Measurement of associated Z + charm production in proton-proton collisions at sqrt(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 > 20 GeV, |η`| < 2.1, 71 < m`` < 111 GeV, and heavy flavour jets with p T > 25 GeV and |ηjet| < 2.5. The Z + c production cross section is measured to be σ(pp → Z + c + X)B(Z → `+`−) = 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. Submitted to the European Physical Journal C c © 2017 CERN for the benefit of the CMS Collaboration. CC-BY-4.0 license ∗See Appendix A for the list of collaboration members ar X iv :s ub m it/ 20 61 45 1 [ he pex ] 6 N ov 2 01 7

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