What comes after the Large Hadron Collider?

Chris - It is an awesome machine though, the LHC. I remember going to a lecture when it was being commissioned and beginning to run up and someone was saying, we are able to guide just handfuls of protons within a gnats whisker - that's not an SI unit, of course - the speed of light and then slam them together. And they're meeting, despite taking this huge journey of tens of kilometres underground, they're meeting on a path which would fit inside the numerical zero on a small coin where it says the value of the coin. And I just thought it is absolutely incredible that you're able to guide these tiny particles around this massive journey and then bring them into collision paths in such a tiny amount of space.

Lyn - Yeah, the analogy that I use, which is not, not easy to check in the UK, but if you take a one Euro coin, then the Iberian Peninsula on that one Euro coin is the size of the aperture that we impose on guiding these beams around the LHC so that there is no, what we call background in the detectors, there are no junk particles coming in. And when the beams collide, of course, the size is much smaller than the human hair, and we have to get them colliding head on. And not to mention the fact that guiding these beams around on their orbits requires superconducting magnets, which are cooled to 1.9 degrees Kelvin, 1.9 degrees above the absolute zero. And the temperature of deep space is 2.7 Kelvin. So we are lower than that. So the whole thing, when I step back, I wonder how we manage to do that? It just looks awesome. When you're in the middle of it, it not at all <laugh>

Chris - People say though, don't they? Because obviously you say, how do we manage to do that? And there are plans for an even bigger collider coming, and we'll talk about that perhaps in a minute. But some people say, why are we spending, it would've cost a few billion for the LHC, more than 10 billion for what's coming next we anticipate, but there must be some fringe spinoffs from this. There must be in the same way that the space race by presenting us with the scientific equivalent of Everest, creates a challenge that we have to surmount that then leads to enormous spinoffs. So are there enormous spinoffs that have come from the LHC that means that life for the average person on Earth has improved as a consequence. They're not just now the beneficiary of billions of pounds worth of investment to discover the Higgs boson. They're also benefiting because of X.

Lyn - First of all, let me say that it's only possible to do something like this by massive collaboration between countries. And there are 21 member states of CERN, which are contributing to the budget. And that's the only way we can build something like that. As far as spin up is concerned, of course we have to push technology to the limit everywhere, absolutely everywhere. And it's not only super connecting magnets, which are used in MRI scanners in hospitals and things. The analysis that we need to do on this data, that is the worldwide web which CERN invented in the late eighties, early nineties. It's not in the general domain yet, but there is a massive infrastructure which is much more powerful than the web, where the collaborations analyse this huge amount of data coming out of the LHC, in their universities, wherever they are in the world. And of course there is the educational value of CERN. We have massive numbers of students coming and doing their PhDs or even technicians learning their trade here. CERN is the kind of scientific university of Europe.

Chris - The next generation of collider announced recently that there are plans afoot to try to build the Future Circular Collider, three or four times bigger than what we have already. Is that based on the same rationale that we need more energy and so we just build a bigger one and just see what happens? What's the target that they're going for with that? Because you were saying the Standard Model, we now can put that together. We have a good understanding of how all the parts relate. So what are the big questions that you'll solve with an even bigger collider?

Lyn - For the LHC, we had a clear objective, which was to find the Higgs boson. There are many other things that have come out of the LHC apart from the Higgs boson, but there was a clear objective. For the future, there is no clear guidance. That's much harder, much harder to justify a huge expenditure just to see what's there. And that's the quandary we are in now. The circular machine is not the only one. There are other options which would allow us to study the Higgs boson. I explained that when we collide the protons together, we get a whole lot of mess and we get very occasional collisions with Higgs bosons, which are very difficult to analyse. There are ways of producing them in a much cleaner way, which would require a new machine, either this big circular machine or other means like linear colliders or whatever. There are three or four options on the table of how to refine our measurements of the Higgs boson and to go further. But there are considerations. Cost of course is a really important thing, but also power consumption is now becoming a serious issue. The bigger the machine, the more power we consume. And in this day and age, it is not cheap anymore. So all of these things have got to be taken into consideration before a decision and the decision will not be taken, probably not, in the next 10 years of what really to build next. We are now upgrading the LHC to produce high luminosity, so more collisions per second so that we can accumulate more data, get more precision, and that upgrade is being done over the next two years. And then the LHC will probably run for another 20 years after that. So what we are looking at in these other options of which one is this big circular thing, is what is the best way forward? There are still unknown problems. It's not just for finishing the Standard Model. We still do not know what is the subtle asymmetry between matter and antimatter, which means that our universe is made of matter, not antimatter. We do not understand dark matter. Dark matter is something which comes from basically astronomical observations. And even more mysterious dark energy. There are still a huge number of questions out there that we don't understand the answers to, and they're being attacked in many ways. One of the ways of course is to probe the very high energy frontier, but we have to be very conscious that there are only limits that society is prepared to support in building just bigger and bigger things.