This week, the Netherlands contributed its national input to the discussion on the new European Strategy for Particle Physics (ESPP). This involves more than just choosing a larger accelerator, says Eric Laenen, member of the ESPP Strategy Group.
To the outside world, only one thing seems relevant: what new particle accelerator will be built at CERN?
Laenen: “The discussions about the European strategy go much broader than just a new accelerator. The Netherlands emphasises this in this addendum: it’s about physics, not only with accelerators, but also, for example, astroparticle physics. And we also want to emphasise the environment, energy and financial viability. And diversification: it cannot be the case that an accelerator project crowds out all other branches of particle physics.”
Why is this actually an addendum?
“Some countries already indicated in March that we should build an FCC. The Netherlands then indicated that there were issues we wanted to discuss and work out in more detail. A sign of caution, I think. That has now been done. The advice and addendum should be read together.”
What is the thrust of the Dutch contribution to the European strategy discussion?
‘I think what is special is that we have always thought in terms of scenarios in the process and not immediately in terms of a choice between accelerators. The main goal in the long term is collisions at 10 TeV for point particles or quarks, in order to explore new physics. But there are various conceivable routes to achieve this.’
What are those routes?
‘Various. As I said, FCC is the favourite, but then in the so-called integrated programme. That means first working towards a 91-kilometre electron-positron collider and later, in the same tunnel, a proton collider with new technology. Then you go all out for the best physics. First a Higgs factory. Then new physics at the very highest energy.’
But with a hefty price tag, for example.
“Certainly. And that could be a reason to opt for a slightly more cautious approach, but also with less physics potential. Another possibility would be to first build a new accelerator in the current LHC tunnel at CERN. That could be a LEP3, an intense electron collider for the production of Higgs particles. Or LHeC, in which you shoot electrons at protons for the same purpose. Only later followed by a new accelerator with much higher energy.”
Such as an FCC proton collider?
That is a possibility, but it has not been decided. There are also ideas about a muon accelerator, in which heavy electron-like point particles collide at enormous energies. It is a nice idea, but there is still a great deal of uncertainty. Whether it is feasible, because muons decay quickly. Whether it is safe, because of the neutrinos that are released. There is a lot of interest in this, especially in the US, but technically there is still a long way to go.”
Does the Netherlands have a preference in this regard?
No, what we are in favour of is a scenario that leads to the desired result. That also depends on conditions other than the necessary technology. For example, for a while there was the question of whether China was going to build an FCC-type accelerator and conduct the same type of research earlier. That seems less likely now. In any case, their CEPC is not part of the five-year plan.
And then there is the issue of financing.
‘The FCC integrated programme cannot be accommodated within the existing CERN budget. So other sources of funding must be sought. The European Union refers to the project as a Moonshot programme. Private funding has been considered, as has a possible increase in national contributions. But even if it has to be cheaper, we still want the best idea.’
Another theme in the discussions is that these are decisions about projects that will only benefit the next generation of physicists.
‘We are talking about very long timeframes, and sometimes that feels uncomfortable. That is why we explicitly involved young physicists, PhD students and postdocs in the discussions, and I think they were listened to carefully.’
For a long time, there was a fear that there would be so much time between the LHC and its successor, if it ever comes, that the whole field of particle physics would fall into decline.
“I’m not so worried about that anymore. You have to remember that the LHC accelerator is still running, and in a few years’ time, the HL-LHC will be back and will deliver ten times as much data. We will all have to analyse that data, and who knows what we will find in it. What’s more, there are some extremely interesting developments in neutrino experiments and in the field of dark matter. Even without an active accelerator, particle physics remains a very lively field. Take a look at CERN, it’s buzzing with activity.”
How will the Netherlands ultimately participate? Nikhef does not build accelerators.
‘The Nikhef partners have traditionally been good at experiments and detectors, data analysis and theory. That will remain the case with the next accelerator at CERN, but a task force is being set up to develop the Nikhef strategy for this.’
Interview: Martijn van Calmthout / Nikhef
