TOP-14-001
Measurement of the top-quark mass in ttbar events with lepton+jets final states in pp collisions at √s =8 TeV

Abstract

The mass of the top quark is measured using a sample of ttbar candidate events with one electron or muon and at least four jets in the final state, collected by CMS in pp collisions at √s=8 TeV at the LHC. The candidate events are selected from data corresponding to an integrated luminosity of 19.7/fb. For each event the mass is reconstructed from a kinematic fit of the decay products to a ttbar hypothesis. The top-quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the known mass of the W boson in qqbar decays. Studies of their kinematic dependence are performed to confirm that the data is well modeled in the simulation. The top-quark mass is measured to be 172.04 0.19 (stat.+JSF) 0.75 (syst.) GeV. The combination with previously published measurements by CMS yields a mass of 172.22 0.73 GeV.

Public Document

The document CMS-PAS-TOP-14-001 published on the CERN document server can be found here.

Result

resulttext.png

Figure Caption
Run2012_mass_vs_JES.png The 2D likelihood (-2 Δ L )) measured for the l+jets final state. The ellipses correspond to statistical uncertainties on m_top and JSF of one, two, and three standard deviations.
cError.png The statistical uncertainty distribution obtained from pseudo-experiments is compared to the uncertainty of the measurement in data.

Combination with previous CMS measurements

topmass_cms.png

Figures

W boson and top quark mass before and after the kinematic fit and final selection step

Figure Caption
lepton_BaselinePerm_hDrecoW1Mass_Ratio.png Reconstructed mass of the W bosons decaying to qqbar pairs prior to the kinematic fitting to the ttbar hypothesis. The number of permutations in simulation is normalized to the number observed in data.
lepton_BaselinePerm_hDrecoTop1Mass_Ratio.png Reconstructed mass of the corresponding top quarks, prior to the kinematic fitting to the ttbar hypothesis. The number of permutations in simulation is normalized to the number observed in data.
lepton_hDrecoW1Mass_Ratio.png Reconstructed mass of the W bosons decaying to qqbar pairs after the goodness-of-fit selection and the weighting by P_gof. The number of permutations in simulation is normalized to the number observed in data.
lepton_hDfitTop1Mass_Ratio.png Fitted top-quark masses after the goodness-of-fit selection and the weighting by P_gof. The number of permutations in simulation is normalized to the number observed in data.

Fit validation

Figure Caption
fit_Bias_lepton.png Mean difference between the calibrated and generated values of m_top and JSF as a function of different generated top-quark mass values and three values of JSF for combined lepton+jets events. The colored dashed lines correspond to straight line fits, the black solid line corresponds to a constant fit to all calibration points. The error bars indicate the statistical uncertainty on the mean difference for the uncalibrated likelihood.Fitted top-quark masses after the goodness-of-fit selection and the weighting by P_gof. The number of permutations in simulation is normalized to the number observed in data.
fit_Pull_lepton.png Width of the pull distributions for the combined channel after the single-channel calibration. The black solid line corresponds to a constant fit to all calibration points. Fitted top-quark masses after the goodness-of-fit selection and the weighting by P_gof. The number of permutations in simulation is normalized to the number observed in data.

Dependence of the top-quark mass measurement on event kinematics

Figure Caption
diff_DeltaRqq_Entries.png diff_DeltaRqq_JES.png diff_DeltaRqq_MT1D.png diff_DeltaRqq_MT2D.png Measurements in dependency of ΔR_qqbar: (top left) Number of permutations per ΔR_qqbar bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_TopPt_Entries.png diff_TopPt_JES.png diff_TopPt_MT1D.png diff_TopPt_MT2D.png Measurements in dependency of pT of the top: (top left) Number of permutations per top pT bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_TopEta_Entries.png diff_TopEta_JES.png diff_TopEta_MT1D.png diff_TopEta_MT2D.png Measurements in dependency of eta of the top: (top left) Number of permutations per top eta bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_HT_Entries.png diff_HT_JES.png diff_HT_MT1D.png diff_HT_MT2D.png Measurements in dependency of HT: (top left) Number of permutations per HT bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_TTBarMass_Entries.png diff_TTBarMass_JES.png diff_TTBarMass_MT1D.png diff_TTBarMass_MT2D.png Measurements in dependency of invariant mass of the ttbar pair: (top left) Number of permutations per ttbar invariant mass bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_TTBarPt_Entries.png diff_TTBarPt_JES.png diff_TTBarPt_MT1D.png diff_TTBarPt_MT2D.png Measurements in dependency of pT of the ttbar system: (top left) Number of permutations per ttbar pT bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_NJet_Entries.png diff_NJet_JES.png diff_NJet_MT1D.png diff_NJet_MT2D.png Measurements in dependency of the numbers of jets: (top left) Number of permutations per jet multiplicity bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_B1Pt_Entries.png diff_B1Pt_JES.png diff_B1Pt_MT1D.png diff_B1Pt_MT2D.png Measurements in dependency of pT of the b jet assigned to the hadronic decay branch: (top left) Number of permutations per b-jet pT bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_B1Eta_Entries.png diff_B1Eta_JES.png diff_B1Eta_MT1D.png diff_B1Eta_MT2D.png Measurements in dependency of eta of the b jet assigned to the hadronic decay branch: (top left) Number of permutations per b-jet eta bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_DeltaRbb_Entries.png diff_DeltaRbb_JES.png diff_DeltaRbb_MT1D.png diff_DeltaRbb_MT2D.png Measurements in dependency of ΔR_bbbar: (top left) Number of permutations per ΔR_bbbar bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_Q1Pt_Entries.png diff_Q1Pt_JES.png diff_Q1Pt_MT1D.png diff_Q1Pt_MT2D.png Measurements in dependency of pT of the leading light jet assigned to the hadronic decay of the W boson: (top left) Number of permutations per leading light jet pT bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_Q1Eta_Entries.png diff_Q1Eta_JES.png diff_Q1Eta_MT1D.png diff_Q1Eta_MT2D.png Measurements in dependency of eta of the leading light jet assigned to the hadronic decay of the W boson: (top left) Number of permutations per leading light jet eta bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_WPt_Entries.png diff_WPt_JES.png diff_WPt_MT1D.png diff_WPt_MT2D.png Measurements in dependency of pT of the hadronically decaying W boson: (top left) Number of permutations per W pT bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.
diff_WEta_Entries.png diff_WEta_JES.png diff_WEta_MT1D.png diff_WEta_MT2D.png Measurements in dependency of eta of the hadronically decaying W boson: (top left) Number of permutations per W eta bin; (top right) m_top from the 1D analysis; (bottom left) JSF and (bottom right) m_top from the 2D analysis, respectively. The systematic uncertainties are added in quadrature to the statistical uncertainties of the data. The hatched areas indicate the statistical uncertainty on the ttbar simulation.

Tables

Systematic uncertainties

sys. table

Dependence of the top-quark mass measurement on event kinematics

dependency table

-- AndreasMeyer - 26 Mar 2014

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Topic revision: r10 - 2014-03-27 - AndreasMeyer
 
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