Measurement of the ZZ production cross section and Z $\to \ell^+\ell^-\ell'^+\ell'^-$ branching fraction in pp collisions at $\sqrt s$=13 TeV

Abstract

Four-lepton production in proton–proton collisions, $pp → \ell^+\ell^-\ell'^+\ell'^-$ , where ℓ,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 2.6 fb$^{−1}$ . The ZZ production cross section, $σ(pp→ZZ)=14.6_{−1.8}^{+1.9}(stat)_{−0.3}^{+0.5}(syst)±0.2(theo)±0.4(lumi)pb$ , is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region $60<m_{\ell^+\ell^-},m_{\ell'+\ell'}<120 GeV$ . The Z boson branching fraction to four leptons is measured to be $B(Z → \ell^+\ell^-\ell'^+\ell'^-)=4.9_{−0.7}^{+0.8} (stat)_{−0.2}^{+0.3} (syst)_{−0.1}^{+0.2}(theo)±0.1(lumi)×10^{−6}$ for the four-lepton invariant mass in the range $80<m_{ \ell^+\ell^-\ell'^+\ell'^-}<100 GeV$ and dilepton mass $m_{\ell^+\ell^-}>4 GeV$ for all opposite-sign, same-flavor lepton pairs. The results are in agreement with standard model predictions.