P5 report supports Higgs factory including the ILC, says the chair

| 22 February 2024

The Particle Physics Project Prioritization Panel (P5) is a panel established under High Energy Physics Advisory Panel (HEPAP) that advises the U.S. Department of Energy (DOE) Office of High Energy Physics and the National Science Foundation (NSF) Division of Physics. On December 7th of last year, this panel released a report called “Exploring Quantum Universe –Pathways to Innovation and Discovery in Particle Physics–.” The report outlines a strategic plan for the particle physics research in the United States.

ILC NewsLine asked the P5 Chair Hitoshi Murayama what this report meant for the future of the ILC.

What is the position of the ILC in this report?

Regarding the ILC, I believe that the report we have compiled is the best one possible, given the current situation surrounding the project. The report highlights five key priorities, the third priority being the establishment of a Higgs Factory. We all agree on the significance of constructing an accelerator that can generate a significant number of Higgs bosons for precision measurements.

There were some proposals to build a Higgs Factory in the U.S., but they just wouldn’t fit into the budget profile given by DOE. Therefore, we should actively participate in the projects that have already begun, such as FCC-ee and ILC, and establish a process for the US to take the lead.

However, we do not know at this time which Higgs Factory will be realized and when. So, we also recommend that an interim panel be set up so that when new developments and information become available, a decision can be made to decide the level of the US contribution without waiting for the next P5.

The ILC being listed together with the FCC-ee has caused some to think that the importance of the ILC has decreased. What are your thoughts on that?

I would say this report is actually very supportive of the ILC, even more so compared to the previous report. The last P5 report said, If the budget scenario is unlimited, then we should commit to the ILC. And this time, it says that we should commit to a Higgs Factory, whatever the scenario may be. We don’t know if that will be the ILC or FCC-ee, but we must do it. We recommended investing in collider R&D, including Higgs Factory and ILC technology networks, as well as detector R&D for Higgs Factory experiments. That means we have put much effort into ensuring that the US program would have a significant component in a Higgs Factory. 

At the beginning of the discussion, certain panel members were under the impression that the ILC was dead and that the Higgs Factory had to be FCC-ee. But after looking at the details, it became clear that the ILC is shovel-ready and technologically mature, with no technological showstopper. The only thing missing is a global framework that would allow ILC to be put together somewhere in the world. On the FCC side, there is no guarantee that it can actually be built. It is an expensive machine, and the financial feasibility is still not clear. So, in that sense, neither one of them is guaranteed. Based on these findings, we came to the conclusion of listing two projects in parallel. After all, we are all researchers, and we make decisions based on data. However, I would like to mention that there was one thing repeatedly pointed out during the discussion: the ILC has no host. CERN is the host of the FCC-ee, but the ILC has no foundation, so it is unclear who will lead the project. Anyway, whatever would happen to either of the possibilities, the U.S. doesn’t want to miss the opportunity.

An interim panel will be set up when “crucial information is available, but what is the “crucial information?

In the case of the ILC, once the dialogue among the interested governments is realized and the prospect for a global project is identified, a panel will be set up. For the FCC-ee, if the results of the feasibility study currently underway show that it is feasible not only in terms of technology but also in terms of finance, the US will decide to participate. After the feasibility study of FCC-ee, further discussions will be needed by the next European Strategy Update followed by the Council decision. CERN is also participating in R&D for linear colliders and other future collider projects, even at a low priority. The DOE will look at the situation and decide on when to convene a panel.

– What is your vision for the future of particle physics research in the U.S.?

For the past 20 years, the US budget for particle physics research has not kept pace with inflation. It finally caught up with inflation when the neutrino experiment DUNE, the second highest priority for the US in the last P5 report, started and was budgeted. But due to the higher than anticipated budget of DUNE, we are in a difficult situation where we will not be able to do any new projects for the next five years or so. This time, our goal was to create a program that would cover not only DUNE but also many other things in the subsequent five years. We took the time to listen to various opinions and believe that we have produced a well-balanced report. We have expressed our aspiration that is quite far in the future, which is to aim for an energy equivalent to 10 times the energy of the HL-LHC, and if possible, we would like to build a muon collider on US soil. It is very difficult, but if would like to work in developing the technology, and the accelerator technology in the US will get a boost, and it may support next experiments in many different areas. I think the right way to go is to build a system that allows us to do various kinds of science along the way while running toward the muon collider as a distant goal. Without a dream, everyone will stop, so we need to have a destination to run toward.

-Thank you!

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