Measurement of the ttbar charge asymmetry with lepton+jets events at 8 TeV

Abstract

The ttbar charge asymmetry is measured in events containing a charged lepton (electron or muon) and at least four jets, one of which is identified as originating from b-quark hadronization. The analyzed dataset corresponds to an integrated luminosity of 19.7/fb collected with the CMS detector at the LHC. An inclusive and three differential measurements of the ttbar charge asymmetry as a function of rapidity, transverse momentum, and invariant mass of the ttbar system are presented. The measured inclusive ttbar charge asymmetry is 0.005 +-0.007 (stat.) +-0.006 (syst.). This result and the three differential measurements are consistent with the predictions of the Standard Model.

Background estimation

Figure / Table Caption
Results for the numbers of events for background and ttbar contributions from fits to data, along with their statistical uncertainties. The uncertainties quoted for the single-top-quark and Z+jets backgrounds are related to the constraints used as input for the likelihood fit.
Comparison of the combined lepton+jets data with simulated contributions for MTW. The simulated signal and background contributions are normalized to the results of the fits in Table 1. Additionally the ratio of the data to the sum of the simulated contributions is shown, with the statistical uncertainties of the simulated contributions in blue (including the uncertainties of the fit results). (pdf)
Comparison of the combined lepton+jets data with simulated contributions for M3. The simulated signal and background contributions are normalized to the results of the fits in Table 1. Additionally the ratio of the data to the sum of the simulated contributions is shown, with the statistical uncertainties of the simulated contributions in blue (including the uncertainties of the fit results). (pdf)
Comparison of the combined lepton+jets data with simulated contributions for abs(Delta(y)). The simulated signal and background contributions are normalized to the results of the fits in Table 1. Additionally the ratio of the data to the sum of the simulated contributions is shown, with the statistical uncertainties of the simulated contributions in blue (including the uncertainties of the fit results).(pdf)

Measurement of the ttbar charge asymmetry

Figure / Table Caption
Background-subtracted asymmetry as a function of the reconstructed abs(y_ttbar). (pdf)
Background-subtracted asymmetry as a function of the reconstructed p_T,ttbar. (pdf)
Background-subtracted asymmetry as a function of the reconstructed m_ttbar. (pdf)
Migration matrix between the generated and the reconstructed values in Delta(abs(y)) after the event selection.(pdf)
Migration matrix between the generated and the reconstructed values in Delta(abs(y)) for the measurement differential in m_ttbar.(pdf)
Selection efficiency as a function of generated Delta(abs(y)), defined with respect to inclusive ttbar production.(pdf)
Selection efficiency as a function of generated Delta(abs(y)) for the measurement differential in m_ttbar.(pdf)

Estimation of systematic uncertainties

Figure / Table Caption
Systematic uncertainties for the inclusive measurement of A_C and ranges of systematic uncertainties for the differential measurements.

Results

Figure / Table Caption
The measured inclusive asymmetry at the different stages of the analysis and the corresponding theory prediction from the SM.
Unfolded inclusive Delta(abs(y)) distribution.(pdf)
Corrected asymmetry as a function of abs(y_ttbar). The measured values are compared to NLO calculations for the SM and to the predictions of a model featuring an effective axial-vector coupling of the gluon (EAG). The inner error bars on the differential asymmetry values indicate the statistical uncertainties while the outer error bars represent the statistical and systematic uncertainties added up in quadrature.(pdf)
Corrected asymmetry as a function of p_T,ttbar. The measured values are compared to NLO calculations for the SM. The inner error bars on the differential asymmetry values indicate the statistical uncertainties while the outer error bars represent the statistical and systematic uncertainties added up in quadrature.(pdf)
Corrected asymmetry as a function of m_ttbar. The measured values are compared to NLO calculations for the SM and to the predictions of a model featuring an effective axial-vector coupling of the gluon (EAG). The inner error bars on the differential asymmetry values indicate the statistical uncertainties while the outer error bars represent the statistical and systematic uncertainties added up in quadrature.(pdf)
Unfolded asymmetry for m_ttbar < 450 GeV and m_ttbar > 450 GeV. The measured values are compared to NLO calculations for the SM and to predictions of a model featuring an effective axial-vector coupling of the gluon (EAG). The inner error bars on the differential asymmetry values indicate the statistical uncertainties while the outer error bars represent the statistical and systematic uncertainties added up in quadrature.(pdf)

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