talk051905

SUSY Analysis at Chicago: 

SUSY Analysis at Chicago Martina Hurwitz University of Chicago MWPG meeting 5/19/05

DC1: 

DC1 SUSY should be easy to find in events with high jet multiplicities, large missing ET Defining Meff = ETmiss + pT(4 hardest jets), simple cuts give clear signal above SM background SM backgrounds negligible Top W+jets Z+jets QCD jets

Goals: 

Goals Investigate standard model backgrounds more carefully using Rome production data samples Investigate SUSY focus point SU1 = coannihilation region, which contains interesting physics Work in progress: still a lot to do!

Software: 

Software Work with AODs available on Tier2 prototype at Chicago; quite a bit of effort goes into transferring relevant files AOD analysis done in framework of SUSYPhys package, which does some general particle selection independent of input data sample Write out ntuple for easy analysis and apply some more selections to make histograms in root “Ntuple dumper” has proven useful, cut down significantly on time required when making small changes in cuts, etc.

Background data samples: 

Background data samples Top: T1 MC@NLO One of tops decays to Blνl Weighted sample: ~13% of events have weight = -1 QCD jets: J1-J8 Dijets Different samples correspond to different PT ranges for the jets; J1 has lowest PT, J8 highest Haven’t investigated multi-jet backgrounds yet Z->invisible Don’t have this sample, so estimate using Z->e+e- and Z->μ+μ- Z->ττ Haven’t investigated yet W->l+invisible Haven’t investigated yet

General Particle cuts: 

General Particle cuts Electrons/Muons |η| < 2.5 Pt > 15 GeV Jets: “ConeTowerParticleJets” = cone with δR < 0.7 |η| < 5 Pt > 15 GeV If Jet “matches” electron, it is removed from jet collection Eliminate events classified as both electrons and jets Matches if δR<0.2 and ET(elec)/ET(jet)>0.95

Inclusive SUSY cuts: first try: 

Inclusive SUSY cuts: first try At least 4 jets 2 jets with PT > 50 GeV, 2 additional jets with PT > 100 GeV ETmiss > 100 GeV ETmiss > 0.2*Meff For counting purposes: Meff > 1000 GeV

Results: 

Results

Meff: 

Meff SUSY Dijet, all pT bins

Dijet missing energy: 

Dijet missing energy (for 560 < pT < 1120 dijet sample)

Possible way to cut out dijet background: 

Possible way to cut out dijet background “Transverse sphericity” = circularity of event in transverse plane Dijets tend to have lower “sphericity” than SUSY or top events Highly correlated with other SUSY cuts

Lepton cuts: 

Lepton cuts In TDR, Meff plot cuts events with a muon or isolated electron with pT > 20 GeV in |η| < 2.5 Expect to see high lepton multiplicity in SUSY events – will reduce signal significantly Meant to reduce backgrounds when SUSY mass close to top mass Reduces sensitivity for higher SUSY masses

Effect on signal: 

Effect on signal

Conclusions: 

Conclusions Have started using Rome AODs for analysis of SUSY backgrounds Goal is to get better estimate of SM background Have started investigating effects of cuts given in TDR on backgrounds Not enough statistics! Can include some more Rome samples, but probably won’t have enough with full simulation

DC1 (II): 

DC1 (II) After discovery, want to calculated some parameters of model Simplest decay: Location of edge in dilepton invariant mass distribution related to masses of neutralinos Need good understanding of electron and muon reconstruction Ambreesh has started this work

Muon Reconstruction: 

Muon Reconstruction

Electron Reconstruction: 

Electron Reconstruction