TOP-14-002
Measurement of the top-quark mass in ttbar events with all-jets final states in pp collisions at √s =8 TeV

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. The sample is selected from data collected with the CMS detector in pp collisions at √s=8 TeV in 2012 and corresponds to an integrated luminosity of 18.2/fb. For each event, a kinematic fit of the jets to a ttbar hypothesis is performed to reconstruct W-boson and top-quark candidates. From these the top quark mass is simultaneously determined with an overall jet energy scale factor (JSF), constrained by the known mass of the W boson in qqbar decays. The top-quark mass is measured to be 172.08 0.36 (stat.+JSF) 0.83 (syst.) GeV.

Public Document

The document CMS-PAS-TOP-14-002 published on the CERN document server can be found here.

Result

top14002_result.png

Figure Caption
MJP12__v1_data_mass_vs_JES.png The 2D likelihood (-2 Δ log L ). The ellipses correspond to contours of -2 Δ log L = 1, 4, and 9 allowing the construction of the one, two, and three σ intervals of m_top.

Figures

Plots after the kinematic fit and final selection step

Figure Caption
alljets_phdPFcut_hDfitTop1MassBest_Ratio.png Reconstructed top-quark mass from the kinematic fit. The simulated ttbar signal and the background from event mixing are normalized to the data.
alljets_phdPFcut_hDrecoWAveMassBest_Ratio.png Average reconstructed W-boson mass after the final selection step. The simulated ttbar signal and the background from event mixing are normalized to the data.
alljets_phdPFcut_hDfitProbBest_Ratio.png Goodness-of-fit probability. The simulated ttbar signal and the background from event mixing are normalized to the data.
alljets_phdPFcut_hDdeltaRbbBest_Ratio.png The separation of the two b-tagged jets after all selection steps. The simulated ttbar signal and the background from event mixing are normalized to the data.

Fit validation

Figure Caption
fit_Bias_1.png Mean difference between the calibrated and generated values of m_top and JSF as a function of different generated top quark mass values and three values of JSF after the calibration. The colored dashed lines correspond to straight line fits, the black dashed line corresponds to a constant fit to all calibration points. The error bars indicate the statistical uncertainty on the mean difference for the uncalibrated likelihood.
fit_Pull_1.png Width of the pull distributions after the calibration. The black dashed line corresponds to a constant fit to all calibration points.

Tables

Systematic uncertainties

sys. table

-- HartmutStadie - 03 Jul 2014

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Topic revision: r5 - 2014-07-16 - AndreasMeyer
 
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