1. Status Update: Search for Low Mass Strings at CMS Andy Yen

2. 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

3. 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 [5000000,250000]  Ckin(3)>1400, 100k/.5M

4. Photon Reconstruction  Require dR within 0.15 of MC.  32x eff (string signal): 95.465 [right]  22x eff (pt>470 GeV pho+jet): 96.406 [left]

5. 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

6. Jet Response (continued)  iterativeCone5CaloJets  CMSSW 2.2.x vs 3.2.1  Arbitrary normalization 6 Mean: 0.79 Sigma:.106 Mean: 0.77 Sigma:.123

7. Jet Energy Response  CMSSW 3.2.1  IterativeCone5CaloJets vs sisCone5PFJets  Crystal Ball Fit with 2 polynomial tails 7 Mean: 0.77 Sigma:.123 Mean: 0.94 Sigma:.082

8. 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]

9. 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!

10. Response Improvements Mean: 0.95 Sigma:.0596

11. Jet Reco Efficiency

12. Event Selection  Describe the selection here + cut efficiencies for signal and backgrounds