Measurement of the Muon Charge Asymmetry in Inclusive pp W (μν) + X Production at s = 7 TeV. Saranya Ghosh (EHEP, TIFR) India-CMS meeting

Transcription

1 Measurement of the Muon Charge Asymmetry in Inclusive pp W (μν) + X Production at s = 7 TeV Saranya Ghosh (EHEP, TIFR) India-CMS meeting 18th December, 2012

2 Contents Introduction Datasets Details of analysis Selection Criteria Method Corrections applied Efficiency Scaling in MC Muon momentum scale corrections Corrections for Boson transverse momentum (qt) in MC Background Study and Signal Estimation Overview of Method Correcting MET in MC Fit Results Systematic Uncertainties Results Comparison of 2011A, 2011B and 2011AB Summary 2

3 Introduction In pp collisions primary process of W production: ud W+ and du W- Excess of W+ since number of uv > dv in a proton Measurement of lepton charge asymmetry in bins of pseudorapidity of the lepton due to presence of neutrino in W lν decay. Previous CMS measurements: Electron channel (lepton pt>35), 840/pb (SMP-12001) Muon channel (lepton pt>25), 236/pb (EWK-11005) This analysis updates measurement of muon charge asymmetry with much larger dataset than before : ~2.31/fb for 2011A and ~2.35/fb for 2011B Previous muon channel measurement (EWK ) compared to predictions by different PDF models 3

4 Datasets CMSSW_4_4_x used Data sample details: /SingleMu/Run2011A-08Nov2011-v1/AOD : for 2011A /SingleMu/Run2011B-19Nov2011-v1/AOD : for 2011B JSON : Cert TeV ReRecoNov08 Collisions11 JSON v2.txt for 2011A, Special JSON used for 2011B where trigger is un-prescaled that is subset of the Golden JSON Trigger : HLT IsoMu15/24 (only those Lumi Sections used where trigger is unprescaled) MC samples: Process W+ μν MC Sample /WplusToMuNu_M-20_CT10_TuneZ2_7TeV-powheg-pythia/Fall11-PU_S6_START44_V9B-v1/AODSIM W- μν /WminusToMuNu_M-20_CT10_TuneZ2_7TeV-powheg-pythia/Fall11-PU_S6_START44_V9B-v1/AODSIM W+ τν /WplusToTauNu_M-20_CT10_TuneZ2_7TeV-powheg-pythia-tauola/Fall11-PU_S6_START44_V9Bv1/AODSIM W- τν /WminusToTauNu_M-20_CT10_TuneZ2_7TeV-powheg-pythia-tauola/Fall11-PU_S6_START44_V9Bv1/AODSIM Z/γ* μμ /DYToMuMu_M-20_CT10_TuneZ2_7TeV-powheg-pythia/Fall11-PU_S6_START44_V9B-v1/AODSIM Z/γ* ττ /DYToTauTau_M-20_CT10_TuneZ2_7TeV-powheg-pythia-tauola/Fall11-PU_S6_START44_V9Bv1/AODSIM tt /TT_TuneZ2_7TeV-powheg-tauola/Fall11-PU_S6_START44_V9B-v1/AODSIM QCD /QCD_Pt-20_MuEnrichedPt-15_TuneZ2_7TeV-pythia6/Fall11-PU_S6_START44_V9B-v1/AODSIM Trigger : HLT IsoMu15 4

5 Details of Analysis - Selection Criteria Filters used : FilterOutScraping, GoodVertexFilter, HBHENoiseFilter Muon selection criteria: tight muon selection criteria for 2011 Data η < 2.4 Global muon and Tracker muon χ2/ndf of global track <10 # of valid muon chamber hits > 0 # of muon chamber matches > 1 # of tracker layer hits > 8 δrvertex <0.2 Isolation criteria : Σ0.3 Pttrack/PTμ < 0.1 W selection criteria: muons passing selection criteria are sorted in order of pt, then: # of pixel hits > 0 Leading muon matched to HLT object: ΔR < 0.1 (HLT_IsoMu24 for Data and HLT_IsoMu15 for MC) Tracker pt of leading muon > 25GeV Drell_Yan veto: conditions on next-to-leading muon: pt>15 GeV η < 2.4 5

6 Details of Analysis - Method Asymmetry calculated in 11 bins of η : [0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.85, 2.1, 2.4] MC samples used to estimate backgroud and extract signal form the data Muon momentum correction is applied to data and MC to remove the momentum bias The distributions in the MC samples are corrected to better match the Data distributions. The corrections are described later. MET distribution in MC samples fitted to that in Data to extract the signals and estimate the backgrounds associated with the other processes that contribute as background The efficiency of reconstructing and identifying muons is calculated in Data in order to apply corrections in certain cases and to assign systematic errors arising related to the efficiency Systematic error is studied for the analysis items and will be described later 6

7 Muon efficiency scaling in MC Efficiency scaling in MC: Efficiency is calculated in Data and MC and the efficiency scale factor is obtained. The efficiency scale factor of the data to MC is applied into MC to match the signal shape between data and MC DY slelected events in Data and MC in bins of η of leading muon Before Efficiency correction After Efficiency correction 7

8 Muon momentum scale corrections Muon momentum scale and misalignment based corrections applied to Data and MC : Correction applied to remove the bias from the misalignment effect or mis-modeling of the magnetic field Rochester muon momemntum scale corrections used. Corrections based on Q(charge), pt, θ, φ of muons obtained using Drell-Yan sample described in AN , AN Additive and muliplicative corrections factors based on <1/pT> obtained separately for different Q in bins of θ, φ of muons Additional corrections based on Z mass Corrections used in the analysis are obtained in CMSSW_4_4_x corresponding to the η bins used for asymmetry measurement 8

9 Corrections Applied Corrections for Boson transverse momentum (qt) in MC Boson transverse momentum (qt) correction applied to W and DY MC : The modelling of boson transverse momentum (qt) does not match the Data closely in Z events in the powheg MC used for this measurement Correction is derived to compare the Z qt spectrum in the reconstruction level and applied into the generated Z qt spectrum Using the gen-level qt information, this correction is applied to the W and the Drell-Yan MC samples Z boson qt before (left) and after (right) qt corrections in data and MC. Ratio of Data to MC shown below. 9

10 Background Study and Signal Estimation - Method Fit of MC MET distributions to that of Data to estimate backgroung and estimate signal The following processes considered as signal and background: W μν W τν Z μμ Z ττ QCD tt To extract the signal from Data, the MET and MT (of MET and muon) distributions of the MC was fitted to that of Data. Fitting in 11 bins of η of muon Stacked MC fitted to Data to extract signal and background. Combined fit performed separately for μ+ and μ- events. Floated parameters of fits: 1. Total signal events(w μν) 2. Asymmetry of W+ and W3. Total QCD events For other processes, crossection fixed wrt W μν from MC. The asymmetry of W+ and W- for W τν taken to be same as that for W μν. 10

11 Background Study and Signal Estimation Correcting MET in MC samples Using the u and u components for Z μμ to smear MC Parallel and perpendicular component of Hadronic recoil wrt Z boson for Z μμ boson events considered individually. Resolution of the components of the recoil compared for Data and MC. Data found to have poorer resolution than MC. The difference in resolution between Data and MC taken in quadrature and used to smear MC. New value of MET and phi of MET calculated using the above smeared parallel and perpendicular components of MET. Corrections also performed based on number of jets in event. 11

12 Background Study and Signal Estimation Correcting MET in MC samples Using the u and u components for Z μμ to smear MC Basic definitions (Z) qt : Electroweak boson (Z) momentum in transverse plane. ut (or u in slides): Hadronic recoil in the transverse plane ull : component that is parallel to qt ET : Missing Transverse Energy (MET) Resolution for raw PF MET parallel (left) and perpendicular(right) components of u Scale factor corrections for MET depends on ET /qt which is related to l<ull>l/qt or the 'response' Resolution of u related to that of ET The difference between the Data and MC taken in quadrature and used to smear the MC to get better 12 agreement with Data.

13 Background Study and Signal Estimation Correcting MET in MC samples Using the u and u components for Z μμ to smear MC The difference in quadrature of RMS of Data and MC plotted against q T for PF MET parallel (left) and perpendicular(right) components of u. Polynomial used to fit the distribution. Parallel component Perpendicular component The difference between the Data and MC taken in quadrature and used to smear the MC to get better agreement with Data. 13

14 Background Study and Signal Estimation Fits Fit of MC to Data for η bin (top), (bottom) : μ+ events μ- events μ+ events μ- events Data, MC match in the signal region 14

15 Systematic Errors PDF uncertainties: For QCD, the central values taken Obtainined fits using the different distributions and calculated systematics Weighting the MC distributions based on PDF variations of the CT10 PDFs. Also looked at MSTW2008nlo, NNPDF21_100. Using the difference of the asymmetry obtained from the diffrent sets wrt that from the central value to get systematics and correlations (different for NNPDF, using similar method as described below for that) Methodology for other systematics (PU, muon scale Correction, MET Smearing (recoil correction), DY TTbar crossection): Varying different paramenters (PU, Rochester Correction, MET Smearing (recoil correction)) using Gaussian random numbers within the errors for those parameters 60 times. Entire procedure of obtaining the MET fits repeated for each iteration for each of the parameters (including muon pt cut in case of rochester correction) Asymmetry calculated from the MET fits separately for each iteration For every parameter, the aymmetry obtained from the different iterations used to calculate the systematic errors taken as the RMS. The aymmetry obtained from the different iterations used to calculate the the corelations. 15

16 Systematic Errors Systematics due to PU reweighting: PU reweighting done based on changed Data PU distribution and MET fits redone and systematics calculated Systematics due to smearing MET in MC (recoil corrections): Vary the minimum bias cross-section used to obtain PU distribution in Data with error as ±5% Varying the smearing factors of the MC based on the errors propagated in calculating the smearing factor Obtained fits after smearing using smear factor after taking errors into account and used that to calculate systematics Systematics due to muon scale corrections: The corrections factors were varied wihtin their errors. Made some modification to the code or Rochester correction to set the random number being calculated internally to be same as sysdev Procedure carried out separately for Data and MC and to obtain MET fits and asymmetry once keeping taking the correct muon scale correction for MCs but varying those in Data and once taking the correct corrections in Data and varying that in the MC samples The different values of asymmetry obtained to be used to calculate the systematics from Muon Scale in Data and MC and the correlations 16

17 Systematic Errors Systematics due to DY and TTbar crossection Varied the relative crossections of W, DY and TTbar crossections For W and TTbar, took the experimental errors scaled to the central value used from theoretical predictions, for DY took errors on theoretical predictions Theoretical values and errors from: Experimental values from: CMS-EWK (W cross-section), CMS-EWK (TTbar) Systematics due to boson qt Varied the qt corrections by ± 10% Obtained fits using the changed qt weights Compared the difference in the asymmetry in the different bins with central values The maximum absolute difference in asymmetry wrt the central value in each eta bin taken as the systematic error 17

18 Systematic Errors Systematics due to QCD estimation Using anti-isolation sample of Data and QCD MC to correct the shape of MET in QCD MC with isolation criteria The ratio of the MET distribution in different bins of MET taken for Data and QCD MC with anti-isolation criteria. Ratio obtained used to correct MET shape in QCD MC for isolation case by multiplying the MET distrbution of isolation QCD sample in bins of MET by the ratio obtained from anti-isolation case. The absolute difference in asymmetry wrt the central value in each eta bin taken as the systematic error For different efficiency of μ+ and μ- : Expected change in Asymmetry due to efficiency: Systematic errors assigned as: 18

19 Results : 2011A Results for 2011A dataset 19

20 Results : 2011A Correlations for for 2011A dataset 20

21 Results Results for 2011A dataset compared to previous results Comparison with previous muon channel result Without Efficiency Correction With Efficiency Correction Without Efficiency Correction Comparison with previous electron channel result With Efficiency Correction 21

22 Comparison of asymmetry in η in 2011AB with 2011A and 2011B Without Efficiency Correction With Efficiency Correction Good agreement between 2011AB, 2011A and 2011B without efficiency corrections Asymmetry for 2011AB falls between that for 2011A and 2011B in most η bins After asymmetry corrections, difference in certain bins 22

23 Comparison of asymmetry in η in 2011AB with previous result Without Efficiency Correction With Efficiency Correction Good agreement with old result taking errors into consideration 23

24 Summary Obtained Asymmetry with 2011A dataset after applying corrections to Data and MC Result is largely consistent with previous results Performed preliminary study including 2011B dataset and the results are consistent with 2011A Dataset Plan to complete the measurement for the 2011A+B dataset Plan to finish evaluation of all systematics. 24

25 Other CMS related activities Shifts : Have taken 25 Trigger Online Shifts in 2012 Scheduled to take more Trigger Online Shifts in January and February 2013 Work related to the Performace of MET for the MET working group. More details tomorrow. Thank you. 25

26 Summary Obtained Asymmetry with 2011A dataset after applying corrections to Data and MC Result is largely consistent with previous results Performed preliminary study including 2011B dataset and the results are consistent with 2011A Dataset Plan to complete the measurement for the 2011A+B dataset Plan to finish evaluation of all systematics. 26

27 Back Up 27

28 Details of Analysis - PU reweighting Pile-Up (PU) reweighting in MC: The PU is significant in the data sample with the average number of reconstructed vertices being quite high MC simulation is reweighted to match reconstructed vertices in MC to that in Data 68mb p-p inelastic crossection ( s = 7 TeV) is used to calculated the PU distribution in Data to which that in MC is matched True PU distribution in MC is matched to that in Data μ+ events μ- events Reconstructed vertices distribution in Data (black) and stacked MC (histograms) for W selected events 28

29 Muon momentum scale corrections Muon momentum scale and misalignment based corrections applied to Data and MC : Z mass profile in muon φ and η. Before muon scale correction Data MC MC gen level After muon scale correction Correction applied remove the momentum bias 29

30 eta distribution of muon in Data and MC muon pt distribution of MC samples stacked using fit values from MET fits after smearing Rochester correction and efficiency scaling performed pt distribution of MC compared to that of Data for entire eta range: μ+ μ30

31 eta distribution of muon in Data and MC muon eta distribution of MC samples stacked using fit values from MET fits after smearing Rochester correction and efficiency scaling performed eta distribution of MC compared to that of Data for entire eta range: μ+ μ31

32 Results : 2011A Results for 2011A dataset 32

33 Results : 2011A Results for 2011A dataset 33

34 Comparison of + and eta sides in 2011A & 2011B Without Efficiency Correction With Efficiency Correction 2011A 2011B 34

35 Comparison of + and eta sides in 2011AB Without Efficiency Correction With Efficiency Correction 35