Measurements of Z g and Z gg production in pp collisions at sqrt(s)= 8 TeV with the ATLAS detector

H. WAHLBERG Y ATLAS COLLABORATION

PHYSICAL REVIEW D - PARTICLE AND FILDS

aps

Año: 2016

0556-2821

The production of√ Z bosons with one or two isolated high-energy photons is studied usingpp collisions at s = 8 TeV. The analyses use a data sample with an integrated luminosityof 20.3 fb −1 collected by the ATLAS detector during the 2012 LHC data taking. The Zγ andZγγ production cross sections are measured with leptonic (e + e − , μ + μ − , ν ̄ ν ) decays of the Zboson, in extended fiducial regions defined in terms of the lepton and photon acceptance.They are then compared to cross-section predictions from the Standard Model, where thesources of the photons are radiation off initial-state quarks and radiative Z-boson decay tocharged leptons, and from fragmentation of final-state quarks and gluons into photons. Theyields of events with photon transverse energy E T > 250 GeV from + − γ events and withE T > 400 GeV from ν ̄ νγ events are used to search for anomalous triple gauge-boson coup-lings ZZγ and Zγγ. The yields of events with diphoton invariant mass m γγ > 200 GeV from+ −γγ events and with m γγ > 300 GeV from ν ̄ νγγ events are used to search for anomalousquartic gauge-boson couplings ZZγγ and Zγγγ. No deviations from Standard Model pre-dictions are observed and limits are placed on parameters used to describe anomalous tripleand quartic gauge-boson couplings.