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

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

2. Introduction • W’s may present in the SUSY events and could be an indicator to distinguish various SUSY scenarios. • Since we have LSP’s, reconstructing W’s using lepton plus MET is difficult. Thus Wjjwill be important, even if we face a huge combinatorial background. • We are testing a data-driven method to estimate the dijet mass distribution from non-W sources. 2 Hadronic W decays in the Jets+MET Final State at the LHC

3. 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 2 Hadronic W decays in the Jets+MET Final State at the LHC

4. tt production @ LHC Data: TTbar_0jet_Et30alpgen/Summer08_IDEAL_V12_AODSIM_v1/AODSIM Expected shoulder due to b-jets contamination Same event Peak position Mixed event after normalization MW M(jj) (GeV/c2) M(jj) (GeV/c2) 3 Hadronic W decays in the Jets+MET Final State at the LHC

5. Generator Level Study for • In order to verify the data-driven method and investigate the shoulder from b jets the generator level jets were used M(jj) for jets from W and b M(jj) for jets only from W Before subtraction Before subtraction After subtraction After subtraction M(jj) (GeV/c2) M(jj) (GeV/c2) Hadronic W decays in the Jets+MET Final State at the LHC 4

6. Comparing with and without B jets Exclude B Jets All Jets M(jj) (GeV/c2) 5 Hadronic W decays in the Jets+MET Final State at the LHC

7. b-tag analysis • According to the gen level analysis, the shoulder is due to the b jets contamination • In order to remove this shoulder, b-tag algorithm is needed • There are 2 types of b-tag algorithms recommended to use in the PAT version 1 on • CMSSW_2_2_9 • "Track Counting" algorithm : This is a very simple tag, exploiting the long lifetime of B hadrons. It calculates the signed impact parameter significance of all good tracks, and orders them by decreasing significance. Its b tag discriminator is defined as the significance of the N'th track , where good tracks are N = 2 for high efficiency and N = 3 for high purity • "Simple Secondary Vertex" algorithm: This reconstructs the B decay vertex using an adaptive vertex finder, and then uses variables related to it, such as decay length significance to calculate its b tag discrimatinator • The cut number is recommended by b-tagging analysis group for Summer08 sample • HighEff less than 2.03 • HighPur less than 1.47 • Simple Secondary Vertex less than 1.25 6 Hadronic W decays in the Jets+MET Final State at the LHC

8. b-tag analysis No b tag HighEff b tag HighPur b tag simSecondVer b tag • b-tag removing efficiency can be calculated from this results HighEff 70.7% HighPur 54.8% simSecondVer 56.6% For CaloJet ET > 30 GeV and abs(eta) < 2with MC b matching 7 Hadronic W decays in the Jets+MET Final State at the LHC

9. b-tag analysis • The result shows that the HighEff b-tagging can remove b jets better than other b discriminators • Apply the HighEff b-tagging into the data-driven method to eliminate the b jets contamination Before subtraction Same event Mixed event after normalization After subtraction M(jj) (GeV/c2) M(jj) (GeV/c2) 8 Hadronic W decays in the Jets+MET Final State at the LHC

10. b-tag analysis Peak position Zoom-in M(jj) after Subtraction MW 9 Hadronic W decays in the Jets+MET Final State at the LHC

11. b-tag analysis No b tag algorithm HighEff b tag algorithm • Using maximum entry to normalize with and without HighEff b-tag algorithm and imposing both on the same histogram • It is clearly see that b-tagging algorithm can eliminate the shoulder from b jet contamintaion 10 Hadronic W decays in the Jets+MET Final State at the LHC

12. Conclusions and Plans • At this point, data-driven method gives good result for analyzing hadronic W decay, however we need to test this method by mixing the signal with some backgrounds • The generator level study confirms the result and identifies the reason of the shoulder due to b jet contamination • The High Efficiency b –tagging algorithm is used to eliminate the shoulder from the calo level jets • Without b jet contamination, dijet mass distribution shows good peak as expected • However, peak position is still higher than 80 GeV i.e. W mass • The JES correction is the next step to do in order to fix the higher than expect peak position • Also, moving the analysis to the new version of PAT on CMSSW3xx 11 Hadronic W decays in the Jets+MET Final State at the LHC

13. Back up

14. Case 1: tt production @ LHC Data: TTbar_0jet_Et30alpgen/Summer08_IDEAL_V12_AODSIM_v1/AODSIM 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 - ΔR(jj) > 0.5 13 Hadronic W decays in the Jets+MET Final State at the LHC

15. Case 2: SUSY Production @ LHC Data: SUSY_LM7-sftsht/Summer08_IDEAL_V9_AODSIM_v1/AODSIM Event Pre-Selection • ETmiss > 180 GeV; • N(J) > 2 with ETJ1,J2 > 200 GeV; • ETmiss + ETJ1 + ETJ2 > 600 GeV W b W - N(ji) > 2 with pT > 30 GeV ΔR(jj) > 0.5 b • J : represented the 1st and 2nd • leading jets • j: represented the other jets that • are not the 1st and 2nd leading jets 14 Hadronic W decays in the Jets+MET Final State at the LHC

16. Data Driven M(jj) Extraction for SUSY Step 1: Normalization 300-500 GeV/c2 Same event Mixed event after normalization Log Scale Normalization Region M(jj) (GeV/c2) M(jj) (GeV/c2) Normalize the mixed event to the shape of the tail of the same event with the ratio 15 Hadronic W decays in the Jets+MET Final State at the LHC

17. Data Driven M(jj) Extraction for SUSY Step 2: Subtraction Zoom-in M(jj) after Subtraction Peak position MW MW M(jj) (GeV/c2) M(jj) (GeV/c2) After subtraction Before subtraction 16 Hadronic W decays in the Jets+MET Final State at the LHC