The CERN Council is meeting today and tomorrow, and should approve the long-awaited 2020 update of the European Strategy for Particle Physics. There will be a live webcast of the open part of the Council meeting on Friday.
My understanding is that the most difficult and contentious decision, that of how and whether to go forward with a new energy frontier collider, has been put off until 2026, when there will be a new update. In the meantime, design work will emphasize studies for the leading contender: a new large circular electron-positron machine. Studies of a linear collider design (CLIC) will continue at a reduced rate. New work will begin on the possibility of a muon collider, as well as other advanced accelerator technologies that might someday be usable.
There will be some move in the direction of the US program, which has abandoned the energy frontier, including more participation in the US and Japanese neutrino programs. A “scientific diversity program”, Physics Beyond Colliders, will receive new support. This program will try and come up with new experiments that don’t require a new energy frontier machine. For more about it, see this CERN report and this article in Nature.
In other news from CERN, work on the LHC should start resuming this summer, with the ongoing LS2 extended by a few months because of the COVID shutdown, so beams back in the LHC late next summer. There likely will be no significant new data coming from the LHC during 2021. The extended shutdown may provide the time for magnet quench training needed to bring the machine to its design energy of 7 TeV/beam.
The headline news is that this backs the FCC plan: a 100km new ring, first run as an electron-positron collider, then as a much higher energy proton-proton collider. There are however a whole bunch of very significant caveats:
- No plan for how to finance this very expensive proposal.
- The press release mentions a construction start timescale of “less than 10 years after the full exploitation of the HL-LHC, which is expected to complete operations in 2038”. This is twenty years or so away, a very long time.
- The main near-term goal mentioned is work on designing the magnets needed for the proton-proton machine, to know by 2026 whether a pp machine is feasible. If the design of appropriate magnets with an acceptable cost for the pp machine is not possible, the implication is that there would be no point in building the large ring and ee machine.
- The main competitor to the FCC plan, CLIC, is not at all canceled, but work will continue on it.
- A new project to try and design a muon collider will be funded, with a planned 2026 decision about whether to move forward on a test facility for that. The technology for this still does not exist (muons decay very quickly…) but if such a collider were feasible, it would be much smaller and likely much cheaper than something like the FCC project.
So, those who want to argue one way or another about whether it’s a good idea to spend a lot of money on building a new collider should rest assured that the future holds many, many more years in which to conduct such arguments…
Update: I find it very frustrating to see that the online discussion of this is dominated by a pointless argument about whether, as reported, CERN should be going ahead and spending more than \$20 billion or so on a new machine. THEY ARE NOT DOING THIS. What has happened is that, after a lot of work, they have identified the best possible way forward at the energy frontier (the FCC proposal) and decided not to go ahead with it now but to keep studying it and the required technologies. If the cost of this proposal had been a few billion dollars, they likely would have tried to come up with a plan to allocate much of the over billion \$/year CERN budget in future years to the project and start construction. Instead, for the next six years they are allocating .1 – .2% of the CERN budget to further studies of the proposal. Those who have been loudly complaining that this is too expensive a proposal for the HEP community to afford should declare victory, not go to war over this.
Update: The CERN press release has been changed, with “construction” starting within ten years after 2038 changed to “operation” starting within ten years after 2038. This makes more sense, the earlier version seemed absurdly far in the future. My understanding is that the current plan is essentially to put off to 2026 a decision about going ahead with FCC. By 2027 the HL-LHC will be in place, freeing up some money for a new project, possibly the FCC. A 2027 start to FCC construction would allow a start of operations within ten years after the 2038 HL-LHC end date.
Update: Adrian Cho at Science magazine has a report on this that gets it right, headlined European physicists boldly take small step toward 100-kilometer-long atom smasher. It includes the crucial:
However, CERN Director-General Fabiola Gianotti emphasizes that no commitment has been made to build a new mammoth collider, which could cost $20 billion. “There is no recommendation for the implementation of any project,” she says. “This is coming in a few years.”
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