Combination of the CMS top-quark mass measurements from Run 1 of the LHC


A combination of eight measurements of the top-quark mass from the CMS exper- iment is presented. The combination is based on the analyses of the data recorded during 2010, 2011 and 2012 with a combined integrated luminosity of 25/fb. It uses the results from the analyses performed in the dilepton, lepton+jets and all-jets decay channels that correspond to the full datasets from each year. The combined result for the top-quark mass is 172.38 0.10 (stat.) 0.65 (syst.) GeV, which corresponds to a precision of 0.38%.

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This result supersedes the results from the previous CMS top-quark mass combination CMS PAS TOP-13-002 and the result of the combination presented in CMS PAS TOP-14-001.


The combined mass from eight input measurements (3 dilepton, 3 lepton+jets, 2 all-jets) is 172.38 +/- 0.20 (stat.) +/- 0.65 (syst.) GeV. The $\chi^2$ is 3.4 / 7 d.o.f. This corresponds to a probability of 85%.


Figure Caption
Figure_1.png Figure 1: Summary of the eight CMS mt measurements and their combination.
Figure_2a.png Figure 2 a): BLUE combination coefficients for CMS combination.
Figure_2b.png Figure 2 b): Pulls for CMS combination.
Figure_3.png Figure 3: The top-quark mass determined separately from the three decay modes.
Figure_4a.png Figure 4 a): Variation of the combined mt result as a function of variations in the correlation assumptions.
Figure_4b.png Figure 4 b): Variation of the total uncertainty as a function of variations in the correlation assumptions.


Table Caption
Table_1.png Table 1: CMS measurements of mt and their statistical and systematic uncertainties in GeV.
Table_2.png Table 2: Categorized uncertainties for the eight CMS mt measurements. All of the mass and uncertainty values are expressed in GeV. The entries labeled n/a and n/e refer to terms that were not applicable or not evaluated for the specific measurement.
Table_3.png Table 3: BLUE combination coefficients and pulls showing the contribution of each measurement to the final combination.
Table_4.png Table 4: Correlations between the input measurements. The elements in the table are labelled according to the analysis they correspond to (rows and columns read 2010, 2011, 2012 followed by the ttbar decay channel name.
Table_5.png Table 5:Nominal correlations assumed in the combination and the combined uncertainty values in GeV as a function of source. The term rho_year is the correlation factor for measurements in the same top-quark decay channel, but different years and the term rho_chan is the correlation between measurements in different channels from the same year. For the correlated terms in the combination the coefficients are set equal to sigma_i/sigma_j, where these are the uncertainties on measurements i and j, respectively (see Section 6.1). The coefficient values of unity are only used in the cross check described in Section 6.2.

-- StephenWimpenny - 01 Oct 2014

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Topic revision: r5 - 2014-10-11 - AndreasMeyer
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