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

Hadronic W decays in the Jets+MET Final State at the LHCEventJetsM(jj)M(jj) 1 1a, 1b, 1c 2 2a, 2bM(2a, 1a), M(2a, 1b), M(2a, 1c) M(2b, 1a), M(2b, 1b), M(2b, 1c) M(2a, 2b) 3 3a, 3b, 3c, 3dM(3a, 2a), M(3a, 2b), M(3b, 2a), M(3b, 2b), M(3c, 2a), M(3c, 2b), M(3d, 2a), M(3d, 2b) M(3a, 3b), M(3a, 3c), M(3a, 3d), M(3b, 3c), M(3b, 3d), M(3c, 3d) 4 j i XM(j i j k ) j k X  1 For each j i in Event X, M(j i j k ) is calculated with j k in Event X  1 Data Driven Method Forming M(jj) Distributions  Same Event: any pairs of jets of the current event  Mixed Event: any pairs of jets of the current + previous events [Step.1][Step.2] 2

tt LHC Hadronic W decays in the Jets+MET Final State at the LHC Data: TTbar_0jet_Et30alpgen/Summer08_IDEAL_V12_AODSIM_v1/AODSIM M(jj) (GeV/c 2 ) Same event Mixed event after normalization Expected shoulder due to b-jets contamination M(jj) (GeV/c 2 ) MWMW Peak position 3

Generator Level Study for Hadronic W decays in the Jets+MET Final State at the LHC In order to verify the data-driven method and investigate the shoulder from b jets the generator level jets were used After subtraction Before subtraction M(jj) (GeV/c 2 ) After subtraction Before subtraction M(jj) (GeV/c 2 ) M(jj) for jets from W and bM(jj) for jets only from W 4

Comparing with and without B jets Hadronic W decays in the Jets+MET Final State at the LHC All Jets Exclude B Jets M(jj) (GeV/c 2 ) 5

b-tag analysis Hadronic W decays in the Jets+MET Final State at the LHC 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 1."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 2."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

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

b-tag analysis Hadronic W decays in the Jets+MET Final State at the LHC 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 Same event Mixed event after normalization M(jj) (GeV/c 2 ) Before subtraction After subtraction M(jj) (GeV/c 2 ) 8

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

b-tag analysis Hadronic W decays in the Jets+MET Final State at the LHC 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 No b tag algorithm HighEff b tag algorithm 10

Conclusions and Plans Hadronic W decays in the Jets+MET Final State at the LHC 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

Back up

Case 1: tt LHC Event Selection - Electron p T > 20 GeV/c - Electron Isolation < Standard Electron Identification - Electron < Missing Transverse Energy > 20 GeV Event Selection - Electron p T > 20 GeV/c - Electron Isolation < Standard Electron Identification - Electron < Missing Transverse Energy > 20 GeV M(jj) Reconstruction - Jet p T > 30 GeV/c - ΔR(jj) > 0.5 M(jj) Reconstruction - Jet p T > 30 GeV/c - ΔR(jj) > 0.5 Hadronic W decays in the Jets+MET Final State at the LHC Data: TTbar_0jet_Et30alpgen/Summer08_IDEAL_V12_AODSIM_v1/AODSIM 13

Case 2: SUSY LHC Event Pre-Selection E T miss > 180 GeV; N(J) > 2 with E T J1,J2 > 200 GeV; E T miss + E T J1 + E T J2 > 600 GeV j i N(j i ) > 2 with p T > 30 GeV ΔR(jj) > 0.5 W W - b J : represented the 1 st and 2 nd leading jets j : represented the other jets that are not the 1 st and 2 nd leading jets Hadronic W decays in the Jets+MET Final State at the LHC Data: SUSY_LM7-sftsht/Summer08_IDEAL_V9_AODSIM_v1/AODSIM 14

Hadronic W decays in the Jets+MET Final State at the LHC Data Driven M(jj) Extraction for SUSY Step 1: Normalization GeV/c 2 Log Scale Normalization Region Normalize the mixed event to the shape of the tail of the same event with the ratio M(jj) (GeV/c 2 ) Same event Mixed event after normalization 15

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