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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 jet T > 25 GeV and |η jet | < 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. IntroductionThe CERN Large Hadron Collider (LHC) has delivered a large sample of pp collisions containing events with a vector boson (V) accompanied by one or more jets (V+jets). Some of these events involve the production of a vector boson in association with jets originating from heavy flavour (HF) quarks and can be used to study specific predictions of the standard model (SM).These V+jets events constitute an important background to many ongoing searches for new physics beyond the SM. A e-mail: cms-publication-committee-chair@cern.ch proper characterization of these processes and validation of their theoretical description is important to provide a reliable estimate of their specific backgrounds to the various searches. For example, third-generation scalar quarks (squarks) that are predicted by supersymmetric theories to decay via charm quarks have been searched for in final states with a charm quark jet (c jet) and a large transverse momentum imbalance [1][2][3]. A dominant background to this process is the associated production of a c jet and a Z boson that decays invisibly into neutrinos. An improved description of this background can be obtained from a measurement of the same process with the Z boson decaying into charged leptons.Similarly, the associated production of a Z boson and HF jets is a significant background to the production of the Higgs boson in association with a Z boson (pp → Z+H+X ; H → qq). Experimental studies of this process in the context of the SM focus on an analysis with b quarks in the final state [4][5][6][7], although some models beyond the SM also predict enhanced decay rates in the cc final state [8]. In either case, it is important to understand the relative contribution of the different flavours to the Z+HF jets background to minimize the...

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