There are two highly active projects to design a linear collider that would collide electrons and positrons at energies higher than those achieved at LEP. Recently there were workshops discussing the state of the projects.
The ILC is the farthest along of the two and uses more conventional technology. It is a design for a 250+250GeV collider, upgradeable to 500+500Gev. There’s a very jazzy new web-site aimed at selling the idea to the US public. This week Fermilab is hosting a workshop on the ILC, talks available here. Michael Peskin gave an introductory talk with an unfortunate title (“The Physics Landscape”, I really think serious physicists should not be reminding people of this, especially when they’re making a pitch to the public for money). He argues that the LHC will see a spectrum of new particles (in order to solve the hierarchy and dark matter problems), and motivates the ILC as the machine to study these. This of course depends on their existence, at a mass low enough to allow production at the ILC, but high enough to evade bounds from LEP and the LHC (for some new results from the latter, see here). It now appears certain that no decision about building the ILC will be made until results are in from the LHC (2010?) that will resolve whether there are new particles in the mass range that the ILC is capable of studying.
DOE’s Ray Orbach gave a talk about the ILC project, emphasizing:
It is critical that planning for the ILC takes into account the realities of the funding situation, the need to formalize the ILC arrangements between governments, the changing scientific landscape, the scientific capabilities at other facilities, and the health of our national scientific structure.
Orbach seems concerned that the ILC project does not have a realistic schedule (“I judge that these arrangements will require more time than the currently proposed schedule of the GDE”) , and does not have commitments from other countries. I’m guessing that he sees financing it out of the current and expected DOE budget is not doable without large contributions from other countries, and a relatively long time-frame. He emphasized that there is now a well-defined process for projects like this: they have to survive a series of “critical decisions”. The ILC is not yet ready for the first critical decision “CD-0, Mission Need” and won’t be until after the LHC results are in. He also mentions “other planned international projects”, and the importance of not duplicating their activities (I take this to be a reference to CLIC). Finally, he is critical of the plan of the ILC project to move to an “Engineering Design Report” that would give detailed engineering plans for the machine, since he sees it as still in an R and D phase.
Over at CERN, the Resonaances blog reports on a workshop devoted to CLIC, a more ambitious and less technologically developed plan for a 1500 + 1500 Gev collider (upgradeable to 2500 + 2500 Gev). If CLIC really turns out to be feasible, and buildable on a time-scale close to that of the ILC, it will not be possible to justify building the ILC, since it would operate at much lower energy.
This week internet access is more iffy, since I’m in Lisbon, for a conference late in the week on “Is Science Near Its Limits?”, sponsored by the Gulbenkian Foundation. After it is over, I’ll write about it here, and I think I can post a copy of the talk I’ll be giving.
Update: Science magazine has a short piece about the Orbach talk, see here:
Orbach said physicists must follow the department’s protocol that requires a large project to pass five critical decision milestones. The ILC has not passed the first, which allows researchers to proceed from basic R&D to design, Orbach said. Previously, DOE officials had been “completely open” to a less formal approach, says Caltech’s Barry Barish, who leads the design team. What counts as “engineering design” remains to be determined, he says.
Another piece of this story recently pointed out to me is that the new CERN director is from DESY and associated to the ILC project there. This might cause people at CERN to wonder how hard he’ll push for its CLIC projector, which is in some ways an ILC competitor.
Ah, commitments! How about we just design the next virtual collider and put it on Second Life? Who needs the ILC? 😉 Have a safe trip,
B.
Hi Peter, just a quick question, to revisit an issue before it got derailed,
you don’t think that there is a “hierarchy” problem (requiring SUSY as the antidote to radiative corrections to the higgs, and hence, string theory) I am curious as to whether you think there is a higgs boson and higgs field, and what prevents it from gaining mass from the EW-scale to the GUT scale. Do you think that the higgs boson is fined tune to 32 decimal places and that is the end of that – no SUSY required?
dan,
This is off-topic, and I don’t really want to start yet another discussion of supersymmetry, but, in brief, I’ve never been convinced by the “supersymmetry eliminates the need for fine-tuning argument”, for several reasons:
1. We don’t even know there is a GUT scale. There is zero evidence for such a thing.
2. We don’t know that the Higgs field is an elementary scalar.
3. If supersymmetry really was going to eliminate all fine-tuning, it would have shown up by now.
Wow Peter,
for an answer to an off-topic comment you did pretty good 🙂 Let me add my own:
4. Speculating susy exists but was not detected so far because there was some symmetry breaking mechanism making susy particles much more massive than ordinary ones is legitimate, but it stinks. It flies in the face of Occam’s razor, which becomes nervous and comes a-slashing.
Instead, why not giving some more tentative credit to Alejandro Rivero’s idea that sparticles (bosons) are composites of two fermions ?
Cheers,
T.
Hi Tommaso,
Yes, supersymmetry is a beautiful idea, until you have to break it…
The problem with composite models is you have to find some dynamics that doesn’t screw up the fact that the standard model works perfectly. The idea that the Higgs field is a composite field of a fundamental fermion field is an old one, well motivated by what happens in superconductivity (Cooper pairs). Technicolor is one way of doing this. People have looked at this, but maybe if they had put as much effort into is as into SUSY, other better ideas might have shown up.
It would surely liven up the field again, if the Higgs mechanism, supersymmetry, technicolor, etc … and all of their variations + combinations, all turned out to be complete failures in the end.
If this indeed turns out to be the case, then I would have no idea offhand what would be a fruitful path to follow afterwards. I suppose one could skim mindlessly through older theoretical particle and/or condensed matter journals, searching for long forgotten ideas to resurrect and try out.
Woit, just to be clear– are you saying you consider it probably the case that the Higgs is not an elementary scalar? Or are you just saying that an elementary scalar nature of the higgs cannot or should not be assumed?
Also, more on topic, kind of a dummy question: Why is it that all the big “vacuum cleaner” accelerators, like the LHC and Tevatron, seem to be cyclic/synchrotrons– whereas the new proposed colliders we’re seeing described in this post for the lower-power but more “fine-tuned” measurements are all linear? Is there something about a linear collider that makes the fine-resolution stuff easier to do than it would be with a synchrotron? Or what?
Coin,
Above LEP energies, synchrotron radiation loss is just too high for electrons (goes as fourth power or the energy), so you have to have a linear accelerator.
I don’t know if the Higgs is an elementary scalar or not. If I had to guess, I’d guess not (not asymptotically free, for one thing…)
I see, thanks.
In reponse to Peter’s answers to Dan’s questions:
1. It doesn’t matter if there’s a GUT scale or not. Quantum corrections to the Higgs mass will push it to whatever the next energy scale is, and if there is no GUT scale then this would be the Planck scale.
2. It’s true that the Higgs might be a composite boson. However,
such Technicolor models were studied very seriously in the 70’s and 80’s, but were eventually rejected due to some serious shortcomings. Namely, in order to generate mass hierarchies for the SM fermions, one ends up with serious problems with FCNC’s. Nevermind that it requires adding another gauge sector to the SM with strong dynamics which would have led to a plethora of technimesons for which there is absolutely no evidence. Occam’s razor anyone? Oh right, we only reserve this for things we don’t like like SUSY.
3. The amount of fine-tuning required in the Higgs potential in order to give a large enough Higgs mass is very small and perfectly reasonable. In any case, what Peter’s means is that to eliminate all fine-tuning, the Higgs should have been observed by now, not that the superpartners should have already been observed.
Keep your eyes peeled for the November issue of Physics Today, which has an interview with Aymar on the issue of which project CERN will support, CLIC or ILC. Toni Feder also has a good piece on Fermilab’s project X (doi:10.1063/1.2800091) in the October issue.
Peter Woit said “… If CLIC really turns out to be feasible, and buildable on a time-scale close to that of the ILC, it will not be possible to justify building the ILC, since it would operate at much lower energy …”.
So, in CLIC’s favor is its higher energy.
What about cost?
If ILC were to cost on the order of USA2007$10 billion,
how would that compare with the cost of CLIC ?
If the USA dollar were to continue to decline with respect to the Euro,
how would that affect the cost comparison ?
How would site location (Illinois, Europe, or Asia) affect the cost comparison ?
If CLIC were to be built in Europe or Asia, would the USA get to use it on terms as favorable as the USA has with respect to use of LHC ?
Tony Smith
Slide 38 of the file CLIC07_JPD.pdf from the CLIC workshop web site shows:
CLIC Old Parameters
Accelerating field – 150 MV/m
RF frequency = 30 GHz
Total cost (a.u.) = much higher than 2
CLIC New Parameters
Accelerating field – 100 MV/m
RF frequency = 12 GHz
Total cost (a.u.) = 1.15
What does a.u. mean ?
(is it effectively a comparison with the cost of the ILC?)
Tony Smith
What does a.u. mean ?
“Astronomical Units”? 🙂
Tony,
I don’t think anyone has a good estimate of what CLIC will cost. From what I remember, the size they are talking about is similar to the ILC, presumably based on the fact that that should make the cost somewhat similar. Not sure if exchange rates make much difference, although I suppose if the US currency collapses and we become a third-world country, it will be much cheaper to build something here. No matter where it’s built, there will be physicists from all countries working on it.
Paul,
Thanks for the heads-up, looking forward to hearing what Aymar has to say about this. I get the impression that it’s a delicate issue, with people on both sides choosing their words carefully…
Eric,
We also don’t know that the Planck scale is relevant…
See Distler’s explanation
http://golem.ph.utexas.edu/~distler/blog/archives/000336.html
of why current bounds on the Higgs mass imply a very heavy stop, and amounts of fine-tuning that are not “very small”.
Eric, you’d better read http://arxiv.org/abs/0708.3550
Why? Is the desert (susy or not) a well established experimental fact? Has a new physics threshold at, say, 30TeV, been definitively ruled out?
In any case, is it true that we have everything figured out all the way up to the GUT scale, so if it’s not there then only the Planck scale is left?
Conrad,
The expected next scale between the electroweak and GUT scale is the SUSY breaking scale which should be around 1 TeV in order to stabilize the Higgs mass. It’s always possible, in fact likely, that there are hidden sector gauge groups which become strong at some higher scale. However, this would have no effect on the quadratic divergence to the Higgs mass since the Higgs states are doublets of the SM SU(2) and not of the hidden sector groups. Regarding Peter’s comment that there is no evidence that the Planck scale is relevant, it doesn’t matter. That would just mean there is no cutoff and the Higgs mass becomes infinite.
As far as the fine-tuning in the Higgs potential, this is presently a few percent at most. The problem is if the lower limit on the Higgs mass gets pushed up much beyond 114 GeV, say to around 130 GeV. If the Higgs mass is in the range 114-121 GeV as expected, then the fine-tuning is not a real problem. Also keep in mind that this depends strongly on the top quark mass, which was recently revised downward to ~171 GeV.
> Eric, you’d better read http://arxiv.org/abs/0708.3550
Picture a particularly vast, featureless Zen Garden with a gnarly stone at one end. Now meditate.
T. writes
“4. Speculating susy exists but was not detected so far because there was some symmetry breaking mechanism making susy particles much more massive than ordinary ones is legitimate, but it stinks. It flies in the face of Occam’s razor, which becomes nervous and comes a-slashing.”
Let me write an analog of this, frequently heard in the seventies:
“4. Speculating gauge symmetry exists but was not detected so far because there was some symmetry breaking mechanism making gauge particles much more massive than ordinary ones is legitimate, but it stinks. It flies in the face of Occam’s razor, which becomes nervous and comes a-slashing.”
Who turned out to be right then?
U(1) gauge symmetry, i.e. electromagnetism, was understood in the ’70s, right? At least in the 1970s. A better analog from the 1870s would be the ether wind: people speculated it existed but was not detected.
Andr, I thought gauge symmetry SU(2) is based on simplicity and elegance and describes the weak force well, and predicted the masses of the W and Z massive gauge bosons in advance of experimental discovery? The reasons I was taught for why the gauge symmetries of the SM are physics (unlike susy) is that they
(1) come from experimental observations of fundamental forces and fundamental particles,
(2) are the simplest known ways to represent physical facts,
(3) predict reaction cross-sections, etc., that make it useful,
(4) predicted W and Z gauge bosons observed at CERN in 1983.
So I don’t understand what you are saying. Either I’m a moron or you don’t know the difference between fact and fantasy (susy).
Now if you are going to defend susy by saying some really great discovery in physics was suppressed, you need an analogy to a religious belief system that can’t make quantitative falsifiable predictions. Try the analogy of susy to epicycles.
Moron,
what Andr says is correct, both historically and factually. Historically, Weinberg proposed SU(2)XU(1) because it was the simplest possibility consistent with phenomenology, but he didn’t know whether it was the correct group. After his famous “model of leptons” appeared, many people (including Weinberg himself, you may want to check Phys. Rev. Lett. 38, 1237 – 1240 (1977) which appeared ten years after his model of leptons) started exploring other groups. It turned out that there are three massive weak bosons, and SU(2)XU(1) was the end of the story. But, also, many people didn’t believe in intermediary bosons — until they were experimentally observed. Something similar happened with quarks, gluons, jets, etc, etc
Factually, there is no reason why SUSY shouldn’t be there. There is also no reason, IMHO, why it should be. The only consistent argument I’ve seen for SUSY is naturalness, and I personally don’t buy it. But just like with weak bosons, experimentalists will hopefully resolve the mystery soon.
Eric,
my answer to your post was rejected by the server. In any case, thanks for your detailed answer.
‘Factually, there is no reason why SUSY shouldn’t be there. There is also no reason, IMHO, why it should be. The only consistent argument I’ve seen for SUSY is naturalness, and I personally don’t buy it. But just like with weak bosons, experimentalists will hopefully resolve the mystery soon.’
conrad, the weak gauge bosons were predicted to have a mass around 80-100 GeV.
When you are looking for sparticles ‘predicted’ by susy, you don’t have any predictions of what energies they should have.
Therefore, experimentalists who fail to find sparticles below 1 TeV will then have to continue trying at ever higher, arbitrarily higher in fact, energies. At what point do you say that experiments have finally ‘tested’ susy? You can go on testing a theory which makes no falsifiable predictions for eternity.
Testing susy is like testing ESP or religious miracles: if you fail after one effort, you can simply go on and on forever. That’s not science. It’s more like religion. You pray for experimental confirmation by a miracle, but if it doesn’t occur, you can keep on trying and believing in the speculations. That’s why falsifiability is the criteria that separates religion from science.
Moron,
You’re way off here. First off, the fact that a symmetry should be broken is no argument against having it in the theory. MANY symmetries which we know and love are broken, either by the vacuum or else by excitations.
Second, obviously SUSY is falsifiable as a solution to the hierarchy problem (in fact, it’s already under pressure). If you give that up, then you loose one of the strongest motivations for SUSY. Also, SUSY has a DM candidate. It should be possible to determine whether the DM in our universe is the lightest stable SUSY partner. If it’s not, then that motivation could get killed too. If these two motivations get killed then a lot of people will loose interest. But, of course, the theory has not strictly been ruled out. SUSY is very predictive, I’m not sure why people here are so keen to argue otherwise. (Also, SUSY is not string theory. We could have the MSSM quite independently of whether or not it’s UV completed to some string model.)
If we stuck to theories which are falsifiable in the sense which you’re asking for, then we wouldn’t have much left to work with. According to your philosophy scalar-tensor gravity is on the same logical footing as religion. You’re entitled to think that, but it certainly doesn’t reflect mainstream physics.
Moron,
I should like to add that the superpartners must be less than or equal to the TeV range in order to explain the hierarchy problem, which was mentioned but not emphasized by Mo above. If LHC doesn’t see the superpartners, then it means that SUSY is not the solution to the hierarchy problem. Supersymmetry could still be a part of nature even in this case, but then most of the interest in it will evaporate because it would not have any relevance for low-energy physics. The thing to keep in mind is the saying of Feynmann that in quantum mechanics anything which is not strictly forbidden is compulsory. If nature doesn’t incorporate supersymmetry, it would strongly violate this principle.
The thing to keep in mind is the saying of Feynmann that in quantum mechanics anything which is not strictly forbidden is compulsory. If nature doesn’t incorporate supersymmetry, it would strongly violate this principle.
This is the most confused thought I’ve seen around here in a long time. Feynman is turning at 60K RPM in his grave at the extrapolation from
“What is not forbidden in QM is compulsory” to
“What is not forbidden in nature is compulsory”.
The thing to keep in mind is the saying of Feynmann that in quantum mechanics anything which is not strictly forbidden is compulsory. If nature doesn’t incorporate supersymmetry, it would strongly violate this principle.
This is the most bass-ackwards reasoning I’ve ever seen, and a complete misunderstanding of the “totalitarian principle” (which I think is usually credited to Gell-Mann, not ‘Feynmann’).
Dear Arun and Anon,
Obviously, neither of you knows anything at all about quantum mechanics. If there is an allowed symmetry of your Lagrangian, it will be realized in nature. End of story.
Eric,
So what you’re saying is if I wrote down a Lagrangian with a U(17) symmetry it would be realised in nature, because that’s allowed by my Lagrangian? I’m afraid not, just take a look at SU(5).
Eric, quite entertaining!
Andrew,
You misunderstand me. What I’m saying is that there is a fundamental symmetry between fermions and bosons that will be a symmetry of any Lagrangian which includes fermions and/or bosons regardless of the gauge group.
Putative terms in the Lagrangian compatible with the symmetries will be generated by radiative corrections and are hence compulsory. This does not imply that any symmetry principle is compulsory.
Well, I would expect the symmetry between fermions and bosons to be as compulsory as Lorentz symmetry. In any case, it’s the radiative corrections involving fermionic partners which stabilizes the Higgs mass…
Eric,
If I misunderstood you, it is because you made a generic statement that anything not disallowed is compulsory. Now you seem to be saying something else. OK, thanks for the clarification. So why is the symmetry between bosons and fermions inevitable? You say yourself that you merely expect it (i.e. can’t prove it), so why such high confidence in this symmetry?