Measurement of associated Z + charm production in proton-proton collisions at √(s) = 8 TeV

A study of the associated production of a Z boson and a charm quark jet (Z + c), and a comparison to production with a b quark jet (Z + b), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb^-1, collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with p_T^l > 20 GeV, vertical stroke η^l vertical stroke < 2.1, 71 < m_ll < 111 GeV, and heavy flavour jets with p_T^jet > 25 GeV and vertical stroke η^jet vertical stroke < 2.5. The Z + c production cross section is measured to be σ(pp → Z + c + X)B(Z → l⁺l^-) = 8.8 ± 0.5(stat)±0.6(syst)pb. The ratio of the Z + c and Z + b production cross sections is measured to be σ(pp → Z + c + X)/σ(pp → Z + b + X) = 2.0 ± 0.2(stat)±0.2(syst). The Z + c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions. (orig.)