Large Hadron Collider to restart in 2021

2021 should see the re-opening of the Large Hadron Collider. This enormous particle accelerator, the largest ever built, was designed to test leading theories in particle physics; and after a recent three year shutdown it will soon be starting its third operational run. Rhodri Jones is head of the beams department at CERN, the organisation that runs the collider. He gave Phil Sansom, as well as special guest Giles Yeo, the details...

Rhodri - We've been shut down for the past two years. In fact, we're coming to the end of a two year shutdown period at the moment to upgrade and consolidate a lot of our equipment. One of the major upgrades that we've undergone is in the physics experiments themselves, where they've upgraded their detectors basically to better detect the particles that actually come out of these collisions. The other major upgrade is an upgrade of the injector complex: what we call the chain of machines that's used to accelerate particles from the hydrogen gas bottle, which is where we get all our protons from, up to nearly the speed of light by the time they come into the LHC. And then in the LHC itself, we've undergone a consolidation of our superconducting magnets; so we have around 12,000 of these big superconducting magnets, which are used basically to bend the protons in this large circle that we have, allowing them to come round and round and round again and again, to provide us with collisions for a very long time.

Phil - What's the outcome of all this? What amazing physics are you going to get once you reopen, because of this?

Rhodri - Well, the hope is that when we restart - which will now probably be in early 2022, in fact, for actual physics-taking - that we'll then have the third physics run of the LHC, which is expected to last for another three years. Now up to now we've been colliding at what we call a 13 tera electron volts. This is quite high energy, and we're hoping to push this a bit further because the LHC was, in fact, nominally designed to collide at 14 tera electron volts; so this means two proton beams of seven tera electron volts hitting each other. If we manage to reach this energy, this will be the highest energy that we've ever reached with a particle accelerator on the planet. And the hope is that by doing this we can understand physics processes to a higher degree. And if we're very lucky, we may start to see very rare events, slight changes from what we expect, which could indicate new physics. And of course this is what's driving a lot of the research that we're doing.

Phil - Teams using the Large Hadron Collider have managed to find the Higgs Boson, which was one of the aims I think of the project. So what's the next step? Are you analysing it or are you doing other work?

Rhodri - It's a combination of both. So yes, the Large Hadron Collider, one of its main aims was to see whether this Higgs Boson was there or not. We've managed to find it. Now what we're doing is basically refining our picture of the Higgs Boson, so trying to really understand it. And this is the study that's ongoing, and this is why we need these vast amounts of data to actually be able to see how the Higgs Boson interacts and the various different scenarios and conditions. And then the other thing that we're trying to do, like I said, was really look at something new or something different, and this is being done in parallel. So we're looking to see whether there are slight deviations from what we expect the physics to be at this energy, or to see whether there are rare events taking place, where we need a lot of data, and suddenly we'll see something completely unexpected. And this is of course the other thing which would then show that something is out there. We don't understand everything as it is at the moment; I think we've got this standard model of particle physics, which explains everything very, very well, but not all of it.

Phil - Back when it first opened, people were saying, "oh, they're going to open a black hole. They're going to open a parallel universe.” Do people still ask you that?

Rhodri - They do every now and again, like you've done! I think the reply often to this is that nature actually creates big bangs that are much, much, much larger than we do with the Large Hadron Collider. I mean, in the atmosphere all the time, we're getting these very high energy cosmic rays coming through, which have energies much, much higher than the LHC. I think the advantage of the LHC is that we managed to localise these collisions to a very small area. So it means that we can really analyse them, which is difficult to do when we're not sure when they're going to come or where they are going to come. So this is what we've done: we've created the lab itself to allow us to analyse these high energy collisions in an area that we can actually manage.

Phil - Giles?

Giles - How about this whole story that we got a little while back that's for a brief moment in time, neutrinos can go faster than the speed of light; what was all that about?

Rhodri - Yeah, that in the end came down to timing. Basically we created them here at CERN and they were sent down to Italy and you detect them there. And of course they're traveling at the speed of light, so it's very difficult then to actually time this in. And in the end, it was found that there was an issue with the experiment - in fact, on the Italian side - with the timing not being quite as precise as we thought it would be, which when you did the maths actually came out that the neutrinos traveled faster than the speed of light. But in the end, no. Einstein is still there, and everything fits with the speed of light.