on CMS information server CMS CR-2018 / 250 The Compact Muon Solenoid Experiment

The associated production of vector bosons, W or Z, and jets originating from heavy-flavour quarks is a large background source in measurements of several standard model processes, Higgs boson studies, and many searches for physics beyond the SM. The study of events with one or two well-identified and isolated leptons accompanied by heavy-flavour jets is crucial to refine the theoretical calculations in perturbative QCD, as well as to validate associated Monte Carlo techniques. Using the LHC protonproton collision data at centre-of-mass energies of 8 and 13 TeV collected by the CMS detector, Wbb, Zb(b), W+c, and Z+c cross sections are measured. Fiducial differential cross sections are measured as a function of several kinematic observables. The study of the associated production of a vector boson with jets from a c-quark is specially interesting to improve the treatment of heavy quarks in PDF-related studies. The production of a W boson associated with a c-quark allows probing and constraining the strange quark content of the proton. The associated production of a Z boson and c-quark jets may give insight into the existence of an intrinsic charm quark component inside the proton. Presented at ICHEP2018 39th International Conference on High Energy Physics Vector boson plus heavy flavor jets and constraints to PDFs J. P. Fernández∗† CIEMAT E-mail: juanpablo.fernandez@ciemat.es Measurements of the associated production of vector bosons, W or Z (decaying to one or two leptons), and jets originating from heavy-flavour quarks are reported using data corresponding to integrated luminosities of 19.7 (35.7) fb−1, at centre-of-mass energies of 8 (13) TeV collected by the CMS detector at the CERN LHC. Total and differential cross sections as a function of several kinematic observables are measured and compared with several theoretical predictions. The production of a Z boson associated with a c-quark allows probing and constraining the charm quark content of the proton and may give insight into the existence of an intrinsic charm quark component inside the proton. The production of a W boson associated with a c-quark allows probing and constraining the strange quark content of the proton. 39th International Conference of High Energy Physics ICHEP2018, July 4-11, 2018 Seoul (Korea, Republic of) ∗Speaker. †On behalf of CMS Collaboration c © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa. it/ On behalf of CMS Collaboration J. P. Fernández 1. W+c associated production: At the LHC, W+c production is dominated by q̄g→W++ c̄ and qg→W−+ c contributions at the hard scattering level. A key property of a general qg→W+ c process is the presence in the final state of a charm quark and a W boson with opposite sign charges (OS). Gluon splitting processes like dū→W−+ g→W−+ cc̄ also give rise to final states with a W and a charm quark, but in this case, there is an additional charm quark with the same sign (SS) as the W boson. Most of the background processes deliver evenly OS and SS events, whereas qg→W+ c is always OS. A pure sample of c-jets can thus be obtained by statistical OS-SS subtraction. Measurements are presented of the associated production of a W boson and a charm quark (W+ c) in proton-proton collisions at a center-of-mass energy of 13 TeV [1]. The data correspond to an integrated luminosity of 35.7 fb−1. The W bosons are identified by their decays into a muon and a neutrino. The charm quark is identified by the full reconstruction of the D∗±(2010) meson in its decay D∗−(2010)→ D̄0 +π− slow→ K++π−+π − slow (+c.c.). The measurements are performed for the transverse momentum of the muon from the W boson decay greater than 26 GeV in the pseudorapidity range |ημ | < 2.4 and for transverse momentum of the charm quark greater than 5 GeV. Measurements of the associated production of a W boson and a charm quark (W+ c) are presented as total cross section, differential cross section as a function of the pseudorapidity of the muon from the W decay and the σ(pp→W++ c̄)/σ(pp→W−+ c) cross section ratio both inclusively and differentially. The total cross section of σ(pp→W+ c) = 1026±31(stat.)+76 −72(syst.) pb is obtained. The measured inclusive and differential cross sections of W+ c are compared to QCD predictions at NLO (O(α2 s )), obtained using MCFM [2] (Fig. 1 (a)). Several PDF sets are used (ABMP16nlo [3], ATLASepWZ16nnlo [4], CT14nlo [5], MMHT14nlo [6], NNPDF3.0nlo [7] and NNPDF3.1nlo [8]). Good agreement between NLO predictions and the measurements is observed, except for the prediction using ATLASepWZ16nnlo. For the cross section ratio σ(pp→ W++ c̄)/σ(pp→W−+ c), all theoretical predictions are in good agreement with the measured value. The present measurement of the W+ c production cross section is used in a QCD analysis because of its potential to access the strange quark distribution directly through the processes above. The measurements of a previous QCD analysis [9] are also included as well as earlier inclusive DIS measurements [10] and results from CMS on the lepton charge asymmetry in W production at 8 TeV [11]. The XFITTER [12] fit framework for PDF determination is used. The strange quark distribution and strangeness suppression factor obtained in the fit agree with results from neutrino-scattering experiments (Fig. 1 (b)). 2. Z+c associated production: A measurement of the production cross section of a Z boson and at least one jet originating from a c-quark (Z+ c) and the cross section ratio σ(pp→ Z+ c+X)/σ(pp→ Z+b+X) in pp collisions at a center-of-mass energy of 8 TeV is presented. [13]. The analysis is conducted with a data sample corresponding to an integrated luminosity of 19.7 fb−1.The Z-boson candidates are identified through their decay into a pair of leptons (electrons or muons). Jets originating from heavy flavour quarks are identified using semileptonic decays of cor b-flavoured hadrons and hadronic decays of charm hadrons. The measurements are restricted to: two leptons with