Measurement of the tt¯ production cross section, the top quark mass, and the strong coupling constant using dilepton events in pp collisions at √s = 13 TeV

Abstract

A measurement of the top quark–antiquark pair production cross section \({\sigma }_{t\overline{t}}\) in proton–proton collisions at a centre-of-mass energy of 13 \(\phantom{\rule{0.166667em}{0ex}}\text{Te}\phantom{\rule{0.333333em}{0ex}}\) is presented. The data correspond to an integrated luminosity of \(35.9\phantom{\rule{0.166667em}{0ex}}{\text{fb}}^{-1}\), recorded by the CMS experiment at the CERN LHC in 2016. Dilepton events ( \(e\) \({}^{±}\) \(\mu \) \({}^{\mp }\), \({\mu }^{+}{\mu }^{-}\), \({e}^{+}{e}^{-}\) ) are selected and the cross section is measured from a likelihood fit. For a top quark mass parameter in the simulation of \({m}_{t}^{\mathrm{MC}}=172.5\phantom{\rule{0.166667em}{0ex}}\text{Ge}\phantom{\rule{0.333333em}{0ex}}\) the fit yields a measured cross section \({\sigma }_{t\overline{t}}=803±2\phantom{\rule{0.166667em}{0ex}}\text{(stat)}±25\phantom{\rule{0.166667em}{0ex}}\text{(syst)}±20\phantom{\rule{0.166667em}{0ex}}\text{(lumi)}\phantom{\rule{0.166667em}{0ex}}\text{pb}\), in agreement with the expectation from the standard model calculation at next-to-next-to-leading order. A simultaneous fit of the cross section and the top quark mass parameter in the powheg simulation is performed. The measured value of \({m}_{t}^{\mathrm{MC}}=172.33±0.14\phantom{\rule{0.166667em}{0ex}}\text{(stat)}{\phantom{\rule{0.166667em}{0ex}}}_{-0.72}^{+0.66}\phantom{\rule{0.166667em}{0ex}}\text{(syst)}\phantom{\rule{0.166667em}{0ex}}\text{Ge}\phantom{\rule{0.333333em}{0ex}}\) is in good agreement with previous measurements. The resulting cross section is used, together with the theoretical prediction, to determine the top quark mass and to extract a value of the strong coupling constant with different sets of parton distribution functions.