TOP-11-017
Measurement of the top-quark mass in all-jets final states

Abstract

The mass of the top quark is measured using a sample of ttbar candidate events with at least six jets in the final state, collected by CMS in pp collisions at √s = 7 TeV. From data collected in 2011 using dedicated high level triggers and corresponding to an integrated luminosity of 3.54/fb, 2418 candidate events are selected. From the kinematic configuration, the top-quark mass is measured to be 173.5 0.7 (stat.) 1.3 (syst.) GeV.

Public Document

The document CMS-PAS-TOP-11-017 published on the CERN document server can be found here.

Result

resulttext.png

Figures

Kinematic distributions after event selection and kinematic fit

Figure Caption
canv_MT2_data.png Reconstructed top-quark mass from the kinematic fit after all selection steps. The simulated ttbar signal and the modeled background from event mixing are normalized to data. The uncertainty band indicates the uncertainty from the signal fraction f_sig. The top-quark mass assumed in the simulation is 172.5 GeV. [Get pdf version]
canv_MW2_data.png Average reconstructed W-boson mass after all selection steps. The simulated ttbar signal and the modeled background from event mixing are normalized to data. The uncertainty band indicates the uncertainty from the signal fraction f_sig. The top-quark mass assumed in the simulation is 172.5 GeV. [Get pdf version]
canv_Pr2_data.png Goodness-of-fit probability after all selection steps. The simulated ttbar signal and the modeled background from event mixing are normalized to data. The uncertainty band indicates the uncertainty from the signal fraction f_sig. The top-quark mass assumed in the simulation is 172.5 GeV. [Get pdf version]
canv_DR2_data.png Distance between the two b-tagged jets after all selection steps. The simulated ttbar signal and the modeled background from event mixing are normalized to data. The uncertainty band indicates the uncertainty from the signal fraction f_sig. The top-quark mass assumed in the simulation is 172.5 GeV. [Get pdf version]

Probality density functions and fit calibration

Figure Caption
funcFamily_mass_0_1.png Distributions of the top-quark mass from the kinematic fit of correct permutations for different generated top masses with JES=1, fitted with a Breit-Wigner function convoluted with Gaussian resolution. [Get pdf version]
funcFamily_mass_0_4.png Distributions of the top-quark mass from the kinematic fit of wrong permutations for different generated top masses with JES=1, fitted with the sum of a Landau function and a Gaussian function with a common mean. [Get pdf version]
funcFamily_mass_0_5.png Distributions of the top-quark mass from the kinematic fit of unmatched permutations for different generated top masses with JES=1, fitted with the sum of a Landau function and a Gaussian function with a common mean. [Get pdf version]
funcFamily_jes_0_1.png Distributions of the top-quark mass from the kinematic fit of correct permutations for different JES with m_t,gen=172.5 GeV, fitted with a Breit-Wigner function convoluted with Gaussian resolution. [Get pdf version]
funcFamily_jes_0_4.png Distributions of the top-quark mass from the kinematic fit of wrong permutations for different JES with m_t,gen=172.5 GeV, fitted with the sum of a Landau function and a Gaussian function with a common mean. [Get pdf version]
funcFamily_jes_0_5.png Distributions of the top-quark mass from the kinematic fit of unmatched permutations for different JES with m_t,gen=172.5 GeV, fitted with the sum of a Landau function and a Gaussian function with a common mean. [Get pdf version]
funcFamily_jes_1_1.png Distributions of the average reconstructed W-boson mass of correct permutations for different JES with m_t,gen=172.5 GeV, fitted with an asymmetric Gaussian function. [Get pdf version]
funcFamily_jes_1_4.png Distributions of the average reconstructed W-boson mass of wrong permutations for different JES with m_t,gen=172.5 GeV, fitted with an asymmetric Gaussian function. [Get pdf version]
funcFamily_jes_1_5.png Distributions of the average reconstructed W-boson mass of unmatched permutations for different JES with m_t,gen=172.5 GeV, fitted with an asymmetric Gaussian function. [Get pdf version]
fit_Bias_0.png Difference between the extracted top-quark mass m_t,extr and the generated top-quark mass m_t,gen and between the extracted and generated values of JES before calibration for different generated top-quark masses and three different JES values. The colored dashed lines correspond to fits to first order polynomials which are used to correct the final likelihoods. The black dashed line corresponds to a linear fit to all calibration points.[Get pdf version]
fit_Bias_2.png Difference between the calibrated top-quark mass m_t,cal and the generated top-quark mass m_t,gen and between the calibrated and generated values of JES for different generated top-quark masses and three different JES values. The colored and the black dashed lines correspond to linear fits to all calibration points.[Get pdf version]
fit_Pull_2.png Width of the pull distribution for the calibrated top-quark mass and for the calibrated JES for different generated top-quark masses and three different JES values. The black dashed line corresponds to a constant fit to all calibration points [Get pdf version]

Result (1-D analysis)

Figure Caption
writeFullHadTree_data_2011_0_0_1D.png The 1-D likelihood profile with the JES fixed to unity measured on 3.54/fb 2011 data. [Get pdf version]

Cross-check: Simultaneous fit of mt and JES (2-D analysis)

Figure Caption
writeFullHadTree_data_2011_0_0.png Distribution of the reconstructed top mass after the kinematic fit, for the permutation with the lowest chi^2, in the cross-check analysis. [Get pdf version].
The cross check result is mt = 174.3 1.0 (stat.+JES) 1.5 (syst.) GeV and JES = 0.991 0.008 (stat.) 0.015 (syst.).

Tables

Number of Events and the expected signal fraction after each selection step

sys. table

Overwiew of systematic uncertainties

sys. table

Additional Material

Figure Caption
canv_Pt0 Transverse momentum pT distribution of the leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt1 Transverse momentum pT distribution of the 2nd leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt2 Transverse momentum pT distribution of the 3rd leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt3 Transverse momentum pT distribution of the 4th leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt4 Transverse momentum pT distribution of the 5th leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt5 Transverse momentum pT distribution of the 6th leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt6 Transverse momentum pT distribution of the 7th leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_Pt7 Transverse momentum pT distribution of the 8th leading jet. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG
canv_BRank The rank of the b-jets is shown. The simulated ttbar signal and the modeled background from event mixing are normalized to the data. The uncertainty band indicates the uncertainty from the signal fraction fsig. The top-quark mass assumed in the simulation is 172.5 GeV. PNG

-- HartmutStadie - 10-Sep-2012

Topic attachments
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