Measurement of the top-quark mass in the fully hadronic decay channel from ATLAS data at $\sqrt{s}=7$ TeV

TL;DR

This paper measures the top-quark mass using fully hadronic decay channels in ATLAS data at 7 TeV, employing a novel ratio method to reduce jet energy uncertainties and achieve precise results.

Contribution

It introduces a template fit method based on the ratio of three-jet to dijet masses, minimizing jet energy measurement uncertainties in top-quark mass determination.

Findings

Measured top-quark mass: 175.1 GeV

Statistical uncertainty: 1.4 GeV

Systematic uncertainty: 1.2 GeV

Abstract

The mass of the top quark is measured in a data set corresponding to 4.6 fb$^{-1}$ of proton-proton collisions with centre-of-mass energy $\sqrt{s}=7$ TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top-antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijetproduction is modelled with data-driven methods that utilise the number of identified $b$-quark jets and the transverse momentum of the sixth leading jet,which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay. Using these three jets the dijet mass is obtained from the two jets produced in the $W$ boson decay. The top-quark mass obtained from this fit is thus less sensitive to the uncertainty in the energy measurement of the jets. A binned likelihood fit yields a top-quark mass of $m_{t} = 175.1 \pm 1.4$ (stat) $\pm 1.2$ (syst) GeV.