Thursday, August 04, 2016 ... Deutsch/Español/Related posts from blogosphere

CMS abruptly confirms SM in 22+16+1+15 new papers

But you may raise your eyebrows with me 4+3+0+1 times

First talks have been given at ICHEP 2016 in Chicago, the main annual particle physics conference, and one of the experimental collaborations at the LHC is using this opportunity to impress lots of physicists with their new results.

Very quickly, the CMS Collaboration has released 22 new papers. (A message from the future: A few hours later, 16 were added; I analyzed those later and added some new discrepancies. The same applies to 15=14+1 additional papers a few more hours later.) I actually had to go to the 2nd and 3rd page (with 10 papers per page) – which don't display the date as clearly as the first page – to get all the new papers. That's unusual.

The third term, 1, in the number 22+16+1+15 in the title, is the new CMS diphoton paper killing the \(750\GeV\) cernette. Nothing is there at all. Totally inconclusive excesses emerged at \(620\GeV\), \(900\GeV\), and \(1300\GeV\) where a slight excess was seen by CMS in 2015, too, but nothing was there in ATLAS. (LOL, they later removed the new paper except for pages 1,2 but too bad, I already saw it, and you can see the key graph, too.)

I really recommend to send your almost finished pheno papers on the \(750\GeV\) bump to (a blue submit button is at the top) so that those amateur scientists have some competition and motivation.
I won't pretend that I have read every letter in these 22 papers. My belief is that the number of people in the world outside ATLAS, CMS who actually read all these papers is smaller than 10 and even within the LHC collaborations, the numbers could be very low. But I can offer you the following minimum of the analysis:
  • I see at least 80% of the area of every page of every new ATLAS/CMS paper for at least 0.2 seconds
  • I spend at least 3 seconds by looking at every Brazilian chart in every paper
  • Every paper is searched for the words "excess", "deviation[s]", and "*agree*" and I am looking for anomalous sentences with these words (to increase our combined sensitivity, you shouldn't use exactly the same algorithm)
  • Reading whole paragraphs or pages is optional
OK, in this way, I have quickly "read" these new twenty-two papers by CMS.

What have I seen? Well, the first striking feature of this new bunch of papers is that we may finally read some of the papers that are based on the 2016 \(\sqrt{s}=13\TeV\) data – which were taken at most two months ago or so. The energy is the same as in 2015 so they probably know how to analyze the data and write papers quickly.

The relevant portion of the data taken by CMS in 2016 is usually given by 12.9 inverse femtobarns of data. Note that this whole 12.9 was taken in the first half of 2016. They never combine the 2015 and 2016 data. They could combine them and increase 12.9 by something like 2.7 that is used in many CMS papers based on the 2015 data.

Similarly, ATLAS began to show its results based on 13.3/fb of the 2016 data and e.g. according to this talk, it has seen no gluinos and squarks up to \(1.9\TeV\) – these bold exclusions only hold under many assumptions, however. If you want similar slides from dozens of fresh Chicago talks, perhaps before the participants see it, open this Beyond the Standard Model page and in the cyan boxes, click at the "document" icon in the upper right corners to get the files. (A similar Higgs physics URL and a joint Higgs/BSM one if you need.)

If the 2015 and 2016 data were combined and all the 20/fb of 2016 data were taken, the CMS could possibly publish papers with something like 22/fb of 2015+2016 data as of now. By the end of the year, the total luminosity should almost certainly exceed 50/fb and the 2015 contribution should become negligible.

All the 22 new CMS paper verbally confirm that everything they see is compatible with the Standard Model. Many of the graphs they observe are already very fine and you may see that the agreement is both strikingly good and nontrivial.

The opening ceremony of the 2016 Olympics in Rio is tomorrow. Lots of top athletes will be absent (not only due to the Zika-carrying mosquitoes from the logo), the games may turn out to be a 2nd class event.

This agreement between the theory and the experiment is really impressive and stunning – especially if you compare it with the opinion of a majority of the people in the world who believe that physics can't possibly understand how Nature works – but we are used to this agreement and bored by it (even by the rediscovery of the Higgs whose mass seems to be \(124.5\pm 0.5\GeV\) now). Some people even experience nightmares because of it – I don't.

You surely expect me to inform you about the results that have raised my eyebrows. Here are the coordinates:
  1. Higgses \(H\to b\bar b \tau^+\tau^-\) using 12.9/fb, Page 12, Figure 3, some 2.5-sigma local excess for \(m_H\sim 700\GeV\). Some 2-sigma excess near \(m_H\sim 300\GeV\) is probably worth overlooking
  2. SUSY in same-sign dileptons, 12.9/fb, Page 14, Figure 6a, some 2.3-sigma local excess for \(H_T\sim 1100\GeV\)
  3. Resonances in \(Z\gamma\to\ell^+\ell^-\gamma\), 12.9/fb, Page 6, Figure 3b, some 2-sigma local excess for \(M\sim 375\GeV\). This excess is minor but CMS still seems to confirm the excess at \(375\GeV\) from \(2\times 2\) ATLAS, CMS papers I discussed in March. Note that this new graph is constructed purely from new, 2016 data – the 2015 data behind my March blog post aren't included now so this may be said to be a truly independent confirmation of an older hypothesis (although the weakening of the signal is surprising given the increased luminosity)
  4. Excited quarks \(q^*\to \gamma+{\rm jet}\), using 2.7/fb from 2015, Page 5, Figure 2, locally a 4-sigma narrow excess for \(M_{\gamma,\rm jet}=2\TeV\), see also Figure 5 how it translates to a Brazilian band
  5. From later 16: A dijet resonance, 12.9/fb, Page 7, Figure 4, 2.6 sigma for \(M\sim 850\GeV\)
  6. From later 16: Sbottom search in Higgs-to-diphotons using a razor, 2.3+12.9=15.2/fb (from the year 2015+2016=4031 testing if you sleep), Page 17, Figure 15, sbottom limits some 2-sigma or \(100\GeV\) lower than expected; see Smaria's tweet
  7. From later 16: Multilepton EWK SUSY, 12.9/fb, Page 12, Results, local excesses 1.7 and 2.5 sigma
  8. From the package of 15: Sbottom search in jets-met, 12.9/fb, Page 22, Figure 9, locally 3.1-sigma excess, bounds on sbottom mass by \(150\GeV\) lower than expected, I discuss it below
It's up to you whether any of these anomalies will excite you or arouse you.

The by far largest excess among these four anomalies is the fourth one, the \(2\TeV\) excited quarks from the 2015 data. On Page 7, we're told that for the best choice of the parameter \(f=0.1\), the significance of the bump is 3.7 sigma locally and 2.84 sigma globally. We should look for ATLAS' paper on that (is it already out? Update: ATLAS saw nothing near \(2.0\TeV\) in the photon-jet channel in 2015) and for the CMS, ATLAS papers using the 2016 data to see whether it may be confirmed.

Excesses close to 4 sigma haven't been common but we've encountered several of these. We're still waiting for solid 5-sigma or stronger discoveries of new physics.

I am perhaps even more intrigued by the apparent (#3) resonance in \(M_{Z\gamma\to \mu^+\mu^-\gamma}\sim 375\GeV\) (yes, it seems stronger in the muon channel now) that has basically appeared in the fifth paper. Will ATLAS see an excess over there as well, perhaps a greater one? Update, Saturday morning: Nothing, the ATLAS excess over there has weakened into 1 of 10 very small upticks, so the \(375\GeV\) story is probably dead at this point. ATLAS' new \(Z\gamma\) paper.

Bonus: slides

You may see a CMS 2016 3.1 sigma locally excess in an off-Z, sbottom search – look at pages 7, 8 in this presentation or this lady's tweet. The sbottom limits are correspondingly by \(150\GeV\) lower than expected. It's independent from the (sbottom) anomaly #6 in the list above and I later added it as the entry (paper) #8 in my list.

Slight sbottom excesses are also seen in jets+MET but too small to make it to my list above. See also MT2, Page 11, Figure 7c for a slight excess in "one light squark" and three stop 1.9-sigma fully hadronic excesses.

More interestingly, ATLAS later revealed a 3.3-sigma excess in stops (page 9/36). See also the paper released on August 8th, on Monday.

Matt Buckley believes that some SUSY-like excess is seen in multijets. It must be a talk I haven't seen (?). Or maybe he's intrigued by Page 19/21 of this talk where the gluino limits are some \(100\GeV\) below the expected ones? But it's probably not too many sigmas, is it? The paper is this one, Figures 9,10, just 1 sigma over there.

Dear TRF readers may also ask a question to 3 ICHEP participants at Reddit.

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