The LHC is operating well, hitting record peak luminosities, with integrated luminosity for the year over 11 fb-1. By the end of the year there may be 25 fb-1 per experiment or so. Current plan seems to be to update the results on the Higgs in December, much like last year, so there may not be much news until then.
This week the LHC Machine Advisory Committee was meeting, slides here. The current schedule has this proton run ending mid-December. After a heavy-ion run early next year, the machine will go into a long shutdown starting in March, with main goal to fix the magnet interconnections and commission the machine to run at nearly design energy, 6.5 TeV/beam. First beams at this energy will not be until April 2015, with maybe 20-25 fb-1 of integrated luminosity in the first year’s run.
With no sign of SUSY so far, and little reason to believe it will show up in the rest of the 2012 data since nothing has shown up already, the rallying cry of SUSY enthusiasts is now “Wait Until 2015”, or, maybe more like 2016, since early 2016 may be when analyses of a significant amount of 6.5 TeV data start to appear. I’d been wondering whether David Gross has been getting discouraged at the prospect of having to pay off on his SUSY bets. Someone asked him this recently, with the results here on YouTube. He says he’s still willing to take 50/50 bets on SUSY, but “with the right conditions”, which are 50 fb-1 of analyzed data/experiment (he says this will be “years from now I think”, roughly 2017 maybe if all goes well), and he adds “then we need a judge, because it won’t be so obvious I think”. So, it looks like it’s going to be quite a while before we get to see Gross pay up…
2017? No problem, I’ll still be here reading my favorite physics blog (assuming you’re still writing it).
A naive question. Is this bet about finding no other particles by 2017? Because if any particles are found, isn’t there some conceivable susy framework that could be said to predict it?
Gross’s bet is about SUSY, not just “there will be a new particle”. The reference to “then we need a judge” refers to the fact that if a new particle is found, it may be very unclear whether it is a superpartner, because of the problem you refer to of lots of SUSY possibilities.
A rather amateur question: What happened to the theory of large extra dimensions and Randall-Sundrum model?
At what point are these theories supposed to show up at the LHC?
Have they found them yet?
No extra signs of Randall-Sundrum gravity has been found, nor has any other signs of extra dimensions. See here: http://arxiv.org/abs/1112.2194 for a quite recent one, but just google with keywords such as ATLAS, CMS, randall sundrum, 5 fb^-1 and so on.
An interesting article from Matt Strassler here, about the ATLAS trigger, and how it relates to the search for new physics:
Not news to anyone here I’d say, but interesting to consider just how narrow the parameters of the search are at the LHC, and what unpredicted (and unprogrammed-for) events may go unobserved.
^^ Make that, CMS trigger 🙂
thank you very much indeed. I also found these two: http://arxiv.org/abs/arXiv:1110.6452 and http://arxiv.org/abs/arXiv:1202.3827
One wonders if their theories have proven to be wrong, what’s all the publicity about?
You ask a very pertinent question. The truth is that the absence of any sign of deviation from Standard Model (SM) predictions in pre-LHC precision tests of the SM (such as searches for new forms of transition among “flavors”, ie, types, of quarks or leptons, or subtle changes in the relationship between the very accurately measured Z and W boson masses), disfavoured in a big way large extra dimensions, and also to a lesser but still significant extent Randall-Sundrum theories. That’s part of the reason why the theory community had a preference for SUSY—not that this theory was any near perfect in this regard either! With 20/20 hidsight this lack of evidence in precision tests should have told us that all new beyond-the-Standard-Model physics was at a much higher (factor 10 to 100, maybe more) energy scale than the optimists hoped. Certainly it’s seeming that way if you dispassionately consider the apparent lack of any truly new physics in the LHC data. Christian is right that this applies equally to large extra dimensions, Randall-Sundrum, and SUSY theories (and even more, technicolor, little higgs, composite higgs, higgsless models, and the plethora of other ideas theorists have cooked up over the years!).
So when should we give up with these theories? Well with SUSY it’s getting pretty
clear that we are on the edge of what’s allowable, at least in versions of SUSY that
don’t have some new clever ingredient, or maybe two new clever ingredients…
With RS or LEDs it’s harder to judge where the acceptable boundary is because of a feature of these theories—unlike SUSY models they are “strongly-coupled” theories, which means in simple terms that the usual approximation techniques we use to do calculations fail. This failure is especially severe in the electroweak symmetry breaking, ie, Higgs, sector, and we really have a very poor idea of how high an energy one could push up RS or LEDs theories and still solve the hierarchy problem for the Higgs. (I spoke to one of the world experts on these theories a few weeks ago and he had no good estimate apart from an informed “guess” based on dimensional analysis!–an estimate which would already kill off RS and LED theories given the LHC bounds mentioned by Christian).
All this is part of the reason why the big majority of particle theorists are either very confused about what to work on, or very defensive of their favorite theory. It looks like Nature has chosen the “…something we haven’t been bright enough to think of…” option—that or semi-anthropic reasoning along the lines of Arkani-Hamed–Dimopoulos Split SUSY theories and their ilk (which personally I do
think are an option despite the hatred of the vast majority of the physics community for this approach).
Anyway, that was a long, not very numerically precise answer to your very good question.
It turns out that I like this video of D. Gross. He did solid pre-string theory work (obviously), and is an important contributor and advocate of string theory, but his reputation does not depend on SUSY nor strings. So….. he made a bet, which he may likely lose, OK. He is not prone to hype and recently I admire his stance against the landscape’s implications. Nevertheless, the outcome of the bet is keeping me on the edge of my seat!
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My $1K SUSY bet with Frank Wilczek gets called on July 8, 2015. Looks like that may be before the second run data gets analyzed, which isn’t really fair, but that was the date Frank chose. It was timed to be during a FQXi conference, with Max Tegmark as our judge. I’ve already won a SUSY bet, but it was against two string theory grad students who subsequently left academia. I wonder if SUSY will get less popular as the strongest proponents pay out these bets.
Let me ask you a question. Which of these two scenarios for the LHC do you prefer:
1. No new physics discovered at all for the entire lifetime of the LHC aside from a Standard Model Higgs.
2. New physics discovered, but the only new physics is SUSY.
What Phil is asking you, Peter, is: would you prefer to be a monkey, or a Bishop of the Church of England? My advice is to choose the monkey, as Huxley did.
I’d just like to know what the LHC can find out about the real world, would prefer that it find something that gives us a hint about how to do better than the SM. I don’t have any preferences that the world be one way or another. Of the two alternatives you mention, one seems much more plausible to me than the other.
Phil’s question ws not directed to me, but it’s such a good question, so I wish to volunteer an answer. I want to see as much as possible discovered at LHC, or anything at all in addition to the Higgs, whatever that may be.
SUSY, no-SUSY, weirdo things, whatever works and of course, the weirder the better. I only wish to know that the money that taxpayers put into the LHC has not gone down the drain because we could have used it for some other very urgent purposes (I hear that unemployment in Spain and Portugal has hit some ridiculously high levels).
In other words, since you prefer the LHC to “find something” that can take us beyond the SM, you would prefer senario 2 over scenario 1. A SM Higgs, and nothing else, would tell us nothing about how to do better than the SM because of the plethora of SUSY models you mentioned — both low and higher energy ones — as well as all the other models people have cooked up, all of which could be compatible with a SM Higgs at 125 GeV. So, out of those two possibilities, you’d surely want the SUSY one. Is this correct?
The reason I’m asking is because I’ve been getting these strong vibes from you that you not only think SUSY is not plausible and won’t be discovered, but you don’t WANT SUSY to be discovered at the LHC. For example, I’m sure you’d agree that quantum gravity effects at LHC energies is not very plausible, but you’d definitely WANT the LHC to discover them. However, in the case of SUSY, you neither expect nor WANT SUSY to be discovered at the LHC. In fact, you want every single model that’s been getting media attention to NOT be discovered at the LHC. If SUSY doesn’t get discovered, you’ll feel incredibly vindicated,you’ll gloat on your blog and say “I told you so!”, and all the SUSY proponents will look like fools. And that’s precisely what you want. Also, you’d love for quantum gravity effects to show up at the LHC, as long as those effects are NOT string theory effects, for the same reasons as why you don’t want SUSY to show up, even if it means light would be shed on how to go beyond the Standard Model. Is this correct?
So which one of those two assessments above for you are more accurate? I just want to understand you a bit better before I invest my time in reading your blog because there are many many physics blogs out there and I surely cannot read them all! 🙂 Cheers!
“I just want to understand you a bit better before I invest my time in reading your blog.”
I think this world has some people that really feel entitled.
If you’re honestly interested in my motivation here, it’s pretty simple: I want to understand fundamental physics better, so am very carefully paying attention to what is going on at the LHC and what it is telling us. The motivation for paying a lot of attention to the negative SUSY results is not that I personally want to gloat (this isn’t unexpected, most theorists were expecting this) , but that it seems to me this is one of the discoveries of the LHC, and there’s an active campaign in many quarters to deny this. You’ll note that I’m paying about zero attention to “gloating” about or discussing negative LHC results about extra dimensions, black holes, quantum gravity, strings. Virtually no one ever seriously thought the LHC would see such things, and it’s not at all surprising or interesting that the results of such searches are negative.
why does it matter what anyone WANTS ? it’s nature, it doesn’t care what you WANT.
what are the prospects of directly creating and observing dark matter at these energies and luminosities? not necessarily SUSY. Has there been any reports of dark matter, and if not, what are the ramifications of a null result for both SUSY and CDM cosmology?
The LHC experiments are certainly looking for new particles that would explain dark matter, SUSY or not, but haven’t found anything. The problem with dark matter is that you so far have really only observed it via its gravitational interactions, but have no idea what its other interactions with known particles are (although you know a lot about what they aren’t: can’t be strong, EM, etc…)
If you see evidence for a new particle at the LHC consistent with a dark matter candidate, that would be a fantastic breakthrough. Unfortunately, if you don’t see this, that doesn’t tell you that much, just gives more constraints on what possible interactions a dark matter particle might have.
Can someone kindly recommend something to read for the not-exactly-layman but knows nothing about astrophysics on the status of dark matter. Something straightforward.
There are way too many seemingly independent lines of evidence pointing to dark matter to have a simple explanation for a non-expert: galaxy rotation curves, velocity dispersions of galaxies in clusters, lensing behind the bullet cluster, the velocity anisotropy of stars in the solar neighbourhood, and the growth of structure in the universe.
For a non-expert, I’d recommend focusing on just one of these, the Galactic rotation curves to get started, and the Wikipedia page seems good:
You might also want to check out the bullet cluster paper:
This should be an easy question for some of you. I don’t know a lot about particle detection techniques, so I have to wonder… As I understand it the LHC takes a lot of data, and one has to employ sophisticated algorithms to wade through all this data to see if there is a signal corresponding to a particle with certain properties. OK, is it possible that we might not be aware of a new particle if we’re not looking for it? If we don’t program the right algorithm, could we miss the detection of some kinds of particles at the LHC? Or would any new particle always slap us in the face and there would be no way we could miss it? Thanks.
The answer completely depends on the properties of the conjectured particle, which will determine how often if it produced, in conjunction with what other particles, and what it decays into. Some sets of properties will make a particle easy to see, others extremely hard to impossible.
The LHC is colliding strongly interacting particles, and if your conjectured particle has strong interactions, it will get produced relatively copiously. Right now the LHC null results for SUSY are mainly for the superpartners of strongly interacting particles, since these must be strongly interacting. Particles with only weak interactions (such as conjectured dark matter particles) are produced relatively rarely, so much harder to see. Still, even if something is produced rarely, it may be observable if its production and decay involve some very unusual, distinctive signal. Of course,then the problem is that you need to be looking for that unusual distinctive signal. There’s a legitimate worry that the LHC is producing some new particle with properties that make it observable in principle, but no one has been looking for the right signal.
It’s beginning to look as though they have been looking in the wrong place… no sign of SUSY or Strings. And it sounds like anyone with a new theory will have to convince a lot of Ph.Ds before they will even look for those new signals. Or can the data be searched in restrospect for signals predicted by a new theory?
These experiments have not just been looking for SUSY or strings, but also much more generically for the kinds of signals you expect from production of an unknown particle, or from some other deviation from the Standard Model. If they’re missing something, it’s going to be something with quite unexpected properties.
The data from the experiment is stored and will be available to try out different analyses for many years to come. As time goes by and the obvious searches and searches for SUSY get done, I suspect any plausible suggestion for what else to look for in the data will start to be able to get a hearing. The real worry is the triggering: only a small fraction of the data is stored, that which satisfies some conditions that indicate it’s possibly interesting. The nightmare is some un-thought of new phenomenon which shows up only in events that the trigger is now dropping. But people do worry about how to avoid this nightmare, and the LHC is going to be around gathering data for many, many years, with many opportunities to try different triggers if someone comes up with a good reason.
@ David Nataf,
That’s great. Thank you.
I’m afraid I don’t have the time or interest to run a general discussion board about physics, so please don’t submit comments unrelated to the posting. Physics Stack Exchange is one of several examples of a better place for such discussions.
Just want to point out that Matt Strassler has recently written a long article about which events are recorded in LHC (what triggers an event as worth keeping) and why and how they are now storing some different data that will only be analyzed later during the upgrade shutdown as compute resources become available. See: