Observation of top quark pairs produced in association with a vector boson in pp collisions at sqrt(s) = 8 TeV

TL;DR

This paper reports measurements of top quark pair production in association with W and Z bosons at 8 TeV, providing key insights into top quark interactions and testing the Standard Model predictions.

Contribution

First measurement of ttW and ttZ production cross sections at 8 TeV, with bounds on anomalous dimension-six operators affecting these processes.

Findings

ttW cross section: 382 +117 -102 fb, 4.8 sigma significance

ttZ cross section: 242 +65 -55 fb, 6.4 sigma significance

Set bounds on five anomalous operators

Abstract

Measurements of the cross sections for top quark pairs produced in association with a W or Z boson are presented, using 8 TeV pp collision data corresponding to an integrated luminosity of 19.5 inverse femtobarns, collected by the CMS experiment at the LHC. Final states are selected in which the associated W boson decays to a charged lepton and a neutrino or the Z boson decays to two charged leptons. Signal events are identified by matching reconstructed objects in the detector to specific final state particles from ttW or ttZ decays. The ttW cross section is measured to be 382 +117 -102 fb with a significance of 4.8 standard deviations from the background-only hypothesis. The ttZ cross section is measured to be 242 +65 -55 fb with a significance of 6.4 standard deviations from the background-only hypothesis. These measurements are used to set bounds on five anomalous dimension-six operators that would affect the ttW and ttZ cross sections.