LHC: chance to find SUSY quickly

This linker-not-thinker blog post will largely show materials of ATLAS. To be balanced, let me begin with a recommendation for an UCSB article Once More Unto the Breach about the CMS' excitement before the 13 TeV run. Note that the CMS (former?) boss Incandela is from UCSB. They consider the top squark to be their main target.

ATLAS is more into gluinos and sbottoms, it may seem. On March 25th, ATLAS released interesting graphs

Expected sensitivity studies for gluino and squark searches using the early LHC 13 TeV Run-2 dataset with the ATLAS experiment (see also PDF paper)

There are various graphs but let's repost six graphs using the same template.




These six graphs show the expected confidence level \(p_0\) (the probability of a false positive; see the left vertical axis) or \(X\)-sigma (see the dashed red lines with explanations on the right vertical line) that a new superpartner will have been discovered after 1, 2, 5, and 10 inverse femtobarns of collisions.




First, the bottom squark production. The sbottom decays to the neutralino and the bottom quark. If the uncertainty of the Standard Model backgrounds is at 40 percent, the graph looks like this:



You see that if the sbottom is at least 700 GeV heavy, even 10/fb will only get you to 3 sigma. Things improve if the uncertainty in the Standard Model backgrounds is only 20%. Then you get to 4.5 sigma



Now, the production of gluino pairs. Each gluino decays to a neutralino and two quarks. With the background uncertainty 40%, we get this:



With the background uncertainty 20%, things improve:



You see that even a 1350 GeV gluino may be discovered at 5 sigma after 10 inverse femtobarns. I do think that I should win a bet against Adam Falkowski after 10/fb of new data because only 20/fb of the old data has been used in the searches and the "total deadline" of the bet is 30/fb.

Things look similar if there is an extra W-boson among the decay products of each gluino. With the 50% uncertainty of the Standard Model backgrounds, the chances are captured by this graph:



If the uncertainty of the Standard Model backgrounds is reduced to 25%, the discovery could be faster:



If you're happy with 3-sigma hints, they may appear after 10/fb even if the gluino is slightly above 1500 GeV.

The probability is small but nonzero that the gluino or especially the sbottom may be discovered even with 5/fb (if not 2/fb and perhaps 1/fb) of the data.

After 300/fb of collisions, one may see a wider and safer region of the parameter space, see e.g. this CMS study.