Studies of vector boson production at CMS

Abstract

The most recent diboson production and electroweak physics results from CMS are presented. This overview is focused on the precise measurement of WW, WZ, ZZ and γγ production, as well as W or Z production in association with a photon. These results are interpreted in terms of constraints on anomalous triple gauge couplings, while the study of WWγ and WZγ production is used to set limits on anomalous quartic gauge couplings. Selection of the latest electroweak results is also presented. Presented at LaThuile 2015 XXIXth Rencontres de Physique de la Vallee dAoste IL NUOVO CIMENTO Vol. ?, N. ? ? Studies of vector boson production at CMS Milos Dordevic on behalf of the CMS Collaboration European Organization for Nuclear Research (CERN), Geneva, Switzerland Summary. — The most recent diboson production and electroweak physics results from CMS are presented. This overview is focused on the precise measurement of WW, WZ, ZZ and γγ production, as well as W or Z production in association with a photon. These results are interpreted in terms of constraints on anomalous triple gauge couplings, while the study of WWγ and WZγ production is used to set limits on anomalous quartic gauge couplings. Selection of the latest electroweak results is also presented. PACS 14.70.Fm – W bosons. PACS 14.70.Hp – Z bosons. PACS 14.70.Bh – Photons. 1. – Introduction The measurement of the diboson production and studies of the electroweak processes represent a fundamental test of the Standard Model (SM). The self-interaction between the vector bosons is precisely predicted by the SM and results from the non-Abelian nature of the SU(2)xU(1). Any difference of the measured cross section from the SM prediction, or a deviation in the kinematic distribution of the diboson pair, would indicate a presence of new physics. Therefore, such studies are an excellent probe for the possible existence of the anomalous triple and quartic gauge couplings, aTGC and aQGC. Moreover, diboson and electroweak processes are often irreducible background for Higgs boson studies and various beyond SM searches. The CMS experiment at CERN [1] has recorded data from the proton-proton collisions, delivered by the Large Hadron Collider (LHC) in 2011 and 2012 at center-of-mass energies of 7 and 8 TeV, that allowed the CMS Collaboration to measure the diboson production cross sections and study the electroweak physics at the energy scale never probed before. 2. – Measurement of ZZ production The inclusive and differential cross section of the ZZ production in the four lepton final state were measured using 19.6 fb−1 of data recorded at the energy of 8 TeV [2]. c © Societa Italiana di Fisica 1 2 MILOS DORDEVIC ON BEHALF OF THE CMS COLLABORATION The mutually exclusive sets of 4e, 4μ, 2e2μ and llττ were first studied individually and then combined using a simultaneous fit, to obtain the measured cross section of σdata = 7.7±0.5(stat.) −0.4(syst.)±0.4(th.)±0.2(lum.)pb, found to be in a good agreement with the SM prediction of 7.7±0.6pb. Both Z bosons are required to be produced within the mass window of 60 to 120 GeV. The differential cross section normalised to the fiducial cross section is shown in fig. 1. A good agreement with respect to the NLO theory prediction from MCFM 6.0 [3] was found. The measurement of the ZZ production cross section was also performed in the final state with two leptons (electrons or muons) and two neutrinos, at both 7 and 8 TeV, using 4.9 fb−1 and 19.6 fb−1, respectively [4]. This channel profits from the six times larger branching ratio than the four lepton, but is largely contaminated from the backgrounds, in particular from the Drell-Yan (DY) process. The crucial part here is the reconstruction of the missing transverse energy (MET), where the reduced-MET variable [5, 6, 7] was applied, shown to be effective in suppressing the instrumentally induced MET of the DY process. The cross section was extracted using a profile likelihood fit to the reduced MET and measured to be σdata = 5.0 +1.5 −1.4(stat.) +1.3 −1.0(syst.) ± 0.2(lumi)pb and σdata = 6.8 +0.8 −0.8(stat.) +1.8 −1.4(syst.)± 0.3(lumi)pb at 7 and 8 TeV, respectively. Results are in a good agreement with the SM prediction at NLO. The reduced MET distribution is shown in fig. 1, after the final event selection. (GeV) ZZ m 100 200 300 400 500 600 700 800 ) (1 /G eV )