TOP-15-002: Measurement of the top-quark mass from b-jet energy spectrum

Abstract

The top-quark mass is measured using the peak position of the energy distribution of b jets produced from top-quark decays. The analysis is based on a recent theoretical proposal. The measurement is carried out selecting ttbar events with one electron and one muon in the final state in proton-proton collision data at √s = 8 TeV, corresponding to an integrated luminosity of 19.7 fb-1. The fitted peak position of the observed energy distribution is calibrated using simulated events and translated to a top-quark mass measurement using relativistic kinematics, with the result mtop = 172.29 1.17 (stat.) 2.66 (syst.) GeV.

Public Document

The CMS Physics Analysis Summary is available on CDS.

Figures

Eb_emu_rec_log.png

Figure 1: Logarithmic energy distribution of b-tagged jets in the 2012 dataset in events with one or two b-tagged jets. Simulated events are normalized to the prediction.

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Eb_ttbar_fit.png

Figure 2: Fitted log(E) distribution in the whole simulated sample of $t\bar{t}$ events with a mass hypothesis of 172.5 GeV. The Gaussian fit yields a log(E) peak position of 4.199 ± 0.002, corresponding to an uncalibrated value of mtop= 171.01 ± 0.25 GeV.

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Ereco_cal.png

Figure 3a: Measurement and calibration test on pseudo-experiments: calibration curve. The blue line shows the calibration curve that we would expect to fit without bias effects in the measured energy peak position.

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Emeasured_cal.png

Figure 3b: Measurement and calibration test on pseudo-experiments: distribution of calibrated energy peak position.

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Pull_fit.png

Figure 3c: Measurement and calibration test on pseudo-experiments: pull distribution.

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systematics.png

Figure 4: Comparison of nominal and dominant systematics variation shapes with data. The templates are normalized to the event yields in the data. The background contributions are included.

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data_fit.png

Figure 5a: Fitted log(E) distribution in data. The calibrated mass measurement yields a value of mtop = 172.29 ± 1.17(stat.) ± 2.66 (syst.) GeV.

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Uncertainty.png

Figure 5b: Calibrated statistical uncertainty on the energy peak position in pseudo-experiments (the arrow indicates the value measured in data).

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topmass_cms.png

Figure 6: Comparison between the mt measurement presented in this note and measurements at the CERN LHC and Fermilab Tevatron. In this comparison are considered the 2014 world combination (arXiv:1403.4427), the CMS Run 1 mt measurements and their combinations (arXiv:1509.04044), and the 2014 Tevatron combination (arXiv:1407.2682)

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Tables

Table1.png

Table 1. Observed and predicted event yields for events with 1 or 2 b-tagged jets. Statistical uncertainties are quoted.

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Table2.png

Table 2. Sources of systematic uncertainties and their contributions to the total uncertainty. The bJES estimated uncertainty covers uncertainties related to b-quark fragmentation.

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-- AndreasMeyer - 2015-08-27

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Eb_emu_rec_log.pdf r1 manage 25.9 K 2015-09-16 - 10:47 PedroSilva  
PNGpng Eb_emu_rec_log.png r2 r1 manage 66.7 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Eb_ttbar.pdf r1 manage 18.3 K 2015-09-16 - 10:47 PedroSilva  
PDFpdf Eb_ttbar_fit.pdf r1 manage 18.3 K 2015-09-11 - 19:25 DanielGuerrero  
PNGpng Eb_ttbar_fit.png r2 r1 manage 68.8 K 2015-09-16 - 10:57 PedroSilva  
PDFpdf Emeasured_cal.pdf r2 r1 manage 15.6 K 2015-09-16 - 10:47 PedroSilva  
PNGpng Emeasured_cal.png r2 r1 manage 60.0 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Ereco_back_mar_nocal.pdf r1 manage 15.6 K 2015-09-16 - 10:47 PedroSilva  
PDFpdf Ereco_cal.pdf r1 manage 15.6 K 2015-09-11 - 19:33 DanielGuerrero  
PNGpng Ereco_cal.png r2 r1 manage 59.6 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Pull_fit.pdf r2 r1 manage 15.5 K 2015-09-16 - 10:47 PedroSilva  
PNGpng Pull_fit.png r2 r1 manage 51.6 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Table1.pdf r1 manage 30.5 K 2015-09-11 - 10:23 DanielGuerrero  
PNGpng Table1.png r2 r1 manage 58.3 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Table2.pdf r1 manage 76.2 K 2015-09-11 - 10:23 DanielGuerrero  
PNGpng Table2.png r2 r1 manage 180.5 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Uncertainty.pdf r1 manage 14.8 K 2015-09-11 - 08:40 DanielGuerrero  
PNGpng Uncertainty.png r2 r1 manage 50.0 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf Uncertainty_fit.pdf r1 manage 14.8 K 2015-09-16 - 10:47 PedroSilva  
PDFpdf data_fit.pdf r2 r1 manage 19.2 K 2015-09-16 - 10:47 PedroSilva  
PNGpng data_fit.png r2 r1 manage 70.3 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf divide.pdf r1 manage 24.5 K 2015-09-16 - 10:47 PedroSilva  
PDFpdf systematics.pdf r2 r1 manage 24.5 K 2015-09-16 - 10:47 PedroSilva  
PNGpng systematics.png r2 r1 manage 68.8 K 2015-09-16 - 10:38 PedroSilva  
PDFpdf topmass_cms.pdf r1 manage 14.5 K 2015-09-16 - 10:47 PedroSilva  
PNGpng topmass_cms.png r1 manage 128.9 K 2015-09-16 - 10:54 PedroSilva  
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Topic revision: r14 - 2015-09-16 - PedroSilva
 
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