Measurement of t t ¯ normalised multi-differential cross sections in pp collisions at √s=13TeV , and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

Normalised multi-differential cross sections for top quark pair (t t ¯) production are measured in proton-proton collisions at a centre-of-mass energy of 13TeV using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of 35.9fb-1. The double-differential t t ¯ cross section is measured as a function of the kinematic properties of the top quark and of the t t ¯ system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the t t ¯ system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength α_S and the top quark pole mass (mtpole) using several sets of parton distribution functions (PDFs). The measurement of mtpole exploits the sensitivity of the t t ¯ invariant mass distribution to mtpole near the production threshold. Furthermore, a simultaneous fit of the PDFs, α_S, and mtpole is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of α_S and mtpole. The values αS(mZ)=0.1135-0.0017+0.0021 and mtpole=170.5±0.8GeV are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the t t ¯ production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of mtpole of the order of +1GeV, which can be regarded as additional theoretical uncertainty in the current mtpole extraction.