Measurement of the mass difference between top and antitop quarks

Abstract

The invariance of the standard model under the CPT transformation predicts equality of particle and antiparticle masses. This prediction is tested by measuring the mass difference between the top and the antitop quark (∆mt = m_t − m_tbar ), using events with a muon or an electron and at least four jets in the final state. The analysis is based on data collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 18.92 0.76 fb−1 , and yields a value of ∆mt = −272 196 (stat.) 122 (syst.) MeV that is consistent with the standard model prediction. The accuracy of this result is significantly higher than that of existing measurements.

Some further explanation about the analysis

The ttbar events where one W boson decays hadronically (t → bW+ → bqq , or its charge conjugate), and the other W decays leptonically (t → bW+ → b + ν , or its charge conjugate), where the lepton is a muon or an electron. The data are split into − and + samples that contain, respectively, three-jet decays of the associated top or antitop quarks. For each event category, the Ideogram likelihood method is used to measure the mass of the top quark (m_t) or antitop quark (m_tbar), from which a measurement of the difference, ∆mt ≡ m_t − m_tbar, is obtained.

This analysis reports an updated measurement of this quantity with the same techniques as in the 7 TeV analysis, but with significantly reduced uncertainties.

Approved Results from TOP-12-031

Result Abbreviated Caption
finalResult.png Main top mass difference result.

Approved Data/MC comparison plots from TOP-12-031 (click on plot to get .pdf)

Figure lepton^{+}+jets Figure lepton^{-}+jets Abbreviated Caption
Transverse Momentum of the four leading jets after applying the event selection.
Fitted top-quark mass of the jet combination with the lowest chisquare.
Minimum chi^2 of the kinematic fit, for the jet combination with the lowest chi^2.

Other Approved plots from TOP-12-031 (click on plot to get .pdf)

Figure Abbreviated Caption
Width of the pull distribution as a function of the generated top quark mass, for inclusive lepton+jets events.
Bias on the estimated top quark mass as a function of the generated top quark mass, for inclusive lepton+jets events.
Bias on the estimated top quark mass as a function of the generated top quark mass after inclusive lepton+jets calibration, for lepton^{+}+jets events.
Bias on the estimated top quark mass as a function of the generated top quark mass after inclusive lepton+jets calibration, for lepton^{-}+jets events.
Width of the pull distribution as a function of the generated top quark mass after inclusive lepton+jets calibration, for lepton^{+}+jets events.
Width of the pull distribution as a function of the generated top quark mass after inclusive lepton+jets calibration, for lepton^{-}+jets events.

Tables from TOP-12-031

Result Abbreviated Caption
dataMcTable.png Event yields in data and MC simulation for the various contributing processes after all selection steps.
systematics.png Overview of the systematic uncertainties. For each contribution the larger of the estimated shift or its statistical uncertainty is taken, as indicated by the bold script.

-- StijnBlyweert - 11-Mar-2013

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf AllJets_pt_leptonMinus_StackAreaNormLogY.pdf r1 manage 24.6 K 2013-03-11 - 10:43 StijnBlyweert  
PNGpng AllJets_pt_leptonMinus_StackAreaNormLogY.png r1 manage 39.9 K 2013-03-11 - 10:43 StijnBlyweert  
PDFpdf AllJets_pt_leptonPlus_StackAreaNormLogY.pdf r1 manage 24.5 K 2013-03-11 - 10:43 StijnBlyweert  
PNGpng AllJets_pt_leptonPlus_StackAreaNormLogY.png r1 manage 39.3 K 2013-03-11 - 10:43 StijnBlyweert  
PDFpdf MinChi2ndf_Fit_leptonMinus_StackAreaNormLogY.pdf r1 manage 23.6 K 2013-03-11 - 10:43 StijnBlyweert  
PNGpng MinChi2ndf_Fit_leptonMinus_StackAreaNormLogY.png r1 manage 33.4 K 2013-03-11 - 10:43 StijnBlyweert  
PDFpdf MinChi2ndf_Fit_leptonPlus_StackAreaNormLogY.pdf r1 manage 23.5 K 2013-03-11 - 10:43 StijnBlyweert  
PNGpng MinChi2ndf_Fit_leptonPlus_StackAreaNormLogY.png r1 manage 32.8 K 2013-03-11 - 10:43 StijnBlyweert  
PDFpdf bias_all.pdf r1 manage 15.3 K 2013-03-11 - 10:32 StijnBlyweert  
PNGpng bias_all.png r1 manage 1651.1 K 2013-03-11 - 10:51 StijnBlyweert  
PDFpdf bias_minus_calibrated.pdf r1 manage 15.3 K 2013-03-11 - 10:32 StijnBlyweert  
PNGpng bias_minus_calibrated.png r1 manage 1651.1 K 2013-03-11 - 10:51 StijnBlyweert  
PDFpdf bias_plus_calibrated.pdf r1 manage 15.2 K 2013-03-11 - 10:32 StijnBlyweert  
PNGpng bias_plus_calibrated.png r1 manage 1651.1 K 2013-03-11 - 10:51 StijnBlyweert  
PNGpng dataMcTable.png r1 manage 2293.1 K 2013-03-11 - 11:06 StijnBlyweert  
PNGpng finalResult.png r1 manage 247.4 K 2013-03-11 - 10:32 StijnBlyweert  
PDFpdf mTop_Fit_leptonMinus_StackAreaNorm.pdf r1 manage 22.7 K 2013-03-11 - 10:44 StijnBlyweert  
PNGpng mTop_Fit_leptonMinus_StackAreaNorm.png r1 manage 42.9 K 2013-03-11 - 10:44 StijnBlyweert  
PDFpdf mTop_Fit_leptonPlus_StackAreaNorm.pdf r1 manage 22.7 K 2013-03-11 - 10:43 StijnBlyweert  
PNGpng mTop_Fit_leptonPlus_StackAreaNorm.png r1 manage 42.9 K 2013-03-11 - 10:43 StijnBlyweert  
PDFpdf pull_all.pdf r1 manage 15.3 K 2013-03-11 - 10:32 StijnBlyweert  
PNGpng pull_all.png r1 manage 1651.1 K 2013-03-11 - 10:51 StijnBlyweert  
PDFpdf pull_minus_calibrated.pdf r1 manage 15.4 K 2013-03-11 - 10:32 StijnBlyweert  
PNGpng pull_minus_calibrated.png r1 manage 1651.1 K 2013-03-11 - 10:51 StijnBlyweert  
PDFpdf pull_plus_calibrated.pdf r1 manage 15.3 K 2013-03-11 - 10:32 StijnBlyweert  
PNGpng pull_plus_calibrated.png r1 manage 1651.1 K 2013-03-11 - 10:51 StijnBlyweert  
PNGpng systematics.png r1 manage 2864.1 K 2013-03-11 - 11:06 StijnBlyweert  
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Topic revision: r2 - 2013-03-11 - RobertoTenchini
 
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