Results from EPS-HEP 2011
Results from the EPS-HEP 2011 conference that began today are starting to appear. These include the first results making use of most of the 2011 LHC run data. This is a factor of 30 or so more data than that from the 2010 run, which was the source of almost all previous results released by the LHC experiments. Some of the news so far:
ATLAS pretty much says here that there are no squarks or gluinos below 1 TeV (see page 9). Comparing to analyses of the regions considered mostly likely (see for example here, figure 7) pre-LHC, significantly more than half of the region in which supersymmetry was supposed to appear is now ruled out. Another factor of 10 or so in data should come in during the rest of the 2011/2012 run, which should allow limits to be pushed a bit higher. At this point, it looks like SUSY is on its way out. It will be interesting to see if die-hards insist that the factor of 2 in energy at the next (starting in 2014-5) run will make a difference.
For results relevant to strings, black holes, extra dimensions, split supersymmetry, and other exotica, CMS has them appearing here, for ATLAS they’re here. No such objects are being seen, with limits being pushed up dramatically from those coming from the 2010 data. Again, it’s going to be very hard to argue that there’s a significant probability that such things will be seen in the rest of this run, or even later ones at full energy.
CDF results available here say no Higgs between 156 and 175 GeV, D0 exclusion (here) looks like it covers about 160-170 GeV. Fermilab has issued a press release about this, advertising the release of the combined numbers at a July 27 talk. This should also include low mass searches which might provide exclusion above the 114 GeV LEP limit. The press release mentions a “most likely” range of 114-137 GeV for the Higgs mass, and links to earlier Tevatron exclusion limits, but I suspect the 137 number comes from a different source, not a Tevatron direct search result.
CMS and ATLAS results on the Higgs are to be announced tomorrow afternoon (an early version of the CMS results leaked here). A combination of results from the two camps will be done after the conference, planned to be announced at Lepton Photon 2011 in late August, although a rough guess as to what that will look like should be available just from seeing the two independent results.
Philip Gibbs is keeping a close eye on this at viXra log.
Update: Tommaso Dorigo has some more news here: CMS is not seeing the SM violating forward-backward top pair production asymmetry seen at the Tevatron (more about it here).
Update: ATLAS results on the Higgs are 95% exclusion 155-190 GeV and 295-450 GeV. They see a 2.8 sigma excess of events in the 120-140 GeV range.
Update: I just noticed that Matt Strassler now has a blog and is blogging from Grenoble.
Update: Matt Strassler reports from the CMS Higgs combination talk that they exclude 145-480 GeV at the 90% confidence level. Some excess 120-145 GeV, smaller than ATLAS.
So, in summary, it looks like the LHC + Tevatron have pretty much excluded a high mass Higgs, narrowed the possible mass range down to 114-150 GeV or so. No evidence at all of anything but the SM. The big story of the next few months will be to watch and see if a Higgs signal emerges in the last non-excluded region. Or not….
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Btw, QED is beautiful.
The SM and gauge theories are not, there is a lot of ugliness that people tend to forget about. Like ghosts, BRST and so on…
And who cares about the Planck scale? The Higgs sector has problems even without looking at such an high scale. EWPT? Little hierarchy problem? On the other hand if we forget about the Higgs boson there is loss of unitarity in W scattering. I don’t think i have to go on with such famous old stories (even if it seems people forget them too).
PW: “…new symmetries, all of which do nothing but relate degrees of freedom we know about to ones that can’t possibly exist.”
Is spontaneous breaking against the law now?
Unknown: “You’re really concerned about QED then?”
Or, more to the point, the U(1) of hypercharge…
Unknown: “Yeah, like the flavour sector.”
I think Peter meant exactly that in the comment before when talking about the Higgs taking away our inability to calculate most parameters. That phrasing is maybe a bit obscure. I suppose he hopes for an alternative which tells us all about flavor at the TeV scale where we can observe the mechanisms, as do I. Wouldn’t that be nice indeed. Unfortunately, we do not have any hard reason to think that nature is this nice to us , not theoretical nor phenomenological, apart maybe from the hierarchy problem itself, which he however discusses away.
Repeating the slogan “susy has 120 parameters” over and over again is not good style. I’m also not in favor of hyping anything, but throwing wrong statements around is not the way to respond to a hype. A little more nuance is all I would be asking for. There are more adequate ways to criticize the idea of TeV scale supersymmetry than repeating simplistic half-truths like that, there really are. Talk about how gruesome difficult many models of SUSY breaking are, and how msugra is nonsense and why.
“taking away our inability”
erm, I meant “taking away our ability” of course.
Personally I think the ghosts/BRST issue does involve beautiful mathematics. The problem is that we don’t completely understand it (which makes it more interesting, and it’s why I work on it..). Mathematically, this is about using Lie algebra cohomology to understand fundamental issues in representation theory. The question of exactly how “beautiful” this is does await a fuller understanding.
Going from QED to the SM – Higgs is just going from U(1) to slightly larger Lie groups, so the “beauty” issue doesn’t change much. The fact that this requires a more sophisticated way to deal with imposing gauge symmetry may be a feature, not a bug.
The problem of the 120 extra parameters and the problems of models of spontaneous SUSY breaking are functionally the same. I don’t see anything wrong with avoiding a long description of the various ugly and complex ways people have found to spontaneously break SUSY without contradicting experiment, and just referring to the bottom line: lots of undetermined parameters. In general, I think it’s misleading for anyone to go on about the beautiful physics of their favorite symmetry, when they have to introduce a lot of ugliness to avoid contradicting experiment.
“…new symmetries, all of which do nothing but relate degrees of freedom we know about to ones that can’t possibly exist.” I beg your pardon, maybe you published some proof of the inconsistency of SUSY?
You deleted the first part of this sentence “with no symmetry breaking”, which is the point. Without SUSY breaking, your symmetry relates each particle to one with the same quantum numbers and the same mass, something that is known not to exist.
“What you get out of SUSY is the ability of explore experimentally, through the SUSY spectrum, physics at extremely high energies” This is just unadulterated hype. So far SUSY has told you zero about physics at the GeV/TeV scale. Conviction that it’s going to not only appear, but in a form that tells you about “extremely high energies”, is nothing but wishful thinking.
No, I’m not a huge fan of the see-saw mechanism. Introducing yet another higher energy scale as an explanation isn’t very convincing. Maybe it’s right, who knows, but the bottom line is that we now really don’t know anything about where fermion mass matrices come from.
The problem of the SM U(1) being non-asymptotically free can be evaded with GUT unification. The cost of course is adding yet more scalars, so the problem with scalars like the Higgs has to be dealt with somehow.
“Excuse me?” Maybe you’ve heard that Higgs Yukawa couplings give fermions masses? These are unconstrained in the SM. I suppose the standard ideology about this these days though is that we’re supposed to give up, and just bow down to the glory of the multiverse, which picks such couplings out at random.
The flavour sector is a beautiful structure (the Dirac equation coupled to gauge fields) IF you throw out the Higgs couplings.
“Sometimes one wonders if you’re really a particle theorist.”
Besides being a mathematician, I am a trained particle theorist, although my training (late 70s-early 80s) was in a period when supersymmetry was around, but it had not hardened into a hype-filled ideology. My concern is that the standard training of many theorists over the past 25 years has been within an ideological framework based on some wrong assumptions. The LHC is in the process of blowing up some of the underpinnings of this ideology. The interesting question is whether many people will admit this is what has happened or hold fast to their ideology in the face of contradiction by experiment. I’m afraid that even post 2015-6, when LHC results at the highest energies are in, SUSY die-hards will be repeating the same mantras, unwilling to give up on the idea, no matter what. You can already see that happening with string theory….
Thanks for that piece of information. I’m curious whether Wilczek is still willing to take bets on the same odds post this summer’s LHC results. If you hear that he is, let me know…
Thanks for your perspective, piscator.
“With no symmetry breaking”
D’oh, one should always go to the primary literature!
I see your point that merely talking about the beauty of supersymmetry misrepresents the difficulty of constructing a realistic low energy susy model. That being said, there may be one that is simple
>>In any case, first of all the question is whether the Higgs really is there, and it’s >>very exciting that the next few months might see an answer to this question after >>so many years.
Amen to that.
Cheers, no problem.
To misquote a movie villain:
“This bickering is pointless. LHC will provide us with the location of the Higgs mass by the time this year is over. We will then crush the doubters with one swift stroke!”
I have to say, it’s truly, truly wonderful to start seeing the first hints of theoretical people arguing about…lots of data! Nothing at all against theorists of any kind, but I’ve felt the field of HEP has suffered long enough without some fresh meat to chew on. As a huge fan of physics, especially that golden era of the 20th century when the SM was born and matured, the idea that we might be on the verge of seeing something utterly new is exciting.
Higgs at ~120GeV and nothing else. looks like i’ll win by bet about what LHC is going to find 🙂
SUSY isn’t dead yet but it’s certainly sick. I suspect that the experimentalists are going to lose interest in it completely if the LSSP is not found under ~1.2TeV, for one simple reason: the best pointer to new physics we have is the high mass of the top quark. If something isn’t found that can explain that then there will be plenty of work for theorists – but not on supersymmetry and string theory (superstrings were originally attractive because they could save supersymmetry from its internal contradictions: that won’t be necessary if SUSY is no go).
Searches for supersymmetry will probably continue even if a blank is drawn but really they will be searches for new physics (and a reason for the top quark mass).
I personally wasn’t expecting evidence for supersymmetric particles below ~0.9 TeV since I think that there would be some evidence in the form of effects on lower-energy physics which would have already been puzzling us so the current results haven’t changed my opinion (that SUSY is unlikely) either way.
The measurements I am looking forward to are the ones of the various coupling “constants” (alphas) at increasing energies. The most reasonable interpretation of the current data is that Unification does not happen. If there isn’t some evidence of a tendency for the coupling “constants” to head for a common asymptope by 14 TeV, Grand Unification hypotheses will look far less tenable. As it is, I am amazed by how many people seem to be taking the Unification Energy as a data point.
But even if only a single, SM-like Higgs is found, its dynamics should be pretty interesting. Without SUSY (if it’s actually not there) the naturalness problem remains unsolved. And it is quite doubtful that a simple quartic potential put by hand into the lagrangian just for the purpose of breaking the symmetry is the end of the story. More statistics, and eventually more energy, are going to reveal a lot of interesting stuff.
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