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Study of Hadronic W Decays in the Jets + MET Final State

Study of Hadronic W Decays in the Jets + MET Final State. Kittikul Kovitanggoon * & Sung-Won Lee Texas Tech University Michael Weinberger & Teruki Kamon Texas A&M University. Outline. Motivation : Why W  jj? Review of Data-Driven Method to detect W bosons

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Study of Hadronic W Decays in the Jets + MET Final State

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  1. Study of Hadronic W Decays in the Jets + MET Final State Kittikul Kovitanggoon*& Sung-Won Lee Texas Tech University Michael Weinberger & Teruki Kamon Texas A&M University

  2. Outline • Motivation : Why W  jj? • Review of Data-Driven Method to detect W bosons • Introduce the new jet energy correction “ quark jet energy” • Testing with TTbar events • Testing with SUSY LM7 events • Summary The analysis has done on CMSSW_3_3_5 with PAT. 2 Hadronic W decays in the Jets+MET Final State

  3. Motivation: Why Wjj? Bunch Crossing Proton Collisions Parton Collisions W j+jhadronic decays 67.60% W e+ν 10.70% W μ+νleptonic decays 10.50% W τ+ν 11.20% Standard Model particles (e.g. tt…) & New Particles (Higgs, SUSY, ....) Detecting W bosons in the Jets+MET final state is a key in a SUSY scenario. We have been testing a Data-Driven method to extract hadronic W decays. 3 Hadronic W decays in the Jets+MET Final State

  4. Forming M(jj) Distributions Data Driven Method [Step.1] [Step.2] • Same Event: any pairs of jets of the current event • Mixed Event: any pairs of jets of the current + previous events 4 Hadronic W decays in the Jets+MET Final State

  5. Previous studies • The last talk on this analysis can be found at http://indico.cern.ch/conferenceDisplay.py?confId=81844 • We moved from CMSSW_2_2_9 to CMSSW_3_3_5. The main different from both versions is the jet algorithms i.e. IC5 and Antikt 5. The study showed that there is no much difference between both algorithms. • Two b-tag algorithms, track counting high efficiency and track counting high purity, were studied. The result showed that track counting high efficiency give us better efficiency. • Also, on ttbar sample double b tags was applied. We get the better shape of W mass but loss a lot of statistic. 5 Hadronic W decays in the Jets+MET Final State

  6. Review of Quark Jet Energy (QJE) Correction • Due to the over-calibration of the L2L3 energy correction which is the default in PAT • the new energy correction is required for reconstructing W mass • Based on CMS AN-2010/004 by Alexandre Nikitenko, Efe Yazgan • http://indico.cern.ch/getFile.py/access?contribId=2&resId=0&materialId=6&confId=81091 • This method is optimized to quark-rich sample • Correction factors are eta and pTdependent of jets up to eta < 3.2 and are applied to raw jet pT • Data Set /TTbar/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO Entries • Jets selection • Required that jets pT> 30 GeV with corresponding correction • MC matching to selecting the jets from W M(jj) (GeV/c2) 6 Hadronic W decays in the Jets+MET Final State

  7. TOP Production Data Set /TTbar/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO Event Selection - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification  - Electron < 2.5 - Missing Transverse Energy > 20 GeV M(jj) Reconstruction - Jet pT > 30 GeV/c - Jet < 3 -HighEfficenecy b tag < 2.03 - ΔR(jj) > 0.5 7 Hadronic W decays in the Jets+MET Final State

  8. M(jj) in Data-Driven Method with L2L3 Same event 300-500 GeV/c2 Mixed event after normalization Same Events Mixed Events Log Scale Normalization Region Entries Entries M(jj) (GeV/c2) M(jj) (GeV/c2) Entries Entries M(jj) (GeV/c2) M(jj) (GeV/c2) 8 Hadronic W decays in the Jets+MET Final State

  9. Wjj with L2L3 Peak position Entries MW M(jj) (GeV/c2) • On the slide the important of b-tag will be discussed • The analysis was repeated by using L2L3+L5 and quark-jet energy correction 9 Hadronic W decays in the Jets+MET Final State

  10. B-tag Analysis • According to the previous gen-level analysis, the shoulder is due to the b-jets contamination • In order to remove this , b-tag algorithm is needed • The b-tag algorithm is “Track counting high efficiency” with discriminator < 2.03 • http://indico.cern.ch/getFile.py/access?contribId=8&resId=0&materialId=slides&confId=50255 Entries Without b-tag With b-tag With double b-tags M(jj) (GeV/c2) b-tag is needed to eliminate b-jet contamination Based on previous study, “track counting high efficiency” discriminator < 2.03 is the best for eliminate b jet contamination Hadronic W decays in the Jets+MET Final State 10

  11. M(jj) with L2L3, L2L3L5 and QJE Correction Entries L2L3 L2L3 + L5 Quark jet energy correction MW M(jj) (GeV/c2) Conclusions The quark-jet energy correction give us better peak position of W mass. However, we lost some jets due to the lower energy after the correction. Although we still see a large backgrounds even after the subtraction we will be able to see the W mass. 11 Hadronic W decays in the Jets+MET Final State

  12. SUSY LM7 production @ LHC Event Pre-Selection • ETmiss > 180 GeV; • N(J) > 2 with ETJ1,J2 > 200 GeV; • ETmiss + ETJ1 + ETJ2 > 600 GeV N(ji) > 2 with pT > 30 GeV jets < 3 ΔR(jj) > 0.5 W b W - • J : represented the 1st and 2nd • leading jets • j: represented the other jets that • are not the 1st and 2nd leading jets b Data Set: /LM7/Summer09-MC_31X_V3_7TeV_AODSIM-v1/AODSIM 12 Hadronic W decays in the Jets+MET Final State

  13. M(jj) in Data-Driven Method with L2L3 Same event 300-500 GeV/c2 Mixed event after normalization Same Events Mixed Events Log Scale Normalization Region Entries Entries M(jj) (GeV/c2) M(jj) (GeV/c2) Entries Entries M(jj) (GeV/c2) M(jj) (GeV/c2) 13 Hadronic W decays in the Jets+MET Final State

  14. Wjjwith L2L3 Peak position Entries MW M(jj) (GeV/c2) • The analysis was repeated by using L2L3+L5 and quark jet-energy correction 14 Hadronic W decays in the Jets+MET Final State

  15. Wjj with L2L3, L2L3+L5, QJE Correction Entries L2L3 L2L3 + L5 Quark jet energy correction MW M(jj) (GeV/c2) Conclusions The quark jet-energy correction give us better peak position of W mass. Although we still see a large backgrounds even after the subtraction (larger than ttbar case) we will be able to see the W mass. The study of the new event selections is required to eliminate more background 15 Hadronic W decays in the Jets+MET Final State

  16. Summary • The data-driven method seem to work on extracting hadronic W decay in TTbar and LM7 events. • The b-tag algorithm is necessary for eliminate the b jet contamination. • The quark jet energy correction solves the overcorrected jet energy. This correction give us the better W mass peak at around 80 GeV. • More systematic study will be planned: • Mixing signal with background Z+jets, W+jets, etc • Optimizing the event section for SUSY LM7 16 Hadronic W decays in the Jets+MET Final State

  17. Back up

  18. Quark-Jet Calibration using Z+Jet Events Alexandre Nikitenko, Efe Yazgan CMS AN-2010/004 http://indico.cern.ch/getFile.py/access?contribId=2&resId=0&materialId=6&confId=81091 The calibration coefficients for the quark jets, cq, canbeobtainedfrom: measure s(Z+g)/sTOT cq/cq=ratio of the quark And gluon jet calib. Coefficients from MC (ETj and hjdependent) s(Z+q)/sTOT Ratio of Z+q (Z+g) Cross section to the Total cross section. (function of PTZ and hj) 18

  19. Determining Correction Coefficients Alexandre Nikitenko, Efe Yazgan • Determine each parameter for each hj, PTZ interval (using 2D maps), and then find the quark coefficients, cq. dh=0.4, dPT=20 GeV 19

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