Observation of ${\rm Y}$(1S) + Z associated production and measurement of the effective double-parton scattering cross section in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

The observation of associated production of an ${\rm Y}$(1S) meson with a Z boson and a measurement of the ratio of its fiducial cross section to the fiducial cross section of the Z boson are presented. Both the ${\rm Y}$(1S) meson and the Z boson are identified via decays into a pair of opposite-sign muons. The analysis is based on proton-proton (pp) collision data at $\sqrt{s}$ = 13 TeV, collected with the CMS detector in 2016$-$2018 and corresponding to an integrated luminosity of 138 fb${}^{-1}$. Using the production of the Z boson decaying into four muons as a normalization channel, the ratio of the fiducial cross sections $\sigma$(pp $\to$ Z $+$ ${\rm Y}$(1S))$\mathcal{B}$(Z $\to$ ${\mu }^{+}{\mu }^{-}$)$\mathcal{B}$(${\rm Y}$(1S) $\to$ ${\mu }^{+}{\mu }^{-}$ ) to $\sigma$(pp $\to$ Z)$\mathcal{B}$(Z $\to$ 4$\mu$) is measured to be ${\mathcal{R}}_{\mathrm{Z}+\mathrm{{\rm Y}}(1S)}$ = (21.1 $\pm$ 55 (stat) $\pm$ 0.6 (syst) $\times$ 10${}^{-3}$), where stat and syst denote the statistical and systematic uncertainties, respectively. The result is used to extract the effective double-parton scattering cross section ${\sigma }_{\text{eff}}$ = 13.0 ${}_{-3.4}^{+7.7}$ mb. In addition, for the first time, ${\sigma }_{\text{eff}}$ is measured in bins of the transverse momentum of the ${\rm Y}$(1S) meson or of the Z boson.

arXiv commentReplaced with the published version. Added the journal reference and the DOI. All figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-23-007 (CMS Public Pages)