First measurement of the cross section for top quark pair production with additional charm jets using dileptonic final states in pp collisions at √{ s } = 13TeV

Abstract The first measurement of the inclusive cross section for top quark pairs ( t t ‾ ) produced in association with two additional charm jets is presented. The analysis uses the dileptonic final states of t t ‾ events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 41.5 fb − 1 , recorded by the CMS experiment at the LHC. A new charm jet identification algorithm provides input to a neural network that is trained to distinguish among t t ‾ events with two additional charm ( t t ‾ c c ‾ ), bottom ( t t ‾ b b ‾ ), and light-flavour or gluon ( t t ‾ LL ) jets. By means of a template fitting procedure, the inclusive t t ‾ c c ‾ , t t ‾ b b ‾ , and t t ‾ LL cross sections are simultaneously measured, together with their ratios to the inclusive t t ‾ + two jets cross section. This provides measurements of the t t ‾ c c ‾ and t t ‾ b b ‾ cross sections of 10.1 ± 1.2 (stat) ± 1.4 (syst) pb and 4.54 ± 0.35 (stat) ± 0.56 (syst) pb , respectively, in the full phase space. The results are compared and found to be consistent with predictions from two different matrix element generators with next-to-leading order accuracy in quantum chromodynamics, interfaced with a parton shower simulation.