abstract
- The observation of the associated production of an ϒ(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 ϒ(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 σ[pp→Z+ϒ(1S)]B(Z→μ^{+}μ^{-})B[ϒ(1S)→μ^{+}μ^{-}] to σ(pp→Z)B(Z→4μ) is measured to be R_{Z+ϒ(1S)}=[21.1±5.5(stat)±0.6(syst)]×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 σ_{eff}=13.0_{-3.4}^{+7.7} mb. In addition, for the first time, σ_{eff} is measured in bins of the transverse momentum of the ϒ(1S) meson or of the Z boson.