CMS-TOP-17-008

CMS-TOP-17-008 ; CERN-EP-2018-310
Measurement of the top quark mass in the all-jets final state at $\sqrt{s} = $ 13 TeV and combination with the lepton+jets channel
CMS Collaboration
27 December 2018
Eur. Phys. J. C 79 (2019) 313
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. The measurement uses the $ \mathrm{t\bar{t}} $ all-jets final state. A kinematic fit is performed to reconstruct the decay of the $ \mathrm{t\bar{t}} $ system and suppress the multijet background. Using the ideogram method, the top quark mass ($ {m_{\mathrm{t}}} $) is determined, simultaneously constraining an additional jet energy scale factor (JSF). The resulting value of ${m_{\mathrm{t}}} =$ 172.34 $\pm$ 0.20 (stat+JSF) $\pm$ 0.70 (syst) GeV is in good agreement with previous measurements. In addition, a combined measurement that uses the $ \mathrm{t\bar{t}} $ lepton+jets and all-jets final states is presented, using the same mass extraction method, and provides an $ {m_{\mathrm{t}}} $ measurement of 172.26 $\pm$ 0.07 (stat+JSF) $\pm$ 0.61 (syst) GeV. This is the first combined $ {m_{\mathrm{t}}} $ extraction from the lepton+jets and all-jets channels through a single likelihood function.
Links: e-print arXiv:1812.10534 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The $ {\Delta R(\mathrm{b\bar{b}})} $ (left) and $ {P_\text {gof}} $ (right) distributions of data compared to simulated signal and the multijet background estimate. The hashed bands represent the total uncertainty in the complete prediction. The lower panels show the ratio of data and prediction.
png pdf	Figure 1-a: The $ {\Delta R(\mathrm{b\bar{b}})} $ distribution of data compared to simulated signal and the multijet background estimate. The hashed bands represent the total uncertainty in the complete prediction. The lower panel shows the ratio of data and prediction.
png pdf	Figure 1-b: The $ {P_\text {gof}} $ distribution of data compared to simulated signal and the multijet background estimate. The hashed bands represent the total uncertainty in the complete prediction. The lower panel shows the ratio of data and prediction.
png pdf	Figure 2: The fitted top quark mass (left) and reconstructed W boson mass (right) distributions of data compared to simulated signal and the multijet background estimate. The shown reconstructed W boson mass is the average mass of the two W bosons in the event. The hashed bands represent the total uncertainty in the prediction. The lower panels show the ratio of data and prediction.
png pdf	Figure 2-a: The fitted top quark mass distribution of data compared to simulated signal and the multijet background estimate. The lower panel shows the ratio of data and prediction.
png pdf	Figure 2-b: The reconstructed W boson mass distribution of data compared to simulated signal and the multijet background estimate. The shown reconstructed W boson mass is the average mass of the two W bosons in the event. The hashed bands represent the total uncertainty in the prediction. The lower panel shows the ratio of data and prediction.
png pdf	Figure 3: Difference between extracted and generated top quark masses (upper panel) and JSFs (lower panel) for different input masses and JSFs after the calibration in the all-jets channel. The values are extracted using the 2D method.
png pdf	Figure 4: Difference between extracted and generated top quark masses (upper panel) and JSFs (lower panel) for different input masses and JSFs after the single-channel calibrations for the combined measurement. The values are extracted using the 2D method.
png pdf	Figure 5: Likelihood contours for $-2\Delta \ln {\mathcal {L}} =$ 2.3, corresponding to the 68% confidence level, in the ${m_{{\mathrm {t}}}} - {\text {JSF}}$ plane (upper panel) and the likelihood profiles for the top quark mass (lower panel), where the level corresponding to one standard deviation ($\sigma $) is indicated. The hybrid measurement results for the all-jets and lepton+jets channels, as well as for the combination, are shown.

Tables
png pdf	Table 1: List of systematic uncertainties for the all-jets channel. The signs of the shifts ($\delta x = x_\text {variation} - x_\text {nominal}$) correspond to the $+1$ standard deviation variation of the systematic uncertainty source. For linear sums of the uncertainty groups, the relative signs have been considered. Shifts determined using dedicated samples for the systematic variation are displayed with the corresponding statistical uncertainty.
png pdf	Table 2: List of systematic uncertainties for the combined mass extraction. The signs of the shifts ($\delta x = x_\text {variation} - x_\text {nominal}$) correspond to the $+1$ standard deviation variation of the systematic uncertainty source. For linear sums of the uncertainty groups, the relative signs have been considered. Shifts determined using dedicated samples for the systematic variation are displayed with the corresponding statistical uncertainty.
png pdf	Table 3: Comparison of the hybrid mass uncertainties for the all-jets and lepton+jets [17] channels, as well as the combination. The signs of the shifts follow the convention of Tables 1 and 2.

Summary

A measurement of the top quark mass ($ {m_{\mathrm{t}}} $) using the all-jets final state is presented. The analyzed data set was collected by the CMS experiment in proton-proton collisions at $\sqrt{s}=$ 13 TeV that correspond to an integrated luminosity of 35.9 fb$^{-1}$ . The kinematic properties in each event are reconstructed using a constrained fit that assumes a $ \mathrm{t\bar{t}} $ hypothesis, which suppresses the dominant multijet background and improves the mass resolution.

The value of $ {m_{\mathrm{t}}} $ and an additional jet energy scale factor (JSF) are extracted using the ideogram method, which uses the likelihood of the values of $ {m_{\mathrm{t}}} $ and JSF in each event to determine these parameters. The resulting $ {m_{\mathrm{t}}} $ is measured to be 172.34 $\pm$ 0.20 (stat+JSF) $\pm$ 0.70 (syst) GeV. This is in good agreement with previous CMS results obtained at $\sqrt{s} = $ 7, 8, and 13 TeV. The modeling uncertainties are larger than in the previous measurements at lower center-of-mass energies because of the use of new alternative color reconnection models that were not previously available.

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