Hello, and welcome to the Physics World Weekly podcast. I'm Hamish Johnston. The European Organization for Nuclear Research or CERN was founded in Geneva in 1954. Today, it's most famous for the Large Hadron Collider, which accelerates protons and nuclei in opposite directions around a 27 kilometer ring before smashing them together at high energies. In 2012, '2 experiments on the LHC announced the discovery of the long sought after Higgs boson.
And that's just one of the many important breakthroughs made at the lab. But CERN isn't just about colliding particles. It's a leader in the study of antimatter, the place where the world wide web was invented. And CERN was home to John Bell, whose famous theorem marked a profound step forward in our understanding of quantum physics.
In this podcast, I'm joined by my physics world colleague, Margaret Harris, who is back from a visit to CERN with an update on the exciting physics that's being done there. Hi, Margaret. Welcome to the podcast. Hi, Amish. Now if there's one lab that every physicist should visit once in their lifetime, it's got to be CERN, the the sort of preeminent, particle physics lab in Europe and and maybe in the world. What was it like? How would you describe, your trip? What's it like being at CERN?
Certainly, at the moment, it is the world's premier high energy physics laboratory. And I was told by one of my tour guides, Sarah Aldewelt, who's an early career researcher at the University of Edinburgh when she's not working at the ATLAS detector at CERN. She said that this is an interesting time to visit CERN, and I hope to have her on the podcast at some point to explain this in more detail. But, essentially, if you're a particle physicist, you have several possible modes of operation.
You can be in data taking mode. You can be in data analysis mode, so dealing with the data you've already got, and you can be in the upgrading the experiment mode, or you can be thinking about future upgrades. And future in that in this case could mean five years from now or could mean, in extreme cases, you know, up to fifty years away. And right now, CERN is operating in all
but one of those modes. There wasn't any data collection when I was going on because the collider shut down over the winter. This is to save on electricity costs, and also to help avoid putting too much demand on the French or Swiss electrical grids at a time when demand for heating is already high. The it's funny. The the LHC actually requires as much electricity as the entire city of Geneva when it's running. This is the Large Hadron Collider, the main collider at CERN. Wow.
So so there's no new science data being generated during the winter, but absolutely everything else is happening right now. In a couple months months, there'll be spring. The LHC will restart. But then in 2026, it will enter a longer shutdown, one that will last all the way until 2030, during which it will get what will probably end up being its last major upgrade. So unlike a previous upgrade where they went from colliding protons at energies of five oh,
so sorry. Seven teraelectron volts TeV to clotting them at 14 TeV, this upgrade isn't an energy increase. Instead, it's an increase in luminosity. Now what's that mean? Well, the the beep beams of the LHC are made up of bunches of protons, and every bunch contains about a hundred billion protons. But because protons are so small, the vast majority of them don't collide when you cross the beams. You might get a few tens of collisions per crossing.
Now that might sound really low, but because those crossings happen 40,000,000 times per second, you do still get a lot of data. In fact, you get so much data that CERN pioneered the handling of big data, and they have really complex algorithms to help them decide which data points to keep for future analysis and which to throw away because they're not gonna be very interesting. But the high luminosity upgrade is going to bring that up to
200 collisions per crossing. So now you're talking about an order of magnitude more data that could be generated per unit time. And and this high luminosity upgrade, I mean, it's not just simply a matter of pumping more, protons into the accelerator. I mean, I'll I mean, just about am I right in thinking that just about every aspect of the LHC and and the experiments that are on it have to be modified or tweaked in some way just to to to achieve this?
Certainly, the the two main, biggest experiments, ATLAS and CMS, have have to undergo major tweaks for this. So but I think there's actually 17 different work packages involved, and I saw only two of them. So I can tell you about those two. I don't know about the the totality of the upgrades going on. But the first upgrade that I saw on my tour involved something called a crab cavity.
And what these cavities do is that they tilt the proton bunches so the protons in them appear to be moving sideways like a crab walks. Oh, that's why it's called a crab cavity. Yeah. That's why it's called a crab cavity. I always wondered about that. Well, listeners, you learn something new every day. They don't look anything like a crab. But the reason they they want to make the move sideways is because at the moment, the beams of the LHC cross I mean, it's not at right angles exactly.
It's more like a sort of flattened x shape, but the area overlap isn't huge. But once the crab cavity is installed, they'll get a much fuller overlap. So if you can imagine this difference between placing your two fists in a cross at the wrists and aligning your hands so that your entire arms are sort of all crossing in front of you. And that means every proton in a bunch is gonna have to pass through the whole length of the bunch moving in the opposite direction.
And that on its own will increase the number of collisions per crossing by around 20%. Now of course if you're getting more collisions you're also gonna need a detector and readout electronics that can handle that. And that's where the other work package I saw, the inner tracker or ITK systems upgrade comes in. And this is gonna become the new heart of the ATLAS detector. I guess you could say the detector is having a heart transplant effectively. And right now, this inner tracker doesn't look
like much. It looks like an empty tube. It's about as tall as I am with slots in it, and these slots are gonna be filled by long strip like silicon based sensors. I see. And I have to say, Margaret, I'm very, very jealous that you got to see, ATLAS. I mean, I I I suppose that's one of the bonuses of visiting CERN when the, collider isn't running, that you could actually go down and see the experiment. So what what what was that like? Was it I mean, you you hear stories of it being huge.
How huge is it? Can you can you can you give us, I don't know. Is is is it small office building huge or, what's the story? Yeah. It's I don't know the exact numbers. It's several stories tall. It's a hundred meters underground. To get in there, you have to go through a security system that's sort of like walking into a if you can imagine that, an old fashioned telephone booth with a door on the front and a door in the back. So you walk into the the front
of the telephone booth. You stand on a a square that is apparently like testing your weight as well as sort of scanning you like an airport scanner. And then the doors open, you get to go out. And if you're carrying anything and you want to carry some tools or a backpack or anything like that, it has to go through a separate slot.
And they they were a little bit cagey about exactly what this is doing, but it's essentially making sure that everybody is counted in and counted back out and that the same people go in as come out and they're not they're not carrying undue amounts of extra stuff with them while either on the way in or on the way out. So you can, you know, appreciate the sort of security. It's it's both for security and also for safety. You don't want there to
be an incident. You forget that there's one of your people is still down a hundred meters underground. Yeah. So so it's got there's a lot a lot of preamble or build up to it. And then you get down to the detector itself, and it's absolutely enormous. And I think the thing that that most impressed me about it, this enormous machine, it's probably one of the biggest machines that humankind has ever constructed. The thing that most impressed me about it
was the cable ties. And that's not because cable ties were impressive or because they were really fancy or whatever. It's because each of those cable ties, and I could probably see hundreds from just where I was standing, each of them was put in place by a human being who knew exactly what he or she was was doing, and they had to be put together in this whole giant machine was fabricated entirely by hand, by human hands and human brains who
knew exactly what they were doing. And that's just, I think that's that's the thing that got me about the detector, not its sheer size or the fact that there's, you know, above you, there's a hole in the ceiling that lets new new components be lowered down. It was seeing those cable ties and just realizing the immense amount of effort that went into to making this this machine.
And I I I suppose the information that flows through a lot of those cables is, you know, just a tiny bit of the information that the the detector produces, and then that that's all put together Yeah. You know, to tell you, you you know, to tell physicists about, the details of a of a collision. Yeah. It is it is just amazing, really. I mean, I've never seen ATLAS. I have seen CMS, which I don't I don't think is quite as big, but it was,
it was definitely impressive. So so was ATLAS was it more or less intact when you saw it, or had they was it taken apart? Was it in pieces on the floor or sort of halfway in between? I mean, it looked pretty intact to me. There wasn't a big, gigantic chunk missing, which is absolutely what will happen when they put this, this new ITK, inner tracker in. And one of the advantages of this new design that goes in is that it should be more radiation hard than the inner detector that's in Atlas now.
The scientists have showed me around the Integration Hall where this, inner tracker is being assembled before it gets lowered through that that hole in the roof down a hundred meters underground. They said that the existing detector would actually need replacing anyway even if they weren't doing this high luminosity upgrade because it's absorbed so much radiation over the, you know, decade or more that it's been in ATLAS.
It's absorbed so much radiation from the all the particle collisions and all the the debris of those collisions that it's becoming harder to supply enough voltage to deplete the silicon in
the detector itself. Oh, wow. Yeah. Yeah. So, you know, this is is you don't think I personally don't think of the LHC as being that older device, but it's actually you know, it's been going for quite a while, and there's there are thing there are things there there's, you know, a lot of of science has been done about the auxiliary systems that go
into it. You know, think of where silicon semiconductor electronics was in, I don't know, the early two thousands when they were designing and building this thing, and think about where it is now. You know, there's a real reason for upgrades that have, you know, all everything to do with lots of different areas of of science, not just particle physics. So the new system can deal with a higher number of collisions, as well as being able to to cope with, the the radiation.
It's just far more granular, faster channels, faster electronics. Right. And the the the other thing I I remember is when you go to see these detectors, you you actually have to leave the main site of, of CERN, don't you? At least with CMS. So is did you have to get on a bus and sort of go across the border into France? And, you know, did they tell you to remember your passport just in case? They didn't mention the passport. My phone was going off all the time saying, welcome to
France. Welcome to Switzerland. You have this much data on your your plan. So I guess that that was actually the only indication I had that we were crossing the border at the particular places I went because it is, you know, relatively open border. There are checkpoints, but, you know, there's it's part of Central Europe. There's a lot of of freedom to cross the border, which is good for the scientists to work there because a lot of them live in France and then work in Switzerland or vice versa.
But yeah. No. It it's I think one people we I spoke to said that he he compares it. He's from from Glasgow originally. He compares it to Glasgow subway system in terms of the the length of it. Oh, that's famously a big loop, isn't it? The Glasgow subway system. Yeah. Yeah. Yeah. Because I I, you know, I I've been discerned twice, and I think the first time was in
the nineties. And back then, you know, whatever the arrangement was between France and Switzerland, there was actually a border to cross, you know, there there was a kiosk there with somebody, you know, we I had to flash my passport, and we drove through. But then the second time, yeah, as you say, the the border had magically disappeared as it has in, yeah, in a lot of Europe. It's certainly a softer border than it than it has been sometimes in the past. Yeah.
So so Margaret, the we've got this where we will have this high luminosity LHC running at some point in the future. What what does that mean for the the physics that's being done at experiments like ATLAS? Why is it important to to see more collisions? Well, it will allow the the the two, high energy physics experiments at the LHC, ATLAS and CMS, to collect 10 times more data than they have now, and to explore the energy frontier with more potential for discovery.
And this is kind of amazing to me. You know, the LHC has been running off and on since 02/2008, but it's actually only collected 10% of the data it's ever going to collect. It will get the remaining 90% during this high Lumi run, which is scheduled last from 2030 through to about 2040 or thereabouts. And a key focus for the high luminosity LHC will be studying something something called a dye Higgs event, which is not where the Higgs boson dies.
It's where you create not one Higgs boson, but two of them at once. And once you have two Higgs boson at once, that means you can study what happens when the Higgs interacts with itself. Fabiola Giannati, who's the current CERN director general, called this self interaction a portal to exploring interactions in the early universe. So within about a picosecond or ten to the minus twelve seconds of the big bang, this is when the Higgs field first became established.
And so understanding how that came about is crucial to understanding how initially massless elementary particles end up gaining mass by interacting with this Higgs field and turning into the massive quarks and electrons we see around us today, which are what you need to be have in order to form atoms. And this Higgs pair production also has some implications for matter, antimatter asymmetry. So we might learn about that too.
I see. And, I mean, the LHC and, you know, that sort of high energy particle physics is not the only science that's done at CERN. And, you know, to me, I think one of the most interesting, group, of experiments that, are being done there at the moment are the antimatter experiments. And I think you you also paid a visit to the was it the antimatter factory? Do I have that right? At Yeah. At CERN. Yeah. The antimatter factory.
There's actually I think it's a little bit, question of what the boundary between different experiments lies, but I think there's actually five experiments at the antimatter factory. And all of them are in various ways and with different techniques looking for differences, actually, between the matter and look exploring this matter antimatter asymmetry asymmetry
in a different way. They're looking for differences between the behavior of matter and the behavior antimatter, whether that's the behavior antimatter under gravity as with the alpha g, g bar, and AEGIS experiments, or different magnetic moments as with the base experiments or spectra as with, the Asakusa experiments. I see. And and and the reason this is important, is that what we know that at least in the visible universe, there's much more matter than antimatter.
And if we could we we could sort of work out why by looking for differences between the two, that could that could tell us a lot about, well, what we don't know about physics. So so what, I mean I mean, I think, you know, the most famous experiment that was that's been done there is, you know, testing this idea that does antimatter fall up, or, you know, does it somehow respond to gravity
in a different way? And I think this so far, the answer is no. But there's lots of really interesting experiments there, aren't there? Doing spectroscopy on anti atoms and I mean, it's some amazing stuff they do there when you consider that antimatter doesn't really want to hang around for too long. No. And I think this area of CERN actually you know, I'm talking about the Hi Lumi upgrade for ATLAS and CMS, but this area of CERN actually had its big upgrade relatively recently.
As recently as 2018, each of those animator experiments got eight hours of beam time per day, which is, you know, a decent working day, but, you know, you've got a machine. You could run it twenty four seven if you wanted to. But due to an upgrade of the Elena ring that provides actually slower particles, everywhere else at CERN wants fast particles, the antimatter factory wants slower particles.
This Elena ring upgrade provides half a million anti protons per two minute shot, and that became fully operational in 2021. And now it delivers anti protons to four experiments at once twenty four seven while it's running. And what that means is that alpha, which is what I heard about most because my tour guide, April Cridland, is a research fellow at CERN who's part of the alpha collaboration.
What that means is whereas they used to take make maybe 20 or 30 atoms of anti hydrogen every four minutes, now they're making more than a hundred, which is a huge step because what used to take weeks now takes a day. So so she was saying that, actually, there's lots of alpha results due out later this year, including, sympathetically cooling antimatter with beryllium. So putting antimatter into contact with beryllium to maximize the number of anti hydrogen atoms trapped.
So definitely stay tuned on that. Yeah. I I I mean, I think that's really exciting. And, you know, we we we shouldn't forget that, okay, we might see a a huge breakthrough beyond the standard model of particle physics from the LHC, you know, in the high luminosity upgrade. But, you know, it's possible that, the big, big discovery at CERN will come from one of those antimatter factories. So, lot there's lots going on there. Isn't there?
Yeah. And and people are also, you know, starting to think about what the next machine might look like. That's kind of the final sort of component. And that's interesting to me because the time scales are so long on that Mhmm. That the older generation of scientists will probably never get to work on that next machine, although they may live to see it built after they've retired.
And even today's early career researchers will be well into their careers, maybe even heading towards retirement on their own before it gets going. You have to have a long term perspective. And you mentioned this question of antimatter following up. This is this is kind of relevant for me because one of the very first stories I ever wrote as a science journalist, as a student, an undergraduate, was about a researcher at my university who was interested in finding out whether antimatter fell up.
And so when, you know, the the antimatter experiments at CERN found started finding evidence that it does in fact fall down just like normal matter, I mean, it's kind of disappointment. Right? Because you wanna see some Oh, yeah. Unusual physics. But it was also kind of, you know, it felt very satisfying for me even as an observer of this to sort of have finally found the answer to a question I was asking researchers, you know, twenty years ago as a student.
So, you know, this is definitely, you have to have a long term perspective, I think, to be a particle physicist, to think not just about the discoveries that are happening now, but the discoveries that are gonna be made in the future and what you need to do to get there to have that happen. And that's where I think everything kinda comes together. You you mentioned the sort of next generation.
So the I suppose the LHC is going to run-in its high luminosity mode and, you know, gather lots more data. But at some point, it's it's just gonna run out of of of road, I suppose. When you when you spoke to people at CERN, did you have any feeling for what they thought the next generation
collider would be? What I mean, are people very keen on this humongous collider that would sort of go under Lake Geneva, you know, this hue but much larger version of the LHC at CERN, I suppose, or, you know, maybe a linear collider somewhere else, or is it it is I mean, so I I suppose the community has to decide on what it wants to do, but to to to people there, is it still really far in the future, or are they focusing on the LHC at the moment? I think that, you know, it probably depends
on what level you're talking about. You know, the Fabiola Gianati and, actually, the the upcoming CERN director general director general designate Mark Thompson, who I think was on the podcast a couple weeks ago. Mhmm. They're very much thinking about the long term future as well as thinking about how to run the the experiments and the the collider in its current operational
phase. I think I get the impression that the CERN is very much pushing for the establishment of the future circular collider, as it's called, this this big, even bigger version of the LHC. But I think that you're you're right. The community still has to sort of decide because it's clear that, you know, we're we're gonna get, you know, no more than one or two big ex additional big machines like this. The Chinese government is talking about building some
sort of high energy facility there. It's a question about whether that will happen independently of what's going on in Europe or, you know, maybe The US. And these things just have to still still have to sort of shake out in the in the wash, really. Yeah. Well, it it'll be very interesting to see what happens. And, you know, for I mean, for our listeners, I mean, I think you'd agree with me, Margaret, that, CERN is a great day out. And I I don't think you have to be a member of the press
to go. I think they do maybe do they have an open day every year? I know, certainly, one of our colleagues is gone as a sort of a normal citizen. Oh, yeah. You you can absolutely day. You can absolutely tour tour CERN as as an ordinary citizen. I believe it's actually the top ranked activity in Geneva on TripAdvisor or maybe the second after going to Lake Geneva itself.
So, you know, you may not be able to go down and see the ATLAS detector like I did, but you can certainly go and, you know, have a look around the, you know, the control center and look around the the buildings on campus and as part of a a public tour group. And, yeah, it's it's whatever you get to see is absolutely impressive. Mhmm. There's also really, a really good museum there, the the CERN Gateway. Mhmm. That's, I think that's probably, like, number four on the list of things to do in
if you go to visit visit Geneva. So that's also a a great attraction. Great. Well, thanks for the update, Margaret. You're welcome, Hamish. Nice to talk to you. That was Margaret Harris, and there'll be much more about CERN from Margaret in physics world, so stay tuned. Twenty twenty five is the international year of quantum science and technology, and celebrations are well underway here at Physics World.
Our latest contribution to the festivities is a fun quiz about all things quantum, and here are three of my favorite questions. Which celebrity was spotted in the audience at a meeting about quantum computers and music in London in December 2022? Was it Peter Andre, Peter Capaldi, Peter Gabriel, or Peter Schmeichel? So which one of those Peters is interested in quantum music? The next question is which of the following versions of the quantum hall effect has not been observed so far in the lab?
Is it the fractional quantum hall effect, the anomalous fractional quantum hall effect, the anyonic fractional quantum hall effect, or the excitonic fractional quantum hall effect? So which of those effects hasn't been observed in the lab? And finally, what destroyed the Helgoland guesthouse where Werner Heisenberg stayed in 1925 while developing quantum mechanics. Was it a bomb, a gas leak, a rat infestation, or a storm?
The quiz has 15 more questions to test your quantum knowledge, and you can find it on the Physics World website. Just look for the headline, test your quantum knowledge in this fun quiz. The commercial quantum technology sector is burgeoning, and I'm sure that some podcast listeners are keen on pursuing quantum careers. So if you'd like some inspiration and a few tips for success, check out our interview with Michelle Lawley, who is an advanced laser scientist at Quantinium.
There, she supports the design, development, and construction of complex optical systems that will serve as the foundations of quantum computers. After studying finance at university, Michelle worked for several years as an investment banker. But after reading a scientific paper about quantum teleportation, she packed that in to become a physicist, gaining a PhD in quantum optics. You can read all about her career shift in the article From Banking to Michelle Lawley's Unique Journey.
And you can find that on the Physics World website. I'm afraid that's all the time we have for this week's podcast. Thanks to Margaret Harris for speaking to me today, and a special thanks to our producer, Fred Isles. We'll be back again next week. See you then.