Measurements of the pp→ZZ production cross section and the Z→4ℓ branching fraction, and constraints on anomalous triple gauge couplings at √s =13 TeV

Abstract

Four-lepton production in proton-proton collisions, pp → (Z/γ[superscript ∗]) (Z/γ[superscript ∗]) → 4ℓ, where ℓ= e or μ, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 35.9fb[superscript -1]. The ZZ production cross section, σ(pp→ZZ)=17.2±0.5(stat)±0.7(syst)±0.4(theo)±0.4(lumi) pb, measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 < m[subscript ℓ+ℓ-] < 120GeV, is consistent with standard model predictions. Differential cross sections are measured and are well described by the theoretical predictions. The Z boson branching fraction to four leptons is measured to be B(Z → 4ℓ) =4.83[superscript +0.23][subscript -0.22](stat)[superscript +0.32][subscript -0.29](syst)±0.08(theo)±0.12(lumi)×10[superscript -6] for events with a four-lepton invariant mass in the range 80 < m[subscript 4ℓ] < 100GeV and a dilepton mass m[subscript ℓℓ]> 4 GeV for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZγ couplings at 95% confidence level: -0.0012 < f[superscript Z][subscript 4] < 0.0010, -0.0010 < f[superscript Z][subscript 5] < 0.0013, -0.0012 < f[superscript γ][subscript 4] < 0.0013, -0.0012 < f[superscript γ][subscript 5] < 0.0013.