Wednesday, March 16, 2016 ... Deutsch/Español/Related posts from blogosphere

A small but interesting ATLAS gluino/stop excess

The LHC is continuing its powering tests and the schedule says that on Tuesday, March 29th, after the Easter, the beam should be resuscitated just like Jesus Christ and it should return to the ring.

Meanwhile, ATLAS and CMS are releasing additional papers. Most of them show good agreement with the Standard Model or less than 2-sigma excesses. But...

But the ATLAS paper

Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in \(\sqrt{s} = 13\TeV\) \(pp\) collisions of ATLAS data
released a few hours ago is interesting although the excess in the signal region 1 (SR1) is just 2.3 sigma. But look what it does to the exclusion graphs on Figure 8.

(Note that the final state contains jets, MET, and one lepton. The arguably clearest previous ATLAS' SUSY excess, the on-Z 3-sigma excess, has jets, MET, and a lepton pair so it's a different channel.)

Look at Figure 8 on page 20 – which I reproduced below (click the image to magnify it). The expected excluded regions are bounded by the black contour; the observed exclusion contour is the red one. The thinner lines around the main thick red/black lines are the 1-sigma intervals.

The first plane is the gluino-stop mass plane. The second one is the stop-neutralino mass plane.

The first graph shows a rather clear excess preventing the experimenters from excluding the region with the gluino mass between \(1.0\) and \(1.3\TeV\) and the stop around \(750\GeV\). You may see a somewhat similar excess in the upper left portion of the graph on Figure 12 of this CMS paper.

The second plane shows something even more dramatic: the excluded region decays into two. It was expected that the half-disk-shaped region of the neutralino mass up to \(200-250\GeV\) and the stop mass up to \(750\GeV\) would be excluded. Instead, ATLAS – using 3.2 femtobarns of the 2015 data – only excluded two much smaller regions for small stop masses; and stop masses around \(760\GeV\).

Pretty much the entire region of the stop mass between \(620\GeV\) and \(740\GeV\) remained alive!

A similar preference for stops in this mass range could be indicated by a CMS paper based on the 2012 data using the MT2 variable which I mentioned here. Look at that CMS pMSSM paper, e.g. on Figure 5a for the stop mass. The dark blue curve shows a rather clear excess for the stop mass between \(600\) and \(900\GeV\).

The excess 2.3 sigma in SR1 came from 3.2 inverse femtobarns of the 2015 ATLAS data. One would like if this excess is due to the actual superpartners. In that case, ATLAS should better double the significance to get close to 5 sigma. To do so, it will need about 4 times as much data, or 13 inverse femtobarns or so of the \(13\TeV\) data. It's a realistic goal for 2016, assuming that Nature doesn't consider 13 to be an unlucky number.

If Nature is generous enough, the gluinos below \(1.5\TeV\) (Gordon Kane's currently preferred value) and stops below \(750\GeV\) could be discovered by the LHC in 2016. My $100/$10,000 bet against Adam Falkowski could become a very tense thing because the "deadline" is specified as 30 inverse femtobarns. (Yes, my $100 is ready for him.) Falkowski could claim that the 20/fb evaluated in 2012 counts as well, so if he were this kind of a jerk, I only have 10/fb left for the \(13\TeV\) data. 13/fb could be too late for me to win. ;-)

Needless to say, the discovery of SUSY would be way more important than a $10,000 bet. If I were asked to quantify the value of the discovery of SUSY, I could say "priceless". But because I am a realist who likes clear and non-dogmatic answers, I would say something like $200 billion.

Event Horizon Telescope

PBS wrote an article mainly about the Event Horizon Telescope. Using Kate Becker's cute analogy, numerous millimeter-wavelength radio telescope from the whole world team up to become an all-star team for a week or two in a year. In a way, this team may look like an Earth-sized telescope, with the corresponding huge increase of the resolution. The goal is to see an ordinary image of the black hole – the absence of light (radio waves) inside the approximate disk where the black hole is located, and this surrounded by light.

The experiment is getting started – and should focus the telescopes on the 4-million-Suns black hole at the galactic center. Can we directly see that there is a hole producing no light in that direction? BTW is it really what our current models predict? Isn't the black hole surrounded by some sources of radiation (ordinary matter) from all sides?

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