Measurement of (hbox {t}{ar{hbox {t}}}) normalised multi-differential cross sections in ({ext {p}}{ext {p}} ) collisions at (sqrt{s}=13,{ext {TeV}} ) , and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

摘要

Normalised multi-differential cross sections for top quark pair ($$hbox {t}{ar{hbox {t}}}$$ ttˉ) production are measured in proton-proton collisions at a centre-of-mass energy of 13$$,{ext {TeV}}$$ TeV 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 $$35.9{,{ext {fb}}^{-1}} $$ 35.9fb-1. The double-differential $$hbox {t}{ar{hbox {t}}}$$ ttˉ cross section is measured as a function of the kinematic properties of the top quark and of the $$hbox {t}{ar{hbox {t}}}$$ ttˉ 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 $$hbox {t}{ar{hbox {t}}}$$ ttˉ 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 $$lpha _{S}$$ αS and the top quark pole mass ($$m_{{ext {t}}}^{{ext {pole}}}$$ mtpole) using several sets of parton distribution functions (PDFs). The measurement of $$m_{{ext {t}}}^{{ext {pole}}}$$ mtpole exploits the sensitivity of the $$hbox {t}{ar{hbox {t}}}$$ ttˉ invariant mass distribution to $$m_{{ext {t}}}^{{ext {pole}}}$$ mtpole near the production threshold. Furthermore, a simultaneous fit of the PDFs, $$lpha _{S}$$ αS, and $$m_{{ext {t}}}^{{ext {pole}}}$$ 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 $$lpha _{S}$$ αS and $$m_{{ext {t}}}^{{ext {pole}}}$$ mtpole. The values $$lpha _{S}(m_{{ext {Z}}}) = 0.1135{}^{+0.0021}_{-0.0017}$$ αS(mZ)=0.1135-0.0017+0.0021 and $$m_{{ext {t}}}^{{ext {pole}}} = 170.5 pm 0.8 ,{ext {GeV}} $$ 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 $$hbox {t}{ar{hbox {t}}}$$ ttˉ production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of $$m_{{ext {t}}}^{{ext {pole}}}$$ mtpole of the order of $$+1 ,{ext {GeV}} $$ +1GeV, which can be regarded as additional theoretical uncertainty in the current $$m_{{ext {t}}}^{{ext {pole}}}$$ mtpole extraction.