TOP-14-014
Determination of the top-quark mass from the mlb distribution in dileptonic ttbar events at √s = 8 TeV

Abstract

The top-quark mass is determined by exploring the distribution of the invariant mass, $m_{lb}$, of the lepton and the b-quark originating from top-quark decays. The analysed data set was recorded at the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 8 TeV, and corresponds to a luminosity of 19.7/fb. A high-purity top-quark pair event sample with one electron, one muon and two jets is selected. The observed invariant mass distribution is confronted to theory predictions using a Monte Carlo simulation and a fixed-order calculation MCFM at leading and next-to-leading-order QCD. A top-quark mass of $172.3 \pm1.3$ GeV is obtained using the prediction of the MadGraph simulation for the shape of the $m_{lb}$ distribution. This result is consistent with other measurements at the LHC and with the world average.

Public Document

The document CMS-PAS-TOP-14-014 is available here.

Results

Figure Caption
m_lb_min.png Observed $m_{lb}^{min}$ distribution as compared to the simulation using $m_t $= 172.5 GeV. The data are represented by the bullets and their uncertainties are indicated by the vertical error bars. The simulated rates for signal and different background contributions are represented by the histogtams of different styles. The corresponding ratios of observed and predicted event rates are shown in the bottom panel. Here, the filled cyan area represents the statistical uncertainties on the prediction. The total uncertainty, comprising the statistical and systematic uncertainties is indicated by the hatched areas in both top and bottom panels. The systematic uncertainty do not account for the luminosity and the background normalization.
PDF PNG
shaperate_dependence_theo.png The predicted absolute signal rates as a function of $m_{lb}^{min}$.
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shape_dependence_theo.png The predicted relative signal rates as a function of $m_{lb}^{min}$.
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shaperate_response_matrix.png The response matrix, describing the detector effects, presented as a function of generated and reconstructed $m_{lb}^{min}$.
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bins_plus_fits_nominal.png Dependence of the event yields on the top mass hypothesis. The grey (red) bands represent $N_{obs} (N_{pred})$ with the band width showing the statistical uncertainty.
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global_chi2_nominal.png The estimator as a function of $m_t$.
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shape_spread_inlay.png The normalized event yield for top-quark pair production at the LHC at =8 TeV, presented as a function of $m_{lb}^{min}$. The observed yields are shown by closed symbols, with error bars representing statistical uncertainty. For illustration, the predictions at $m_t$=178.5 GeV (red band), $m_t $=172.5 GeV (green band) and $m_t$=166.5 GeV (blue band) are also shown. The width of the bands represent the statistical uncertainties of the predictions. The inlay picture illustrates the distributions for the ”shape” fit, as a function of $m_t$.
The resulting top-quark mass value is $m_t=172.3 \pm 0.3 (stat.)^{+1.3}_{-1.3} (syst.)$ GeV.
PDF PNG
shaperate_spread_inlay.png The absolute event yield for top-quark pair production at the LHC at =8 TeV, presented as a function of $m_{lb}^{min}$. The observed yields are shown by closed symbols, with error bars representing the statistical uncertainty. The predictions at $m_t$=178.5 GeV (red band), $m_t $=172.5 GeV (green band) and $m_t$=166.5 GeV (blue band) are shown. The width of the bands represent the statistical uncertainties of the predictions. The inlay picture illustrates the distributions for the ”shape+rate” fit as a function of $m_t$.
The resulting top-quark mass value is $m_t= 173.1\pm 0.2 (stat.) \pm 1.8 (syst.)$ GeV.
PDF PNG
shape_mcfm_nlo_spread_inlay.png The normalized event yield for top-quark pair production at the LHC at =8 TeV, presented as a function of $m_{lb}^{min}$. The observed yields are shown by closed symbols, with error bars representing statistical uncertainty. For illustration, the MCFM (NLO in production) predictions at $m_t$=178.5 GeV (red band), $m_t $=172.5 GeV (green band) and $m_t$=166.5 GeV (blue band) are shown. The width of the bands represent the statistical uncertainties of the predictions. The inlay picture illustrates the distributions for the ”shape” fit as a function of $m_t$.
The resulting top-quark mass value employing these MCFM predictions is $m_t= 171.4\pm 0.4 (stat.) ^{+1.0}_{-1.0} (syst.)$ GeV.
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leading_b-jet_pt.png leading_b-jet_eta.png lead_lepton_pt.png lead_lepton_eta.png seclead_lepton_pt.png seclead_lepton_eta.png
click on the figures to retrieve them in PDF format
Event distributions, shown as functions of the transverse momenta and pseudorapidities of the leading b-jet, the leading lepton, and the second leading lepton, respectively. The closed symbols denote the experimental measurement with the total uncertainty shown by the vertical error bars. The simulated rates for signal and different background contributions are represented by the histograms. The corresponding ratios of the observed and the predicted event rates are shown in the bottom panels. Here, the filled cyan areas represent statistical uncertainties on the prediction. These are combined with the systematic uncertainties into a total uncertainty, shown by the hatched areas in both top and bottom panels. The systematic uncertainties do not account for the luminosity and the background normalization.

-- AndreasMeyer - 01 Oct 2014

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf bins_plus_fits_nominal.pdf r1 manage 5.1 K 2014-09-30 - 17:49 AndreasMeyer  
PNGpng bins_plus_fits_nominal.png r1 manage 18.0 K 2014-09-30 - 17:49 AndreasMeyer  
PDFpdf global_chi2_nominal.pdf r1 manage 8.2 K 2014-09-30 - 17:49 AndreasMeyer  
PNGpng global_chi2_nominal.png r1 manage 18.3 K 2014-09-30 - 17:49 AndreasMeyer  
PDFpdf lead_lepton_eta.pdf r1 manage 9.8 K 2014-09-30 - 17:53 AndreasMeyer  
PNGpng lead_lepton_eta.png r1 manage 31.0 K 2014-09-30 - 17:53 AndreasMeyer  
PDFpdf lead_lepton_pt.pdf r1 manage 8.0 K 2014-09-30 - 17:53 AndreasMeyer  
PNGpng lead_lepton_pt.png r1 manage 29.0 K 2014-09-30 - 17:54 AndreasMeyer  
PDFpdf leading_b-jet_eta.pdf r1 manage 9.8 K 2014-09-30 - 17:54 AndreasMeyer  
PNGpng leading_b-jet_eta.png r1 manage 31.4 K 2014-09-30 - 17:54 AndreasMeyer  
PDFpdf leading_b-jet_pt.pdf r1 manage 7.7 K 2014-09-30 - 17:53 AndreasMeyer  
PNGpng leading_b-jet_pt.png r1 manage 27.1 K 2014-09-30 - 17:53 AndreasMeyer  
PDFpdf m_lb_min.pdf r1 manage 11.2 K 2014-09-30 - 17:53 AndreasMeyer  
PNGpng m_lb_min.png r1 manage 32.5 K 2014-09-30 - 17:53 AndreasMeyer  
PDFpdf seclead_lepton_eta.pdf r1 manage 9.7 K 2014-09-30 - 17:53 AndreasMeyer  
PNGpng seclead_lepton_eta.png r1 manage 31.1 K 2014-09-30 - 17:53 AndreasMeyer  
PDFpdf seclead_lepton_pt.pdf r1 manage 7.9 K 2014-09-30 - 17:51 AndreasMeyer  
PNGpng seclead_lepton_pt.png r1 manage 28.4 K 2014-09-30 - 17:51 AndreasMeyer  
PDFpdf shape_dependence_theo.pdf r1 manage 13.3 K 2014-09-30 - 17:51 AndreasMeyer  
PNGpng shape_dependence_theo.png r1 manage 46.1 K 2014-09-30 - 17:51 AndreasMeyer  
PDFpdf shape_mcfm_nlo_spread_inlay.pdf r1 manage 59.8 K 2014-09-30 - 17:51 AndreasMeyer  
PNGpng shape_mcfm_nlo_spread_inlay.png r1 manage 39.6 K 2014-09-30 - 17:51 AndreasMeyer  
PDFpdf shape_spread_inlay.pdf r1 manage 60.2 K 2014-09-30 - 17:49 AndreasMeyer  
PNGpng shape_spread_inlay.png r1 manage 39.6 K 2014-09-30 - 17:49 AndreasMeyer  
PDFpdf shaperate_dependence_theo.pdf r1 manage 13.3 K 2014-09-30 - 17:49 AndreasMeyer  
PNGpng shaperate_dependence_theo.png r1 manage 45.9 K 2014-09-30 - 17:49 AndreasMeyer  
PDFpdf shaperate_response_matrix.pdf r1 manage 12.8 K 2014-09-30 - 17:49 AndreasMeyer  
PNGpng shaperate_response_matrix.png r1 manage 36.8 K 2014-09-30 - 17:49 AndreasMeyer  
PDFpdf shaperate_spread_inlay.pdf r1 manage 57.2 K 2014-10-13 - 11:08 AndreasMeyer  
PNGpng shaperate_spread_inlay.png r1 manage 37.2 K 2014-10-13 - 11:08 AndreasMeyer  
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