539 research outputs found
W and Z studies at CMS
No full textWe present selected measurements done with W and Z bosons detected in the CMS detector, based on samples of events collected during 2011 at 7 TeV and 2012 at 8 TeV physics runs. In this talk, we discuss the measurements of the inclusive W and Z cross sections and the lepton charge asymmetry in the reconstructed W events decaying to a lepton and a neutrino, obtained in the electron and muon decay channels. We also report on the measurements of the differential cross section, forward-backward asymmetry and electroweak couplings of events coming from the Drell-Yan process
Associated production of heavy flavors and W, Z bosons at CMS
No full textThe mechanism of production of heavy-flavoured jets, originated by the hadronization of b or c quarks, in association with vector bosons, W or Z, in the Standard Model is of primary importance. The study of events with one or two well-identified and isolated leptons accompanied by b-jets or displaced secondary vertices is therefore crucial to refine the theoretical calculations in perturbative QCD, as well as validate associated predictions from simulation. The understanding of these processes is furthermore required by Higgs and Beyond the Standard Model searches with similar final states. Using the LHC proton-proton collision data collected at a center of mass energy of 7 TeV by the CMS detector, measurements of the W+b, W+c, Z+b and Z+B hadrons cross sections are presented, comparing experimental data with several theoretical predictions in quantum chromodynamics
Beam test evaluation of electromagnetic calorimeter modules made from proton-damaged PbWO4 crystals
No full textThe performance of electromagnetic calorimeter modules made of proton-irradiated PbWO4 crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO4 crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 1013 and 1.3× 1014 cm−2. These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb−1 and 3000 fb−1 respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL
Measurements of the production of a vector boson in association with jets in the ATLAS and CMS detectors
No full textThe production of a vector boson (V = W, Z) in association with jets is can be used for a precise test of perturbative QCD and is a dominant background process in many searches for physics beyond the Standard Model. The differential cross section measurements from CMS and ATLAS collaborations would be presented, and several theoretical predictions at leading order (LO) and next-to leading order (NLO) are compared to data, after the deconvolution of detector effects, with proton-proton collisions at a center of mass energy of 7, 8 and 13 TeV at LHC
Collider studies on jet and heavy flavour properties
No full textThe Large Hadron Collider at CERN is the world's most efficient jet factory. In this report the properties of jets will be discussed, with focus on reconstructed jets in the ATLAS, CMS and LHCb experiments. After a brief introduction of jet physics at colliders, a selection of the results on inclusive QCD jet production cross sections, jets originated from the hadronization of b quarks and top quarks final states will be shown, with special attention on the comparisons with the Monte Carlo generators predictions at the highest possible order in perturbative QCD,using proton-proton collisions data at the center of mass energy of 7, 8 and 13 TeV. Details on the measurements of the running of the strong coupling constant as well as the differential cross sections for the inclusive jet production in ATLAS and CMS are presented. An overview of the state-of-art algorithms for the b-quark tagging, following the measurement of the b-jets production in association with a Z boson in CMS and the decay of a Z boson to bottom quarks in LHCb are shown. The top quark pair production physics is then introduced, and the relative cross section measurement in forward region with LHCb is shown. Finally, predictions of the color flow between quarks are tested using angular considerations in top events in ATLAS
Phenomenological MSSM interpretation of CMS searches in pp collisions at sqrt(s) = 7 and 8 TeV
No full textSearches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at s√=7 and 8 TeV and have integrated luminosities of 5.0 fb−1 and 19.5 fb−1, respectively. A global Bayesian analysis is performed, incorporating results from a broad range of CMS supersymmetry searches, as well as constraints from other experiments. Because the pMSSM incorporates several well-motivated assumptions that reduce the 120 parameters of the MSSM to just 19 parameters defined at the electroweak scale, it is possible to assess the results of the study in a relatively straightforward way. Approximately half of the model points in a potentially accessible subspace of the pMSSM are excluded, including all pMSSM model points with a gluino mass below 500 GeV, as well as models with a squark mass less than 300 GeV. Models with chargino and neutralino masses below 200 GeV are disfavored, but no mass range of model points can be ruled out based on the analyses considered. The nonexcluded regions in the pMSSM parameter space are characterized in terms of physical processes and key observables, and implications for future searches are discussed
Measurement of the transverse momentum spectra of weak vector bosons produced in proton-proton collisions at sqrt(s) = 8 TeV
No full textThe transverse momentum spectra of weak vector bosons are measured in the CMS experiment at the LHC. The measurement uses a sample of proton-proton collisions at s√=8 TeV, collected during a special low-luminosity running that corresponds to an integrated luminosity of 18.4 ± 0.5 pb−1. The production of W bosons is studied in both electron and muon decay modes, while the production of Z bosons is studied using only the dimuon decay channel. The ratios of W− to W+ and Z to W differential cross sections are also measured. The measured differential cross sections and ratios are compared with theoretical predictions up to next-to-next leading order in QCD
Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV
No full textMultiplicity and rapidity dependence of strange hadron production in pp, pPb, and PbPb collisions at the LHC
No full textMeasurements of strange hadron (View the MathML sourceKS0, View the MathML sourceΛ+Λ ̅, and View the MathML sourceΞ−+Ξ ̅+) transverse momentum spectra in pppp, pPbpPb, and PbPb collisions are presented over a wide range of rapidity and event charged-particle multiplicity. The data were collected with the CMS detector at the CERN LHC in pppp collisions at View the MathML sources=7TeV, pPbpPb collisions at View the MathML sourcesNN=5.02TeV, and PbPb collisions at View the MathML sourcesNN=2.76TeV. The average transverse kinetic energy is found to increase with multiplicity, at a faster rate for heavier strange particle species in all systems. At similar multiplicities, the difference in average transverse kinetic energy between different particle species is observed to be larger for pppp and pPbpPb events than for PbPb events. In pPbpPb collisions, the average transverse kinetic energy is found to be slightly larger in the Pb-going direction than in the p-going direction for events with large multiplicity. The spectra are compared to models motivated by hydrodynamics
Search for the standard model Higgs boson produced in association with W and Z bosons in pp collisions at sqrt(s) = 7 TeV
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