Sung-Won Lee 1 Study of Hadronic W Decays in the Jets + MET Final State Study of Hadronic W Decays in the Jets + MET Final State Kittikul Kovitanggoon Department of Physics Texas Tech University

Proton Collisions Parton Collisions Bunch Crossing Standard Model particles (e.g. tt…) & New Particles (Higgs, SUSY,....) Detecting W bosons in the Jets+MET final state is a key in a SM and SUSY scenario. But, a huge combinatorial background in multi-jet final state is a serious problem. We introduce a Data-Driven method to extract hadronic W decays. Hadronic W decays in the Jets+MET Final State 2 Motivation: Why W  jj? W  j+j hadronic decays 67.60% W  e+ν 10.70% W  μ+ν leptonic decays 10.50% W  τ+ν 11.20%

Outline Hadronic W decays in the Jets+MET Final State 3 Extraction Hadronic W Jet Energy Correction Calo Collection Data-Driven Method Generator Level and B-Tagger Analysis Techniques pp Colision at 7 TeV For Luminosity 110 nb -1 η swapping Data- Driven Method PF Collection Monte Carlo Data pp Colision Data SUSY LM7

Analysis Software Hadronic W decays in the Jets+MET Final State 4 The analysis is based on CMSSW. The Physics Analysis Toolkit (PAT) is a high-level analysis layer in the framework of the CMSSW. Jet energy corrections: - L2(η dependent)+L3(p T dependent) is currently the default correction in CMS. - L2L3+L5(jet Flavor dependent) which uses light quarks i.e. up, down, and strange quarks. - Quark-jet energy correction. Jet Collections:

Data-Driven Method Forming M(jj) Distributions Hadronic W decays in the Jets+MET Final State 5 Event JetsM(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) X 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 for normalization M(jj) M cut  Same Event: any pairs of jets of the current event  Mixed Event: any pairs of jets of the current + previous events

Review of Quark Jet Energy (QJE) Correction Due to the over-calibration of the L2L3 energy correction the new energy correction is required for reconstructing W mass. Based on CMS AN-2010/004 by Alexandre Nikitenko, Efe Yazgan This method is optimized to quark-rich sample. Correction factors are η and p T dependent of jets up to η < 3.2 and are applied to raw jet p T. Hadronic W decays in the Jets+MET Final State 6 Jets Selections 1.Required that jets p T > 30 GeV with corresponding correction. 2.MC matching to selecting the W jets.

Review of Jet Energy Corrections Hadronic W decays in the Jets+MET Final State 7 Entries Data Set: Data Set: WW MWMW MWMW The QJE give us the best calibration for reconstructing hadronic W boson

TOP Production with Calorimeter Jets 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 - Jet < 3 - ΔR(jj) > 0.5 M(jj) Reconstruction - Jet p T > 30 GeV/c - Jet < 3 - ΔR(jj) > 0.5 Data Set Summer08 with CMSSW_2_2_9 and corresponding PAT Hadronic W decays in the Jets+MET Final State 8 Using 300 to 500 GeV as normalization range

First Result of TOP Pair Production of Data-Driven Method Hadronic W decays in the Jets+MET Final State 9 Expected shoulder due to b-jets contamination MWMW Peak position Without b-tagger and proper energy correction, the over calibrated mass and shoulder are presented. Entries

Generator Level Study for Hadronic W decays in the Jets+MET Final State at the LHC 10 Entries In order to confirm the effect of b jet contamination, the generator level jets were used in data- driven method. The result shows that the shoulder is due to the b jets contamination.

b-tagger Analysis Hadronic W decays in the Jets+MET Final State at the LHC In order to remove this shoulder, b-tag algorithm is needed. The two "Track Counting" algorithms based on impact parameter i.e. “High efficiency”” and “High Purity” were recommended to use. The track counting approach identifies a jet as b by calculating the signed impact parameter significance (S) of all good tracks, and orders them by decreasing significance. Its b tag discriminator is defined as the significance (S) of the N'th track. S of N = 2 is high efficiency and N = 3 for high purity. The higher the discriminator value, the more likely the jet is b jet. The cut number is recommended by b-tagging analysis group: 11 We chose the loose cuts for b-taggers because it can pick the most b jets.

b-tagger Analysis Hadronic W decays in the Jets+MET Final State at the LHC 12 This study was done on CMSSW_3_3_5 with PAT on summer09 sample. The plot show the dijet mass after the subtraction with high efficiency < The Parton flavor of jets with and without b-tagger. The b-tagger eliminates the shoulder from our dijet mass. Entries

b-tagger Analysis Hadronic W decays in the Jets+MET Final State at the LHC 13 Two track counting algorithms is studied. High efficiency gives us the better shape than high purity in the same loose point. We also study how changing b discriminator values affect the mass shape. Decreasing the value should give us the better mass shape? Decreased the value worst mass shape. Increased the value same mass shape. Entries M(jj) (GeV/c 2 )

b-tagger Analysis Hadronic W decays in the Jets+MET Final State at the LHC 14 To understand how the changing discriminator values effect the shape of dijet mass. Investigating the b discriminator values of the W jets and b jets with MC matching. Decreased the discriminator value lose W more than b. Increased the discriminator value gain W as many as b. Impossible to lose b while gain W. We decided to use the high efficiency discriminator value of 2.03 Entries

TOP Production with Calorimeter Jets Event Selections - Electron p T > 20 GeV/c - Electron Isolation < Standard Electron Identification - Electron < Missing Transverse Energy > 20 GeV - At least 1 b jet (discriminator >2.03) Event Selections - Electron p T > 20 GeV/c - Electron Isolation < Standard Electron Identification - Electron < Missing Transverse Energy > 20 GeV - At least 1 b jet (discriminator >2.03) M(jj) Reconstruction - Jet p T > 30 GeV/c - Jet discriminator < Jet < 3 - ΔR(jj) > 0.5 M(jj) Reconstruction - Jet p T > 30 GeV/c - Jet discriminator < Jet < 3 - ΔR(jj) > 0.5 Data Set TTbar Sping10 with CMSSW_3_5_7 and corresponding PAT Hadronic W decays in the Jets+MET Final State 15 Using 300 to 500 GeV as normalization range

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 16 Same Events Mixed Events Entries Result of Calorimeter Jets

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 17 Entries Log Scale Normalization Region GeV/c 2 Result of Calorimeter Jets

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 18 Result of Calorimeter Jets Peak position MWMW As we expect, the b-tagger help us to eliminate the b jet contmination. The mass peak at around 95 GeV is over calibrated by L2L3 JEC Entries

M(jj) in Data-Driven Method with L2L3 + L5 and QJE Hadronic W decays in the Jets+MET Final State 19 Result of Calorimeter Jets Peak position MWMW MWMW Entries

M(jj) in Data-Driven Method with all JECs Hadronic W decays in the Jets+MET Final State 20 Result of Calorimeter Jets Entries MWMW The data-driven method seem to work. The high efficiency b-tagger and JEC are important to this analysis.

TOP Production with Particle Flow Jets Event Selections - Electron p T > 20 GeV/c - Electron Isolation < Standard Electron Identification - Electron < Missing Transverse Energy > 20 GeV - At least 3 PF jets with L2L3 p T > 25 GeV - At least 1 jet with L2L3 p T > 25 GeV is b jet Event Selections - Electron p T > 20 GeV/c - Electron Isolation < Standard Electron Identification - Electron < Missing Transverse Energy > 20 GeV - At least 3 PF jets with L2L3 p T > 25 GeV - At least 1 jet with L2L3 p T > 25 GeV is b jet M(jj) Reconstruction - Jet p T > 25 GeV/c - Jet discriminator < Jet < 3 - ΔR(jj) > 0.5 M(jj) Reconstruction - Jet p T > 25 GeV/c - Jet discriminator < Jet < 3 - ΔR(jj) > 0.5 Data Set TTbar Sping10 with CMSSW_3_5_7 and corresponding PAT Hadronic W decays in the Jets+MET Final State 21 Using 300 to 500 GeV as normalization range

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 22 Entries MWMW Result of PF Jets Entries With track information, the over calibrated jet energy is not an issue. Combined with high efficiency b-tagger, the clear peak at 80 GeV of W mass is evident.

Super Symmetry Low Mass Point 7 (SUSY LM7) Hadronic W decays in the Jets+MET Final State 23 Supersymmetry (SUSY) provides an elegant solution for a cold dark matter candidate. The minimal SUGRA framework indicate that gluinos is lightest. The gluinos decay to pairs of tops plus the lightest supersymmetric particle (LSP). Pointm 0 Gev m 1/2 Gev tanβSgn μ A0A0 LM LM LM LM LM LM LM LM LM LM mSUGRA is characterized by five free parameters: m 0 the common mass of scalar particle at GUT scale m 1/2 the common fermion mass A 0 the common trilinear coupling μ the sign of the higgsion mass parameter tanβ the ratio between the expectation values of 2 Higgs doublets

SUSY LM7 LHC Event Pre-Selection MET > 180 GeV; N(J) > 2 with E T J1,J2 > 200 GeV; MET + E T J1 + E T J2 > 600 GeV j i N(j i ) > 2 with p T > 30 GeV jets < 3 ΔR(jj) > 0.5 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 Data Set SUSY LM7 Spring10 with CMSSW_3_5_7 and corresponding PAT Hadronic W decays in the Jets+MET Final State 24 Using 300 to 500 GeV as normalization range

First Result of SUSY LM7 Production of Data-Driven Method Hadronic W decays in the Jets+MET Final State 25 Entries MWMW This results show that data-driven method seem to work on SUSY signal. However, this analysis is still in the early state. More detail studies are required. Entries Result of Calorimeter Jets MWMW

Early LHC Data at = 7 TeV Hadronic W decays in the Jets+MET Final State 26 Time for the real data from CMS LHC

η Swapping Data-Driven Method Hadronic W decays in the Jets+MET Final State 27 #1 #2 #3 #  An interesting physics? Yes, W jj.  Large QCD cross section.  ∆φ(jj) ~ 180 deg.  Special treatment in mix event.  Choose two leading jets in each event.  Swap the η’s, not φ’s, to maintain “QCD dijet” structure. Event #nEvent #n+1

Test on Early LHC Data at = 7 TeV Hadronic W decays in the Jets+MET Final State 28 Data set are: - /MinimumBias/Commissioning10-SD_JetMETTau-Jun14thSkim_v1/RECO - /JetMETTau/Run2010A-Jun14thReReco_v2/RECO -/JetMETTau/Run2010A-PromptReco-v4/RECO Corresponding JSON files: - Cert_ _7TeV_June14thReReco_Collisions10_JSON.txt - Cert_ _7TeV_June14thReReco_Collisions10_JSON.txt - Cert_ _7TeV_StreamExpress_Collisions10_JSON.txt The data set is corresponding to an integrated luminosity of 110 nb -1 This analysis is done on CMSSW_3_7_0_patch2 with corresponding PAT.

Test on Early LHC Data at = 7 TeV Hadronic W decays in the Jets+MET Final State 29 Event Selections - ak5 calo jets - Trigger 0 AND NOT (36 OR 37 OR 38 OR 39) - Scraping veto - Good Primary vertex - HLT bits: HLT_Jet15U - JEC: L2+L3 “spring10” - |η jet1 | < 1.3 && |η jet2 | < leading jets passing the loose jet id - Jet p T > 30 GeV - Jets back to back i.e. ||Δφ| - π|<0.2 Using 200 to 500 GeV as normalization range and using the variable bin size to gain more statistic in the high mass region. The first result showed the negative entries due to the high number of QCD jets compared to W jets. Moreover, the low entries in the region of normalization in mix event. New techniques are required.

Techniques for Analyzing Early LHC Data at = 7 TeV Hadronic W decays in the Jets+MET Final State 30 We studied the behavior of between W jets and QCD dijets Studying is done on spring10 data by matching hadronic W and on QCD4Jets spring10 data. Entries of QCD jets is broader range than that of W jets. The signal (W) over background (QCD) shows us that the optimized point is around = 0.8. Imposeing the requirement of jet p T ratio between the second jet in the same event and the jet in the mix event greater than 0.8 to increase the mix event at high mass region.

Test on Early LHC Data at = 7 TeV Hadronic W decays in the Jets+MET Final State 31 Event Selections - ak5 calo jets - Trigger 0 AND NOT (36 OR 37 OR 38 OR 39) - Scraping veto - Good Primary vertex - HLT bits: HLT_Jet15U - JEC: L2+L3 “spring10” - | η jet1 | < 1.3 && | η jet2 | < leading jets passing the loose jet id - Jet p T > 30 GeV - Jets back to back i.e. ||Δφ| - π|<0.2 - |Δη| < Pt ratio between second jet in same event and jet in mix event > 0.8 Using 200 to 500 GeV as normalization range and using the variable bin size to gain more statistic in the high mass region.

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 32 Same Events Mixed Events Entries Result of Calorimeter Jets

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 33 Entries Log Scale Normalization Region GeV/c 2 Result of Calorimeter Jets

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 34 Result of Calorimeter Jets Peak position MWMW Entries

M(jj) in Data-Driven Method with L2L3 Hadronic W decays in the Jets+MET Final State 35 Result of Calorimeter Jets Entries New techniques can eliminate negative mass and give us the better mass window. The peak position lower than W mass because many QCD jets passed our event selections. This method is still pre-mature. We need more detailed studies.

Summary and Plans Hadronic W decays in the Jets+MET Final State 36 Extracting the hadronic W decay is important for both Standard Model and SUSY events. The studies show that the data-driven method seems to work on extracting hadronic W. Proper b-tagging could help us to see clearly mass peak with less combinatorial background. Various jet energy corrections and PF jets can solve the over-calibrating energy. The future plans are: 1.Mixing the signal with the backgrounds. 2. More detail studies of η swapping data-driven method. 3.Optimizing new event selections for SUSY LM7. 4.Test on SUSY LM0.