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 41.5fb−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¯tc¯c), bottom (t¯tb¯b), and light-flavour or gluon (t¯tLL) jets. By means of a template fitting procedure, the inclusive t¯tc¯c, t¯tb¯b, and t¯tLL cross sections are simultaneously measured, together with their ratios to the inclusive t¯t + two jets cross section. This provides measurements of the t¯tc¯c and t¯tb¯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.