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We present the most recent studies of diboson production and electroweak physics in proton-proton collisions at 7 TeV and 8 TeV center-of-mass energy based on data recorded by the CMS detector at the LHC in 2011 and 2012. These include precise measurements of γγ, ZZ and WZ production. Results on triboson production of WWγ and WZγ are also presented. The results are interpreted in terms of constraints on anomalous triple or quartic gauge couplings. We also review some recent electroweak physics results, including the purely electroweak Z bosons production cross section and the muon charge asymmetry measurement. The results are compared with Standard Model prediction. Presented at LaThuile 2014 XXVIIIth Rencontres de Physique de la Vallee dAoste IL NUOVO CIMENTO Vol. ? , N. Diboson and electroweak physics at CMS A. Calderon on behalf of the CMS Collaboration Instituto de Fisica de Cantabria (IFCA), CSIC-UC, Santander, Spain Summary. — We present the most recent studies of diboson production and electroweak physics in proton-proton collisions at 7 TeV and 8 TeV center-of-mass energy based on data recorded by the CMS detector at the LHC in 2011 and 2012. These include precise measurements of γγ, ZZ and WZ production. Results on triboson production of WWγ and WZγ are also presented. The results are interpreted in terms of constraints on anomalous triple or quartic gauge couplings. We also review some recent electroweak physics results, including the purely electroweak Z bosons production cross section and the muon charge asymmetry measurement. The results are compared with Standard Model prediction. PACS 14.70. -e – . PACS 12.15. -y – . 1. – Introduction The diboson production and electroweak processes are expected to take place at the LHC and their cross sections, as well as detailed kinematic differential distributions, are precisely predicted in the framework of the Standard Model (SM). The cross section measurement provide excellent tests of the Quantum Cromodynamics (QCD) and the Electroweak (EW) sectors. Furthermore the diboson and electroweak processes are themselves sources of background to the SM Higgs searches, as well as searches for new phenomena. Moreover, the measurement of diboson production cross section and kinematics provides direct information on trilinear and quartic gauge couplings (TGC and QGC). The SM predicts precisely the possible self-interactions of gauge bosons, and any deviation would be attributable to anomalous couplings (aTGC, aQGC), indicating the presence of new physics. Theore, it is mandatory to have precise diboson and electroweak production cross section measurements as well as reliable and accurate theoretical predictions of these processes. During 2011 and 2012, the Large Hadron Collider (LHC) delivered proton-proton collisions at center-of-mass energies of 7 and 8 TeV, allowing the measurement of diboson and electroweak processes and tests of the SM up to energy scales never reached before. c © Società Italiana di Fisica 1 2 A. CALDERON ON BEHALF OF THE CMS COLLABORATION These proceedings present precise measurements of γγ, ZZ and WZ production, in association or not with a photon (ZZγ and WZγ) with the CMS detector [1]. The same measurements are also used to set upper limits on aTGC and aQGC parameters. We also review some recent electroweak physics results, including the purely electroweak production of Z bosons cross section and the muon charge asymmetry measurements. 2. – Measurement of diphoton production The measurement of the isolated diphoton production cross section in pp collisions at center of mass energies of 7 TeV and 5.0 fb−1 integrated luminosity is presented [2]. The measurement is probing a phase-space with asymmetric pT selection to enhance sensitivity to higher order diagrams: two isolated photons with transverse momentum above 40 GeV and 25 GeV respectively, in the acceptance η < 2.5, η 6∈ [1.44, 1.57] and with an angular separation ∆R > 0.45. A new data-driven method is used to extract the prompt diphoton yield in data, based on the photon component of the particleflow isolation, modified in such a way that the photon energy deposit leakage inside the isolation cone is subtracted event by event. The measured total cross section is: σdata = 16.8±0.2(stat.)±1.8(syst.)±0.4(lumi)pb in agreement with the NNLO prediction σ(2γNNLO) = 16.2 −1.3(scale)pb. The cross section is also measured differentially as a function of the diphoton invariant mass, the diphoton transverse momentum, the azimuthal angle difference between the two photons, and the cosine of the polar angle in the Collins-Soper frame of the diphoton pair. Fig. 1 shows the comparisons of the differential cross section between data and the DIPHOX + GAMMA2MC NLO and 2γNNLO predictions for the invariant mass and the ∆φγγ observables. NNLO predictions with 2γ NNLO show an improved agreement with the data for the kinematic distributions with respect to the DIPHOX + GAMMA2MC, especially in the low ∆φγγ region. It is the first time that a phase space defined by such an asymmetric pT selection is probed at hadron colliders. 3. – Measurement of ZZ production The ZZ production cross section have been measured using the high purity four lepton (ZZ→2l2l′) at center of mass energies of 8 TeV and 19.6 fb−1 integrated luminosity [3]. The branching ratio to four lepton final state is small, however this process is really clean, with negligible amount of background. Events are selected by requiring two pairs of electrons or muons, with opposite charge and same flavour. The invariant mass of each pair is compatible with the Z boson mass. The challenge in the four lepton analysis is the optimization for lepton efficiencies, especially for low pT leptons. Some leptons might fall outside the acceptance of the detector while some others may fail the criteria used to select a lepton. The measured cross section is σdata = 7.7 +0.5 −0.5(stat.) +0.5 −0.4(syst.)± 0.4(theo.) ± 0.3(lumi.)pb at √ s = 8 TeV in the four lepton channel, for both Z bosons produced in the mass region of 60 to 120 GeV. Differential cross section distributions normalized to fiducial cross sections are also measured, as shown in fig. 2, and well described by the NLO theoretical predictions. The ZZ production cross section is also measured in the 2 leptons and 2 neutrinos (ZZ→ 2l2ν) decay channel, at center of mass energies of 7 and 8 TeV. The data sample corresponds to about 5.1 fb−1 and about 19.6 fb−1 respectively, of integrated luminosity [4]. Events are selected by requiring a pair of oppositely charged, isolated electrons or muons, with invariant mass within a Z mass window and no additional leptons, other DIBOSON AND ELECTROWEAK PHYSICS AT CMS 3 0 0.5 1 1.5 2 2.5 3 ( p b /r a d )