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Photon + Jet Events from MC-OnlSel

Photon + Jet Events from MC-OnlSel. Michael Anderson University of Wisconsin - Madison. Photon + Jet Events. A reducible background to H-> gg Can be used to calibrate jet energies Today, compare Level-1 Trigger EM Cand. Gen & Reco Photons Jets. Photon + Jet Events.

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Photon + Jet Events from MC-OnlSel

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  1. Photon + Jet Eventsfrom MC-OnlSel Michael Anderson University of Wisconsin - Madison

  2. Photon + Jet Events • A reducible background to H->gg • Can be used to calibrate jet energies • Today, compare • Level-1 Trigger EM Cand. • Gen & Reco Photons • Jets

  3. Photon + Jet Events • Gen+Sim made with 1_2_0 for MC-Online selection • Digi+L1T+Reco done with 1_3_1_HLT6 at Wisconsin CMS Tier-2 Center • Used only events which • Passed Level-1 Trigger • The gen photon had |h| < 2.4 • Min pt in hard scattering > 20 GeV

  4. Level 1 Trigger EM Cand. • Isolated Level-1 Electromagnetic Candidates • (6 bits to represent Et so can max represent Et=63) Gen Photon Et L1 EM Cand Et Gev

  5. Level 1 Trigger EM Cand. • Higher  bins are wider • Distributions are not adjusted for bin size h f

  6. Level 1 Trigger EM Cand. • Highest Et Non-Isolated Objects • Underflow = no nonIsolated EM objects found (92% of these events) Et Gev

  7. Reconstructed Photons • Built from ECAL SuperClusters • Hybrid clustering algorithm in the ECAL barrel • Island algorithm in endcaps • All SuperClusters are considered as candidate Photons • But only highest Et photon plotted here

  8. Photon Et • Generated & Reco Photon Et Et Gev Longer tail on positive side (reco energy lower near crack between barrel & endcap) DEt

  9. Nearest Track • Nearest track to reco photon with • pt > 0.5 GeV • r = √((Dh)2+(Df)2) • 11% of reco photons have track Dr < 0.08 Dr pt Gev

  10. Photon h and f • Events where the gen photon went into crack between barrel & endcap less likey to pass level-1 trigger h f

  11. Photon Dh and Df •  = hgen - hreco •  = fgen - freco Dh Df

  12. Reco Photon Energy in 3x3 crystal Energy in SC • R9 = • Photons with R9 < 0.9 are most likely converted photons • R19 = 27% of the g have R9<0.9 Emax Energy in 3x3 crystal

  13. After R9 Cut • 73% of events remain • ET = (Egen-Ereco)/Egen DEt

  14. After R9 Cut • Between gen & reco photon Dh Df

  15. Jets • Iterative Cone Algorithm for Jets (r=0.5) • Found Highest pt Jet with • 0.8p < |fjet - fg| < 1.2p • pt > 10 GeV Gev

  16. Jet h and f h f

  17. Jet Dh and Df Dh Df

  18. Next Steps • Port analysis to 160 running on CSA07 Gen+Sim • Data is being imported • Will start using 160 as soon as it is available • Study HLT photon trigger and use additional cleaning cuts to lower the threshold • Current thresholds are a bit high • Begin collaboration with Photon+Jet team in QCD group • Determine jet correction based on photon energy • Eventually interested in Photon fakes • If in a photon+jet event, the jet fluctuates to an energetic po it can fake a photon -- back to back photons • Can we use these to estimate the probability of a jet faking a photon?

  19. Extra

  20. After R9 Cut • Nearest Track • r = √((Dh)2+(Df)2) Dr

  21. Level 1 EM Cand. • Et of Iso Level-1 Em Cand

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