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

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 multijet production 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 of a top-quark decay. Using these three jets the dijet mass is obtained from the two jets of 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.