Measurements of W Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings
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2016
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Physical Review D - Particles and Fields
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PHYSICAL REVIEW D 93, 092004 (2016) Measurements W±Z production cross sections in pp collisions at s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings G. Aad et al. * (ATLAS Collaboration) (Received 8 March 2016; published 13 May 2016) This paper presents measurements of W Z production in pp collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider and correspond to an integrated luminosity of 20.3 fb −1 . The measured inclusive cross section in the detector fiducial region is σ W Z→l 0 νll ¼ 35.1 0.9ðstatÞ 0.8ðsysÞ 0.8ðlumiÞ fb, for one leptonic decay channel. In comparison, the next-to-leading-order Standard Model expectation is 30.0 2.1 fb. Cross sections for W þ Z and W − Z production and their ratio are presented as well as differential cross sections for several kinematic observables. Limits on anomalous triple gauge boson couplings are derived from the transverse mass spectrum of the W Z system. From the analysis of events with a W and a Z boson associated with two or more forward jets an upper limit at 95% confidence level on the W Z scattering cross section of 0.63 fb, for each leptonic decay channel, is established, while the Standard Model prediction at next-to-leading order is 0.13 0.01 fb. Limits on anomalous quartic gauge boson couplings are also extracted. DOI: 10.1103/PhysRevD.93.092004 I. INTRODUCTION The study of W Z diboson production is an important test of the Standard Model (SM) for its sensitivity to the gauge boson self-interactions, related to the non-Abelian structure of the electroweak interaction. It provides the means to investigate vector boson scattering (VBS) proc- esses, which directly probe the electroweak symmetry breaking sector of the SM, and to extract constraints on anomalous triple and quartic gauge boson couplings (aTGC and aQGC). Improved constraints can probe scales of new physics in the multi-TeV range and provide a way to look for signals of new physics in a model- independent way. Precise measurements of W Z production will also help to improve the existing QCD calculations of this process. This paper presents measurements of the W Z produc- tion cross section and limits on the aTGC and aQGC obtained by analyzing proton-proton (pp) collisions at a p ffiffiffi center-of-mass energy of s ¼ 8 TeV. The leptonic decay modes of the W and Z bosons are used and all quoted fiducial production cross sections include the branching ratio of the gauge bosons into channels with electrons or muons. The analyzed data sample was collected in 2012 by the ATLAS experiment at the Large Hadron Collider Full author list given at the end of the article. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distri- bution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. (LHC), and corresponds to an integrated luminosity of 20.3 fb −1 . Experimentally, W Z production has the ad- vantage of a higher cross section than ZZ production. At the same time, with three charged leptons and the require- ment that two of them originate from a Z boson, the leptonic W Z final states are easier to discriminate from the background than the leptonic WW final states. Measurements of the W Z production cross section have been reported in proton-antiproton collisions at a center- p ffiffiffi of-mass energy of s ¼ 1.96 TeV by the CDF and D0 collaborations [1,2] using integrated luminosities of p ffiffiffi 7.1 fb −1 and 8.6 fb −1 , respectively, and for s ¼ 7 TeV proton-proton collisions, using an integrated luminosity of 4.6 fb −1 , by the ATLAS Collaboration [3]. Limits on anomalous charged-current gauge couplings were also reported previously by the LEP, Tevatron, and LHC experi- ments [4–6]. In hadron collisions, the selection of W Z final states allows direct access to the WWZ gauge coupling without the need of disentangling it from the WWγ gauge coupling as in W W ∓ events from hadronic or e þ e − collisions. Compared to the previously published measurements, this paper uses data collected at a higher center-of-mass energy with a fourfold increase in integrated luminosity and presents additional measurements. The production cross section is measured in a fiducial phase space inclusively and as single differential cross sections as a function of each of several kinematic variables: the transverse momen- tum p T of the W and Z bosons, the jet multiplicity, the transverse mass of the WZ system, m WZ T , and the p T of the neutrino associated with the W boson decay. An interesting © 2016 CERN, for the ATLAS Collaboration
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Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Abeloos, B., Aben, R., Abolins, M. & et al. 2016. Measurements of W Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings. Physical Review D - Particles and Fields. 93(9):174 - 177. http://hdl.handle.net/11427/34634