Status Update: Search for Low Mass Strings at CMS Andy Yen
Intro Superstrings can lead to the following non-SM process: gg→gγ Extra contribution to the SM gamma+jet. Ms ~ 1 TeV, 100 evt for 200pb-1 2
Data Samples Strings Signal: 10k events, Ms=1 TeV, ckin(3)>200 GeV, correct kinematics, incorrect matrix element weights. CMSSW 3.2.x Photon+Jet/QCD Dijet (CMSSW 2.2.x) Ckin(3)>170, 1M/1.5M [19400pb-1, 24pb-1] Chin(3)>300, 300k/1M [71548, 273] Ckin(3)>470, 100k/3M [221484, 9500] Ckin(3)>800, 100k/3M [ ,250000] Ckin(3)>1400, 100k/.5M
Photon Reconstruction Require dR within 0.15 of MC. 32x eff (string signal): [right] 22x eff (pt>470 GeV pho+jet): [left]
Jet Reconstruction Jets Objects used iterativeCone5CaloJet sisCone5PFJet iterativeCone algorithm Colinear unsafe Infrared unsafe sisCone algorithm “seedless infrared safe cone” Particle Flow Reconstruct ALL particles in event Uses all CMS subdetectors
Jet Response (continued) iterativeCone5CaloJets CMSSW 2.2.x vs Arbitrary normalization 6 Mean: 0.79 Sigma:.106 Mean: 0.77 Sigma:.123
Jet Energy Response CMSSW IterativeCone5CaloJets vs sisCone5PFJets Crystal Ball Fit with 2 polynomial tails 7 Mean: 0.77 Sigma:.123 Mean: 0.94 Sigma:.082
Collinear Safety? Even in the PF Jet, there is still a tail at low values. Approximately 10% of reconstructed Jets have 2 nd Jet within dR<1 [for sisCone PF jets]
Collinear correction Take the vector sum of the momentum of the two jets Use Pt-weighted average of eta and phi (account for phi discontinuity). Improvements in eta/phi and energy response!
Response Improvements Mean: 0.95 Sigma:.0596
Jet Reco Efficiency
Event Selection Describe the selection here + cut efficiencies for signal and backgrounds