Measurement of the top quark mass with the template method in the top antitop -> lepton + jets channel using ATLAS data

TL;DR

The paper presents a direct measurement of the top-quark mass $m_{ m top}$ with the template method in $t\bar{t}$ events decaying to lepton+jets, using ATLAS data at $\sqrt{s}=7$ TeV and $1.04~\text{fb}^{-1}$. It introduces two estimators: a 1d approach based on the mass ratio $R_{32}$ and a 2d approach that simultaneously fits $m_{ m top}$ and the JSF, both applied to $e+$jets and $\mu+$jets channels. Systematics, notably JES, $b$-jet energy scale, and ISR/FSR, dominate the total uncertainty; the analyses employ pseudo-experiments and in-situ calibrations to mitigate these effects. The final ATLAS result from the 2d-analysis is $m_{ m top}=174.5\pm0.6_{stat}\pm2.3_{syst}$ GeV, demonstrating consistency with Tevatron measurements while highlighting the ongoing challenge of systematic control in precision top-quark mass determinations.

Abstract

The top quark mass has been measured using the template method in the top antitop -> lepton + jets channel based on data recorded in 2011 with the ATLAS detector at the LHC. The data were taken at a proton-proton centre-of-mass energy of sqrt(s) = 7 TeV and correspond to an integrated luminosity of 1.04/fb. The analyses in the electron + jets and muon + jets decay channels yield consistent results. The top quark mass is measured to be m_top = 174.5 +/- 0.6_stat +/- 2.3_syst GeV.

Figures (10)

• Figure 1: Distributions for the selected events of the common event selection in the $e\hbox{+jets}$ channel on the left and the $\mu\hbox{+jets}$ channel on the right. Shown are (a, b) the measured jet multiplicities, (c, d) the $p_{\mathrm{T}}$, and (e, f) the $\eta$ distributions of all selected jets. The hatched area is the total uncertainty on the prediction described in the text. In (c, d) the rightmost bin also contains the overflow.
• Figure 2: $\hbox{1d-analysis}$: Performance of the likelihood fit in the $e\hbox{+jets}$ channel. Shown in (a) are the predicted $\ln\,L$ distributions for various jet permutations in the $t\bar{t}$ signal Monte Carlo. The figures (b, c) compare two output variables of the likelihood fit as observed in the data with their respective prediction. These are (b) the $\ln\,L$ value, and (c) the $p_{\mathrm{T}}$ of the $b\hbox{-jet}$ associated to the hadronic decay of the top quark.
• Figure 3: $\hbox{1d-analysis}$: The reconstructed $R_{\mathrm{32}}$ constructed from the selected jet permutation using the unconstrained four-vectors of the jet triplet for (a) the $e\hbox{+jets}$ channel, and (b) the $\mu\hbox{+jets}$ channel. The rightmost bins also contain the overflow.
• Figure 4: $\hbox{1d-analysis}$: Template parameterisations for (a) signal and (b) background contributions in the $e\hbox{+jets}$ channel. The background fit is labelled $P_{\mathrm{bkg}}$.
• Figure 5: $\hbox{2d-analysis}$: Reconstructed $W$ boson and top quark masses, $m_{\mathrm{W}}^{\mathrm{reco}}$ and $m_{\mathrm{top}}\xspace^{\mathrm{reco}}$, observed in the data together with the signal and background predictions. Shown are (a, c) the $e\hbox{+jets}$ channel, and (b, d) the $\mu\hbox{+jets}$ channel.