Monday, 26 August 2013

SUSY 2013 Live Blog: Day 1 Session 3

We progress to the first parallel session of the conference.  I've decided to attend the SUSY phenomenology talks, which in this case appears to actually be SUSY experimental results.  So, four talks saying variations of "we find no signal".  Curiously, we have three CMS talks to only one ATLAS talk.

2:30pm: Marc Hohlfeld, "Inclusive Searches for Squarks and Gluinos with the ATLAS detector"

Searches all based on the full 2012 data set.  Production is inclusive pair production, one of the oldest workhorses at the LHC.  Searches classified by number of leptons and jets in the usual way.  Results presented using simplified models.

Irreducible backgrounds controlled using MC distributions normalised using control regions.  Reducible backgrounds handled in a fully data-driven way.  Analysis tested using validation regions; another type of control region that is closer in nature to the signal region.

Zero-lepton channel has usual problem of large backgrounds.  Ten signal regions plus four control regions per signal region, to handle different background sources.

Limits for 2 to 6 jets go to 1.25 (1.4) TeV for gluino (squark) for massless LSP, other sparticles decoupled.  With more jets, limits weaken but still around 1 TeV.

One lepton search uses soft lepton selection criteria to have sensitivity to compressed spectra.  Gluinos excluded up to 700GeV provided mass difference with LSP is greater than 25GeV.

Two lepton channel (NEW): Uses Razor variables based on defining two mega-jet objects.

Combined searches in CMSSM exclude gluinos above 1.3 TeV for all squark masses.

Question: what of Dirac gluinos?  (I plan to have a post on this soon, probably after SUSY).  Done on 2011 data, but not yet.

2:50pm: Joshua Thompson, "Search for SUSY in hadronic final states at CMS"

First note: 1.4TeV gluinos, only one in 2011 data but 17 produced in 2012.  Best gain in SUSY with mass increase.

Signals considered here not just jets plus MET, but also bottom/top jets plus MET.  Latter obviously inspired by natural SUSY.

Backgrounds based as much as possible on data.  Limited at large MET, HT and jet multiplicity as we have few events in those regions.  Corrections often end up being done with Monte Carlos, leading to additional checks against data to confirm that.

Interpretations use simplified models.  Light LSP excludes 1.1 TeV gluinos, while in the degenerate case we drop down to a few hundred.  Squarks limited up to 800 GeV in similar massless LSP case.

Sbottom searches use alphaT, better than MET at removing QCD background.  Missed the limits.

Search using Razor variables (NEW): uses b-tagged samples.  Two razor variables, so 2D plots to separate signals and backgrounds.  Excludes gluinos to 1.4TeV or so, for massless LSP.

3:10pm: Marco Andrea Buchmann, "Search for SUSY in the di-lepton final state at CMS"

Despite the title, this talk is on single lepton and same-sign dilepton channels.

SSDL probes Majorana nature of gauginos and is old standby for cutting backgrounds.  B-tags useful with natural spectra in mind.  Main background is fake leptons, controlled using data-driven methods.  Rare SM processes controlled with Monte Carlos.  New background is charge misidentification; small, controlled with eµ data sample.

Note that SSDL can set limits on many models including RPV SUSY (separate talk).  Gluinos decaying to tops (2- and 3-body) excluded at about 1TeV for LSPs up to 600 GeV.

Single lepton search requires at least three jets; again I think we're focused on final states with tops.  Backgrounds controlled by looking at either lepton spectrum or angle with W.  Again, we have gluinos excluded at around 1.3TeV.

3:30pm: Andrea Gozzelino, "Search for SUSY in multilepton final states at CMS"

We finish this session with a talk on SUSY in three or more lepton final states.  Really, it's all the same as before in sufficient generality.  New interpretation, though; GMSB with light gravitinos.

I think my travel might be catching up with me.  My focus is certainly gone.

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