HEP News

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.

Update: The CERN strategy report is here, also see here, here and a press release here. There is press coverage here, here and here.

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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37 Responses to HEP News

  1. DB says:

    … so we will have many, many more years of Arkani-Hamed spending a lot of time talking about this issue.

  2. Peter Woit says:

    Arkani-Hamed seems to have turned into a mathematical physicist searching for a replacement for quantum mechanics and GR, so maybe he won’t be talking about this so much. He was involved in the Chinese version of this kind of proposal, it may be that will be the one that has some hope of happening in our lifetimes, so attention will move to that. I have no idea what its prospects are.

    On the CERN front though, arguments about this are effectively now moot until 2026, since there’s no plan for them to do anything other than to continue to study the possibilities until then.

  3. DB says:

    Yes Peter,
    Nima has moved over to other things. His ideas about all his “hedrons” seem very interesting, but only time will tell if he’s on the right track. No other top theoretical physicist seems to be following that road. So patience is going to be of the utmost importance here.
    He was considered to become the director of that Chinese collider, but I’m not sure if that will come to pass either. As you know, the world economy is heading towards a great reset, and I guess that something like that huge collider might well be hanging in the balance at the moment.

    And yes, sure. Re the CERN, 2026 is the new date to be paying attention to. The HEP world is moving very slowly, as expected. No surprises there.

  4. vmarko says:

    Any mention of the Chinese collider in the CERN report?


  5. Peter Woit says:

    The existence of the CEPC proposal is mentioned, as well as the fact that it’s similar to the FCC proposal. Another good reason to put off a decision on FCC to 2026 or so is to see what the Chinese will do. If they go ahead with CEPC, I doubt anyone in Europe will want to try and raise the money for a second similar project.

  6. Gianni says:

    Peter, the quoted report on ‘Physics Beyond Colliders’ (on arxiv) states on page 7

    “more questions than ever remain open.”

    The report provides exactly three questions: dark matter, dark energy and the baryon-antybaryon asymmetry in the universe.

    These three questions are then summed up by stating that there is “exceedingly convincing evidence that there must be Physics Beyond the Standard Model”. (All this is on page 7.)

    It seems hard to imagine that these three arguments will be sufficient to build a new machine. The arguments are much weaker (but also much more honest!) than they were before the building of the LHC.

    We are indeed in an unprecedented situation in high-energy physics: many researchers and possibly little to discover. The situation is extremely difficult to manage, especially for policy makers. I think it is essential to acknowledge this difficulty. There do not seem to be easy solutions. A careful approach, like that of CERN, seems appropriate.

  7. I says:

    One reason to build a collider after the LHC is the massive loss of technical experience and knowledge needed to make one. But it seems plausible that alternative projects listed in the report, and elsewhere, would foster the same expertise. Do you (dis)agree Peter?

  8. Peter Woit says:

    I think the new strategy document does get the main physics case right: the Higgs field remains a central mystery of fundamental physics. The LHC has done a lot to study it, but a Higgs factory able to study it in much greater depth is the logical next step for the field. The problem is whether there’s an affordable way to do this, or whether we should just give up, decide that it’s not worth it to find out more about this fundamental aspect of reality. I wrote about this in detail here

    The FCC proposal seems to me an honest attempt to lay out what the best way forward is, but the scale and expense of it is highly problematic. The fact that there was no decision to actually move forward on the project, that the decision is being put off for another 6 years, seems to me an acknowledgement of this.

    Yes, there’s a good case being made that one reason to not completely give up and stop research at the energy frontier is that once you do this, it will be hard to impossible to restart, since all the people with relevant expertise will be gone. Ideally, some smaller scale, less expensive projects can be found to keep the field active. There’s clearly a lot of hope in some quarters that for instance a muon collider project will turn out to be feasible. That would use current expertise, while requiring also the development of new technology and solution of new problems.

  9. tulpoeid says:

    “THEY ARE NOT DOING THIS. After a lot of work, they have identified the best possible way forward at the energy frontier and decided not to go ahead with it now.”

    After reading the press release that’s the impression I got. Then, the next day I read some media headlines and articles and was surprised to see that I had completely misunderstood CERN’s statement. Eventually the quoted clarification just made me feel better about my wits, and once more totally pessimistic about how science is reported these days. (Can’t we get even things like this straight anymore?) (Can it be that the relevant articles were written ahead of time based on rumours and then nobody noticed the difference?)

  10. tulpoeid says:

    this report is for the opposite of “building a new machine”. It’s a program literally for physics beyond colliders; so the arguments might be differently weighted than for the case for a new collider.

  11. Gianni says:


    It seems to me personally that a high price is worth investing for the final theory, and surely 20 000 million. But still I remain worried. The Nature paper you quote, based on the CERN report arxiv.org/abs/1901.09966, presents eleven options for physics beyond the standard model. They also claim that this represents the *phenomenology* of *all possible* extensions to the standard model. The options are based

    – on dark photons,

    – on light dark matter particles,

    – on millicharged particles,

    – on Higgs-mixed scalars,

    – on heavy neutral leptons,

    – on axion-like particles.

    Do we really think that there is a chance to find something on these fronts? I must admit that I am sceptical. In my view, the first question to settle is: are we looking everywhere possible? Or more specifically: did the authors miss some option?

  12. Peter Woit says:

    Sorry, tulpoied is right, I missed that you were referring to that “Physics Beyond Colliders” report, which is about non energy frontier possibilities. These are much much cheaper, may make sense to do them even though quite unlikely they’ll find something. There may very well be quite a few other such possibilities beyond the ones they mention.

    I think this is somewhat CERN’s fault: they emphasized the decision to concentrate on the FCC proposal, hoping I think to generate enthusiasm about it, with the fact that they hadn’t actually made the decision to go ahead with this (and had no idea how to pay for it…) deemphasized. The journalists writing articles were likely writing them based on early access to an embargoed version of the press release.

    One thing that makes much clearer what is going on is the detailed spending plans in CERN’s proposed new medium term budget plan for the next 5-6 years, but I don’t think this is a public document right now.

  13. Not that my opinion fucking matters, but Gianni’s skeptical list of places to search is very telling:
    – on dark photons,
    – on light dark matter particles,
    – on millicharged particles,
    – on Higgs-mixed scalars,
    – on heavy neutral leptons,
    – on axion-like particles.
    Every one of these entails shoehorning unimaginative dross into a theoretical architecture to which the mainstream has been addicted for decades – since Dirac and Feynman – and in none of these cases -NONE – should any of these chewing gum fixes succeed to any limited extent – will the community of theorists loudly proclaim: of course, this was inevitable. I know you won’t publish this rant, but this is why I’m strongly opposed to building another collider anywhere, whatever technological expertise we may lose in waiting. The lack of imagination behind the proposed endeavor is staggering. Gianni was being far too polite in casting shade on his list of suspect motivations.

  14. Amitabh Lath says:

    If you are not at the energy frontier, you are doing chemistry….not that there is anything wrong with that. That was the advice of an eminent theorist when I was considering different subfields of (experimental) particle physics. He was not wrong. If we don’t build the FCC (or CEPC) the field will still do good work, map out the higgs potential, measure the neutrino mixing angles, etc. But it will not be frontier physics.

    I do not think $20 billion over a couple of decades is such a big deal, especially when you think about how much will come back into the economy as jobs and taxes. Sabine Hossenfelder has an article in Scientific American arguing against the next collider. The sub heading is: “the money could be better spent researching threats like climate change and emerging viruses” which frankly is the most naive thing I have ever read. Does she really think national and international economies work like that? How much of a bump did non-high-energy fields get when the SSC got cancelled?

  15. Peter Woit says:

    I basically agree with you, although I see “mapping out the Higgs potential” (in the sense of measuring Higgs self-interactions) as energy frontier physics, one of the reasons for an FCC-ee and FCC-hh.

    I also think the way numbers are being thrown around is problematic. I can’t find where the “20 billion euro” number came from. The numbers I have seen are 10 billion dollars for the FCC-ee, another 17 billion for the later FCC-hh. As they have been for the past couple years, people are loudly arguing about numbers in a way completely disconnected from the crucial questions of exactly what those numbers would buy and how they would be raised. The immediate question to me seems to be “can 10 billion dollars be raised to pay for a tunnel + FCC-ee?” Until there’s a plan on the table for how to do that, the argument is too disconnected from reality to be worth having.

  16. Niclas says:

    Carlo Rubbia has been arguing strongly for the muon option here in Europe. He says it is very realistic and basically the technology can be worked out. Assuming the Chinese go the FCC route then a muon factory could be good for CERN with a lot of opportunity for discovery.

  17. Peter Woit says:

    Geoffrey Dixon,
    You’re making the same mistake I originally did. That list of things to look for that Gianni refers to is from the “Physics Beyond Colliders” report, written by the group looking into possible projects other than a new collider. I agree this is an extremely unlikely and sad list of things to look for, but it’s what the future of the field looks like if you don’t build a new collider, not a list of what you could look for with a new collider.

  18. Feeling less cranky now. I agree that Sabine’s suggestion that the money could be more fruitfully spent making the planet able to support more humans is unrealistic. And although I am not immune to the occasional bout of dudgeon regarding trends in high energy physics, as regards its place among all the things humanity gets up to, it is – relatively speaking – an idyllic oasis. A shining city on a hill, as it were … and keeping it shining, and keeping physicists employed in pursuit of some lofty (preferably not misdirected – but even if misdirected) goal … that to me provides some solace, and quiets the inner Thanos. As to Sabine’s suggestion, I am reminded of JFK’s moon speech (“and do the other things”), and although JFK evidently didn’t really care about getting to the moon, it was a good speech, and relevant to this discussion. WTF, build it (or them), for if we do not, we lessen our reason for existing.

  19. Peter Woit says:


    Here’s my prediction for the future (assuming no new developments from theory or experiment changing the HEP landscape). In 2026-7 CERN will decide to go ahead with a muon collider test facility. The cost of this will eat up the available funds (100 million or so dollars/year) freed up by the ending of HL-LHC construction expenses. The FCC project will remain a goal for the future, with studies continuing, but no plausible funding plan.

    By the way, Alessandro Strumia has a negative piece about the FCC as a guest post here
    As he himself points out, he has personal reasons for not being a fan of CERN, so you might want to take that into account when reading him. His point of view I think is not uncommon though among theorists, many of whom have decided they’re pretty sure there will be no new physics at FCC-accessible energies.

    My advice remains that one should not be paying attention to what theorists think about this, given the sad history of theorists promoting the LHC as a machine that would produce SUSY particles and black holes. They were completely wrong about this, could very well be completely wrong again with the no new physics prejudice. If the experimentalists and machine builders are able to get behind a viable project, that should be supported.

  20. Gianni says:

    Yes, the list from “Physics Beyond Colliders” is indeed for low-energy experiments. I searched for a similarly long report on physics with a new collider, but could not find one. Does anybody know a long report from CERN with arguments in favor of the 100TeV machine or with a list of experiments to be done with it?

  21. Amitabh Lath says:

    Peter, it is not sensible to talk about the cost of a mega project like a new collider as if it were an off-the-shelf item like a new microscope. A lot of the money will come with strings about where it will be spent. A lot of it will be “in kind” esp. manpower and software from developing countries. These should be considered infrastructure and/or stimulus spending.

    Let’s say the FCC gets power supplies and digitizers from CAEN. This is the Italian/INFN contribution. The understanding is that CAEN will build design and manufacturing facilities in a depressed region in the south. The hope is the technicians and engineers spark a tech boom. The Italian govt. is not simply writing a check.

    The effect is even bigger in developing economies, think of Pakistan designing and building the CMS tracker alignment and barrel yoke, or India supplying superconducting corrector magnets and precision positioning jacks for the LHC.

    We need large, ambitious, technically difficult projects to strive towards. It keeps us from turning into navel-gazers concerned only about our own conveniences. JFK understood that of course.

  22. Alessandro Strumia says:

    Actually I was not much interested in staying at CERN precisely because high-energy physics, as we knew it, is over. No new physics at LHC and no new collider in the next decades makes big change unavoidable.

  23. Low Math, Meekly Interacting says:

    What I am struck by most is the temporal scale. If the FCC is ever built, a significant fraction of the scientists involved in planning it (and taxpayers paying for the effort) will never live to see it completed. The EU could dissolve in the interim. Western Civilization may be obsolete before its finished. The Great Pyramid of Khufu is a mid-scale capital improvement by comparison.

    Increasingly I’m in the sustainability camp. Maybe building a muon collider is not feasible, but it seems like a more worthwhile bet. I want humanity to explore the energy frontier, and I don’t need to be persuaded to support it. But my faith in the durability of the institutions needed to see such a project to a fruitful completion has been severely shaken in the past few years. New technology might be the answer.

  24. A reader says:

    To Alessandro Strumia: “because high-energy physics, as we knew it, is over.” With all due respect, is yours a scientific statement? Confidence level? Please do not let your personal hate, your personal agenda and your sour grapes help destroy HEP. The same applies to Sabine Hossenfelder. As a humble physicist, and a long term reader of this blog, I completely agree with Peter Woit’s view: “If the experimentalists and machine builders are able to get behind a viable project, that should be supported.”

  25. Peter Woit says:

    It’s exactly because the sources of financing for a new collider will be a complicated story that I don’t think now is a fruitful time for arguments over that financing. Because people don’t have anything specific to argue about, what you end up getting is “we shouldn’t build a new collider, no matter how little the cost”, and “we should build a new collider, not matter how much it costs” arguments, which seem to me disconnected from reality.

  26. Alessandro Strumia says:

    Dear reader, I would like to see a 100 TeV pp collider, but we reached the point where the usual “positive” view backfires and repels people like Sabine. You worry about people who discuss problems, I worry about problems. For example, do you expect that creative smart young students will enter a field that might produce discoveries with 10K authors when they will be near retirement, unless everything stops earlier?

  27. A reader says:

    Dear Alessandro Strumia, Sabine Hossenfelder is 1 (one) very talkative physicist with access to mainstream media platforms she very much enjoys using to support her personal views. Not all, but some of what she says sounds ideological, absolute views accompanied by (sometimes understandable) rage. I have read Peter Woit’s blog for longer than a decade, so I know where that rage comes from and I can understand it. But hers are opinions, and when they are about the future I can’t see confidence levels attached to them. I’m not that old, but I am definitely too old to like ideology. I much prefer sane pragmatism.
    One of my best teachers, a very good man, old school, he taught us the basics of QFT, his view, I completely agree with, was that EXPERIMENTAL HEP is like an epic endeavour undertaken by an extremely large orchestra. It is astonishing that mankind (mankind!) managed to pull it off (more than once!). Think about the whole history of EXPERIMENTAL HEP. The women and the men whose commitment made all those GIANT achievements possible. I mean, we descend from apes! Much is dysfunctional with HEP THEORY, but why this eagerness to destroy ALL HEP? ALL!?!?
    And to reply to your question, yes, I do believe there are still creative smart young students around who are romantic enough to be willing to be part of this epic and dedicate decades of their lives to it. Much of our world is grotesque cynicism and despair. I still remember the intense thrill to be part of a large collaboration at FNAL as a summer trainee, for a very short time, a couple of months, a long time ago, as a 3rd-year undergrad. There was some very special atmosphere there, so special I can still remember it vividly 20 years later, and that “magic” I believe it was that there was some epic going on there. So yes, I do think there are still creative smart young students willing to be part of some epic, in this very ugly time in human history, even if that epic is going to take 40 years of their lives. Just be upfront, state it clearly to them with honesty and without lies.

  28. Alessandro Strumia says:

    Dear reader, FNAL now left the high-energy frontier, because higher energy needs more money until it’s no longer sustainable. I remember a similar atmosphere once upon a time in CERN: Soviet-style buildings and first-class physicists. They now got Renzo Piano building, but the epic is over. Buffalo Bill’s show is no longer Wild West.

  29. Amitabh Lath says:

    Alessandro Strumia, as Peter concurs above, money is not the issue. The world economy is fully capable of building multiple energy frontier machines. Nor is the interest of young students: every year we get applications from amazing students and can only accept a fraction of them. Of course some turn out to be impatient and want earth-shattering discoveries now dammit! and show no interest in staying. But a core group realize they are part of an epic slog that is generations long.

    Think of the bevy of e+e- machines in the 80’s that failed to find the top. Were they failures? Of course not. Nature placed her secrets as she wished, not so humanity could make a new discovery every decade.

  30. Gianni says:

    Peter and all,

    This is what I found searching. The CERN paper “FCC Physics Opportunities”, published in Eur. Phys. J. C 79, 474 (2019), written by hundreds of authors, defines three aims of the FCC: (1) the search for unexpected phenomena around the Higgs and the electroweak gauge bosons, (2) the search for new particles, including dark matter, and (3) the search for “tiny deviations” (they call its this way themselves) from the standard model.

    In my opinion, the real question seems to be: will the FCC just confirm the standard model or will it find something new?

    We need to be very honest about answering it. Are we reasonably sure that there is something new to be discovered at higher energies? Would we put our hands into fire for our own answer?

  31. Alessandro Strumia says:

    Dear Amitabh, now we are a few years after the LHC peak of interest, and we still have work to do. If nothing new is discovered, the issue I mention will develop in due time.

  32. Peter Woit says:

    This is the heart of the problem: there is no strong theoretical argument for new physics accessible to a new collider, and that’s why you are seeing some theorists arguing against building one. The counter-argument is that you do science by testing theoretical arguments, not by just accepting them. An analogy some people are making is that, pre-1998 and to this day, there was and is no good theoretical argument for a non-zero CC. So, why go look for one?

    What makes the collider issue difficult is the high cost. If looking for a non-zero CC cost over ten billion dollars, I bet it would never have been done. I don’t think it makes sense to decide not to build a collider just because theorists don’t expect it to find something new. Deciding not to build such a thing will be a decision to give up on this fundamental field of science with a long and distinguished history, because it’s not worth the expense to test the theory at this new higher energy scale. This is a question of values and I come down on the side of those who think it’s worth the likely expense. I also though think this debate over values is a sterile one until there’s a definite plan for how to pay for this on the table.

  33. Paolo says:

    From the ITER & SSC lesson, 10 years -> 20 years and \$ 20 billions -> \$ 40 billions; some peoples do live in alternative reality.

  34. Peter Woit says:

    My impression is that CERN has a fairly good track record for completing large projects at more or less the projected time and cost. In any case, even in your bad case scenario, the fundamental problem “where are you going to find 2 billion/year?” doesn’t change, just goes on for more years…

  35. Pingback: The road to a bigger collider? | particle linguistics

  36. Peter Shor says:

    Delaying the decision is clearly the correct decision. Suppose that in the next ten years, evidence emerges for interesting new physics somewhere in the neutrino sector, which could only be investigated with some kind of $5 billion neutrino factory (this is, of course, wild speculation). Then if CERN had already committed to the FCC, the neutrino factory would likely end up being built elsewhere, and CERN would be spending tens of billions to be in the rearguard of new discoveries in HEP physics.

  37. LK2 says:

    I was hit by the “reader” comment about the magical atmosphere at FNAL at the Tevatron times. It was really true and I also lived that as a student. There you had the feeling that something was really going on. As a person who stayed in exp. particle physics, I see this feeling completely lost in gigantic collaborations, endless meetings, true work done only by students while the others are sitting in meetings discussing budgets, schedules, reports. That’s the way it is now, fine: I just decided to work on smaller scale experiments for having more fun. I still would love to see a new energy frontier project launched in the future: as physicists, we have to chart uncharted territory. What P. Shor says is also very relevant: better carefully look at the direction before committing. The muon collider option at least would be a big novelty also from the technological point of view. And handling dense muon beams can be useful also for a neutrino program!

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