we’ll have tomorrow by a real particle physicist, 13 00:00:56,090 --> 00:00:58,720 at least a bit more than myself. 14 00:00:58,720 --> 00:01:02,460 And it’s called “Desperately Seeking SUSY” which is about particle theories 15 00:01:02,460 --> 00:01:05,959 and the real cutting edge physical questions. This is going to be 16 00:01:05,959 --> 00:01:09,950 happening tomorrow. Allright, so we’re going to start out with my talk 17 00:01:09,950 --> 00:01:14,510 and I’m going to be talking about the questions of “what are we doing?”, 18 00:01:14,510 --> 00:01:18,330 “why?” and “what kind of stuff do we use?”. And I’m gonna spend some time 19 00:01:18,330 --> 00:01:22,190 on explaining this last part especially. What is it that we do 20 00:01:22,190 --> 00:01:27,780 and how does this work? So, what we do is we give a very high energy 21 00:01:27,780 --> 00:01:32,020 to small particles which we call accelerating. 22 00:01:32,020 --> 00:01:36,520 But from a certain level of energy this doesn’t really make sense, 23 00:01:36,520 --> 00:01:40,710 because we don’t actually make them go faster. Once they reach the speed of light 24 00:01:40,710 --> 00:01:43,930 they can’t go any faster. We just turn up the energy and the speed 25 00:01:43,930 --> 00:01:48,140 doesn’t really change. This is technically useful but it also gives rise 26 00:01:48,140 --> 00:01:53,520 to doubts about the term accelerating, but anyway, we just call it ‘accelerate’. 27 00:01:53,520 --> 00:01:56,710 There’s 2 basic types of devices that you see there, you have storage rings, 28 00:01:56,710 --> 00:02:00,450 which are the circular facilities that most of you know. And then there is 29 00:02:00,450 --> 00:02:03,270 linear accelerators which are in comparison very boring, so I’m 30 00:02:03,270 --> 00:02:07,720 not going to be talking about them a lot. We make the particles collide 31 00:02:07,720 --> 00:02:11,370 which is the reason for giving them high energies, we want them to smash head-on. 32 00:02:11,370 --> 00:02:14,950 And then this last part which is about the most difficult thing is we just 33 00:02:14,950 --> 00:02:19,680 see what happens. Which is not at all as easy as it might sound. 34 00:02:19,680 --> 00:02:23,520 So why are we doing this? You all know this formula but I’m going to try 35 00:02:23,520 --> 00:02:26,690 and put it in terms which are a little bit closer to our hearts, 36 00:02:26,690 --> 00:02:30,570 as we are here at Congress. I might postulate that 37 00:02:30,570 --> 00:02:35,760 parts, like electrical parts, building parts, are actually the same as a device. 38 00:02:35,760 --> 00:02:39,200 Now this is not quite wrong but it doesn’t feel exactly right, either. 39 00:02:39,200 --> 00:02:44,040 I mean, if you have some parts and then build a device from it, it’s not the same. 40 00:02:44,040 --> 00:02:49,220 It’s made from the same thing but you do require a certain amount of conversion. 41 00:02:49,220 --> 00:02:53,039 You have a building process, you have specific rules how you can assemble 42 00:02:53,039 --> 00:02:56,940 the parts to make a device and if you do it wrong it will not work. 43 00:02:56,940 --> 00:03:01,400 And this is actually pretty similar to the notion of energy being equivalent to mass, 44 00:03:01,400 --> 00:03:04,970 because energy can be converted into mass but it’s not at all easy and it follows 45 00:03:04,970 --> 00:03:08,910 a lot of very strict rules. But we can use this principle 46 00:03:08,910 --> 00:03:12,749 when we analyze how particle reactions are used to take a look at 47 00:03:12,749 --> 00:03:17,900 what mass and what energy forms there are. Now suppose we are 48 00:03:17,900 --> 00:03:21,840 thinking about a device which is very, very rare, 49 00:03:21,840 --> 00:03:26,640 such as a toaster that runs Net-BSD. *laughter* 50 00:03:26,640 --> 00:03:29,980 Now as you can see from the photo and the fact that you see a photo, 51 00:03:29,980 --> 00:03:33,520 I’m not making this shit up. There is a toaster that runs Net-BSD but 52 00:03:33,520 --> 00:03:37,100 that’s beside the point. Now if we are particle physicists and we want 53 00:03:37,100 --> 00:03:41,320 to research this question, we know that parts are the same as a device, 54 00:03:41,320 --> 00:03:45,630 so if we just get enough parts and do the right kind of things to them, 55 00:03:45,630 --> 00:03:49,340 there might just turn out, out of nowhere a toaster that runs Net BSD. 56 00:03:49,340 --> 00:03:54,580 So let’s give it a try. We produce collisions with technical parts 57 00:03:54,580 --> 00:03:58,790 and if we do enough of it, and if we do it right, then there is going to be 58 00:03:58,790 --> 00:04:02,520 this result. Now from these pictures you can see, that doesn’t seem 59 00:04:02,520 --> 00:04:07,250 to make a lot of sense. You will not get a toaster from colliding vehicles. 60 00:04:07,250 --> 00:04:10,590 *laughter* But as particle physics go, 61 00:04:10,590 --> 00:04:14,159 this is the best we can do. We just smash stuff into each other 62 00:04:14,159 --> 00:04:17,750 and we hope that some other stuff comes out which is more interesting. 63 00:04:17,750 --> 00:04:22,600 And that’s what we do. So to put it in the technical terms, 64 00:04:22,600 --> 00:04:26,569 we use storage rings which are this one circular kind of accelerator 65 00:04:26,569 --> 00:04:30,520 to produce collisions. Lots of them with high energy. 66 00:04:30,520 --> 00:04:34,879 And then we put some enormous experimental devices there 67 00:04:34,879 --> 00:04:38,480 and we use them to analyze what happens. Now first let’s talk about 68 00:04:38,480 --> 00:04:43,029 these storage rings. This schematic view is what a storage ring is 69 00:04:43,029 --> 00:04:47,009 mostly made of, and you can see right away, that it’s not actually a circle. 70 00:04:47,009 --> 00:04:50,279 And this is true for any storage ring. If you look at them closely they are 71 00:04:50,279 --> 00:04:54,229 not a perfect circle, you always have acceleration parts which are 72 00:04:54,229 --> 00:04:58,219 not actually curved. So we have the 2 basic elements 73 00:04:58,219 --> 00:05:02,270 of a curved part which is just “the curve” and then you have a straight part 74 00:05:02,270 --> 00:05:06,539 which is there for acceleration. Now you have this separation, it would be nicer 75 00:05:06,539 --> 00:05:11,009 to have a ring but it’s much more easy this way. You have the acceleration 76 00:05:11,009 --> 00:05:13,789 where it is straight and because it is straight you don’t need to worry about 77 00:05:13,789 --> 00:05:18,060 making the particles go on a curved path. So you can just leave out 78 00:05:18,060 --> 00:05:22,509 the magnetic fields. We need magnetic fields 79 00:05:22,509 --> 00:05:26,669 to keep them on a curve, but we need electrical fields to accelerate them. 80 00:05:26,669 --> 00:05:30,469 Now we could try and assemble these into one kind of device. A device 81 00:05:30,469 --> 00:05:34,409 that uses an electric field to accelerate the particles and at the same time 82 00:05:34,409 --> 00:05:38,040 uses a magnetic field to keep them on a curved path. Now this is the first thing 83 00:05:38,040 --> 00:05:41,280 that was tried. These kinds of accelerators where called cyclotrons, 84 00:05:41,280 --> 00:05:43,710 but they were very inefficient, you couldn’t go to high energies, it was 85 00:05:43,710 --> 00:05:47,839 very difficult. So the evolution went to 86 00:05:47,839 --> 00:05:51,440 this way where you just physically separate the 2 tasks. 87 00:05:51,440 --> 00:05:54,990 You have a straight part for acceleration, you have a curved part for the curve 88 00:05:54,990 --> 00:05:57,890 and then that’s much more easy. Okay, so let’s take a look at the 89 00:05:57,890 --> 00:06:01,260 acceleration part of things. You may know computer games 90 00:06:01,260 --> 00:06:05,339 where you go racing about and then you have some kind of arrows 91 00:06:05,339 --> 00:06:08,559 on the ground and if you go over them in the right direction they make you faster. 92 00:06:08,559 --> 00:06:12,270 This is a kind of booster if you will. 93 00:06:12,270 --> 00:06:16,229 If you happen to go around the wrong way and you go onto these arrows, 94 00:06:16,229 --> 00:06:19,599 they will slow you down, which makes sense because you’re going the wrong way, 95 00:06:19,599 --> 00:06:23,670 you shouldn’t be trying that. And this is 96 00:06:23,670 --> 00:06:27,629 the same effect we can think of when we think about what an electrical field does 97 00:06:27,629 --> 00:06:31,589 to a charged particle. If a charged particle moves through an electrical field 98 00:06:31,589 --> 00:06:36,080 in the ‘right’ direction so to speak it will speed the particle up, 99 00:06:36,080 --> 00:06:38,889 taking energy from the field and to the particle making it go faster. But if you 100 00:06:38,889 --> 00:06:42,430 go the wrong way, then this particle will slow down and it will 101 00:06:42,430 --> 00:06:48,170 give off energy. If we where to try and… 102 00:06:48,170 --> 00:06:51,610 let’s say we have a level editor, right? And we can edit this level 103 00:06:51,610 --> 00:06:55,610 where this little vehicle is going and we want to make it go really fast. 104 00:06:55,610 --> 00:06:58,060 So what do we do? We just take this acceleration path, we just take 105 00:06:58,060 --> 00:07:02,449 these arrows and we put them in a long line. Let’s put 4, 5, 10 of them 106 00:07:02,449 --> 00:07:06,159 in a row, so if we go over them we’ll be really fast at the end. 107 00:07:06,159 --> 00:07:09,280 Now suppose the level editor does not allow this. It’s just 108 00:07:09,280 --> 00:07:12,800 by the rules of the game it’s not possible to put a bunch of arrows in a row. 109 00:07:12,800 --> 00:07:17,659 Which sucks, because then we can’t really make them go really fast. 110 00:07:17,659 --> 00:07:22,349 But then we just ask an engineer who’s got this shit together. 111 00:07:22,349 --> 00:07:25,919 And what is he going to suggest? You know what he’s going to suggest. 112 00:07:25,919 --> 00:07:30,239 Can I hear it? Come on, “inverse the polarity”, that’s what he always does! 113 00:07:30,239 --> 00:07:39,050 *laughter and applause* 114 00:07:39,050 --> 00:07:43,420 So we inverse the polarity. And we are going to make our track look like this. 115 00:07:43,420 --> 00:07:46,599 So we have an arrow which gives us a boost in the right direction and then there’s 116 00:07:46,599 --> 00:07:50,260 an arrow in the wrong direction. If we go over the track in this way, 117 00:07:50,260 --> 00:07:54,180 we’ll speed up and slow down and speed up and slow down. And in the end 118 00:07:54,180 --> 00:07:57,530 we won’t win anything. But here is where Geordi comes into play, because 119 00:07:57,530 --> 00:08:01,729 we’ll be switching polarities at just the right moment and if we switch polarities 120 00:08:01,729 --> 00:08:05,319 at the precise moment that we are in between two of these fields, 121 00:08:05,319 --> 00:08:09,069 then the next one will be an accelerating field. And it goes on and on like this, 122 00:08:09,069 --> 00:08:12,270 we always switch the direction of the arrows at the right moment 123 00:08:12,270 --> 00:08:16,429 when we are in between the two. And from the point of view of the vehicle 124 00:08:16,429 --> 00:08:19,849 it will look like there is an accelerating field followed by an accelerating field, 125 00:08:19,849 --> 00:08:23,720 followed by an accelerating field. Which is the same as we tried to build 126 00:08:23,720 --> 00:08:27,069 but which the game, or in the case of real accelerators the universe 127 00:08:27,069 --> 00:08:30,899 just wouldn’t allow. So we’re tricking the universe by using Geordi’s tip 128 00:08:30,899 --> 00:08:34,720 and inversing the polarity at just the right moments. And this is what is done 129 00:08:34,720 --> 00:08:41,580 in particle accelerators and this is called Radio Frequency Acceleration. 130 00:08:41,580 --> 00:08:44,450 Now this kind of device that you see there is the device that is used 131 00:08:44,450 --> 00:08:48,329 for this actual process in actual accelerators. It’s about as big 132 00:08:48,329 --> 00:08:51,670 as a human child, but it weighs a bit more, it weighs 133 00:08:51,670 --> 00:08:55,810 several hundred kilograms. And in contrast to a child 134 00:08:55,810 --> 00:08:59,779 it’s made of a metal called Niobium. Now Niobium is a rare metal, 135 00:08:59,779 --> 00:09:03,410 but it’s not super rare, and it fulfills 136 00:09:03,410 --> 00:09:06,779 3 basic requirements that we have for these devices. 137 00:09:06,779 --> 00:09:10,480 It’s ductile, which means you can easily shape it, because you see 138 00:09:10,480 --> 00:09:14,170 that this shape is really weird, you got these kind of cone things going on, 139 00:09:14,170 --> 00:09:19,670 and they must be very precise. If these cones on the inside of the cavity 140 00:09:19,670 --> 00:09:25,130 are off by just micrometers the whole thing won’t work. So you need a metal 141 00:09:25,130 --> 00:09:28,389 which can be formed very well. 142 00:09:28,389 --> 00:09:31,970 Then you must be able to make it superconductive, to cool it down 143 00:09:31,970 --> 00:09:35,770 to a temperature where it will lose its electrical resistance. 144 00:09:35,770 --> 00:09:39,029 The electrical resistance will go down to almost zero, some nano-Ohms 145 00:09:39,029 --> 00:09:43,169 is what’s left. So that’s the second requirement for this metal, 146 00:09:43,169 --> 00:09:46,220 and the third one is: it shouldn’t be ‘super’ expensive. I guess 147 00:09:46,220 --> 00:09:50,480 you could use platinum or something but then you couldn’t pay for the accelerator 148 00:09:50,480 --> 00:09:54,779 and as we are going to see, the accelerator is expensive enough as it is. 149 00:09:54,779 --> 00:09:58,060 So Niobium is what is used for this kind of device and 150 00:09:58,060 --> 00:10:04,690 as I said, we cool it down to about 4 Kelvins, which is -269°C 151 00:10:04,690 --> 00:10:09,589 or 4°C above absolute Zero. And at this temperature, 152 00:10:09,589 --> 00:10:12,670 the electrical resistance of the metal is almost zero which we need 153 00:10:12,670 --> 00:10:16,569 for the high frequency fields that we put in. 154 00:10:16,569 --> 00:10:19,949 What we used to cool these things is liquid helium, so when they’re in use 155 00:10:19,949 --> 00:10:23,580 inside the accelerator they’re not naked, exposed like you see here, 156 00:10:23,580 --> 00:10:27,300 they are enclosed by huge tanks which are super tight and must 157 00:10:27,300 --> 00:10:31,890 hold on to large pressures and be super temperature efficient, 158 00:10:31,890 --> 00:10:36,190 very well insulating because these must keep 159 00:10:36,190 --> 00:10:39,839 the liquid helium inside. But on the outside there is the tunnel 160 00:10:39,839 --> 00:10:43,510 of the accelerator and that’s where people walk around. Not while the accelerator is 161 00:10:43,510 --> 00:10:46,750 running, but people walk around to do maintenance and stuff. So you must have 162 00:10:46,750 --> 00:10:51,060 a temperature differential between room temperature next to the accelerator 163 00:10:51,060 --> 00:10:55,779 and 4 Kelvin inside the tank where this cavity is sitting. 164 00:10:55,779 --> 00:10:59,300 So you have a temperature difference of 300 degrees, which this tank 165 00:10:59,300 --> 00:11:02,540 around the cavity must keep. So that’s a very hard job, actually cooling 166 00:11:02,540 --> 00:11:07,360 is one of the more difficult things 167 00:11:07,360 --> 00:11:11,640 from an engineering point of view. The thing which feeds the fields 168 00:11:11,640 --> 00:11:16,089 – the actual changing electrical fields are polarity switched – 169 00:11:16,089 --> 00:11:19,660 into these cavities are called klystrons. There’s a picture of a klystron, 170 00:11:19,660 --> 00:11:23,890 it’s the longish device sitting on the bottom. And they’re usually about 171 00:11:23,890 --> 00:11:28,749 as big as a refrigerator or two. And these klystrons produce 172 00:11:28,749 --> 00:11:31,990 radio waves not very much unlike that 173 00:11:31,990 --> 00:11:35,440 which you hear in your car when you just turn on the radio. It’s not modulated 174 00:11:35,440 --> 00:11:38,730 in the same way, so there’s no sound information encoded, 175 00:11:38,730 --> 00:11:42,290 but it’s extremely strong. You can see on the bottom 176 00:11:42,290 --> 00:11:46,290 that one of these klystrons as it is in use at the LHC has a transmitting power 177 00:11:46,290 --> 00:11:51,680 of 300 Kilowatts. Now if you think of the transmitting power of the Fernsehturm 178 00:11:51,680 --> 00:11:54,860 like the Hertz-Turm which is right next - no, that way - 179 00:11:54,860 --> 00:11:59,070 which is right next to the conference center, or even the Fernsehturm in Berlin. 180 00:11:59,070 --> 00:12:02,899 It has about half the transmitting power of one of these klystrons. 181 00:12:02,899 --> 00:12:06,389 Now for the LHC accelerator 16 of them are used. 182 00:12:06,389 --> 00:12:09,490 So that’s a lot of transmitting power. And because the power is so high 183 00:12:09,490 --> 00:12:13,110 we don’t actually use cables. Usually you transfer your… 184 00:12:13,110 --> 00:12:15,629 when you have some oscillator and you’re checking out some signals, 185 00:12:15,629 --> 00:12:18,560 you just put cables between your source and your device. 186 00:12:18,560 --> 00:12:22,620 This is not what’s used here, because cables get way too complicated 187 00:12:22,620 --> 00:12:26,240 when you have these high energies. 188 00:12:26,240 --> 00:12:28,750 So what is used, is waveguides and that is what you can see on the top there 189 00:12:28,750 --> 00:12:32,590 in this picture. It looks like an air duct, it looks like there’s some 190 00:12:32,590 --> 00:12:36,089 sort of air conditioning system and the air moves through. That’s not what it is. 191 00:12:36,089 --> 00:12:39,800 It is a waveguide which is designed to have the radio waves inside 192 00:12:39,800 --> 00:12:44,510 radiate in a certain direction. Think of a series of mirrors, 193 00:12:44,510 --> 00:12:50,620 long rectangular mirrors and you put them all with the mirroring area inside. 194 00:12:50,620 --> 00:12:54,119 So you have a tube which is mirroring inside. And then at one side 195 00:12:54,119 --> 00:12:57,090 you shine in a bright light. Now the light can’t escape anywhere and it 196 00:12:57,090 --> 00:13:00,089 always hits the mirrors so it goes on in a straight path. 197 00:13:00,089 --> 00:13:04,010 You’ve built yourself a waveguide for light. Now this here, 198 00:13:04,010 --> 00:13:07,220 this clunky looking metal part is a waveguide 199 00:13:07,220 --> 00:13:12,110 but for high frequency, high energy radio waves which are fed into the cavities. 200 00:13:12,110 --> 00:13:16,040 And that’s how acceleration happens. Now let’s talk about the curves. 201 00:13:16,040 --> 00:13:21,490 This is where it gets less fidgety and more… boom! 202 00:13:21,490 --> 00:13:24,639 So these devices you see here, there’s 2 devices sitting next to each other, 203 00:13:24,639 --> 00:13:27,689 identical devices. These are the cryo-dipoles. 204 00:13:27,689 --> 00:13:30,290 Again, they have the word “cryo” in them because they are also cooled 205 00:13:30,290 --> 00:13:36,450 by liquid helium down to a temperature of about -270°C. 206 00:13:36,450 --> 00:13:40,129 They’re 40 meters long, they weigh 35 tons and each of these babies 207 00:13:40,129 --> 00:13:44,750 costs about half a million Swiss Francs. 208 00:13:44,750 --> 00:13:49,670 And as you can see one line above that, there’s 1200 of these curve dipoles 209 00:13:49,670 --> 00:13:54,719 in the LHC. So there you have a cost of 1.5 to 2 billion dollars 210 00:13:54,719 --> 00:13:57,850 in the curve magnets alone. We’re not talking acceleration, 211 00:13:57,850 --> 00:14:01,589 we’re not talking about power use, we are not talking about the helium that you need 212 00:14:01,589 --> 00:14:05,550 for cooling or the power that you need for cooling. It’s just building these things, 213 00:14:05,550 --> 00:14:08,769 just building the curve, 27 kilometers. 214 00:14:08,769 --> 00:14:12,250 And that’s what you have there as a cost. Now what they do is, they make 215 00:14:12,250 --> 00:14:15,420 a huge magnetic field, because in a magnetic field a charged particle 216 00:14:15,420 --> 00:14:19,300 will go on a curve. That’s what we want, right? But 217 00:14:19,300 --> 00:14:23,970 to make these particles with a very high energy and keep them on a tight curve… 218 00:14:23,970 --> 00:14:27,009 now in particle physics’ terms let’s say that 27 kilometers 219 00:14:27,009 --> 00:14:30,920 to go around one way is a tight curve. 220 00:14:30,920 --> 00:14:35,459 We need a current of 12,000 amps. Which is a large current 221 00:14:35,459 --> 00:14:38,579 that goes through these dipoles. Which is the reason why we have them 222 00:14:38,579 --> 00:14:44,850 superconductingly cooled, because otherwise you put 12,000 amps 223 00:14:44,850 --> 00:14:48,460 through a piece of metal and it just melts away. You don’t get a magnetic field, 224 00:14:48,460 --> 00:14:52,820 maybe for a microsecond or 2. But you want to sustain a stable field 225 00:14:52,820 --> 00:14:57,029 of 8.5 Tesla to make these protons go around on a curve. 226 00:14:57,029 --> 00:15:00,890 So, yeah, that’s a big thing. There’s also niobium in there, 227 00:15:00,890 --> 00:15:05,569 not the big clunky parts like the cavity we saw, but thin niobium wires, 228 00:15:05,569 --> 00:15:09,500 actually half niobium, half titanium most of the time. But since 229 00:15:09,500 --> 00:15:14,430 there are so many magnets and it’s so long a curve, there is 600 tons 230 00:15:14,430 --> 00:15:18,759 of atomic niobium in this entire accelerator thing. 231 00:15:18,759 --> 00:15:22,610 And this was a fourth of the world production of niobium 232 00:15:22,610 --> 00:15:26,950 which comes mostly from Brazil by the way. This was a fourth of the world production 233 00:15:26,950 --> 00:15:30,970 of niobium for 5 years. So that’s where it all went. 234 00:15:30,970 --> 00:15:35,769 It just went into the accelerator. And now if we have this running, 235 00:15:35,769 --> 00:15:39,259 we have it up, we have it cooled, we have a large current going, we got our nice 236 00:15:39,259 --> 00:15:43,109 big magnetic fields. And there is energy stored. 237 00:15:43,109 --> 00:15:46,910 I mean we put in a lot of power and the magnetic fields are up and they’re stable 238 00:15:46,910 --> 00:15:50,920 and that means that there’s magnetic energy stored in this. And the amount 239 00:15:50,920 --> 00:15:53,990 of energy that is stored in the curve magnets alone of the LHC when it’s running 240 00:15:53,990 --> 00:15:58,009 is 11 gigajoules. Sounds like a lot, 241 00:15:58,009 --> 00:16:03,770 let’s compare it to something: If we have an absurdly long freight train 242 00:16:03,770 --> 00:16:07,699 with let’s say 15,000 tons. I hear that normal freight trains in Germany 243 00:16:07,699 --> 00:16:11,811 or England have about 5000 tons. So let’s take a big freight train 244 00:16:11,811 --> 00:16:18,369 and multiply it by 3. If this freight train goes at 150 km/h, 245 00:16:18,369 --> 00:16:21,899 then the kinetic energy, the movement energy of this train 246 00:16:21,899 --> 00:16:26,839 is equivalent to the magnetic energy that is stored in the LHC. 247 00:16:26,839 --> 00:16:29,969 And that is why we don’t want any problem with the cooling. 248 00:16:29,969 --> 00:16:33,740 *laughter* 249 00:16:33,740 --> 00:16:39,740 Because if we get a problem with the cooling, bad things happen. 250 00:16:39,740 --> 00:16:44,469 This is a photograph of what at CERN at the LHC they just call “the incident”. 251 00:16:44,469 --> 00:16:47,089 *laughter* 252 00:16:47,089 --> 00:16:50,059 Which was a tiny mishap that happened just a few weeks 253 00:16:50,059 --> 00:16:54,060 after the LHC was taken into operation for the first time in 2008. 254 00:16:54,060 --> 00:16:57,230 And it shut the machine down for about 8 months. 255 00:16:57,230 --> 00:17:00,390 So that was a bad thing. It’s a funny story when they where 256 00:17:00,390 --> 00:17:03,290 constructing these magnets; now what you see here is the connection 257 00:17:03,290 --> 00:17:07,850 between 2 of these magnets. I told you that each of them weighs 35 tons. 258 00:17:07,850 --> 00:17:12,740 So here you have a connection between 2 parts that are 35 tons in weight each. 259 00:17:12,740 --> 00:17:18,100 And they’re shifted by almost half a meter. So it takes a bit of boom. 260 00:17:18,100 --> 00:17:21,630 So what happened was: the cooling broke down and the helium escaped and 261 00:17:21,630 --> 00:17:25,569 the sheer force of the helium expanding, because if you have liquid helium 262 00:17:25,569 --> 00:17:29,810 and it instantly evaporates into gaseous helium then the volume multiplies 263 00:17:29,810 --> 00:17:33,650 by a very large amount. And what they had was… 264 00:17:33,650 --> 00:17:36,720 what I hear is that the tunnel of the LHC, which has a diameter of about 265 00:17:36,720 --> 00:17:41,010 let’s say 6 or 7 meters was filled with nothing but helium 266 00:17:41,010 --> 00:17:44,510 which pushed away the air for about 100 meters 267 00:17:44,510 --> 00:17:48,140 around this incident. So the helium evaporated, it pushed everything away, 268 00:17:48,140 --> 00:17:52,960 it made everything really cold, some cables broke and some metal broke. 269 00:17:52,960 --> 00:17:57,010 And the funny thing now is, the engineers that built the LHC, 270 00:17:57,010 --> 00:18:00,210 before they did that, visited Hamburg. Because here there is 271 00:18:00,210 --> 00:18:03,511 a particle accelerator which is not quite as large. The LHC 272 00:18:03,511 --> 00:18:07,770 has 27 kilometers; here in Hamburg we have a particle accelerator called HERA 273 00:18:07,770 --> 00:18:12,490 which had 6.5 kilometers. So it’s the same ballpark, it’s not as big. 274 00:18:12,490 --> 00:18:15,750 And in HERA they had a safety system against these kinds of cryo failures, 275 00:18:15,750 --> 00:18:19,630 they’re called quenches. They had a protection system, 276 00:18:19,630 --> 00:18:23,480 which protects this exact part. Now we’re talking about “Yeah, 277 00:18:23,480 --> 00:18:26,710 how should we build this? Should we have a quench-protection 278 00:18:26,710 --> 00:18:31,030 at the connection between the dipoles?” And the HERA people in Hamburg said: 279 00:18:31,030 --> 00:18:34,690 “Well we have it, it’s a good thing, you shouldn’t leave it out, 280 00:18:34,690 --> 00:18:38,630 if you build the LHC.” Well, they left it out. *laughter* 281 00:18:38,630 --> 00:18:43,470 They ran out of time, they ran out of money, the LHC project was under pressure. 282 00:18:43,470 --> 00:18:45,950 Because they had promised to build a big machine by that time and 283 00:18:45,950 --> 00:18:49,450 they weren’t really finished, so they cut some edges. Well this was 284 00:18:49,450 --> 00:18:53,930 the edge they cut and it cost them 8 months of operation. Which says 285 00:18:53,930 --> 00:18:59,360 that they really should have listened to the people of Hamburg. Okay, so, 286 00:18:59,360 --> 00:19:03,940 in summary of the operations of a storage ring we can just say this: 287 00:19:03,940 --> 00:19:07,040 They get perfectly timed kicks with our polarity switching 288 00:19:07,040 --> 00:19:11,700 at just the right moment by radio waves generated in these large klystrons 289 00:19:11,700 --> 00:19:16,110 from the funny looking metal tubes that we called cavities. 290 00:19:16,110 --> 00:19:18,461 And some big-ass superconducting magnets keep them on a curve 291 00:19:18,461 --> 00:19:22,780 when they are not being accelerated. Now the trick is, one of these kicks 292 00:19:22,780 --> 00:19:26,430 like moving through the cavity once, may not give you all the energy you want, 293 00:19:26,430 --> 00:19:30,160 in fact it doesn’t. But if you make them go round in the ring, 294 00:19:30,160 --> 00:19:34,150 they come by every couple of nanoseconds. So you just have them 295 00:19:34,150 --> 00:19:37,660 run through your acceleration all the time. Which is the big difference 296 00:19:37,660 --> 00:19:40,620 between the storage ring and a linear accelerator. A linear accelerator 297 00:19:40,620 --> 00:19:44,400 is basically a one shot operation but here, you just give them an energy kick 298 00:19:44,400 --> 00:19:48,880 every time they come around, which is often, we’re going to see that. 299 00:19:48,880 --> 00:19:52,880 So that’s the summary of what the storage rings do. Now, 300 00:19:52,880 --> 00:19:56,570 the machine layout, if you look at a research center 301 00:19:56,570 --> 00:20:01,160 which has a bunch of accelerators, it almost always goes like this: 302 00:20:01,160 --> 00:20:05,030 You have some old, small storage rings and then they built 303 00:20:05,030 --> 00:20:08,620 newer ones which were bigger. So this is just 304 00:20:08,620 --> 00:20:12,420 a historical development, first you build small machines, then 305 00:20:12,420 --> 00:20:14,920 techniques get better, engineering gets better, you build bigger machines. But 306 00:20:14,920 --> 00:20:18,640 you can actually use that, it’s very useful because the older machines, 307 00:20:18,640 --> 00:20:22,640 you can use as pre-accelerators. For a variety of reasons it’s useful 308 00:20:22,640 --> 00:20:26,370 to not put in your particles with an energy of zero and then 309 00:20:26,370 --> 00:20:30,180 have them accelerated up to the energy you want. You want to pre-accelerate them, 310 00:20:30,180 --> 00:20:33,460 make them a little faster at a time. That’s what you do, you just 311 00:20:33,460 --> 00:20:37,840 take the old accelerators. And if we look at the accelerator layout 312 00:20:37,840 --> 00:20:42,200 of some real world research centers, you can actually see this. On the left 313 00:20:42,200 --> 00:20:47,020 you have CERN in Geneva and on the right you have DESY here in Hamburg. 314 00:20:47,020 --> 00:20:51,140 And you can see that there are smaller accelerators, which are the older ones, 315 00:20:51,140 --> 00:20:54,140 and you have bigger accelerators which are connected to them. 316 00:20:54,140 --> 00:20:59,410 And that’s this layout of the machines. Okay, now let’s talk about collisions. 317 00:20:59,410 --> 00:21:03,411 This is a nice picture of a collision. It’s not actually a proton collision 318 00:21:03,411 --> 00:21:08,270 but a heavy-ion collision, which they do part of the time in the LHC. 319 00:21:08,270 --> 00:21:11,520 They are extremely hard to produce, we’re going to see that, but still we make 320 00:21:11,520 --> 00:21:15,690 an awful lot of them. So let’s see, first of all 321 00:21:15,690 --> 00:21:19,330 let’s talk about what the beam looks like, because we’re going to be colliding beams. 322 00:21:19,330 --> 00:21:23,220 So what are these beams? Is it a continuous stream of particles? 323 00:21:23,220 --> 00:21:27,780 Well it’s not. Because the acceleration that we use, these radio frequency, 324 00:21:27,780 --> 00:21:31,960 polarity shifting mechanisms, they make the particles into bunches. 325 00:21:31,960 --> 00:21:35,730 So you don’t have a continuous stream, you have separate bunches. 326 00:21:35,730 --> 00:21:38,610 But how large are these bunches? Is there one particle per bunch? 327 00:21:38,610 --> 00:21:41,150 You’ve got a particle, you wait a while, there’s another particle? 328 00:21:41,150 --> 00:21:44,650 Well, it’s not like that. Because if it were like that, 329 00:21:44,650 --> 00:21:49,300 if we had single particles coming after one another, it would be impossible 330 00:21:49,300 --> 00:21:52,750 to hit them. You have to aim the beams very precisely. 331 00:21:52,750 --> 00:21:56,620 I mean, think about it. One comes around 27 kilometers around the ring. 332 00:21:56,620 --> 00:21:59,950 The other comes around 27 kilometers going the other way. 333 00:21:59,950 --> 00:22:03,480 And now you want them to hit. You have to align your magnets very precisely. 334 00:22:03,480 --> 00:22:07,060 You can think of it like this: You have a guy in Munich 335 00:22:07,060 --> 00:22:10,790 and you have a guy in Hamburg and they each have a rifle. And the bullets 336 00:22:10,790 --> 00:22:14,550 of the rifle are let’s say one centimeter in size. So the guy in Hamburg 337 00:22:14,550 --> 00:22:17,390 shoots in the air and the guy in Munich shoots in the air, and they are supposed 338 00:22:17,390 --> 00:22:22,490 to make the bullets hit in the middle, over, let’s say Frankfurt. 339 00:22:22,490 --> 00:22:25,720 Which they’re not going to manage. And which is actually way too simple. 340 00:22:25,720 --> 00:22:32,200 Because if the bullet is really one centimeter in size, 341 00:22:32,200 --> 00:22:37,360 then the equivalent distance that the two shooters should be away from each other, 342 00:22:37,360 --> 00:22:40,650 if we want to make it the same difficulty as these protons, 343 00:22:40,650 --> 00:22:45,050 would not be between Hamburg and Munich. It would be from here to fucking Mars. 344 00:22:45,050 --> 00:22:49,470 *laughter and applause* I calculated that shit. 345 00:22:49,470 --> 00:22:54,200 *applause* 346 00:22:54,200 --> 00:22:57,650 We don’t even have rifles on Mars anyway. *laughter* 347 00:22:57,650 --> 00:23:01,690 So what we got is, we got large bunches, very large bunches. 348 00:23:01,690 --> 00:23:04,890 And in fact there’s 10^11 protons per bunch, which is 349 00:23:04,890 --> 00:23:11,030 100 Billion. This is where I called Sagan “ you going Millions of Millions“ 350 00:23:11,030 --> 00:23:15,120 Okay, so you got 100 Billion protons in one bunch. 351 00:23:15,120 --> 00:23:19,270 And the bunches go by one after the other. Now, if you stand next to the LHC 352 00:23:19,270 --> 00:23:23,160 and you were capable of observing these bunches, you would see one fly by 353 00:23:23,160 --> 00:23:28,170 every 25 nanoseconds. So you go “there’s a bunch, now it’s 25 nanoseconds, 354 00:23:28,170 --> 00:23:32,770 there is the next one”. And there’s about 7.5 meters between the bunches. 355 00:23:32,770 --> 00:23:36,760 Now, 7.5 meters corresponds to 25 nanoseconds, you see that 356 00:23:36,760 --> 00:23:42,940 the speed is very big and indeed it’s almost the speed of light. 357 00:23:42,940 --> 00:23:45,590 Which is just, we accelerate them and at some point they just go 358 00:23:45,590 --> 00:23:48,640 with the speed of light and we just push up the energy, we don’t make them 359 00:23:48,640 --> 00:23:53,750 go any faster actually. And if you were to identify the bunches, 360 00:23:53,750 --> 00:23:58,940 which actually you can, you would see that there are 2800 bunches 361 00:23:58,940 --> 00:24:02,890 going by; and then when you have number 2809, 362 00:24:02,890 --> 00:24:06,620 that’s actually the first one that you counted which has come round again. 363 00:24:06,620 --> 00:24:10,160 Per direction! So in total we have over 5000 bunches 364 00:24:10,160 --> 00:24:15,470 of 100 Billion protons each. So that’s the beam we are dealing with. 365 00:24:15,470 --> 00:24:19,610 Oh, and a funny thing: you get charged particles moving, it’s actually a current, 366 00:24:19,610 --> 00:24:22,680 right? In a wire you have a current running through it, 367 00:24:22,680 --> 00:24:27,150 there’s electrons moving or holes moving and you get a current. If you were 368 00:24:27,150 --> 00:24:31,800 to measure the current of the LHC, it would be 0.6 milliamps, 369 00:24:31,800 --> 00:24:34,330 which is a small current, but we’re doing collisions anyway 370 00:24:34,330 --> 00:24:38,270 and not power transmission, so that’s fine. *laughter* 371 00:24:38,270 --> 00:24:42,780 This is a diagram of what the actual interaction point geometry looks like. 372 00:24:42,780 --> 00:24:46,340 You get the beams from different directions, think of it like the top one 373 00:24:46,340 --> 00:24:50,010 coming from the right, the bottom one coming from the left; 374 00:24:50,010 --> 00:24:53,480 and they are kicked into intersecting paths by magnets. You have 375 00:24:53,480 --> 00:24:57,590 very complicated, very precise magnetic fields aligning them, 376 00:24:57,590 --> 00:25:01,850 so that they intersect. And it’s actually a bit of a trying-out game. 377 00:25:01,850 --> 00:25:05,970 I’ve heard this from accelerator operators. 378 00:25:05,970 --> 00:25:09,410 You shift the position of the beams relative to each other by small amounts 379 00:25:09,410 --> 00:25:12,880 and you just see where the collisions happen. You go like: “Ah yeah, okay, 380 00:25:12,880 --> 00:25:17,220 there’s lots of collisions, ah, now they’re gone, I’m going back.” 381 00:25:17,220 --> 00:25:20,440 And you do it like that. You can save the settings and load them and calculate them 382 00:25:20,440 --> 00:25:24,300 but it’s actually easier to just try it out. 383 00:25:24,300 --> 00:25:28,350 If we think of how much stuff we’ve got going on: you got a packet, 384 00:25:28,350 --> 00:25:31,240 a bunch of 100 Billion protons coming one way, 385 00:25:31,240 --> 00:25:35,100 you got another packet of 100 Billion protons coming the other way. 386 00:25:35,100 --> 00:25:39,640 Now the interaction point area is as small as the cross section of a human hair. 387 00:25:39,640 --> 00:25:43,270 You can see that, it’s one hundredth of a square millimeter. 388 00:25:43,270 --> 00:25:46,110 Now how many collisions do you think we have? We’ve got… 389 00:25:46,110 --> 00:25:48,120 Audience: Three! *Michael laughs* 390 00:25:48,120 --> 00:25:51,850 Michael: …it’s actually not that bad. We got about 20 in the LHC. 391 00:25:51,850 --> 00:25:56,450 And the funny thing is, people consider this a bit too much. 392 00:25:56,450 --> 00:25:59,600 The effect is called pile-up. And the bad thing about pile-up is you’ve got 393 00:25:59,600 --> 00:26:03,590 beams intersecting, you’ve got bunches ‘crossing’ – that’s what we call it. 394 00:26:03,590 --> 00:26:06,720 And there’s not just one collision which you can analyze, there is a bunch of them, 395 00:26:06,720 --> 00:26:10,110 around 20. And that makes that more difficult for the experiments, 396 00:26:10,110 --> 00:26:15,720 we’re going to see why. Well, and if we have 20 collisions every bunch crossing 397 00:26:15,720 --> 00:26:19,580 and the bunches come by every 25 nanoseconds, that gives us a total 398 00:26:19,580 --> 00:26:24,690 of 600 Million collisions per second. Per interaction point. 399 00:26:24,690 --> 00:26:27,770 Which we don’t have just one of. We have 4 experiments, each experiment 400 00:26:27,770 --> 00:26:31,371 has its own interaction point. So in total, we have about 2 Billion 401 00:26:31,371 --> 00:26:36,660 proton-proton collisions happening every second when the LHC is running. 402 00:26:36,660 --> 00:26:39,580 Now let’s look at experiments. *laughs* 403 00:26:39,580 --> 00:26:44,070 Yeah, this is a photograph of one part of the ATLAS experiment being transported. 404 00:26:44,070 --> 00:26:47,690 And as for the scale of this thing, well, in the physics community, we call this 405 00:26:47,690 --> 00:26:53,700 a huge device. *laughter* 406 00:26:53,700 --> 00:26:57,150 I have a diagram of the experiment where this is built in and 407 00:26:57,150 --> 00:27:00,510 you’re going to recognize the part which is the one I’ve circled there. 408 00:27:00,510 --> 00:27:04,290 So the real thing is even bigger. And down at the very bottom, 409 00:27:04,290 --> 00:27:08,190 just to the center of the experiment, there’s people. 410 00:27:08,190 --> 00:27:12,860 Which if I check it like this, they’re about 15 pixels high. 411 00:27:12,860 --> 00:27:16,490 So that’s the scale of the experiment. 412 00:27:16,490 --> 00:27:20,250 The experiment has the interaction point at the center, so you got a beam line 413 00:27:20,250 --> 00:27:23,570 coming in from the left, you got the other beam line coming in from the right. 414 00:27:23,570 --> 00:27:27,280 And in the very core of the experiment is where the interactions, 415 00:27:27,280 --> 00:27:31,140 where the collisions happen. And then you got the experiment in layers, 416 00:27:31,140 --> 00:27:35,240 like an onion, going around them in a symmetrical way. 417 00:27:35,240 --> 00:27:38,370 Inside you have a huge magnetic field which is almost as big 418 00:27:38,370 --> 00:27:42,470 as the curve magnets we were talking about when I was describing the storage ring. 419 00:27:42,470 --> 00:27:46,130 This is about 4 Teslas, so it’s also a very big field. 420 00:27:46,130 --> 00:27:50,160 But now we got a 4 Tesla field not just over the beam pipe 421 00:27:50,160 --> 00:27:54,340 which is about 5 centimeters in diameter, but through the entire experiment; 422 00:27:54,340 --> 00:27:58,080 and this thing is like 20-25 meters. So you’ve got a 4 Tesla field 423 00:27:58,080 --> 00:28:01,910 which should span more than 20 meters. 424 00:28:01,910 --> 00:28:07,410 And, just for shits and giggles, it’s got 3000 kilometers of cables. 425 00:28:07,410 --> 00:28:11,060 Which is a lot; and if you just pull some random plug 426 00:28:11,060 --> 00:28:16,270 and don’t tell anyone which one it was you’re making a lot of enemies. 427 00:28:16,270 --> 00:28:19,980 So the innermost thing is what we call the inner tracking. It is located 428 00:28:19,980 --> 00:28:23,210 just centimeters off the beam line, it’s supposed to be very very close to 429 00:28:23,210 --> 00:28:26,290 where the actual interactions happen. 430 00:28:26,290 --> 00:28:29,180 And this thing is made to leave the particles undisturbed, they should just 431 00:28:29,180 --> 00:28:32,590 fly trough this inner tracking detector. And the detector will tell us 432 00:28:32,590 --> 00:28:35,910 where they were, but not actually stop them or deflect them. 433 00:28:35,910 --> 00:28:40,050 This gives us precise location data, as to how many particles there were, 434 00:28:40,050 --> 00:28:44,030 what way they were flying, and, from the curve, 435 00:28:44,030 --> 00:28:47,570 what momentum they have. Outside of that we’ve got calorimeters. 436 00:28:47,570 --> 00:28:51,300 Now these are supposed to be stopping the particles. A particle goes through 437 00:28:51,300 --> 00:28:55,360 the inner tracking without being disturbed but in the calorimeter it should stop. 438 00:28:55,360 --> 00:28:58,970 And it should deposit all its energy there and which is why we have to put around it 439 00:28:58,970 --> 00:29:03,100 the inner tracking. You see, if we put the calorimeter inside, it stops the particle, 440 00:29:03,100 --> 00:29:07,770 outside of that nothing happens. So we have the calorimeters outside of that. 441 00:29:07,770 --> 00:29:12,070 And then we got these funny wing things going on. That’s the muon detectors. 442 00:29:12,070 --> 00:29:15,490 They are there for one special sort of particle. 443 00:29:15,490 --> 00:29:19,610 Out of the… 50, let’s say 60 – depends on the way you count – 444 00:29:19,610 --> 00:29:22,860 elementary particles that we have. These large parts are 445 00:29:22,860 --> 00:29:26,250 just for the muons. Because the muons have the property, 446 00:29:26,250 --> 00:29:29,990 the tendency to go through all sorts of matter undisturbed. So you just need to 447 00:29:29,990 --> 00:29:33,270 throw a huge amount of matter in the way of these muons, like: 448 00:29:33,270 --> 00:29:36,750 “let’s have a brick wall and then another one”. And then you 449 00:29:36,750 --> 00:29:42,030 may be able to stop the muons, or just measure them. 450 00:29:42,030 --> 00:29:45,060 This is to give you an idea of the complexity of the instrument 451 00:29:45,060 --> 00:29:49,170 on the inside. This is the inner tracking detector, it’s called a pixel detector; 452 00:29:49,170 --> 00:29:52,730 and you see guys walking around in protective suits. That is not for fun 453 00:29:52,730 --> 00:29:56,920 or just for the photo, this is a very, very precise instrument. But it’s sitting 454 00:29:56,920 --> 00:30:00,100 inside this huge experiment which – again, 455 00:30:00,100 --> 00:30:03,910 I calculated that shit – is about as large as a space shuttle 456 00:30:03,910 --> 00:30:07,420 and weighs as much as the Eiffel Tower. And inside 457 00:30:07,420 --> 00:30:12,030 they’ve got electronics, almost a ton of electronics which is so precise 458 00:30:12,030 --> 00:30:16,030 that it makes your smartphone look like a rock. So there you go, 459 00:30:16,030 --> 00:30:19,970 it’s a very, very complicated sort of experiment. Let’s talk about triggering, 460 00:30:19,970 --> 00:30:24,360 because as I said there’s 600 Million events happening inside this. 461 00:30:24,360 --> 00:30:27,600 That’s 40 Million bunch crossings. Now: how are we going to analyze this? 462 00:30:27,600 --> 00:30:31,720 Is there a guy writing everything down? Obviously not. 463 00:30:31,720 --> 00:30:35,540 So this experiment with all the tracking and the calorimeters and the muons 464 00:30:35,540 --> 00:30:39,800 and everything has about 100 Million electronic channels. 465 00:30:39,800 --> 00:30:43,410 And one channel could be the measurement of a voltage, or a temperature 466 00:30:43,410 --> 00:30:47,330 or a magnetic field or whatever. So we’ve got 100 Million different values, 467 00:30:47,330 --> 00:30:52,540 so to speak. And that makes about 1.5 Megabytes per crossing, 468 00:30:52,540 --> 00:30:57,220 per every event readout. Which gives us – multiplied by 40 Million – 469 00:30:57,220 --> 00:31:01,260 gives us about 60 terabytes of raw data per second. 470 00:31:01,260 --> 00:31:05,610 That’s bad. I looked it up, I guess 471 00:31:05,610 --> 00:31:10,340 the best RAM you can do is about 1 terabyte per second or something. 472 00:31:10,340 --> 00:31:14,950 So we’re obviously not going to tackle this by just putting in fast hardware, 473 00:31:14,950 --> 00:31:18,690 because it’s not going to be fast enough. Plus, 474 00:31:18,690 --> 00:31:24,450 the reconstruction of an event is done by about 5 Million lines of C++ code. 475 00:31:24,450 --> 00:31:29,570 Programmed by some 2000-3000 developers around the world. 476 00:31:29,570 --> 00:31:33,330 It simulates for one crossing 30 Million objects, which is 477 00:31:33,330 --> 00:31:36,840 the protons and other stuff flying around. 478 00:31:36,840 --> 00:31:44,410 And it is allocated to take 15 seconds of one core’s computing time. 479 00:31:44,410 --> 00:31:47,770 To calculate it all, you would need about 600 million cores. 480 00:31:47,770 --> 00:31:50,330 That’s not happening. I mean, even if we took over the NSA 481 00:31:50,330 --> 00:31:54,132 *laughter* and used all of their data-centers 482 00:31:54,132 --> 00:31:57,440 for LHC calculations, it still wouldn’t be enough. So we have to do something 483 00:31:57,440 --> 00:32:02,570 about this huge mass of data. And what we do is, we put in triggers. 484 00:32:02,570 --> 00:32:07,170 The trigger is supposed to reduce the number of events that we look at. 485 00:32:07,170 --> 00:32:10,830 The first level trigger looks at every collision that happens. 486 00:32:10,830 --> 00:32:13,840 And it’s got 25 nanoseconds of time to decide: 487 00:32:13,840 --> 00:32:17,410 Is this an interesting collision? Is it not an interesting collision? 488 00:32:17,410 --> 00:32:21,830 We tell it to eliminate 99.7% of all collisions. 489 00:32:21,830 --> 00:32:26,480 So only every 400th collision is allowed for this trigger to go: 490 00:32:26,480 --> 00:32:30,280 “Oh, yeah, okay that looks interesting, let’s give it to Level 2 trigger”. 491 00:32:30,280 --> 00:32:34,150 So then we end up with about 100,000 events per second. Which get us 492 00:32:34,150 --> 00:32:38,660 down to 150 Gigabytes per second. Now we could handle this from the data flow, 493 00:32:38,660 --> 00:32:43,450 but still we can’t simulate it. So we’ve got another level trigger. 494 00:32:43,450 --> 00:32:46,720 This is where the two experiments at the LHC differ: 495 00:32:46,720 --> 00:32:50,030 the CMS experiment has just a Level 2 trigger; does it all there. 496 00:32:50,030 --> 00:32:53,301 The ATLAS experiment goes the more traditional way, it has a Level 2 trigger 497 00:32:53,301 --> 00:32:57,500 and a Level 3 trigger. In the end these combined have about 10 microseconds 498 00:32:57,500 --> 00:33:01,450 of time, which is a bit more and it gives them a chance to look at the events 499 00:33:01,450 --> 00:33:05,920 more closely. Not just, let’s say: “Was it a collision of 2 protons 500 00:33:05,920 --> 00:33:09,300 or of 3 protons?”; “Were there 5 muons coming out of it 501 00:33:09,300 --> 00:33:12,810 or 3 electrons and 2 muons?” This is the sort of thing they’re looking at. 502 00:33:12,810 --> 00:33:16,370 And certain combinations the triggers will find interesting or not. 503 00:33:16,370 --> 00:33:20,120 Let’s say 5 muons, I don’t give a shit about that. “3 muons and 2 electrons? 504 00:33:20,120 --> 00:33:23,480 Allright, I want to analyze it”. So that’s what the trigger does. 505 00:33:23,480 --> 00:33:27,640 Now this Level 2 and 3 trigger, again, have to kick out about 506 00:33:27,640 --> 00:33:31,070 99.9% of the events. They’re supposed to leave us with 507 00:33:31,070 --> 00:33:36,360 about 150 events per second. Which gives a data volume of a measly 508 00:33:36,360 --> 00:33:40,030 300 Megabytes per second and that’s something we can handle. We push it 509 00:33:40,030 --> 00:33:45,780 to computers all around the world. And then we get the simulations going. 510 00:33:45,780 --> 00:33:50,900 This is a display, this is what you see in the media. 511 00:33:50,900 --> 00:33:55,360 If you take one of these events – just one of the interesting events which 512 00:33:55,360 --> 00:34:00,740 actually reach the computers – because those 40 million bunch crossings… well, 513 00:34:00,740 --> 00:34:04,150 most of them don’t reach the computers, they get kicked out by the triggers. 514 00:34:04,150 --> 00:34:08,240 But out of the remaining 100 or 200 events per second, let’s say this is one. 515 00:34:08,240 --> 00:34:12,849 It’s an actual event and it’s been calculated into a nice picture here. 516 00:34:12,849 --> 00:34:17,510 Now, normally they don’t do that, it’s analyzed automatically by code 517 00:34:17,510 --> 00:34:21,089 and it’s analyzed by the physics data. And they only make these pretty pictures 518 00:34:21,089 --> 00:34:25,339 if they want to show something to the press. To the left you have 519 00:34:25,339 --> 00:34:29,330 what’s called a Feynman Diagraph. That’s just a fancy physical way 520 00:34:29,330 --> 00:34:34,040 of saying what’s happening there. And it involves the letter H on the left side, 521 00:34:34,040 --> 00:34:37,180 which means there’s a Higgs involved. Which is why this event was particularly 522 00:34:37,180 --> 00:34:42,280 interesting to the people analyzing the data at the LHC. 523 00:34:42,280 --> 00:34:47,230 And you see a bunch of tracks, you see the yellow tracks all curled up inside, 524 00:34:47,230 --> 00:34:51,290 that’s a bunch of protons hitting each other. The interesting thing is 525 00:34:51,290 --> 00:34:55,710 what happens for example above there with the blue brick kind of things. 526 00:34:55,710 --> 00:35:00,050 There’s a red line going through these bricks. This indicates a muon. 527 00:35:00,050 --> 00:35:05,480 A muon which was created in this event there in the center. 528 00:35:05,480 --> 00:35:08,980 And it went out and the bricks symbolize the way 529 00:35:08,980 --> 00:35:13,140 the reaction was seen by the experiment. 530 00:35:13,140 --> 00:35:16,880 There was actually just a bunch of bricks lighting up. You got, I don’t know, 531 00:35:16,880 --> 00:35:21,320 500 bricks around it and brick 237 says: “Whoop, there was a signal”. 532 00:35:21,320 --> 00:35:24,300 And they go: “Allright, may have been a muon moving through the detector”. 533 00:35:24,300 --> 00:35:28,700 When you put it all together you get an event display like this. Okay, 534 00:35:28,700 --> 00:35:32,590 so we got to have computers analyzing this. And with all the 4 experiments 535 00:35:32,590 --> 00:35:36,570 running at the LHC, which is not just CMS and ATLAS I mentioned but also 536 00:35:36,570 --> 00:35:41,630 LHCb and ALICE, they produce about 25 Petabytes of data per year. 537 00:35:41,630 --> 00:35:46,230 And this cannot be stored at CERN alone. It is transferred to data centers 538 00:35:46,230 --> 00:35:50,780 around the world by what is called the LHC Optical Private Network. 539 00:35:50,780 --> 00:35:55,530 They’ve got a network of fibers going from CERN to other data-centers in the world. 540 00:35:55,530 --> 00:36:00,430 And it consists of 11 dedicated 10-Gigabit-per-second lines 541 00:36:00,430 --> 00:36:04,410 going from CERN outwards. If we combine this, it gives us a little over 542 00:36:04,410 --> 00:36:08,330 100 Gigabits of data throughput, which is about 543 00:36:08,330 --> 00:36:11,880 the bandwidth that this congress has. 544 00:36:11,880 --> 00:36:14,560 Which is nice, but here it’s dedicated to science data and not just porn 545 00:36:14,560 --> 00:36:20,250 and cat pictures. *laughter and applause* 546 00:36:20,250 --> 00:36:23,930 *applause* 547 00:36:23,930 --> 00:36:27,580 From there it’s distributed outwards from these 11 locations to about 548 00:36:27,580 --> 00:36:31,490 170 data centers in all the world. And the nice thing is, 549 00:36:31,490 --> 00:36:35,090 this data, these 25 Petabytes per year, is available 550 00:36:35,090 --> 00:36:38,310 to all the scientists working with it. There’s about… well, 551 00:36:38,310 --> 00:36:41,440 everybody can look at it, but there’s about 3000 people in the world 552 00:36:41,440 --> 00:36:45,270 knowing what it means. So all these people have free access to the data, 553 00:36:45,270 --> 00:36:48,900 you and I would have free access to the data, just thinking it’s cool to have 554 00:36:48,900 --> 00:36:53,260 a bit of LHC data on your harddrive maybe. *laughter* 555 00:36:53,260 --> 00:36:57,850 All in all, we have 250,000 cores dedicated to this task, 556 00:36:57,850 --> 00:37:01,990 which is formidable. And about 100 Petabytes of storage 557 00:37:01,990 --> 00:37:05,730 which is actually funny, because 25 Petabytes of data are accumulated 558 00:37:05,730 --> 00:37:10,090 per year and the LHC has been running for about 4 years. 559 00:37:10,090 --> 00:37:13,600 So you can see that they buy the storage as the machine runs. Because 560 00:37:13,600 --> 00:37:17,540 100 Petabytes, okay, that’s what we have so far. If we want to keep it running, 561 00:37:17,540 --> 00:37:21,730 we need to buy more disks. Right! Now, 562 00:37:21,730 --> 00:37:25,380 what does the philosoraptor say about the triggers? 563 00:37:25,380 --> 00:37:29,110 If the triggers are supposed to eliminate those events which are irrelevant, 564 00:37:29,110 --> 00:37:33,420 which is not interesting, well, who tells them what’s irrelevant? 565 00:37:33,420 --> 00:37:37,230 Or to put it in the terms of Conspiracy-Keanu: 566 00:37:37,230 --> 00:37:43,120 “What if the triggers throw away the wrong 99.something % of events?” 567 00:37:43,120 --> 00:37:48,230 I mean, if I say: “If there’s an event with 5 muons going to the left, 568 00:37:48,230 --> 00:37:52,500 kick it out!”. What if that’s actually something that’s very, very interesting? 569 00:37:52,500 --> 00:37:56,010 How should we tell? We need to think about this very precisely. 570 00:37:56,010 --> 00:37:59,320 And I’m going to tell you about an example in history where 571 00:37:59,320 --> 00:38:02,800 this went terribly wrong, at least for a few years. We’re talking about 572 00:38:02,800 --> 00:38:06,820 the discovery of the positron. A positron is a piece of anti-matter; 573 00:38:06,820 --> 00:38:10,770 it is the anti-electron. It was theorized in 1928, when 574 00:38:10,770 --> 00:38:15,440 theoretical physicist Dirac put up a bunch of equations. And he said: “Right, 575 00:38:15,440 --> 00:38:20,030 there should be something which is like an electron, but has a positive charge. 576 00:38:20,030 --> 00:38:22,470 Some kind of anti-matter.” Well, that’s not what he said, but that’s 577 00:38:22,470 --> 00:38:26,740 what he thought. But it was only identified in 1931. 578 00:38:26,740 --> 00:38:30,310 They had particle experiments back then, they were seeing tracks of particles 579 00:38:30,310 --> 00:38:34,090 all the time. But they couldn’t identify the positron for 3 years, 580 00:38:34,090 --> 00:38:37,210 even though it was there on paper. So what happened? Well, 581 00:38:37,210 --> 00:38:41,230 you see the picture on the left. This is the actual, let’s say baby picture 582 00:38:41,230 --> 00:38:44,460 of the positron. I’m going to build up a scheme on the right 583 00:38:44,460 --> 00:38:48,440 to show you a bit more, to give you a better overview of 584 00:38:48,440 --> 00:38:52,150 what we are actually talking about. In the middle you’ve got a metal plate. 585 00:38:52,150 --> 00:38:55,200 And then there’s a track which is bending to the left, which is indicated here 586 00:38:55,200 --> 00:39:01,890 by the blue line. Now if we analyze this from a physical point of view, 587 00:39:01,890 --> 00:39:05,270 it tells us that the particle comes from below, 588 00:39:05,270 --> 00:39:08,310 hits something in the metal plate and then continues on to the top. 589 00:39:08,310 --> 00:39:12,900 So the direction of movement is from the bottom to the top. 590 00:39:12,900 --> 00:39:17,310 The amount by which its curvature reduces when it hits the metal plate 591 00:39:17,310 --> 00:39:21,780 tells us it has about the mass of an electron. Okay, so far so good. 592 00:39:21,780 --> 00:39:26,020 But then it has a positive charge. Because we know the… 593 00:39:26,020 --> 00:39:29,580 we know the orientation of the magnetic field. And that tells us: “Well, 594 00:39:29,580 --> 00:39:33,280 if it bends to the left, it must be a positive particle.” 595 00:39:33,280 --> 00:39:37,020 So we have a particle with the mass of an electron, but with a positive charge. 596 00:39:37,020 --> 00:39:43,190 And people were like “Wat?”. *laughter* 597 00:39:43,190 --> 00:39:46,160 So then someone ingenious came up and thought of a solution: 598 00:39:46,160 --> 00:39:48,480 ‘They developed the picture the wrong way around!?’ 599 00:39:48,480 --> 00:39:52,300 *laughter and applause* 600 00:39:52,300 --> 00:39:59,470 *applause* 601 00:39:59,470 --> 00:40:02,780 It’s what they thought. Well it’s wrong, of course, there’s such a thing as 602 00:40:02,780 --> 00:40:08,500 a positron. And it’s like an electron, but it’s positively charged. But… 603 00:40:08,500 --> 00:40:13,520 to put it in a kind of summary maybe: you can only discover that 604 00:40:13,520 --> 00:40:17,180 which you can accept as a result. This sounds like I’m Mahatma Gandhi 605 00:40:17,180 --> 00:40:23,200 or something but it’s just what we call science. *laughter* 606 00:40:23,200 --> 00:40:27,740 Okay, so to recap: What have we seen, what have we talked about? 607 00:40:27,740 --> 00:40:32,210 We saw from the basic principle, that if we have energy in a place, 608 00:40:32,210 --> 00:40:36,190 then that can give rise to other forms of matter, which I called ‘parts = a device’. 609 00:40:36,190 --> 00:40:39,360 You got your little parts, you do some stuff, out comes a device. 610 00:40:39,360 --> 00:40:43,100 We have storage rings which give a lot of energy to the particles 611 00:40:43,100 --> 00:40:46,700 and in which they move around in huge bunches. Billions of billions of protons 612 00:40:46,700 --> 00:40:51,020 in a bunch and then colliding. Which gives in the huge experiments 613 00:40:51,020 --> 00:40:55,390 that we set up an enormous amount of data ranging in the Terabytes per second 614 00:40:55,390 --> 00:40:59,740 which we have to program triggers to eliminate a lot of the events 615 00:40:59,740 --> 00:41:03,750 and give us a small amount of data which we can actually work with. And then 616 00:41:03,750 --> 00:41:07,190 we have to pay attention to the interpretation of data, so that 617 00:41:07,190 --> 00:41:11,500 we don’t get a fuck-up like with the positron. Which is a very hard job. 618 00:41:11,500 --> 00:41:16,780 And I hope that I could give you a little overview of how it’s fun. 619 00:41:16,780 --> 00:41:20,250 And it’s not just about building a big machine and saying: 620 00:41:20,250 --> 00:41:24,180 “I’ve got the largest accelerator of them all”. It’s a collaborative effort, 621 00:41:24,180 --> 00:41:28,600 it’s literally thousands of people working together and it’s not just about 622 00:41:28,600 --> 00:41:32,390 two guys getting a Nobel Prize. You see this picture on the top left, that’s 623 00:41:32,390 --> 00:41:36,900 about 1000 people at CERN watching the ceremony of the Nobel Prize 624 00:41:36,900 --> 00:41:40,600 being awarded. Because everybody felt there’s two people getting a medal 625 00:41:40,600 --> 00:41:45,230 in Sweden, but it’s actually an accomplishment… it’s actually an award for 626 00:41:45,230 --> 00:41:49,190 everybody involved in this enormous thing. And that’s what’s a lot of fun about it 627 00:41:49,190 --> 00:41:53,991 and I hope I could share some of this fascination with you. Thank you a lot. 628 00:41:53,991 --> 00:42:19,000 *huge applause* 629 00:42:19,000 --> 00:42:22,410 Before we get to Q&A, I’m going to be answering questions that you may have. 630 00:42:22,410 --> 00:42:25,560 My name is Michael, I’m @emtiu on Twitter, I’ve got a DECT phone, 631 00:42:25,560 --> 00:42:29,550 I talk about science, that’s what I do. I hope I do it well. 632 00:42:29,550 --> 00:42:32,210 And you can see the slides and leave feedback for me please 633 00:42:32,210 --> 00:42:36,770 in the event tracking system. And tomorrow, if you have the time 634 00:42:36,770 --> 00:42:39,720 you should go watch the “Desperately seeking SUSY” talk which is going to be 635 00:42:39,720 --> 00:42:43,480 talking about the theoretical side of particle physics. Okay, that’s it from me, 636 00:42:43,480 --> 00:42:46,540 now on to you. Herald: Okay, if you have questions, 637 00:42:46,540 --> 00:42:50,240 please line up, there’s a mic there and a mic there. And if you’re on the stream, 638 00:42:50,240 --> 00:42:53,770 you can also use IRC and Twitter to ask questions. So 639 00:42:53,770 --> 00:42:55,820 I’m going to start here, please go ahead. 640 00:42:55,820 --> 00:43:00,490 Question: Thanks a lot, it was a very fascinating talk, and nice to listen to. 641 00:43:00,490 --> 00:43:04,030 My question is: Did HERA ever suffer a quench event 642 00:43:04,030 --> 00:43:08,030 in which the quench protection system saved the infrastructure? 643 00:43:08,030 --> 00:43:11,250 Michael: No, actually it didn’t. There were tests where they provoked 644 00:43:11,250 --> 00:43:15,040 a sort of quench event in order to see if the protection worked. But 645 00:43:15,040 --> 00:43:18,100 even if this test would have failed it would not have been as catastrophic. 646 00:43:18,100 --> 00:43:22,020 But there were failures in the operation of the HERA accelerator 647 00:43:22,020 --> 00:43:25,790 and there was one cryo failure. Which is actually a funny story. Which is 648 00:43:25,790 --> 00:43:30,140 where one part of the helium tubing failed 649 00:43:30,140 --> 00:43:33,680 and some helium escaped from the tubing part 650 00:43:33,680 --> 00:43:36,790 and went into the tunnel. Now what happened was that the air moisture, 651 00:43:36,790 --> 00:43:41,180 just the water in the air froze at this point. 652 00:43:41,180 --> 00:43:45,450 And the Technical Director of the HERA machine told us this: at one point 653 00:43:45,450 --> 00:43:49,020 he sat there with a screwdriver and a colleague, picking off… the ice 654 00:43:49,020 --> 00:43:53,120 off the machine for half the night before they could replace this broken part. 655 00:43:53,120 --> 00:43:56,480 So, yeah, cryo failures are always a big pain. 656 00:43:56,480 --> 00:44:01,790 Herald: Do we have questions from the internet? …Okay. 657 00:44:01,790 --> 00:44:04,490 Signal Angel: We have one question that is: 658 00:44:04,490 --> 00:44:09,500 “How are the particles inserted into the accelerator?” 659 00:44:09,500 --> 00:44:13,420 Michael: They mostly start in linear accelerators. 660 00:44:13,420 --> 00:44:19,310 Wait, we’ve got it here. So you got the series of storage rings 661 00:44:19,310 --> 00:44:23,780 there at the top in the middle and you have one small line there. 662 00:44:23,780 --> 00:44:26,900 That’s a linear accelerator. To get protons is actually very easy. 663 00:44:26,900 --> 00:44:30,400 You buy a bottle of hydrogen which is just a simple gas you can buy. 664 00:44:30,400 --> 00:44:34,380 And then you strip off the electrons. You do this by ways of exposing them 665 00:44:34,380 --> 00:44:38,280 to an electric field. And what you’re left with is the core of the hydrogen atom. 666 00:44:38,280 --> 00:44:42,670 And that’s a proton. Then you accelerate the proton just a little bit 667 00:44:42,670 --> 00:44:47,650 into the linear accelerator and from there on it goes into the ring. So that means 668 00:44:47,650 --> 00:44:52,780 basically at the start of these colliding experiments is just a bottle of helium 669 00:44:52,780 --> 00:44:56,590 that somebody puts in there. And at the LHC it’s about, you know, 670 00:44:56,590 --> 00:45:00,430 a gas bottle. It’s about this big and it weighs a lot. At the LHC they use up 671 00:45:00,430 --> 00:45:03,531 about 2 or 3 bottles a year for all the operations, because 672 00:45:03,531 --> 00:45:07,760 a bottle of hydrogen has a lot of protons in it. 673 00:45:07,760 --> 00:45:11,020 Herald: You please, over there. 674 00:45:11,020 --> 00:45:15,120 Question: Actually I have 2 questions: One part is, 675 00:45:15,120 --> 00:45:18,790 you said there are 2 beams moving in opposite directions. 676 00:45:18,790 --> 00:45:22,680 And you explained the way where you switched polarity. How can this work 677 00:45:22,680 --> 00:45:26,010 with 2 beams opposing each other? 678 00:45:26,010 --> 00:45:31,160 Michael: That’s a good question. Now, if I show you the picture of the cryo dipole, 679 00:45:31,160 --> 00:45:36,980 you will see that these 2 beams are not actually in the same tube. 680 00:45:36,980 --> 00:45:40,650 There we go. You see a cryo dipole and 681 00:45:40,650 --> 00:45:44,210 on the inside of this blue tube, you see that there’s actually 2 lines. 682 00:45:44,210 --> 00:45:47,760 You can’t see it very well but there’s 2 lines. So they are 683 00:45:47,760 --> 00:45:51,980 inside the same blue tube, but then inside that is another small tube, 684 00:45:51,980 --> 00:45:56,040 which has a diameter of just about a Red Bull bottle. Say 5 or 6 centimeters 685 00:45:56,040 --> 00:45:58,860 in diameter. And this is where the beam happens. And they are just sitting 686 00:45:58,860 --> 00:46:02,480 next to each other. So the beams are always kept separate 687 00:46:02,480 --> 00:46:06,310 except from the interaction points where they should intersect. 688 00:46:06,310 --> 00:46:10,090 And the acceleration happens obviously also in separate cavities. 689 00:46:10,090 --> 00:46:11,740 Herald: You had a second question? 690 00:46:11,740 --> 00:46:15,890 Question: The second question is: The experiments, where are they placed, 691 00:46:15,890 --> 00:46:18,750 on the curve or on the acceleration part? 692 00:46:18,750 --> 00:46:22,610 Michael: The interaction points are placed between the acceleration 693 00:46:22,610 --> 00:46:25,930 on the straight path. Because, again, it’s much easier if you had the protons 694 00:46:25,930 --> 00:46:30,130 going straight for 200m; then you can more easily aim the beam. 695 00:46:30,130 --> 00:46:34,240 If they come around the curve then they have – you know they have a curve motion, 696 00:46:34,240 --> 00:46:38,000 you need to cancel that. That would be much more difficult. 697 00:46:38,000 --> 00:46:39,410 Herald: And the left, please. 698 00:46:39,410 --> 00:46:42,630 Question: Okay, so you got yourself a nice storage ring and then 699 00:46:42,630 --> 00:46:44,970 you connect it to the power plug and then your whole country 700 00:46:44,970 --> 00:46:48,120 goes dark. Where does the power come from? 701 00:46:48,120 --> 00:46:52,510 Michael: Well, in terms of power consumption of, let’s say 702 00:46:52,510 --> 00:46:56,950 households, cities, or aluminum plants: 703 00:46:56,950 --> 00:47:00,620 accelerators actually don’t use that much power. I mean 704 00:47:00,620 --> 00:47:03,370 most of us don’t run an aluminum plant. So we’re not used to this 705 00:47:03,370 --> 00:47:07,370 sort of power consumption. But’s it’s not actually all that big. I can tell you about 706 00:47:07,370 --> 00:47:11,290 the HERA accelerator that we had here in Hamburg, which I told you is about 707 00:47:11,290 --> 00:47:15,880 6.5 kilometers, not the 27, so you can sort of extrapolate from that. 708 00:47:15,880 --> 00:47:20,230 It used with the cryo and the power current for the fields 709 00:47:20,230 --> 00:47:25,030 and everything – it used about 30 MW. And 30 Megawatts is a lot, 710 00:47:25,030 --> 00:47:29,270 but it’s not actually very much in comparison to let’s say aluminum plants, 711 00:47:29,270 --> 00:47:34,140 our large factories. But in fact, the electricity cost is a big factor. 712 00:47:34,140 --> 00:47:38,530 Now you see the LHC is located at the border between Switzerland and France. 713 00:47:38,530 --> 00:47:41,770 It gets most of its power from France. 714 00:47:41,770 --> 00:47:45,020 And you always have an annual shutdown of the machine. You always have it off about 715 00:47:45,020 --> 00:47:47,890 1 or 2 months of the year. Where you do maintenance, where you replace stuff, 716 00:47:47,890 --> 00:47:51,690 you check stuff. And they always take care to have this shutdown 717 00:47:51,690 --> 00:47:55,500 for maintenance in winter. Because they get their power from France. 718 00:47:55,500 --> 00:47:59,660 And in France many people use [electrical] power for heating. 719 00:47:59,660 --> 00:48:03,670 There’s not Gas heating or Long Distance heat conducting pipes 720 00:48:03,670 --> 00:48:07,480 like we have in Germany e.g. The people just use [electrical] power for heat. 721 00:48:07,480 --> 00:48:11,500 And that means in winter the electricity price goes up. By a large amount. So 722 00:48:11,500 --> 00:48:15,410 they make sure that the machine is off in winter when the electricity prices are up. 723 00:48:15,410 --> 00:48:18,050 And it’s running in the summer where it’s not quite as bad. So it’s a factor 724 00:48:18,050 --> 00:48:21,890 if you run an accelerator. And you should tell your local power company 725 00:48:21,890 --> 00:48:25,130 if you’re about to switch it on! *laughter* 726 00:48:25,130 --> 00:48:28,820 But actually, it won’t make the grid off, even a small country like Switzerland 727 00:48:28,820 --> 00:48:30,890 break down or anything. 728 00:48:30,890 --> 00:48:35,150 Herald: Do we have more questions from the internet? Internet internet, no, 729 00:48:35,150 --> 00:48:39,970 no internet. Okay. Then just go ahead, Firefox Girl. 730 00:48:39,970 --> 00:48:43,000 Question (male voice): So you see a lot of events. And I guess there’s many 731 00:48:43,000 --> 00:48:48,210 wrong ones, too. How do you select if an event you see is really significant? 732 00:48:48,210 --> 00:48:51,470 Michael: Well, you have different kinds of analysis. Like I told you there is 733 00:48:51,470 --> 00:48:57,750 100 Mio. channels you can pick from. 734 00:48:57,750 --> 00:49:01,960 With the simplest trigger that you have, the Level 1 trigger, 735 00:49:01,960 --> 00:49:06,560 it can’t look at the data in much detail. Because it only has 25 ns. 736 00:49:06,560 --> 00:49:09,910 But as you go higher up the chain, as the events get more rare, 737 00:49:09,910 --> 00:49:13,320 you can look at them more closely. And what we end up in the end, these 100, 738 00:49:13,320 --> 00:49:17,890 maybe 200 events per second, you can analyze them very closely. And they get… 739 00:49:17,890 --> 00:49:20,990 they get a full-out computation. You can even make these pretty pictures 740 00:49:20,990 --> 00:49:26,560 of some of them. And then it’s basically, well, theoretical physicists’ work, 741 00:49:26,560 --> 00:49:29,161 to look at them and say: “Well, this might have been that process…”, but 742 00:49:29,161 --> 00:49:33,060 still a lot of them get kicked out. When the discovery of the Higgs particle 743 00:49:33,060 --> 00:49:37,540 was announced, it was ca. 1 1/2 years ago… 744 00:49:37,540 --> 00:49:42,470 Well, the machine had been running for 2 1/2 years. And, like I told you, 745 00:49:42,470 --> 00:49:46,390 there’s about 2 Billion proton collisions per second. Now the number of events 746 00:49:46,390 --> 00:49:51,150 that were relevant to the discovery of the Higgs – the Higgs events – 747 00:49:51,150 --> 00:49:54,890 it was not even 100. Out of 2 Billion per second. 748 00:49:54,890 --> 00:50:00,490 For 2 1/2 years. So you have to sort out a lot. Because it’s very very, very rare. 749 00:50:00,490 --> 00:50:03,400 And that’s just the work of everybody analyzing, which is why 750 00:50:03,400 --> 00:50:06,849 it’s a difficult task, done by a lot of people. 751 00:50:06,849 --> 00:50:08,380 Herald: The right, please. 752 00:50:08,380 --> 00:50:13,060 Question: What I’m interested in: You say ‘one year of detector running’. 753 00:50:13,060 --> 00:50:16,460 How much time in this year does this detector actually run… 754 00:50:16,460 --> 00:50:18,140 …is it actually running? 755 00:50:18,140 --> 00:50:21,560 Michael: Well, yeah, like I said, we have the accelerator off for about 756 00:50:21,560 --> 00:50:25,670 1 or 2 months. Then if something goes wrong it will be off again. 757 00:50:25,670 --> 00:50:29,450 But you want to keep it running for as long as possible, which… 758 00:50:29,450 --> 00:50:33,760 in the real world… let’s say it’s 9 months a year. That’s about it. 759 00:50:33,760 --> 00:50:35,260 Question: Straight through? 760 00:50:35,260 --> 00:50:38,570 Michael: Straight through – ah, well, not in a row. But it’s always on 761 00:50:38,570 --> 00:50:41,350 at least for a week. And then you get maybe a small interruption 762 00:50:41,350 --> 00:50:46,459 for a day or two, but you can also have a month of straight operation sometimes. 763 00:50:46,459 --> 00:50:47,810 Herald: Internet, please! 764 00:50:47,810 --> 00:50:51,580 Signal Angel: Yeah, another question: what would happen if they actually find 765 00:50:51,580 --> 00:50:54,820 what you are looking for? *Michael laughs* 766 00:50:54,820 --> 00:50:58,690 Do we throw the LHC in the dumpster or what do we do? 767 00:50:58,690 --> 00:51:01,930 Michael: That’s a good question! It would be one hell-of-a waste 768 00:51:01,930 --> 00:51:06,310 of a nice-looking tunnel! *laughs* You might consider using it for 769 00:51:06,310 --> 00:51:10,160 – I don’t know – maybe swimming events, or bicycle racing. 770 00:51:10,160 --> 00:51:13,050 Well, but actually that’s a very good question because the tunnel 771 00:51:13,050 --> 00:51:17,700 which the LHC sits in, this 27 km tunnel, it was not actually dug, 772 00:51:17,700 --> 00:51:21,220 it was not actually made just for the LHC. There was another particle accelerator 773 00:51:21,220 --> 00:51:25,620 inside before that. It had less energy, because it didn’t accelerate protons 774 00:51:25,620 --> 00:51:30,030 but just electrons and positrons. That’s why the energy was a lot lower. 775 00:51:30,030 --> 00:51:34,060 But they said: “Well, okay, we’re going to build a very large accelerator, 776 00:51:34,060 --> 00:51:38,200 does anyone have a 30 km tunnel, maybe?” 777 00:51:38,200 --> 00:51:41,460 and then someone came up with: “Yeah, well, we got this 27 km tunnel 778 00:51:41,460 --> 00:51:45,450 where this LEP accelerator is sitting in. And when it’s done with its operations 779 00:51:45,450 --> 00:51:47,470 in…” – I don’t know, by that time, let’s say in – “…10 years, we’re going 780 00:51:47,470 --> 00:51:51,900 to shut it off. Why don’t we put the next large accelerator in there?” So you try 781 00:51:51,900 --> 00:51:55,860 to reuse infrastructure, but of course you can’t always do that. The next big, 782 00:51:55,860 --> 00:52:00,470 the next huge accelerator, if we get the money together as a science community, 783 00:52:00,470 --> 00:52:03,540 because the politicians are being a bitch about it… 784 00:52:03,540 --> 00:52:06,920 if we get the money it’s going to be the International Linear Collider. 785 00:52:06,920 --> 00:52:10,900 And that’s supposed to have 100 km of particle tubes 786 00:52:10,900 --> 00:52:16,240 and, well, you need to build a new tunnel for that, obviously. 787 00:52:16,240 --> 00:52:20,050 Question: First off, couldn’t you use it in something 788 00:52:20,050 --> 00:52:23,829 like material sciences, like example with DESY? 789 00:52:23,829 --> 00:52:27,240 Well okay, if you are done with leptons you can still use it 790 00:52:27,240 --> 00:52:30,590 for Synchrotron Laser or something like this. 791 00:52:30,590 --> 00:52:33,500 Michael: That was thought of. The HERA accelerator at DESY was shut off 792 00:52:33,500 --> 00:52:37,170 and people were thinking about if they could put a Synchrotron machine inside it. 793 00:52:37,170 --> 00:52:41,670 But the problem there is the HERA accelerator is 25 m below the ground. 794 00:52:41,670 --> 00:52:44,960 This is not enough space. With particles accelerating 795 00:52:44,960 --> 00:52:48,730 you just need a small tube. But for Synchrotron experiments you need 796 00:52:48,730 --> 00:52:51,810 a lot of space. So you would have to enlarge the tunnel by a lot, 797 00:52:51,810 --> 00:52:56,210 and this was not worth it, in the case of the HERA accelerator. But interestingly, 798 00:52:56,210 --> 00:53:00,000 one of the pre-accelerators of HERA, one that was older is now used 799 00:53:00,000 --> 00:53:04,100 for Synchrotron science, which is PETRA. Which used to be just an 800 00:53:04,100 --> 00:53:08,200 old pre-accelerator, and now it’s one of the world’s leading Synchrotron machines. 801 00:53:08,200 --> 00:53:11,960 So, yeah, you try to reuse things because they were expensive. 802 00:53:11,960 --> 00:53:15,630 Question: And may I just ask another question? 803 00:53:15,630 --> 00:53:21,830 You said you get… you use just the matter 804 00:53:21,830 --> 00:53:25,420 from a bottle of hydrogen or a bottle of helium. 805 00:53:25,420 --> 00:53:29,980 Well, most helium or hydrogen is protons 806 00:53:29,980 --> 00:53:33,850 or, in the case of helium, helium-4. But 807 00:53:33,850 --> 00:53:37,350 you have a little bit helium-3 or deuterium. 808 00:53:37,350 --> 00:53:41,150 And well, you are looking for interesting things you don’t expect. 809 00:53:41,150 --> 00:53:44,880 So how do you differentiate if it’s really 810 00:53:44,880 --> 00:53:50,320 something interesting or: “Oh, one of these damn deuterium nuclides, again!” 811 00:53:50,320 --> 00:53:54,100 Michael: You don’t get wrong isotopes because you just use a mass spectrometer 812 00:53:54,100 --> 00:53:58,290 to sort them out. You have a magnetic field. You know how large it is. And 813 00:53:58,290 --> 00:54:03,380 the protons will go and land – let’s say – 2 micrometers next to the deuterons, 814 00:54:03,380 --> 00:54:07,230 and they just sort them out. 815 00:54:07,230 --> 00:54:11,240 Question: I have 2 questions. One is: 816 00:54:11,240 --> 00:54:15,100 I guess you mentioned that basically once the experiment 817 00:54:15,100 --> 00:54:19,550 runs at speed of light you just put more energy into it. 818 00:54:19,550 --> 00:54:22,380 But what is actually the meaning of the energy that you put into it? 819 00:54:22,380 --> 00:54:25,230 What does it change in the experiment? Like the Higgs was found 820 00:54:25,230 --> 00:54:28,260 at a particular electron volt… 821 00:54:28,260 --> 00:54:33,410 Michael: Yeah, it was found at 128 GeV. Well, 822 00:54:33,410 --> 00:54:37,610 it’s more of a philosophical question. There is a way of interpreting 823 00:54:37,610 --> 00:54:41,480 the equations of special relativity where you say that, when you don’t increase 824 00:54:41,480 --> 00:54:45,930 the velocity you increase the mass. But that’s just a way of looking at it. 825 00:54:45,930 --> 00:54:50,260 It’s more precise and it’s more simple to say: you raise the energy. 826 00:54:50,260 --> 00:54:53,130 And at some low energies that means that you raise the velocity. 827 00:54:53,130 --> 00:54:55,890 And at some high energies it means the velocity doesn’t change anymore. 828 00:54:55,890 --> 00:55:00,110 But overall you add more energy. It’s one of the weird effects 829 00:55:00,110 --> 00:55:07,769 of special relativity and there is no very nice explanation. 830 00:55:07,769 --> 00:55:10,950 Question: Let’s assume there is an asteroid pointing to earth. 831 00:55:10,950 --> 00:55:14,410 *Michael laughs* Could you in theory point this thing 832 00:55:14,410 --> 00:55:17,980 on the asteroid and destroy it, or would it be too weak? 833 00:55:17,980 --> 00:55:19,830 *laughter* 834 00:55:19,830 --> 00:55:24,290 *applause* 835 00:55:24,290 --> 00:55:26,750 Michael: I’m going to help you out. Because it wouldn’t actually work 836 00:55:26,750 --> 00:55:30,430 because between the accelerator and the asteroid there’s the earth atmosphere. 837 00:55:30,430 --> 00:55:33,750 And that would stop all the particles. But even if there were no atmosphere: 838 00:55:33,750 --> 00:55:37,690 no, it would be much too weak. Well, 839 00:55:37,690 --> 00:55:40,620 you’d have to keep it up for a long time at least. There was this one accident 840 00:55:40,620 --> 00:55:46,210 at the HERA accelerator where the beam actually went off its ideal path 841 00:55:46,210 --> 00:55:50,300 and it went some 2 or 3 cm next to where it should be. 842 00:55:50,300 --> 00:55:54,550 And it hit a block of lead – just, you know, the heavy metal lead – 843 00:55:54,550 --> 00:55:59,070 and the beam shot into this lead thing and the entire beam, 844 00:55:59,070 --> 00:56:02,960 which was a couple of Billions of protons, was deposited into this lead 845 00:56:02,960 --> 00:56:06,670 and some kilograms of lead evaporated within microseconds 846 00:56:06,670 --> 00:56:10,630 and there was a hole like pushed by a pencil through these lead blocks. 847 00:56:10,630 --> 00:56:15,160 So, yeah, it does break stuff apart. But even if you managed to hit the asteroid 848 00:56:15,160 --> 00:56:19,339 you would make a very small hole. But you wouldn’t destroy it. 849 00:56:19,339 --> 00:56:26,800 It would be a nice-looking asteroid then. *laughter* 850 00:56:26,800 --> 00:56:30,820 Question: Before you turned on the LHC the popular media was very worried 851 00:56:30,820 --> 00:56:34,220 that you guys were going to create any black holes. 852 00:56:34,220 --> 00:56:39,080 Did you actually see any black holes passing by? *Michael laughs* 853 00:56:39,080 --> 00:56:43,080 Michael: Well, there may have been some, but they were small, and 854 00:56:43,080 --> 00:56:48,810 they were insignificant. The interesting thing is… sorry, I’m going to recap, yeah. 855 00:56:48,810 --> 00:56:52,010 The interesting thing is that whatever we can do with the LHC – where 856 00:56:52,010 --> 00:56:56,869 we make particles have large energies and then collide – is already happening! 857 00:56:56,869 --> 00:57:00,830 Because out in space there is black holes with enormous magnetic fields 858 00:57:00,830 --> 00:57:04,450 and electrical fields. And these black holes are able to accelerate 859 00:57:04,450 --> 00:57:08,320 electrons to energies much, much higher than anything we can produce 860 00:57:08,320 --> 00:57:12,340 in any accelerator. The LHC looks like a children’s toy 861 00:57:12,340 --> 00:57:16,370 in comparison to the energies that a black hole acceleration can reach. And 862 00:57:16,370 --> 00:57:21,170 the particles which are accelerated in these black holes hit earth all the time. 863 00:57:21,170 --> 00:57:24,630 Not a lot, let’s say one of these super-energetic particles they come around 864 00:57:24,630 --> 00:57:28,840 about once a year for every square kilometer of earth. 865 00:57:28,840 --> 00:57:31,470 But still, they’ve been hitting us for Millions of years. 866 00:57:31,470 --> 00:57:34,900 And if a high-energy particle collision of this sort were able 867 00:57:34,900 --> 00:57:39,140 to produce a black hole that swallows up the earth it would be gone by now. 868 00:57:39,140 --> 00:57:45,499 So: won’t happen. *applause* 869 00:57:45,499 --> 00:57:48,190 Question: Maybe more interesting for this crowd: you talked about 870 00:57:48,190 --> 00:57:52,580 the selection process of the events. 871 00:57:52,580 --> 00:57:56,750 So I guess these parameters are also tweaked to kind of 872 00:57:56,750 --> 00:58:00,430 narrow down like what a proper selection procedure. 873 00:58:00,430 --> 00:58:04,040 Is there any kind of machine learning done on this to optimize? 874 00:58:04,040 --> 00:58:07,230 Michael: Not that I know of. But there is a process which is called ‘Minimum Bias 875 00:58:07,230 --> 00:58:11,690 Data Collection’. Where you actually bypass all the triggers 876 00:58:11,690 --> 00:58:15,290 and you select a very small portion of events without any bias. 877 00:58:15,290 --> 00:58:19,990 You just tell the trigger: “Take every 100 Billionth event” 878 00:58:19,990 --> 00:58:22,940 and you just pass it through no matter what you think. Even if you think 879 00:58:22,940 --> 00:58:28,150 it’s not interesting, pass it through. This goes into a pool of Minimum Bias Data 880 00:58:28,150 --> 00:58:32,830 and these are analyzed especially in order to see the actual trigger criteria 881 00:58:32,830 --> 00:58:37,230 are working well. So yeah, there is some tweaking. And 882 00:58:37,230 --> 00:58:41,230 even for old machines we have data collected 883 00:58:41,230 --> 00:58:44,910 and sometimes we didn’t know what we were looking for. And some 20 years later 884 00:58:44,910 --> 00:58:48,800 some guy comes up and says: “Well, we had this one accelerator way back. 885 00:58:48,800 --> 00:58:52,249 There may have been this and that reaction. Which we just theorize about. 886 00:58:52,249 --> 00:58:56,200 So let’s look at the old data and see if we see anything of that in there 887 00:58:56,200 --> 00:58:59,420 now, because it’s limited because it goes through all the filters”. 888 00:58:59,420 --> 00:59:03,600 You can’t do this all the time with great success. But sometimes, 889 00:59:03,600 --> 00:59:06,810 in very old data you find new discoveries. Because back then 890 00:59:06,810 --> 00:59:11,980 people weren’t thinking about looking for what we are looking now. 891 00:59:11,980 --> 00:59:16,470 Question: I always asked myself about repeatability of those experiments. 892 00:59:16,470 --> 00:59:20,480 Seeing as the LHC is the biggest one around there, so there’s no one out there 893 00:59:20,480 --> 00:59:23,320 who can actually repeat the experiment. So how do we know 894 00:59:23,320 --> 00:59:26,440 that they actually exist, those particles? 895 00:59:26,440 --> 00:59:30,150 Michael: That’s a very good question. I told you that there is 2 main 896 00:59:30,150 --> 00:59:33,940 large experiments. Which is the CMS experiment and the ATLAS experiment. 897 00:59:33,940 --> 00:59:39,020 Now these both sit at the same ring. They have some 10 km between them 898 00:59:39,020 --> 00:59:41,740 because they’re on opposite ends of the ring. But still, obviously, 899 00:59:41,740 --> 00:59:46,690 they’re on the same machine. But these 2 groups, the ATLAS and the CMS experiment, 900 00:59:46,690 --> 00:59:51,910 operate completely separately. It’s not the same people, not the same hardware, 901 00:59:51,910 --> 00:59:55,250 not the same triggers, not even the same designs. 902 00:59:55,250 --> 00:59:58,760 They build everything up from scratch, separate from each other. And 903 00:59:58,760 --> 01:00:02,700 it’s actually funny because when you look at a conference and here is CMS 904 01:00:02,700 --> 01:00:05,570 presenting their results and here is ATLAS presenting their results, 905 01:00:05,570 --> 01:00:08,300 they pretend like the other experiment is not even there. 906 01:00:08,300 --> 01:00:11,730 And that’s the point of it: they’re not angry at each other. It must be 907 01:00:11,730 --> 01:00:16,070 2 separate experiments because obviously you can’t build a second accelerator. 908 01:00:16,070 --> 01:00:18,720 So you try to have redundancy in order 909 01:00:18,720 --> 01:00:22,900 for one experiment to confirm what the other finds. 910 01:00:22,900 --> 01:00:27,900 Herald: Okay. It’s midnight and we’re out of time. 911 01:00:27,900 --> 01:00:31,400 So please thank our awesome speaker! *applause* 912 01:00:31,400 --> 01:00:39,163 *Subtitles created by c3subtitles.de in the year 2016. Join and help us!*