tag:blogger.com,1999:blog-2846514233477399562.post3852557455245822980..comments2024-01-08T09:37:04.406+01:00Comments on RÉSONAANCES: A new boson at 750 GeV? Jesterhttp://www.blogger.com/profile/08947218566941608850noreply@blogger.comBlogger80125tag:blogger.com,1999:blog-2846514233477399562.post-948838669273311582016-04-29T15:37:46.126+01:002016-04-29T15:37:46.126+01:00Could a dark matter particle be the unseen decay a...Could a dark matter particle be the unseen decay as dark matter cannot or does not react with light except at that energyAnonymoushttps://www.blogger.com/profile/17745207599591274391noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-70417044558681089752016-01-04T15:49:42.350+01:002016-01-04T15:49:42.350+01:00It is too early to exclude it, but there is no par...It is too early to exclude it, but there is no particular reason to expect anything for 2 TeV dibosons. The case was never strong given the limited decay channels where it has been seen and the limited significance, and the negative results in 2015 didn't make it stronger.mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-85200690291204746582015-12-30T15:04:16.223+01:002015-12-30T15:04:16.223+01:00Isn't it too early to completely exclude a 2Te...Isn't it too early to completely exclude a 2TeV resonance. Wouldn't we have to wait longer since Atlas does see a week bump and the 13TeV run hasn't even managed to replicate Higgs Able Lawrencehttps://www.blogger.com/profile/13473481547342860067noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-57995443693025157492015-12-25T23:55:25.238+01:002015-12-25T23:55:25.238+01:00@Somdatta Bhattacharya: If you have a model that p...@Somdatta Bhattacharya: If you have a model that predicts a dijet branching ratio of (let's say) 100, you can take the observed diphoton excess and scale it to dijets. And then you'll see that the expected signal strength is a factor of 10 (rough estimate) below the expected exclusion limit for dijet peaks at 750 GeV, and a factor of 5 below the statistical uncertainty of the signal. Even if the signal is there, you cannot see it.<br /><br />Looking at dijets is still interesting, but to have a chance to see a signal there you would need some model that predicts a ~1000 times larger branching fraction to dijets compared to diphotons.mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-79740506907533093732015-12-23T17:25:08.540+01:002015-12-23T17:25:08.540+01:00Hello Jester,
What is your estimate at the moment...Hello Jester,<br /><br />What is your estimate at the moment for this anomaly being new physics ?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-56006489779995494352015-12-23T07:27:11.997+01:002015-12-23T07:27:11.997+01:00"To compare results to the diphoton excess, y..."To compare results to the diphoton excess, you would need specific models that predict relative branching ratios. But even the back-of-the-envelope estimate shows that you are not sensitive to any models that predict a factor lower than a few hundred."<br /><br />OK good, I get your point, but in your back-of-the-envelope estimate you just seem to be basing your analysis on a single standard deviation from the background. That seems to be independent of any model-dependent analysis that might predict a factor lower than a few hundred. So what exactly is the meaning of what you are actually estimating? Somdatta Bhattacharyahttps://www.blogger.com/profile/13293513040406508544noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-1894108207322953262015-12-22T22:20:16.052+01:002015-12-22T22:20:16.052+01:00"The limits being worse necessarily means tha..."The limits being worse necessarily means that more events, bounded from above by (0.6 or 1.6 pb), are seen than those predicted (0.2 pb) (modulo the fact that the former is at 1 TeV and the latter at 750 GeV)."<br />No, it just means the detectors are not perfect. The 0.2 pb standard deviation (or ~0.4 pb limit) would be possible with perfect detectors (apart from calorimeter resolution, which was also assumed to be quite good) and perfect background models.<br /><br />To compare results to the diphoton excess, you would need specific models that predict relative branching ratios. But even the back-of-the-envelope estimate shows that you are not sensitive to any models that predict a factor lower than a few hundred.mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-19813975708153223492015-12-22T18:18:53.711+01:002015-12-22T18:18:53.711+01:00However, here's something I'm still puzzle...However, here's something I'm still puzzled by.<br /><br />mfb has said...<br /><br />"...Even with a perfect (permille-level) background modeling, 1 standard deviation is ~600 events (~0.2 pb). ...<br /><br />...The actual limits are significantly worse, see this CMS paper for example: http://arxiv.org/pdf/1302.4794v2.pdf<br />Even at 1000 GeV, where the background is lower by a factor of 3, the upper limit is 0.6 to 1.6 pb depending on the production process."<br /><br />The limits being worse necessarily means that more events, bounded from above by (0.6 or 1.6 pb), are seen than those predicted (0.2 pb) (modulo the fact that the former is at 1 TeV and the latter at 750 GeV). <br /><br />Now in the paper, various resonances are ruled out for various mass-ranges. The understanding being that the predicted cross-sections of the processes considered for those resonances are greater than the experimental upper bounds in the corresponding mass ranges. <br /><br />So are the cross-sections of those processes involving the putative scalar at hand lower? Who has calculated this? Also isn't it this that one really needs to figure out in order to see whether the bound is violated?Somdatta Bhattacharyahttps://www.blogger.com/profile/13293513040406508544noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-51885005372423708022015-12-22T18:00:40.857+01:002015-12-22T18:00:40.857+01:00I recall seeing some papers considering photon fus...I recall seeing some papers considering photon fusion production of the hypothetical scalar. I forget what the conclusions for such models were, though. I imagine one needs quite large couplings...Alex Knoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-72990953775599345802015-12-22T13:07:40.984+01:002015-12-22T13:07:40.984+01:00OK I finally got the point about the bounds being ...OK I finally got the point about the bounds being weaker. Thanks mfb and jester. Somdatta Bhattacharyahttps://www.blogger.com/profile/13293513040406508544noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-42015993399770230052015-12-22T06:53:01.458+01:002015-12-22T06:53:01.458+01:00Jester said...
...However, experimental bounds on ...Jester said...<br />...However, experimental bounds on dijets in this mass range are much weaker, so there's no problem.<br /><br />Shouldn't there be some explanation for that, why can they be weaker? If the scalars are produced copiously enough, it means the gluons couple substantially to them, which in turn means that the dijet channel ought to contribute strongly in the decay channels. What am I missing? Somdatta Bhattacharyahttps://www.blogger.com/profile/13293513040406508544noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-7649456007951919292015-12-21T22:38:22.612+01:002015-12-21T22:38:22.612+01:00For dijets, the (background) cross section is some...For dijets, the (background) cross section is something like 3 pb/GeV at 750 GeV (within the acceptance of ATLAS/CMS). With ~5% resolution (optimistic), we have ~40 GeV width, so ~120 pb background. Assuming everything else is perfect, ATLAS would have seen ~400 million background events, CMS ~300 million. Even with a perfect (permille-level) background modeling, 1 standard deviation is ~600 events (~0.2 pb). That is 50 times the excess seen with diphotons (~10 events). Give or take a factor of 2.<br /><br />The actual limits are significantly worse, see this CMS paper for example: http://arxiv.org/pdf/1302.4794v2.pdf<br />Even at 1000 GeV, where the background is lower by a factor of 3, the upper limit is 0.6 to 1.6 pb depending on the production process.mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-2217945879299524502015-12-21T11:48:26.810+01:002015-12-21T11:48:26.810+01:00You can always put the hypercharge on hyperdrive :...You can always put the hypercharge on hyperdrive :)Alex Knoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-85220344183417022592015-12-21T09:41:09.218+01:002015-12-21T09:41:09.218+01:00They typically do. However, experimental bounds on...They typically do. However, experimental bounds on dijets in this mass range are much weaker, so there's no problem. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-51089078732650007142015-12-21T07:46:59.665+01:002015-12-21T07:46:59.665+01:00In the case of scalars coupling to both gluons and...In the case of scalars coupling to both gluons and photons why don't dijets dominate over photons in the decay channels?Somdatta Bhattacharyahttps://www.blogger.com/profile/13293513040406508544noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-61532615404202721712015-12-20T21:51:25.157+01:002015-12-20T21:51:25.157+01:00I would like to know the story about v being 246 G...I would like to know the story about v being 246 GeV, except a small area around Pisa. I think I will learn something amusing...Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-445201335124727632015-12-20T09:36:29.791+01:002015-12-20T09:36:29.791+01:00I don't think I understand what you mean. I do...I don't think I understand what you mean. I don't think we have reasons to think that there will be more structures that are very SM like at higher scales - beyond the generic idea that there might be more gauge groups that are broken at different scales, which is quite possible. But there is afaik no reason to think that this repeats in some kind of repetitive pattern. The only physics that I know of which gives you something similar is extra space dimensions. In that case you can have Kaluza Klein resonances which look like repeating broken copies of the SM gauge groups. The more likely scenario would be that there is one or few additional strong interactions providing the higgs, the 750 GeV resonance and then no further fundamental scalars until we're near some higher new physics scale wirh susy or quantum gravity of some sort. But he latter part of that is just daydreaming.Alex Knoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-45931190915191114432015-12-19T16:45:52.659+01:002015-12-19T16:45:52.659+01:00Like, a hierarchy of interlocked SM-like structure...Like, a hierarchy of interlocked SM-like structures in generations each one defining the landscape for the next one, all the way to Planck? Ok, that'd be really, really early to speculateRBShttps://www.blogger.com/profile/05190152376766693948noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-26476369074757208852015-12-19T10:45:39.021+01:002015-12-19T10:45:39.021+01:00v is always 246 GeV, except in a small area aroun...v is always 246 GeV, except in a small area around Pisa :) But don't read too much into this figure, it was just a quick and dirty sketch. A more careful version is e.g. in Fig.5 of 1512.05777Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-10811284472118054372015-12-19T07:58:08.667+01:002015-12-19T07:58:08.667+01:00hi jester -- just a question to clarify the sectio...hi jester -- just a question to clarify the section on "The Model" -- what is "v" -- 170 or 246 GeV (that is weak scale) or 750 GeV (new physics scale)?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-72917644908637516852015-12-19T05:33:18.636+01:002015-12-19T05:33:18.636+01:00Thanks Jester for the links to the 8 TeV Zgamma an...Thanks Jester for the links to the 8 TeV Zgamma and ZZ papers.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-30537136780346751602015-12-19T02:14:10.153+01:002015-12-19T02:14:10.153+01:00Too early to say, but if the 750 GeV particle is r...Too early to say, but if the 750 GeV particle is real then it is very likely to be a part of a larger structure. In any model constructed so far, you need additional particles to explain the signal, for example heavy vector-like quarks. My bet would be on new strong interactions at a few TeV scale, but many other possibilities exist. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-21142085262778958652015-12-18T22:27:49.982+01:002015-12-18T22:27:49.982+01:00Jester, for some time after Higgs celebrations HEP...Jester, for some time after Higgs celebrations HEP community was dreading "desert till Planck scale". If confirmed, would these developments dispel those fears perhaps pointing to some greater structures, hierarchies of symmetries or end up as some technical appendice to SM? What would be a more likely scenario at this point, in your view?RBShttps://www.blogger.com/profile/05190152376766693948noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-68361560156854656512015-12-18T16:13:09.379+01:002015-12-18T16:13:09.379+01:00That's right. If there's a matching excess...That's right. If there's a matching excess in Z-gamma, WW, dijet, or monojets, then the case for the 750 GeV particle will grow stronger. This is in fact what happened with the Higgs boson. The initial hints in December 2011 were strengthened by additional analyses in winter 2012, such that by the time of the official discovery in July 2012 there was little doubt we were seeing a real signal. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-44385526982310860202015-12-18T14:50:29.218+01:002015-12-18T14:50:29.218+01:00Hmmm.
Do you guys think there's a chance that...Hmmm.<br /><br />Do you guys think there's a chance that we don't have to wait till Summer for new insights, maybe to see something in existing 13 TeV Z gamma data by optimizing this analysis? Maybe for a larger width? <br />How well do we expect CMS to do with the Z gamma final state...Alex Knoreply@blogger.com