The CERN makeover

The standard model scrutinised; particle physics could be in for a monumental shake up...
26 April 2022

Interview with 

Steven Abel, Durham University


A view down one of the tunnels of the Large Hadron Collider.


You may have heard that the hadron collider received a recent makeover. This is the large particle accelerator over in Geneva, its circumference is 27km, it’s so large that it straddles France and Switzerland. Here to tell us about the revamp is Steven Abel. Professor of mathematical and theoretical particle physics at the University of Durham...

Steven - So the LHC is a proton proton collider. What we do is we accelerate protons to extremely high energies and we collide them together and sort of pick over their wreckage, basically in order to hope to find things that we don't expect to find, maybe find new things. Since it began, maybe two decades ago, it's just been confirming what we think about the early universe, the nature of matter, and reproducing things from the early universe that we expect.

Harry - At the moment, we've seen in the news that there's been these improvements made to the structure. What are those improvements?

Steven - It's kind of incremental. It's increasing its luminosity as we call it: the intensity of the beam, the number of collisions - we want to increase them as much as we can in order to get more data basically. We're always trying to get as much data as possible because the things we're trying to test and the things we're trying to look for are extremely rare. In order to see those things, to test them, you have to have a huge number of collisions.

Harry - With this coming in, scientists are getting quite excited. What are they excited about finding?

Steven - There wouldn't normally be so much excitement with this sort of upgrade, I don't think, but it's because it seems as if we're on the kind of cusp of finding something completely new. Up to now, we've had something called the standard model, really since the early seventies. That model has described everything to a sort of ridiculously good extent. It's one of the most tested models imaginable.

Harry - And that's the particles, is it, in the standard model? It's a list of what we would see?

Steven - That's right. So, the standard model contains within it, of the fundamental forces of which so far there are four, three of them. Gravity doesn't appear there. Plus, there are matter particles. The matter particles are quarks, and there are six flavours of quarks. They all have different properties. And six flavours of leptons. Leptons are like electrons inside a proton. Then there wll be three quarks.

Harry - And is it thought that the experiments that could come out of CERN at the moment, then, might challenge this well solidified standard theory.

Steven - That's right. A B quark is quite a heavy quark. Occasionally, you produce them, so maybe one in a million collisions will produce a B quark, which decays in a certain way to, say, two electrons, or two muons. Plus something which is called a strange quark. Those particular sorts of decays are showing things which we do not expect in the standard model. They're showing that the muons are behaving differently from electrons. That's called a lepton non universality, and that is not an ingredient of the standard model. So, that's a complete surprise. The reason people are excited is, if you look at one of these things, it wouldn't be so out of kilter, but we're seeing that there's quite a few of them which are all pointing in the same direction. What people are hoping for in the next run is that we're going to get enough data so that we're going to be able to say that this is now something which is definitely not the standard model. We're definitely seeing something new and we can throw away the standard model, finally.

Harry - It feels like it could be a massive shake up for particle physics.

Steven - It'll sort of be the only game in town for a while. Everyone will have to think about what on earth is going on, where does it fit into a larger theory? Eventually, it could have some sort of ramifications for, for example, fifth forces. There's a possibility that there's an additional force, or new particles could be producing this effect, called leptoquarks, that's another idea. It could, ultimately, be the start of changing our perceptions about how everything is arranged.

Harry - Steven, are you expecting to see this come to fruition over the next year or two?

Steven - You're now asking me to place bets. What I think is, we are close enough that it will in this run, it will be confirmed in a sort of technical sense.


Add a comment