Gossip Center

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CAITLIN MALONE: Thank you very much for having us. We're very excited to be here and it's great to see so many people. So I guess as Ibrahim said, our format is sort of-- the first part I guess I think of it as sort of a story time. So there's been a lot in the news, especially in the last six months or so, as we've gone through the Higgs boson discovery process. And that's something that we were both at CERN for. I've been there for a couple years and Jens has been there for? JENS DOPKE: Ages. CAITLIN MALONE: A long time. JENS DOPKE: Too long. CAITLIN MALONE: Yeah. And so I guess our purpose to come and talk to you today is to speak a little bit informally with you, to tell you about what it was like to be there. Because it was actually a really, really interesting process to go through, a discovery like this, maybe teach you a little bit of science, if we can sneak it in between the edges, and then answer whichever questions you have for us. So that having been said, if you have questions as we go, please feel free to interrupt, because every once in a while we can slip into jargon. And it's best if you catch us when we're doing that. So with that, I'll begin. So the place that I want to start is in 1963, actually, which is when the Higgs boson was first theorized by Peter Higgs and a handful of other theorists, who were just a little bit less lucky in getting their name tapped onto the boson. And that's really what it is. But they were looking at what we call the standard model of particle physics, which is a collection of theories that describe all the particles that we know about, and the way that they interact, their masses, their couplings with one another, things like this. And one of the things about the standard model that was a major flaw in the model at the time-- and this is what the Higgs boson solves-- is that there's no mechanism in the standard model for particles to have mass. We all know that particles have mass. Moreover, if they didn't, then nothing would work properly. And so what Higgs and his contemporaries were able to do was to do a manipulation of the equations, basically a change of variables, that introduced a mass term to the equations of the standard model, and therefore sort of endowed all the particles with mass. And the term that allows you to do this introduces what we call the Higgs field, which is a field. Sort of like an electromagnetic field is one type of field or an electroweak field is another less-known type of field. And the Higgs field permeates sort of all the space/time. And as particles travel through it, they interact with it, and that's how they pick up mass. And so when we have fields like this one, one of the things that we know about them is that they have to be conveyed by particles. And so the particle that's corresponding to the Higgs field is Higgs boson. So the Higgs boson is now on the scene in 1963. And the question is can we discover it? So when I say discover the Higgs boson, what I mean is a very specific thing, which is that what we do is we don't discover-- well, actually, let's start with CERN. Can you pull up the slide of CERN? Thanks. Sorry. So let me step back a moment. So we're experimental particle physicists. So what we do is we try to create the particles that we're looking for in high-energy particle collisions. JENS DOPKE: What's [INAUDIBLE]? CAITLIN MALONE: The circles. AUDIENCE: JENS DOPKE: Oh. CAITLIN MALONE: Yeah, that one. Thanks. So we do is we have a particle accelerator. It's 27 kilometers. It runs along the French/Swiss border outside of Geneva. And we run protons through the accelerator in two different directions. It's a ring. And at four points around the periphery of the ring, the protons will actually collide with each other. And we create all kinds of new things that we're trying to study. So underground at the different locations, we then-- let me draw a picture for you here. And the accelerator is sort of going in a ring like this. We have four interaction points going around the detector, where the beams come into collision. And then what we do is we're part of a collaboration. We build a detector basically around the collision point so that we can detect the particles that come out of the collision. It's a cylindrical detector. Sort of encompasses the collision point like this. And we call it Atlas. Now, we have some compatriots across the ring on the other side, which are our competitors, but in a friendly way, called CMS. And they will figure prominently in the story. So just very briefly, when we're searching for a new particle, what we're actually looking for is not the particle itself, but for the particles that it decays into. So for something like the Higgs boson, it only lives for a fraction of a second and then breaks apart into other particles. Sometimes those particles then break apart into still more particles. And so what you need to do is you actually get sprays of particles that come out from the collision point, and then you detect them as they traverse your detector. And from that, you kind of reverse engineer the Higgs boson. And so what you're looking for is for excesses of events in the specific decay branches. And once you see enough of them, then you say, OK, it looks like there's indications in this particular decay channel that there's a particle here. And then once you reach a certain statistical confidence in that statement, you can say we've discovered a new particle. Could you pull up the branch interactions that we had up just a moment ago? Thank you. So there are three decay modes of the Higgs that are really important for this talk today. So what this is showing is basically the different ways that the Higgs boson can decay. And I'll just point out a couple of these to you that are the most important. They can decay in any one of these different channels. But for our story today, the most important ones are WW, it's this green line, ZZ, and gamma-gamma, this purple one down here. So let me point out a couple of things to you that are important about these. And these are the reasons why these are so important. So ZZ, I'll start with ZZ. As it happens, the Higgs is at 125. So the ZZ is a pretty good branching fraction of maybe 30%. ZZ is really nice because it's a very clean channel. You can detect all of the decay products that are coming out of the Higgs collision. And it's a very low background channel. So this is a channel where you can actually make a discovery with dozens of events, which is really nice. Gamma-gamma is also very clean. We can pick up both gamma rays in our detector. So that's really nice. And we can completely reconstruct the Higgs. A little bit higher background, but still relatively low background compared to some of the other ones. The problem with gamma-gamma is how low the branching fraction is. Only one out of 1,000 Higgs bosons decays to gamma-gamma. And when you're only producing something like a few Higgs bosons every hour, this might not be all that many events. You have to collect lots and lots of data to be able to see enough of them in gamma-gamma. And then WW is a really nice channel because it has this nice high branching fraction, even to 100%, depending on what the mass of the Higgs is. But the thing about WW is that when the Ws decay in our detector, one of the particles that they decay to is a neutrino, which is basically impossible for us to detect. And you need specialized detectors to see them. And so what this means is that you can't completely reconstruct the W, because you're missing one of the particles that you would need to reconstruct it. And so you get kind of funny blobs where you had Ws. And then when you take your Ws, add them together to try to get Higgs, you get kind of a fuzzy blob. But these are the three channels that we have to work with to make a discovery. So now I'm gong to fast forward to 2011. So the Higgs-- yes? AUDIENCE: Is there a significance behind the names of those channels? CAITLIN MALONE: Yes. So these are the particles that the Higgs is decaying to. So gamma-gamma is two photons. And WW and ZZ are just different kinds of particles they can decay to. So then let's fast forward to 2011. So at this point, the LHC has been on for a couple of years. And the LHC, there's a twofold purpose to it, I would say, to first order. The first is to look for any kind of physics beyond the standard model. And second, or maybe even first, depending on how you want order these things, is to find the Higgs boson. So the real focus of the collaboration at this point is to find the Higgs boson. And there are hundreds of people who are working on the different decay channels looking for excesses in each of their channels. And in 2011, I had just been at CERN for a couple of weeks, and it was a very interesting weekend. It was Easter weekend, actually. And so it was the Thursday before Easter weekend. And so everyone's kind of-- they're starting to go home. People are ready to have a four-day weekend. And there's an email that goes out that there's a group. There's a small group of people, three or four people, who have been analyzing some data independently, on their own. Not part of one of the major efforts, but sort of as a project that they're doing independently. And they see an excess in one of the channels. So this is big news. And so what's going on here is a little bit of skiing off piste, I think. They weren't doing anything that was inappropriate. But at the same time, now all of a sudden the collaboration is really focused on what's going on in this channel and might this be actually a discovery. One of the things that was really intriguing about it also was that the mass point that they happened to be seeing an excess at was a place where there had been a little bit of an interesting excess on a previous experiment, before that experiment was closed down. So maybe this is corroborating proof of something that we already had a hint at before. And then something very dramatic happened, which was this internal document telling about this hint that they had seen was posted to a blog. And we still don't know who did it. But this was actually a big problem, because it puts a lot of pressure on us to then very quickly figure out what's going on and not work in our usual comfort zone, which is very slow and deliberate. And so as turns out, this was a false alarm. It took a couple weeks of truly working around the clock to figure this out. But we learned something very important from this experience, which was that we had to be very careful about what we said. Because as soon as anyone said Higgs in public, a lot of eyes all of a sudden came on to CERN. And so we wanted to be very sure that we knew what to say when they started asking those questions. So we continued to run the detector. We continued to collect more data. And in general, the more data that you have, the more confidence you can have in detecting a particle. And then there's a round of conferences that come around in the winter. And before those conferences, we wanted to have sort of a status update on the Higgs boson search. And so this was too early for us to say that we thought that there was anything. There wasn't enough data that we would be able to say anything definitive anyway, but just to give a status update. And there was a little nudge in the most interesting channels at 125 or so GeV. So it's right at this point here. Now, I'll just stop for a second to point something out to you, which is that 125 is actually really nice. Because if you draw a vertical line at 125, you hit all of these lines. So you have all of the decay channels that can come into play here. Whereas if you're down here or you're up here, then there's a lot less flexibility that you have for looking for it in different decay channels. But since we're looking now at 125, we have gamma-gamma, we have WW, we have ZZ. So all of the major players are now in the game. But there wasn't enough data that we could say with great confidence that we thought there was something there. There was something like a 1 in 100 chance that what we were seeing was due to a statistical fluctuation in the data, which is simply not enough for us to say anything. The thing that was really interesting for me, personally I remember at the time, was that CMS, which were sort of our doppelganger on the other side of the collider, they saw peaks in the same channels at the same mass. So it's not just us. If it were just us, I think people would have been much less excited. But the fact that CMS was seeing something too was pointing towards that there might be something physical that's actually going on in the detectors here. So now we'll fast forward a little bit further, about six months, to June of 2012. So we're working our way up to the-- yes? AUDIENCE: [INAUDIBLE]? CAITLIN MALONE: Everything is basically as independent as can be. So let me continue to tell my story. And then ask your question again, if I haven't answered it. Because one of the things that's really important is sort of the interplay between the two experiments during the discovery process. So in June of 2012, there was a conference that was coming up in mid-July. And everyone knew that there was going to be a Higgs update that was given, one by Atlas and one by CMS. So at this point, we should have enough data to be able to say something fairly conclusive. And the magic number that we needed to be working towards is 5 sigma significance. This is 5. So if we can reach this number, then we can say that we have a discovery. And this number is the number that corresponds to basically there's one in a 3 and 1/2 million chance that what we're seeing is due to a statistical fluctuation. So it's a pretty high degree of certainty. And the reason we want to do that is, like I said, because you don't have a false alarm. And because there are 3 sigmas and 4 sigmas that have come and gone. So 5 sigma seems to be safe. And this 5 sigma corresponds to the combination of all the decay channels together. So maybe you see 3 sigma in ZZ. That's not enough. But if you see 3 sigma in gamma-gamma also, then you can put those two together statistically, and you can say potentially, depending on how the channels are correlated, that have 5 sigma overall. So 5 sigma is the magic number. And we were at something like to 2 to 2.5, I think, in December. And so I was at a summer conference in France with a bunch of my friends. And some of them are on CMS and some of are on Atlas. And this is something we shouldn't have done, but we were excited enough that we did it anyway. Which was that I as an Atlas member saw some of the CMS data. So what CMS had been doing-- and this is what Atlas does too, is they blind their data. So they specifically set aside the data where they think the signal might be hiding. And they look in side bands or control regions to optimize the entire analysis. And only once that's complete do they unblind and finally look for the particle. And the reason that we do that is because we don't want to bias ourselves and accidentally get excited about something that we see in the data and then amplify it and sort of bias ourselves that way. And so CMS was unblinding. And so there was this big call which had 300 people on the line. And we were all dialed in, and we were huddled around an iPhone, looking to see what the CMS results were. And the CMS results looked really, really good. It was really, really exciting. And so we knew that if CMS was seeing something that was this good, then Atlas should be too. And sure enough, the next week, Atlas unblinded their gamma-gamma, and it looked really good. It was something like 3 and 1/2 sigma. And then analogously in ZZ, now ZZ is starting to come online a couple weeks later. And ZZ now sees something like 2 and 1/2 sigma. So at this point-- and this is the last that I heard of the CMS results until the 4th of July. So there is some bleeding in between the two of them. But we tried very hard, especially at this point, to partition the two collaborations so that the excitement of one doesn't sort of amplify the efforts of the other. So now the race is on to try to get the results for the conference in the summer. So we have a hard deadline that's in the middle of July. And there was a lot of excitement within CERN about what the two collaborations were seeing. And there were rumors that were flying back and forth a little bit. And so the director general of CERN then called a meeting in late June between the spokesperson of Atlas, the spokesperson of CMS, and the director general of CERN, in which the spokespersons sort of tipped their hands to one another-- and this was by agreement-- and to the director general, and said, this is what we see so far. And at this point, the director general of CERN said, this looks like it will probably be good enough that I think we want to have an announcement that's coming out of CERN, rather than having the announcement that's coming out of this conference, which last year happened to be in Australia. Because we kind of feel a little bit of possession, I guess, of this discovery. And we want it to be ours to give to the world as sort from our own home. So this is taken as a very good sign, that all of sudden there's now a special seminar that's been planned at CERN for the 4th of July. And this at this point is several weeks in the future. And so the question is, what are you going to be able to get done before the 4th of July? So at this point the accelerator, as it happens, is running really, really well, and we're getting lots and lots of data every day. And we need every bit of data that we have to be able to get enough confidence in these channels that maybe we can combine them and get the magic number. We can get the 5 sigma. And usually as the data comes in, we have to a round of processing on it, basically, and calibrations and make sure that there was nothing wrong with the detector conditions when it was taken. And there's this whole rigmarole that the data gets put through. And it usually takes something like a couple months. And so at this point, there's this massive mobilization at CERN to bring dozens and dozens of people online from whatever they're working on, to start working on the data processing, so that we can get the data out in a matter of days and weeks, instead of in weeks or months. And it was really magnificent to see this big effort kind of come out of CERN because we had to get all this data just through as fast as we could. And they did it. They added it in really, really quick. It was magnificent to see how fast they were adding in the data. They were taking it one week and it was in a plot the next week. And that's absolutely unheard of. So we're getting more and more data every day. The numbers are being updated, more and more and more every day. The reason I say this is because I wish I could tell you exact numbers and bring you through the progression in numbers as we were watching the significance of these channels grow. But it was hard to keep track, honestly, at this point. Every day there's a new number coming in, depending on which channel it is, which data set they're using. Everything's looking really good. And so there's one channel that I haven't mentioned in a little while, and it's WW. And WW is also in play. But WW had yet to unblind, because they had been a little bit behind the curve, because they hadn't gotten some data sets as soon as they needed them. And so it was only five or six days before the July 4th announcement that we know is coming. And so the question is what to do with WW. So the decision was made that they would talk about unblinding WW, try to decide whether they were ready to look at the data yet in the sigma region. But before they did the unblinding deliberation, they had to decide whether they were going to include WW in the combination. So is this channel, regardless of what we do, and we know personally amongst ourselves this is something that we're going to be ready to tell the world about on the 4th of July. And the decision was that it should not be included in the final calibration, because there was simply not enough time to do all the checks that you would want to do in those four or five days before the seminar. And you have to be extremely careful here, because this is where some of those lessons that we learned the first time around come into play. That if you get too aggressive with WW, and you include it because you unblind it, you say oh, this looks really good, let's include it. But you haven't done all your checks. Maybe there's a problem, and you've accidentally just discovered a particle that isn't really there. Likewise, let's say you unblind it and there's different kind of problem, and WW actually sees less than they should. Well then, let's say you're at 5 sigma before. Now you add in WW, and you've taken yourself down to 4.5. So you just undiscovered a particle. You really want to know what's going on with WW. And the decision was we're not confident that we can do all those checks we need to do. So WW-- this is now the Wednesday before-- this is six days before the announcement. They make the decision to unblind WW. But it's going to stay within the collaboration, and it's not going to be included on the 4th of July. And so this is where the story diverges a little bit in an interesting way. Because now there are two different things that we need to keep track of. One is what's going to be included on the 4th of July, what we're going to be able to tell everyone, whether we can say the Higgs boson has been discovered. And then the other one is sort of what we privately know as collaborators and as people who are privy to this information, whether we know that the Higgs boson has been discovered. So let's say that we only have 4.2 sigma on the 4th of July. But we know the WW is waiting in the wings and WW has 3 sigma, and that's going to push it over the threshold. So at that point, we can't say we've discovered the Higgs boson. But let's be honest, we're going to know for ourselves whether we've discovered the Higgs boson. So this Wednesday afternoon was really, really exciting. Actually, when they unblinded WW at about noon. And so that afternoon, you're just kind of sitting there, and you're like, I'm pretty sure they're discovering a new particle right now. That's really neat. And so the next day, the unblinding had finished running. There was an official talk to be given on Friday. So this was four days before the announcement, but the rumor started to go around. And so they said that they had unblinded and it looked really good. So we're all saying oh, we should have put it in, we should have put it in. So regardless of what we can say the next week, we found it. This is it. So now the issue is what are we going to be able to say next week? And what's happening now is that you need to look at the updates to the gamma-gamma. You need to look at the ZZ. You have a little bit of information from last year's analyses that you can mix in. But gamma-gamma and ZZ are the powerhouse channels. And so it's just an issue of like putting those together and seeing if you have the magic number. And so I have a particularly well-connected friend at CERN, or maybe she was just in the right meeting, I don't know. And so we were eating lunch with her on Thursday. And we were all gossiping about this, because, of course, we're gossiping about this. And so one of my friends kind of leans in. We're speaking very quietly, because it's a cafeteria that's 50% Atlas and 50% CMS. And if you want to learn secrets at CERN, just go sit in the cafeteria and listen for somebody who's too noisy. And so one of my friends, she said they've done the global combination, they know what the number is for next week. They're going to have it in a meeting tomorrow. But if you know the right people, you can find out today. So one of my friends kind of leans in, and he's like how many sigma do they have? And she goes [KNOCKING SOUND] and kind of catching herself. So at this point, you know it's the bag, right? We know it for ourselves because we have the WW. Like if the WW had been mixed in at that point, it's like, I don't even know, 6.56 sigma or something. We're fine. But not only that, but we get to tell everyone. So this perfect. At the same time, the question is, what does CMS have? Because I'm pretty sure that there's a Higgs boson at this point. And if there's a Higgs boson, if we can see it, they can see it. And so now the competition comes into it, back again a little bit. Because OK, so we had 5 sigma. But what do they have? Do they have 6 sigma? I hope they don't have 6 sigma, because I want to find it. So even though we sort of had all the physics cards on the table, even up until the morning of July the 4th, there was still reason to go to seminar because you only have half the story, and you want to see what other guy has. So we go to talk to the next day, and WW looks pretty good. But they're not going to be including it. They need to run some more checks, and it's going to be out in a couple of weeks. They do the global fit, and it's 5.1 sigma, I think something like that. And we all go home, and we have a quiet weekend. But it's a really cool time, because you know that it's going to be a big deal in like in three days. And there's 5,000 people in the world who know this, and you're one of them. Oh, this is going to be so great. So the word had sort of started sneaking out at this point. There were people there-- Peter Higgs said had been called a few weeks before. And they said, you probably shouldn't plan any vacation for early July. We need you to come to the CERN. So now we're seeing Peter Higgs in the CERN cafeteria, and this is a very promising sign. So there's this announcement. It's going to be made on the 4th of July. And everybody wants a seat in the seminar room. And the seminar holds-- I don't know. It's reasonably big, but it's not huge. It's 500 people, maybe 300 people. And half of those seats are going to go to people who funded the experiment and the higher-ups on the collaborations, as they should. But a fraction of the small space is going to be reserved for the schmucks like us. And we had learned our lesson from the December talk because the December talk's seats were hard to come by. And we had showed up four hours early for that. JENS DOPKE: Is this the point at which I should bring up another picture? CAITLIN MALONE: Yeah. Why don't you start bringing up pictures. We have a bunch of pictures. Jens and I were both at this talk. So there's Jens, sitting there on the floor for hours, I'm sure. And we just slept there the night before, honestly. They locked the doors to the seminar room because they knew that people like us were going to do this. And so we all lined up in the hallways, and we watched "The Lion King," and we tried to sleep, and got very excited, and read internal notes because we wanted to get all the plots again, because they looked so great. JENS DOPKE: We should stress here that this was at 5:00 AM, where people came in thinking they were early enough to get into the auditorium. CAITLIN MALONE: Yeah, I don't know what they were thinking I don't know what they were thinking. I think the latest you could get there and get a seat was-- JENS DOPKE: 4:30. CAITLIN MALONE: --4:30, maybe. And so then seminar starts. And we're all trying to stay awake, actually, because we have been up all night. And the CMS talk was first. And so the CMS talk actually was really interesting. Because CMS had done slightly better than Atlas in the respect that they had more data in more channels that was ready. So their WW was more updated than ours, for example. And CMS, if they did the global combination with all of their channels minus one I think, they got to 5.1 sigma. And then they had a little bit of a downer fluctuation in the last channel. And it bumped them to 4.9. And it's just like, oh--- I mean, 4.9. I mean, come on, you discovered a particle. But I thought that was interesting, just because this is a case of where you can get a little bit unlucky. And like I said 4.9, you're fine. But they did happen to get a little bit unlucky there. And then Atlas does the second presentation, which, of course, is less of a surprise, because we've seen all the slides already. But we're, as it happens, able to say the magic words of 5 sigma. And of course if you were to Atlas and CMS together, you would be at, I don't even know, 8 sigma or something. Like there's no doubt at this point. Atlas was just a little bit lucky in that we got to, like I said, say the magic words. And it was very exciting because I think especially crossing that 5 sigma threshold was really meaningful, I think. And there was a big round of applause, and especially for Atlas that I remember. CMS definitely got one too. But I particularly remember the Atlas one, because it went on forever, just for like four minutes of just-- like this is starting to get ridiculous, guys. And it was all very nice, with congratulations from all over the world. And Mr. Higgs was there and may or may not have wiped a tear from his eye at the moment that they flashed up the slide. And it was really great. So in the afternoon, we're all kind of exhausted, and some of us went home for naps. The ones who had a little bit more stamina stuck around for the free champagne. And there's a series more of additional studies that we had to do at this point. I mean, the big discoveries-- I mean, this is sort of the exciting part is now coming to an end a little bit. But one thing that I want to spend just a moment talking about now and sort of gesture towards the future is like, OK, so we found a particle, now what? And the first series of questions that had to be answered was, is it the Higgs boson? Because it looks like a Higgs boson, and it seems about right. But you need to do things like measure all of these branching fractions. You need to do things like measure the spin of the particle, which is just one of its quantum mechanical properties. But if it has the wrong spin, it's not a Higgs boson. It's something else, and it's maybe even more interesting. So there were a series of studies that then had to be done. So we certainly partied on the 4th of July. But we were back at work on the 5th of July trying to figure this stuff out. And they finally wrapped up those studies, at least the first round of them, enough that a couple weeks ago at the Moriond conferences, which is another set of conferences that they have in March, they were able to say definitively this is a Higgs boson. So now we can say things like we found the Higgs. But there's still a lot more that they're trying to find. So I think I'll take the last few minutes here just to gesture towards what we're looking at in the future as far as things like the Higgs is concerned. And that is something like looking for additional Higgs bosons. And the reason that I bring this up in particular is because it's something that I work on. This is my thesis topic, is looking for under certain classes of theories that go beyond the standard model, so these are the kinds of theories that we're most interested in investigating, there's not just one Higgs boson, but there's five. And so it's my job to find the second one. And so there's a number of different efforts on these sorts of fronts, that now we have this great new toy that we can play with and try to crack open the standard model a little bit more. And so that's just one gesture towards some of the additional ways that we'll be doing at CERN. So technologically, just very briefly I'll bring in Jens to say a couple things about-- yeah, just a couple minutes. And then I think we'll be ready for questions in just a minute or two. So CERN right now, it's at an interesting point. We've stopped taking data. The whole goal was to find the Higgs boson in round one, and we've done that. And now what we're doing is upgrading and repairing parts of the accelerator and upgrading and repairing parts of the detector. So there actually won't be a whole lot of new data being taken at CERN for the next two years. But the data analysis of the data that we've already collected will be continued for the next two years. And so hopefully there'll be a couple more surprises to find in there. This is something that Jens is particularly involved in. So Jens, do you want to say a couple words about what they're doing? JENS DOPKE: I don't want to say much. I mostly came here to show pictures. So what Caitie has not shown you is pictures. And I encourage everyone, because you're in Zurich, and particularly the people in the room are in Zurich, get over there and get downstairs. We have a long shutdown now for two years. The caverns are open. So if you're interested, you can just sign up for a visit at CERN and go about 100 meters underground and see the experiments. AUDIENCE: Do you have a website that we can go to and sign up for? JENS DOPKE: You should look at cern.ch and then you'll probably find something like "visits" or how to get there. CAITLIN MALONE: Talk to us, we can-- JENS DOPKE: Talk to us, yeah. AUDIENCE: [INAUDIBLE]. JENS DOPKE: Say again? AUDIENCE: Can you come as a group? CAITLIN MALONE: Yeah. JENS DOPKE: Well, you can come as a group. For typical underground visits, we're limited to 12 persons per visit, which is about 45 minutes. So if you're coming in with 500 people, then better plan for a long week. AUDIENCE: [INAUDIBLE] question. Could you repeat the question for group? CAITLIN MALONE: Yes, of course. The question was how to get underground. JENS DOPKE: The question here in the room was how to visit and how to get underground. OK. CAITLIN MALONE: Yeah. But there's ways through the CERN visit service that they can do these arrangements, yeah. JENS DOPKE: To give an outline, we have about 80,000 visitors per year. And that's only the number that we know of. People like Caitie and I, we typically get our family there, our friends there, or whatever, and we guide them around. And that's not included in the official numbers. So we're talking about a little more than 100,000 visitors per year. That does not include CERN open days, which will happen, for example, in September, I think this year, which is where we have two days on the weekend which are open, one for the families and friends of CERN people and one for the general public, which has another 80,000 visitors in two days. So that's roughly what we're talking about. What you get to see at CERN is things like this. And I cannot really point at it, but maybe-- CAITLIN MALONE: Here-- --Caitie can point at it. CAITLIN MALONE: --let me take the laser. JENS DOPKE: So what you get to see on the ground is pretty large structures. The photos that I took here are partially from 2007, 2008 when the cavern was still empty, which you see here, because the big structures are missing. CAITLIN MALONE: The gap here, for example. JENS DOPKE: There's a large gap. What we do is we build really large detectors on the ground, and they fill the caverns. In the case of Atlas, we built it underground. That means we're bringing parts down and building like a ship in a bottle basically. Whereas CMS builds everything upstairs and then brought it down in nine slices, the central slice being about 3,000 tons and being lowered 100 meters. They rented a shipyard crane for this. The biggest structures Atlas had, you're going to see in one of those pictures, is 280 ton magnets, which are 11 meters in diameter. The hall above the surface is roughly 11 meters high, and the crane is inside the hall. So if you want to attach the crane to the structure, you have to lower the structure halfway into the hole and then attach the crane. That was funny moments back in 2007. As you might realize, Caitie does data analysis, while I do hardware. So I typically have good photographs, she has better plots. We're going to get to some plots too, because we have some that might explain how the discovery works. This is the structure I was talking about. That's an 11-meter diameter magnet. So the thing that looks metallic in the center, supported by this orange structure. It can slide into the detector. CAITLIN MALONE: Like so. JENS DOPKE: So you can actually move this. It has pneumatic feet, where we put in pressure. And then it's supported like a hovercraft and can slide in. It's not as simple to move, but kind of. The structure that you see aside of it, which looks like a large piece of cake, is a 22 meter muon chamber in diameter, which can also slide over it, suspended on rails at the top of the cavern. And it can slide over it to seal off the detector. This is Caitie and another colleague from Great Britain standing on a platform inside the detector. To give you an impression, we have 11 stories on the C side of our detector. There's a C and an A side. The A side has 12 stories inside the cavern. You get to climb up four floors to be where we were standing at that time, through detector material. So you're climbing between active detectors. And in this particular case, you're standing next to a 1,000-ton calorimeter that's filled with liquid argon gas. We have developed 90,000 liters of liquid nitrogen, 40,000 liters of liquid argon in this cavern. And it's a very particular feeling if you're down there. I think Caitie enjoyed the day very much. CAITLIN MALONE: I did. It's like a big, radioactive detector tree house. It's really great. JENS DOPKE: The first time I was there was in summer 2006. I keep getting back there whenever I can because it's the greatest place on Earth. This is when we transported the part that I worked on at the time. This was lowering a four-kilogram detector itself, with lots of support structure, which had to be inserted as the very last component, into the center of the detector. The transportation effort alone was complicated as such, because we couldn't crush it anywhere. We couldn't just roll it over to the cavern and then attach it to the crane because it had to be suspended, such that it wouldn't suffer from shocks during the transport. So we couldn't just roll it over. It was craned over from one hall into the other. Also we had only a half an hour window where the weather forecast was good enough to get it over without it being drowned in rain. CAITLIN MALONE: So just for a sense of scale, let me just jump in here for a second, because I just learned this recently, and I think it's really cool. So you have a sense now that the detector is the size of a large building. But the alignment of the components within the detector is known to the width of a few human hairs. So it's very large, but it's very precisely aligned. And so if you have something like you roll over a pebble wrong, then it can mess up that alignment. That's why we have to be so careful in the installation. We should probably take questions in a few pictures here. JENS DOPKE: We're almost there. OK. So this is where it arrived. But I mean, we're done. CAITLIN MALONE: Oh, OK. Perfect. We overspoke a little bit. But we get carried away. JENS DOPKE: If you want to see results, we do actually [INAUDIBLE] results. Because physicists typically focus on getting data analyzed and then getting papers out. Making this easy to understand for the general public is a tough job and takes a lot of time, that we need to make time for that. That's our weekends. So I suppose that someone messed up this weekend when generating-- and made GIFs like this. CAITLIN MALONE: Right. We can just let this play in the background. But let me just introduce you to it before I take a couple-- so this is the ZZ. So what you're looking for is you're looking for an excess of events that's not explained by basically these colored structures. So the colored structure is the background Monte Carlos. This is our model of what a background will look like in this channel. This axis here is the reconstructed mass of the Higgs. So if you start to see a bump, then that's the mass of the particle that you're looking for. And so what this is doing is it's scrolling through time and it's adding more and more data to the histogram. And so you can start to see that there is-- yeah, if you can reset it-- that there will be a peak that will start to emerge right here that isn't apparent from sort of the red background. And so once you start to see a peak that isn't explained by any of the background, and that's what has to be a signal. So this is actually watching where the points here or the data, actually watching the Higgs peak grow in real time. And then at some point, it'll zoom in on this exact excess and then fill in the Higgs underneath it with sort of the signal Monte Carlo. Say that's what a Higgs would look like. OK, I think with that we've overspoken by probably 10 minutes or so. But-- AUDIENCE: [INAUDIBLE]. CAITLIN MALONE: --15 minutes for questions. AUDIENCE: [INAUDIBLE]? CAITLIN MALONE: As many questions as you can ask in 15 minutes. But thank you very much for your attention. It's been a lot of fun. We hope you've learned something. AUDIENCE: This questions can be about this topic or-- CAITLIN MALONE: This topic or anything else really. JENS DOPKE: We're young. We answer questions most of the time. AUDIENCE: So [INAUDIBLE] organizer of the Australian conference [INAUDIBLE]? CAITLIN MALONE: They were understanding. AUDIENCE: Could you repeat the question? CAITLIN MALONE: Oh, I'm sorry. The question was what did the Australian conference think about their thunder being slightly stolen? I think they understood. They could see that it was maybe going to come. I can't imagine they were that happy, because it would be great if you can be the person who makes the announcement. But we did have a direct line to Melbourne for the seminar. And so a lot of our colleagues were in Australia at that point for the conference, which was starting the next day. And so they called in, and they congratulated us very nicely. And the people who were organizing the conference were a subset of the people who made the discovery. So it was a very collegial feeling. AUDIENCE: How big is the next accelerator? CAITLIN MALONE: How big is the next accelerator? JENS DOPKE: I prepared a picture for that. So the question was the size of the next machine that we're building. AUDIENCE: [INAUDIBLE]? JENS DOPKE: We are not building the next machine yet. We're thinking about building next machines and, well, upgrading the machine that we currently have, which you see on this picture in white. That's the LHC. That's nine kilometers in diameter, 27 kilometers in circumference. We're thinking about upgrading that sometime in 2022 maybe, running up to 2030. That's going to deliver a lot of data to exclude a lot of things that we're-- CAITLIN MALONE: Or discover a lot of things. JENS DOPKE: Well, we're mostly excluding. CAITLIN MALONE: We have many more ideas than we have actual particles that we found. JENS DOPKE: We're very exclusive. CAITLIN MALONE: Yeah. JENS DOPKE: But then the thing is we need a precision machine. So the LHC is a thing that collides protons. Protons are particle combinations of multiple quarks. And so we never know how much energy we actually get in a collision, because what's colliding is not the proton, but the quarks. So depending on how much fraction of momentum of the total proton one of the quarks has as they collide, you get more or less boost in one direction. What we used to have in the past and what we should have again in the far away future, kind of, on my lifetime span measured, or hers, is an electron positron collider. Because those are fundamental particles. They are not made up of other structures as far as we know. So what we got in the large electron positron collider previously was collisions where we could adjust the energy of the incident particles and thereby create a collision at a fixed energy. We would never get something else but the energy that we put in. Because as the two particles collide, they disappear completely. So all of their momentum goes into the collision. And using those machines, you can much more precisely measure the outcome. The energy we need to properly measure Higgs bosons you can roughly grasp from the scales that are shown in this picture, is 500 GeV center of mass is nice. That is because we can most probably create Higgs bosons only in associations with Z bosons. And that means we need to get up to an energy of 240 GeV instead of 125 to create both particles and make them detectable. And then the other thing we want to do is produce some very heavy quarks in pairs and measure them precisely. So producing top quarks in pairs require some 340, 350 GeV center of mass energy. So that's the rough scale we want to go to. And then you want to be able to go slightly beyond, just to measure the full spectrum and not just end exactly what you want to measure. There are also plans for building something like a compact linear collider and not just the standard international linear collider. A standard concept is the one shown in yellow, that's like 30 kilometers long in a straight line. The other concept is the compact linear collider, that's in light blue. That's 42 kilometers. It's only compact because it has a lot more energy in the same length. CAITLIN MALONE: Wait. I should say very quickly too, one of the things that's tricky about electrons and positrons, they give you very nice, clean collisions, and they're very tunable. The thing is that when you try to run them in circles, they radiate away their energy. And if you were to put electrons into the LHC, they would radiate away as much energy in a turn as you could put back in through the accelerator. So the way that we avoid this problem is by not turning them. So that's why you want to build a linear collider. But that technically more difficult. So that's what motivates the geometry there. JENS DOPKE: Linear collider geometry is the problem. As you see from the size of the structures, it's kind of hard to find a place where you can actually drill a tunnel that's this long. You want to typically build a tunnel such that it's easier to control access, such that you don't have radiation at far ends that comes out and disturbs people, which it does. So that's why we generally put structures underground. Japan is thinking about looking into that. The time scale for this is roughly 2030. And then there's other ideas around. We're not very fond of just having one idea. So this here, I zoomed out, is ideas for an 80-kilometer storage ring. That would actually be in the Geneva region. And either it would pass, as seen on the left, underneath the lake of Geneva and beyond the next mountain range that we can see from the CERN cafeteria or it would pass into the [INAUDIBLE], both of which will be complicated because you're going through multiple layers of different types of rock and so drilling tunnels in there is kind of complicated. But then you need the preacceleration structures to get proper energies into these rings. So that you only get here. CAITLIN MALONE: I think I heard a question over here maybe? AUDIENCE: I was just going to ask [INAUDIBLE] collider [INAUDIBLE] you're to do a straight [INAUDIBLE]? JENS DOPKE: So the question is whether the tunnel has to be straight or can be slightly bent on the Earth's surface? CAITLIN MALONE: Oh, to follow the curvature of the Earth over the distance. JENS DOPKE: Curvature of the Earth is not really a big deal. But it would most presumably be a straight tunnel, just to not deal with bending magnets. We'd have to refocus at some points. And we'd probably get something that we call more like a kicker magnet that adjusts the beam. But it's really fixed focusing, and it's not about bending the particle path. There must be a bending somewhere in there, because at the point where you want to collide the beams, you don't want to shoot the positron beam into the electron acceleration line. So that at that point, you have like a one degree angle or so. AUDIENCE: [INAUDIBLE]? CAITLIN MALONE: Ah, the question was about the third detector. So there are four points around this ring. And the two that I haven't spoken about are LHCb and one called ALICE. LHCb and ALICE are both-- so CMS and Atlas we call sort of general purpose detectors. LHCb and ALICE are more focused on particular types of physics. The LHCb is there and doing wonderful physics. They focus on the physics of B hadrons. And the reason that B hadrons are interesting is because we're trying to understand, not to put too fine a point on it, but why the universe is made of matter instead of antimatter. Because there's no physical reason why we should be made of matter, instead of antimatter. And B hadrons, as it turns out, show some asymmetry between Bs and anti-Bs. And so it's a very interesting laboratory for studying the answer to this question. And then ALICE, just briefly while we're talking about other detectors, is designed to do heavy ions. So for a couple months every year, they take all the protons out of the LHC and they put in lead nuclei. And they smash them together to try to basically create the environment that existed just a fraction of a second after the Big Bang, when quarks and gluons were not joined together into protons and neutrons but were actually sort of floating free. And this was obviously a very interesting laboratory for us to try to understand the very beginning of the universe. And that's something that ALICE specializes in. Yes? AUDIENCE: I have question. Are there risk parameters [INAUDIBLE]? CAITLIN MALONE: Like, like-- oh, things like black holes, risks like black holes. JENS DOPKE: Just a quick vote in the audience, like who's heard of black holes? CAITLIN MALONE: I've heard of black holes. I've heard of black holes. Yeah, yeah, yeah, yeah. JENS DOPKE: That's good. Is it clear that when we're talking about black holes in the context of the LHC that A, we have to assume very special theories. And B, we're talking about microscopic black holes. We're not talking about the thing that eats up suns. We're talking about something that's very, very tiny. AUDIENCE: [INAUDIBLE] JENS DOPKE: In the beginning. Yeah, yeah, yeah. Yeah. It does suck for a while and then it grows bigger. CAITLIN MALONE: So to first order, we're pretty sure that they wouldn't be there. There are smarter people that me who crunch the numbers, that says we just don't have enough energy. But let's suppose we got that equation wrong and we do create a microscopic black hole. Stephen Hawking, one of the things that he sort of made his name theorizing was that black holes can actually evaporate. And as it happens, small ones evaporate quite quickly. So they would only live for a fraction of a second. Now, let's suppose that Stephen Hawking is wrong and we have a stable black hole, stable microscopic black hole that's floating around the inside of the detector. And then they did a calculation like it's doing a little PacMan through the detector and it's just gobbling up atoms as it gets close to them. And how long would it have to go before it would be, I don't know, the size of an atom or something like that? And it was millions of years. AUDIENCE: So there could be one in there. JENS DOPKE: Well-- CAITLIN MALONE: And that is why we-- here we go. I think we promised something like wild and irresponsible speculation. And I am glad you're here to provide it for everyone. JENS DOPKE: Let's go further into wild speculations. We do know about objects like neutron stars, which are roughly the mass of the Sun or two, but the size, a diameter of a kilometer. So what these feel like is matter in the core of an atom, the nucleus of an atom, just the size of one kilometer diameter. The moment a microscopic black hole would exist, it would hit a neutron star, and it would just be dissipated. The neutron star would go away at that very moment. Now, we know that cosmic radiation exists. We have some very fancy experiments, for example, in Argentina that has 3,000 square kilometers of Earth's surface monitored for energy deposition from the sky. We look into the sky with telescopes to find gamma ray bursts in the upper atmosphere. We have a South Pole telescope that monitors the cosmic microwave background. We have quite a few things that know that there's cosmic radiation. And we see cosmic radiation in an energy range that we will never reach with any accelerator that we can build on this planet, because the planet's diameter is not large enough. So we have a pretty good idea that if microscopic black holes would exist and were stable, that they would be created a lot more often and a lot bigger in cosmic radiation, hitting anything that's in their way. So if neutron stars exist, then we can safely assume that microscopic black holes, if they existed, were not stable. Because otherwise, they'd be eaten up the moment they existed by something that hits them. AUDIENCE: I think [INAUDIBLE] energies in the black holes. JENS DOPKE: Has anyone ever heard about RHIC? RHIC used to be a heavy ion-- is still a heavy ion collider at Brookhaven National Lab on Long Island. In the '90s I think, when it ramped up the STAR experiment, there was a rumor that they would create black holes and destroy the universe. I think the rumor about the black holes came up ever since someone fancied the theory that it would contains black holes, because black holes are cute. But the problem is the moment someone comes up with a cute idea that sounds kind of vicious, someone else comes up and goes to an American lawyer and says, I want to get money for this. This is mostly how it works. People are more easily scared than assured of being safe. And that's the big deal. That's why we actually have to take care of publishing results the way we communicate with the general public. Because the general public tends to receive the negative message much better than the positive message. CAITLIN MALONE: That having been said, there are analyses that are searching for black holes. I mean, we're looking for them. I wish we had found them, but we haven't. AUDIENCE: How safe is the beam itself and can you slice bread with it [INAUDIBLE]? CAITLIN MALONE: We've tried. JENS DOPKE: So the question was about beam safety. So we've done-- AUDIENCE: That means you can slice bread with it. CAITLIN MALONE: So we're very clear about the bread, yeah. JENS DOPKE: Let's be clear. No, you cannot slice bread with it. You can-- AUDIENCE: Melt. JENS DOPKE: Melt-- you can melt a cubic meter of copper with the energy that's within the beam. AUDIENCE: [INAUDIBLE]? JENS DOPKE: No. You can cut the bread with it. But you'd have to get the beam to the bread. We did test studies with copper. And we can shoot very nice holes into copper. When we're talking about beam safety, we have two so-called beam guns, one for each direction, which are sitting in Point 6 of the LHC, that's somewhat pointing towards Zurich on that ring. No, but the pointing direction then is towards the UK and towards Italy. So they are sitting on the side of Zurich of the ring, but pointing in different directions. Beam dumps are basically a large structure that can be cooled, that heats up to 700 degrees Celsius if you dump the beam into it, which are there for safety. So if we have the full LHC filled with protons, we're talking about 2,808 packages per direction, with about 100 billion to 200 billion protons inside. The protons themselves don't have much energy as such. But there's just so many of them that it makes for a large impact. When we, for any reason, which we do very often because every now and then we have electric glitches or whatever, dump the beam, we realize there's something wrong with the machine so we are not sure we can keep the beam in shape. And that moment, it takes three turns of the protons to dump them into the beam dump. Three turns is less than a millisecond. And the time constant that all the magnets have that we have there, we have the largest magnets that you can find in the world. Magnets tend to be slow in whatever they do. We pump them up with, what, eight kiloamps, 10 kiloamps? So-- CAITLIN MALONE: Yeah. JENS DOPKE: --the time it takes for this current to go down, and if the current goes down, the magnetic field itself induces more current as it collapses, so the time constant of these magnets is so large that within their time constants, if we would just cut the wire between one end and the other, and the current could not flow, A, the current would continue to flow wherever it can. And B, the magnetic field would still be there for a while. And this while is long enough that we dump the beam. We have to defocus the beam. We have to shoot the packages into different directions in the beam dump, so as to not shoot holes into the beam dump. But yes, the beam itself is not a very nice thing. No one is underground when this happens. We have interlocked doors everywhere. So if anyone for any reason manages to open the door, that will cause the beam to be dumped. And those doors are either above surface or at least like six meters of concrete away from the actual beam line. AUDIENCE: [INAUDIBLE]? JENS DOPKE: Yeah, we do shoot holes into stuff. AUDIENCE: [INAUDIBLE] how big would it go [INAUDIBLE]? JENS DOPKE: I have no idea. The beam dump itself is a structure that's like 10 meters long or so, so as to be safe. CAITLIN MALONE: It's roughly analogous to shooting a bolt of lightning into something. That gives you an idea. It's a lot of [INAUDIBLE]. JENS DOPKE: We're talking 1,800 megajoule, if anyone wants to do the calculations. I'm not very good at calculus. AUDIENCE: Speaking of the other [INAUDIBLE], slightly off topic here, faster than light. CAITLIN MALONE: Oh right, faster than light neutrinos. What was the problem? AUDIENCE: [INAUDIBLE]? JENS DOPKE: Sadly, I don't have a picture of CNGS. CAITLIN MALONE: So the neutrinos, just a brief word on neutrinos, the faster than light neutrinos. So what is a neutrino? A neutrino is just a fundamental particle. It's very light. It's almost impossible to detect. We need dedicated detectors to do it. Atlas can't see them. And so that's why, if you remember at the very beginning, WW was so hard was because we can't see the neutrinos coming out of there. But we have dedicated experiments where we make neutrino beams at CERN and elsewhere. But the one in question came from CERN. And then we shot it through the ground to Gran Sasso laboratory in Italy. And what you do is you basically make measurements on the beam at CERN, and at Gran Sasso you look for changes in the composition of the beam between the two points. And so as sort of a warm-up measurement that they did on this experiment was they tried to measure just the time of flight of the neutrinos. And they came up with a number that said the neutrinos were traveling faster than the speed of light, which is something that Einstein might disagree with. And actually, it was an interesting case, because as it turns out, the reason that they measured that was because there was a problem. There was a loose cable in their data acquisition system. And so there was a signal that was traveling through basically their electronics crates a little bit slower than they had calibrated it to travel. And this ended up looking like a delay that the implication was that the neutrinos looked like they were traveling faster than the speed of light. So after a couple of months of very thorough and nervous investigation, they found this problem. They reran the analysis. The neutrinos do not travel faster than the speed of light. It was a really interesting case of that in particular. So the collaboration that did this was the OPERA collaboration. And there was a lot of criticism of OPERA at the time that they were irresponsible for giving this result. And I personally at least-- everyone has an opinion on this-- but I personally at least really admired what they did there. Because it was a tricky result. You put yourself in their position. You've done this analysis, you've checked everything you can think of to check. OK, maybe you didn't check your cables. But that wouldn't be the first thing that I would think of either. And you still have the result. And you can't not release it. And I don't know, maybe neutrinos do travel faster than the speed of light. And you would feel like a fool if you figured this out in six months, and you were sitting on it and then someone else scoops the Nobel Prize from you in the meantime. And so if you look back at the result as they presented it, I thought they did it in quite a responsible way, in the sense that they went for it. They said, look, this is what we find. It doesn't make a whole lot of sense to us. These are all the things we've checked, and it's not any of those. So-- JENS DOPKE: Help us. CAITLIN MALONE: --we said we would give you a result. This is our result. And very pointedly not saying, we think neutrinos travel faster than the of light. And so it was kind of interesting then to watch both the experimental community trying to figure out what's wrong with it and the theoretical community is like, ooh, if neutrinos can travel faster than the speed of light, then-- and following this through their favorite theory and I don't know, coming up with like extra dimensions out of it or something like that. JENS DOPKE: What people should understand here is what is seen on the map now. What we're doing is we're taking protons from the preaccelerator of the LHC, shoot it into a target, where they convert into muons. And then we detect the muons in two places. And as the muons disappear from one place to another, we know that they must have left a muon neutrino behind. That's the way our physics works. That's the way we can explain a lot of things. So there must be a muon neutrino whenever a muon disappeared. So at that point we can say we've produced so many muon neutrinos in this type of distance. And then we shoot them through 738 kilometers of rock and we hit our target, the OPERA detector, close to Rome in the Gran Sasso underground laboratory, with about two centimeters of precision. And they've measured the timing of both the incident beam at CERN and the arrival at Gran Sasso to a little less than two nanoseconds' accuracy. CAITLIN MALONE: Which is two feet at the speed of light. JENS DOPKE: They have GPS receivers, which they have to install above surface to get this timing. And then they have to extrapolate at CERN 100 meters under ground, and at Gran Sasso through the Gran Sasso tunnel. So actually they had to block half of the tunnel. It has two lanes. And they block one of those lanes for quite some time just to extrapolate length measurements from the outside to the inside and get the timing right at the detector. So measuring a 60-nanosecond time difference in time of arrival is complicated. And I think they've put a lot of effort into this. CAITLIN MALONE: I think I saw you had a question. Yes? AUDIENCE: You know you had the results. And then somebody from the media or from a blog grabs it, runs with it, then applies some sweeping generations [INAUDIBLE]? JENS DOPKE: Are we talking about god particles? CAITLIN MALONE: Oh, yeah. JENS DOPKE: So the question is about media and how we get around with them I guess. CAITLIN MALONE: It depends very much, I guess my opinion, on how responsibly I feel like the message has been conveyed. So one example that I'll give is that outlets like the BBC or the "New York Times," usually they have people who when they come to us are responsible about trying to portray things accurately. And sometimes it's not perfect, but that's all right with me. I'm less crazy about-- sometimes bloggers take a little bit more liberty than I would have chosen. I think that it certainly gets people interested in talking. And I think that that is a good thing. But for example, when there was this sort of spurious semidiscovery in 2011, the reason that was a problem was because it got onto a blog and it got public. And so that's an example of how I think it kind of hurt us to have something out there, but then have to say, no, no, no, no, no, don't pay attention to that. And then I guess on the very far extreme are kind of like crackpots. And I guess what can you do? People are going to say what they're going to say about whatever. JENS DOPKE: Handing the question back, how does Google deal with it? There was a question there. AUDIENCE: So when LHC was first supposed to go offline back in what was it, 2007 or 2008, there were some-- JENS DOPKE: Here's a question about the LHC accident in 2008. CAITLIN MALONE: What accident? JENS DOPKE: So the accident. CAITLIN MALONE: I'm just kidding. I know what accident. JENS DOPKE: We only had one. So again, to talk in numbers. We have 1,232 dipole magnets, which are in most places connected to one another. We're filling this whole 27-kilometer ring with magnets or accelerating structure or experiments. But that's all there is. And we only have so many. When this accident happened, what happened was there is an interconnection between multiple magnets. Those are superconducting magnets. They run at a typical temperature of like 1.9 Kelvin. We're cooling them with what we call superfluid helium, which tends to crawl up the wall and cover all surfaces and has, as far as we can measure, infinite heat conductivity kind of. Which is complicated to measure at almost absolute zero. So we're cooling this all so far just because we need the coolant flow. Because helium itself doesn't have a large heat capacity, so we need superfluid helium to get there. The problem is gases tend to expand. Well, liquid gases tend to expand as they evaporate by about a factor of 1,000, which is kind of almost always true. So depending on which gas you have, that's more or less. But a factor of 1,000 is good number. What happened there was that we had an interconnection between two superconductors which was slightly above the resistance that it should have been, plus that the heat conduction at this place was likely below the value that it should have been. So unfortunate, but what happened was that the-- and it's not that simple. There's someone making an extending movement in the background. What happened was this thing got hot. It kind of burned through. So the superconductor didn't work anymore because it was too warm. So at that point, the typical superconductor that we use is niobium titanium. And niobium and titanium are both not very good conductors. It's a wonderful superconductor up to 10 Kelvin. But as soon as it goes beyond that, gone. So what happened was the current, those 8 kiloamps or so, had to go somewhere else. And typically what we have for this is a copper surrounding. So two U-profiles that slide on top of one another, so that if the magnets extend or shrink they can still have contact. And if the current goes through the copper, then at least it can still continue. And you immediately dump the power of the magnet. The problem was in this case even the copper contact wasn't there. So what then happened-- tiny gap. So the current go somewhere else. And what it did was it jumped a little and hit the helium vessel within the magnet. So the helium and the superconductor are not within the same structure. But they are connected through metal. What then happened was the helium vessel opened. The helium sees a sudden under pressure and starts evaporating, getting hot and creating a cloud. And this then pushed partially the magnets by 1 and 1/2 meters. Each of those magnets is about 20 meters long and about 22 tons in weight. And they are bolted into concrete feet with screws roughly the size of my arm. CAITLIN MALONE: And that is why you're not allowed in the cavern when the beam is running. JENS DOPKE: That is why we have interlocked doors. CAITLIN MALONE: Yeah. JENS DOPKE: It moved a total of 55 magnets at the time, which is a long distance. Like a total of 400 meters, I think, was damaged. And it took a year to fix it and get first countermeasures installed. And right now, we're in a shutdown because we want to install more countermeasures to this. Because we are kind of sure that we've pinpointed the problematic locations. And we're trying to measure-- you can try and go online and figure out how to measure the resistance of less than a nanoamp. That's complicated. We've been managing to measure that. And the idea is now to either exchange magnets where we think that the resistances are too high in these junctions points or also install overpressure valves. Because the moment this just happens again, we need to be prepared that there's helium again extending and expanding and moving the magnets. And that would be sad. So that's what we're doing right now. AUDIENCE: How do you test beams? How do you-- JENS DOPKE: Come to CERN. AUDIENCE: --test that's it's working better than. JENS DOPKE: Here is the question then, how do we test this? This is all prototype. Like we're not building a second LHC. So the first time we switch this on is the first time ever someone is trying this. And we're only switching on the real machine. We don't have a second one somewhere in the back yard where we can try out stuff. So this is our one playground. That is why things like this happen. And they have to happen to figure out why stuff is not working. We do have above surface structures where we also have superfluid helium to operate the magnets. But you can only operate so many in a chain, because you need the space. So getting all of this assembled and [INAUDIBLE] our structure only happens underground. AUDIENCE: So basically, [INAUDIBLE]. JENS DOPKE: We only have one system, and that's the production system. There is a preproduction sample. But it never gives you the full feeling. It's like just having the engine of Ferrari and then trying to figure out how it will drive. There's a question here? AUDIENCE: How many rounds of design review [INAUDIBLE]? JENS DOPKE: A good question, in particular for the LHC. CAITLIN MALONE: Yeah. JENS DOPKE: I can tell you that for detectors, the-- oh, the question was how many rounds of design reviews did we do? So I can tell you that from the detector side of things. The technical design report for the detector I worked on was written in 1998. The last changes to that were made, I think, in 2007, probably, just before we installed. Because what we did was installed an additional heater blanket for components that couldn't be operated very cold. That was the last design change that was made. I don't think there's ever been a state at which the detector was clearly defined up until the point where we installed it. We do go through a lot of rounds of design reviews because we're never sure, like did we see everything. So we have a lot of people from, for example, other experiments. We can just go around and pick up people from Atlas or from LHCb and tell them here, look this is what we're going to build. Is this sane? Go through the documentation. Go through the preproduction samples that we have. Like figure out whether we overlooked something. AUDIENCE: How many [INAUDIBLE]? JENS DOPKE: That depends on the project. For me, it's typically electrical engineering. So there's electrical engineers. There's physicists who want to figure out whether, besides the technical aspect of things that will work for a physicist, because you will find that there's a big difference between the electrical engineer and the physicist in approach of trying to build the detector. That's mostly it, I think. It depends on the problem. Like we have IT specialists there. We have kind of specialists for everything there. We have our own department for glues. AUDIENCE: There's five more minutes we will take questions. CAITLIN MALONE: There's one over there. AUDIENCE: [INAUDIBLE] is how reliable? JENS DOPKE: The question is how reliable is the machine now? And last year, last year's operation was on time of, I don't know. We had a so-called [INAUDIBLE] factor of more than 40% I think. CAITLIN MALONE: Yeah. I think when it's running really well-- it's a little bit stop and go at the beginning as they sort of get a feel for the machine. Once it's sort of on that plateau, though, it's running maybe 70% of the time. And then the rest of the time, you're refilling or calibrating, whatever. JENS DOPKE: Once the machine is on, it really operates 24/7 and nicely, actually. Like all the data we've acquired last year, it was more than we initially were told we would get. And it was definitely very good. A question there? AUDIENCE: So [INAUDIBLE], but what are the remaining gaps in the standard model remaining? JENS DOPKE: I sure hope that Caitie is going to answer the question. CAITLIN MALONE: I will try. JENS DOPKE: What's the gaps in the standard model? Like what do we do now that we have the Higgs boson? CAITLIN MALONE: So there's a large class of people who looking for supersymmetry, which is another sort of-- you take the standard model, and you give it another sort of dimension of freedom, if you like. And this gives you a whole new set of particles that we can be looking for that might have escaped our attention so far because we didn't have the energy to see them or because they don't interact with the protons and the atoms that we make our detector out of. So maybe they sneak through because they don't interact with atoms that well. So there's a large group that's looking for that. Other open questions that are related, I think, are things like searching for dark matter. Which is something that we cosmologically has to exist, because we look out there and we see that 25% of the universe is something that we can't see. And so some of the supersymmetric theories in particular have particles that are candidates to be the dark matter particles. So we look for those. There are some other exotic searches that happen at the LHC for things like magnetic monopoles, extra dimensions, black holes. And then yeah, like the other little things. JENS DOPKE: [INAUDIBLE]. CAITLIN MALONE: And then there's some other smaller experiments that you don't hear coming out of CERN as much, but I think are maybe in the long run more impactful on people's lives. So things like learning how to make antihydrogen, and to trap it, and to study its spectrum. And things like that. Potentially antihydrogen, as it turns out, and antiprotons have some really nice properties if you want to fight cancer. As it happens, they're extremely difficult to make. And they're not well studied at all. The first time we ever made antihydrogen was in 1996. So this is not an old thing. This is something that we're really pushing on the edges there. But if they figure out how to make it larger quantities, then there's all kinds of cool stuff you could do with something like antimatter, for example JENS DOPKE: The general drive is to kind of get the full picture of the universe. So if we're looking up into the sky, and we see that like 97% of whatever is out there is not what we understand in our current models, then we're upset. AUDIENCE: [INAUDIBLE]? CAITLIN MALONE: Right. We as much as possible interconnect the two as much as we can, though. But then we also have colleagues in things like astrophysics who can help us [INAUDIBLE]. AUDIENCE: How long does it take [INAUDIBLE]? CAITLIN MALONE: You want to do this? JENS DOPKE: The question is how long does it take to fill? About half an hour. So the filling procedure itself, depending on how stable it goes, is something like 10 to 15 minutes to get lots of packets of protons into the ring. Because you need to like stagger it. So you start at a very small ring accelerator, accelerate protons to medium energy. Get them into the next accelerator, higher energy, and then eventually fill them into the LHC. But as these rings have different radii, you can fill only so many packages into each ring. And so the initial ring gives you the maximum length that you can fill into the next ring. And as we do this, the procedure has to repeat a lot of times before we completely fill the LHC. So that takes 10 to 15 minutes. And then the ramp-up of energy that happens in the LHC takes another let's say 10 to 15 minutes. CAITLIN MALONE: Yeah, 20 minutes maybe. AUDIENCE: [INAUDIBLE]? JENS DOPKE: Well, let's say the energy itself in the LHC doesn't actually cause any energy consumption because the magnets are superconducting. So you only fill them with current. And you can actually withdraw the current eventually. Like you could get it back. I don't think we do. The energy consumption initially, I don't know. CERN has a proper power line. We have problems when we switch from the French to the Swiss network, which is an 18 kilowatt line on one side and an 18 kilowatt line on the other side. And in theory, this should happen seamlessly. It never does. Whenever we're being told that there's a switching of power, then everyone shuts down all the critical systems, because it means less work when you power them up again. We have a maximum of 200 megawatts that we can consume. In standard operation with the LHC on, we're consuming between 145 and 165 megawatts, out of which 85 is just the cooling system for the LHC. RF power to keep the protons at energy is 2.4 megawatts. So that's where we're talking order of the Canton of Geneva in terms of power consumption. That's 400,000 households. This is why we're supposed to switch off in winter, because if we're drawing too much current, Geneva has trouble heating. CAITLIN MALONE: [INAUDIBLE]. AUDIENCE: Yeah. I know there's a lot more questions. But our guests, they have some meetings set up. One's starting in two minutes. CAITLIN MALONE: Thank you very much for having us. Yeah, good questions.