Abstract
A precise measurement of the top quark mass, a fundamental parameter of the Standard Model, is among the most important goals of top quark studies at the Large Hadron Collider. Apart from the standard methods, numerous new observables and reconstruction techniques are employed to improve the overall precision and to provide different sensitivities to various systematic uncertainties. Recently, the normalised inverse invariant mass distribution of the toverline{t} system and the leading extra jet not coming from the top quark decays has been proposed for the ppto toverline{t}j production process, denoted as ℛ(mtpole, ρs). In this paper, a thorough study of different theoretical predictions for this observable, however, with top quark decays included, is carried out. We focus on fixed order NLO QCD calculations for the di-lepton top quark decay channel at the LHC with sqrt{s}=13 TeV. First, the impact on the extraction of mt is investigated and afterwards the associated uncertainties are quantified. In one approach we include all interferences, off-shell effects and non-resonant backgrounds. This is contrasted with a different approach with top quark decays in the narrow width approximation. In the latter case, two cases are employed: NLO QCD corrections to the ppto toverline{t}j production process with leading order decays and the more sophisticated case with QCD corrections and jet radiation present also in top quark decays. The top quark mass sensitivity of ℛ(mtpole, ρs) is investigated and compared to other observables: the invariant mass of the top anti-top pair, the minimal invariant mass of the b-jet and a charged lepton as well as the total transverse momentum of the toverline{t}j system. Once top quark decays are included the invariant mass of the toverline{t} system shows better sensitivity to the top quark mass extraction and smaller dependence on the off-shell effects and non-resonant contributions of the top quark and the W gauge boson than the ℛ(mtpole, ρs) observable.
Highlights
To theoretical predictions generated with different top quark masses
Even though the definition and implementation of the top quark mass in NLO+parton shower (PS) Monte Carlo (MC) tools is based on the on-shell renormalisation scheme of mt at one loop and it is identical to what is used in parton-level calculations, above mentioned effects play an important role as they enter in the relation between mt and physical observables
We start with the R(mpt ole, ρs) observable defined as normalised differential distribution of the tt+ 1 jet cross section with respect to the inverse invariant mass of the final state, Mttj, that can be written in the following form
Summary
Numerical results with complete top quark and W gauge boson off-shell effects and nonresonant backgrounds included, which are the basis for our top quark mass extraction. Where, in the total decay rates for the W and Z gauge bosons, the NLO QCD corrections to W → f1f2 and Z → f fhave been included Further electroweak parameters such as the electroweak coupling and the weak mixing angle are computed in the so called Gμ scheme with the Fermi constant Gμ = 1.16637 · 10−5 GeV−2 through the following formulae. Where ΓNt LO refers to the top quark width with W gauge boson off-shell effects included and ΓNtWLO to the top quark width with an on-shell W gauge boson as used in the NWA [39, 40] Both values are derived for massless b quarks since all leptons and u, d, c, s, b partons are considered to be massless.
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