/ hep-ex CMS-SMP-16-017

Measurements of the pp$\to$ZZ production cross section and the Z$\to 4\ell$ branching fraction, and constraints on anomalous triple gauge couplings at $\sqrt{s} =$ 13 TeV

Abstract: Four-lepton production in proton-proton collisions, $\mathrm{pp}\to (\mathrm{Z}/ \gamma^*)(\mathrm{Z}/\gamma^*) \to 4\ell$, where $\ell = \mathrm{e}$ or $\mu$, 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 35.9 fb$^{-1}$. The ZZ production cross section, $\sigma(\mathrm{pp} \to \mathrm{Z}\mathrm{Z}) = 17.2 \pm 0.5\text{ (stat) }\pm 0.7\text{ (syst) }\pm 0.4(\mathrm{theo}) \pm 0.4\text{ (lum)}$ pb, measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region $60 < m_{\ell^+\ell^-} <$120 GeV, 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 $\mathcal{B}(\mathrm{Z}\to 4\ell) = 4.8 \pm 0.2\text{ (stat) }\pm 0.2\text{ (syst) } \pm 0.1\text{ (theo) }\pm 0.1\text{ (lum) }\times 10^{-6}$ for events with a four-lepton invariant mass in the range 80 $< m_{4\ell} <$ 100 GeV and a dilepton mass $m_{\ell\ell} >$4 GeV for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ$\gamma$ couplings at 95% confidence level: $-0.0012<f_4^\mathrm{Z}<0.0010$, $-0.0010<f_5^\mathrm{Z}<0.0013$, $-0.0012<f_4^{\gamma}<0.0013$, $-0.0012<f_5^{\gamma}< 0.0013$.

Note: *Temporary entry*; Submitted to Eur. Phys. J. C. All figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publicationsSMP-16-017/ (CMS Public Pages)

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