Determination of the top-quark pole mass using -jet events collected with the ATLAS experiment in 7 TeV collisions \AtlasJournalJHEP \PreprintIdNumberCERN-PH-EP-2015-100 \AtlasAbstract The normalized differential cross section for top-quark pair production in association with at least one jet is studied as a function of the inverse of the invariant mass of the -jet system. This distribution can be used for a precise determination of the top-quark mass since gluon radiation depends on the mass of the quarks. The experimental analysis is based on proton–proton collision data collected by the ATLAS detector at the LHC with a centre-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.6 fb. The selected events were identified using the lepton+jets top-quark-pair decay channel, where lepton refers to either an electron or a muon. The observed distribution is compared to a theoretical prediction at next-to-leading-order accuracy in quantum chromodynamics using the pole-mass scheme. With this method, the measured value of the top-quark pole mass, , is:
This result represents the most precise measurement of the top-quark pole mass to date.
In the Standard Model (SM) of particle physics the couplings of the top quark to other particles are fixed through the gauge structure. The only free parameters in the top-quark sector of the SM are the elements of the Cabibbo–Kobayashi–Maskawa mixing matrix and the top-quark mass. Due to its high value compared to the other quark masses, accurate knowledge of the top-quark mass is particularly relevant because it is related to the Higgs-boson and -boson masses through radiative and loop corrections. The precise determination of these quantities allows a stringent test of whether the model is consistent [Baak:2014ora, Moch:2014tta]. In addition, the precise knowledge of the top-quark mass is a crucial ingredient in recent evaluations of the stability of the electroweak vacuum [Degrassi:2012ry, Alekhin:2012py, Buttazzo:2013uya].
The top-quark mass was determined directly at the Tevatron and at the Large Hadron Collider (LHC). A combination of a subset of these measurements yields a value of [ATLAS-CONF-2014-008]. In these measurements, the top-quark mass is inferred from a kinematic reconstruction of the invariant mass of its decay products which is then calibrated to the mass definition used in the Monte Carlo (MC) simulations. These \mtdeterminations lack a clear interpretation in terms of a well-defined top-quark mass theoretical scheme as employed in quantum chromodynamics (QCD) perturbative calculations, electroweak fits or any theoretical prediction in general [Moch:2014tta, ATLAS-CONF-2014-008, ahoang08, GmpLHC:2011bbs, ahoang14]. The values extracted using these methods are usually identified with the top-quark pole mass \mtPole, but present studies estimate differences between the two top-quark mass definitions of (1) GeV [Moch:2014tta, ATLAS-CONF-2014-008, ahoang08, GmpLHC:2011bbs, ahoang14].
The top-quark mass can also be measured from the inclusive cross section for top-quark pair (\ttbar) production [Langenfeld:2009wd]. With this method the top-quark mass scheme is unambiguously defined in the theoretical calculations. However, top-quark mass determinations based on cross-section measurements are less precise, in their current form, than the other techniques based on kinematic reconstruction. This is due to a relatively weak sensitivity of the inclusive top-quark pair production cross section to the top-quark mass, as well as to the large uncertainties on the factorization and renormalization scales and the proton parton distribution function (PDF). To date, the most precise measurement of this type is based on the 7 TeV and 8 TeV data samples collected by the ATLAS experiment during the years 2011 and 2012, which yields GeV [Aad:2014kva]. The results from the CMS experiment using this technique only include data collected during 2011 [Chatrchyan:2013haa, Chatrchyan:2013haaCor].
In this paper the method described in LABEL:Alioli:2013mxa is followed. The top-quark mass is extracted from a measurement of the normalized differential cross section for \ttbarproduction with at least one additional jet, \ttbaronejet, as a function of the inverse of the invariant mass of the \ttbaronejetsystem, . This distribution is sensitive to the top-quark mass because the amount of gluon radiation depends on its value, with large effects in the phase-space region relatively close to the \ttbaronejetproduction threshold. This method combines the rigorous interpretation of the mass inferred from the inclusive cross section with the advantage of a greater sensitivity.
The measurement is performed using 7 TeV proton–proton collision data collected by the ATLAS experiment [Aad:2008zzm], corresponding to an integrated luminosity of 4.6