CMS-PAS-TOP-17-008

CMS-PAS-TOP-17-008
Measurement of the top quark mass in the all-jets final state at $\sqrt{s}= $ 13 TeV
CMS Collaboration
July 2018

Abstract: A top quark mass measurement is performed using 35.9 fb$^{-1}$ of LHC proton-proton collision data collected with the CMS detector at $\sqrt{s}= $ 13 TeV in 2016. The measurement uses the $\mathrm{t}\overline{\mathrm{t}}$ all-jets final state, which comprises a total of six jets. A kinematic fit is performed to reconstruct the decay of the $\mathrm{t}\overline{\mathrm{t}}$ system and suppress QCD multijet background. By means of the ideogram method, the top quark mass is determined, simultaneously constraining an additional jet energy scale factor (JSF). The result of 172.34 $\pm$ 0.20 (stat+JSF) $\pm$ 0.76 (syst) GeV for the top quark mass is in good agreement with previous measurements in the same and different final states.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, EPJC 79 (2019) 313. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The ${\Delta R({\mathrm {b}} {\overline {\mathrm {b}}})}$ (left) and ${P_\text {gof}}$ (right) distributions of data compared to signal simulation and the multijet background estimate. The hashed bands represent the total uncertainty of the prediction.
png pdf	Figure 1-a: The ${\Delta R({\mathrm {b}} {\overline {\mathrm {b}}})}$ (left) and ${P_\text {gof}}$ (right) distributions of data compared to signal simulation and the multijet background estimate. The hashed bands represent the total uncertainty of the prediction.
png pdf	Figure 1-b: The ${\Delta R({\mathrm {b}} {\overline {\mathrm {b}}})}$ (left) and ${P_\text {gof}}$ (right) distributions of data compared to signal simulation and the multijet background estimate. The hashed bands represent the total uncertainty of the prediction.
png pdf	Figure 2: The fitted top quark mass (left) and reconstructed W boson mass (right) distributions of data compared to signal simulation and the multijet background estimate. The shown reconstructed W boson mass is the average of both W bosons in the event. The hashed bands represent the total uncertainty of the prediction.
png pdf	Figure 2-a: The fitted top quark mass (left) and reconstructed W boson mass (right) distributions of data compared to signal simulation and the multijet background estimate. The shown reconstructed W boson mass is the average of both W bosons in the event. The hashed bands represent the total uncertainty of the prediction.
png pdf	Figure 2-b: The fitted top quark mass (left) and reconstructed W boson mass (right) distributions of data compared to signal simulation and the multijet background estimate. The shown reconstructed W boson mass is the average of both W bosons in the event. The hashed bands represent the total uncertainty of the prediction.
png pdf	Figure 3: Difference of extracted and generated top quark masses and JSFs for different input masses and JSFs after the calibration.

Tables
png pdf	Table 1: List of systematic uncertainties for the all-jets channel. The signs of the shifts correspond to the $+1$ standard deviation variation of the systematic uncertainty source. For linear sums of uncertainty groups, the relative signs have been considered.

Summary

In this study, a measurement of the top quark mass using events with at least six jets in the final state has been presented. The analyzed data was collected with the CMS experiment in pp collisions at $\sqrt{s} = $ 13 TeV. This data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ and contains 10799 candidate events after the event selection. The kinematic properties in each event are reconstructed using a constrained fit, assuming a $\mathrm{t\bar{t}}$ hypothesis, which allowed to suppress the dominant QCD multijet background and improve the mass resolution.

The top quark mass and an additional jet energy scale factor were extracted using the ideogram method, which uses the likelihood of the top quark mass and jet scale factor in each event to determine these parameters. The resulting top quark mass is measured to be 172.34 $\pm$ 0.20 (stat+JSF) $\pm$ 0.43 (CR+ERD) $\pm$ 0.63 (syst) GeV = 172.34 $\pm$ 0.20 (stat+JSF) $\pm$ 0.76 (syst) GeV. This is in good agreement with the previous CMS results at $\sqrt{s} = $ 7 and 8 TeV [8], as well as with the result in the lepton+jets channel at $\sqrt{s} = $ 13 TeV [11]. The quoted modeling uncertainties are increased with respect to previous results at lower center-of-mass energies due to the utilization of alternative color-reconnection models which have not been available previously.

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