Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)μ+μ− in proton-proton collisions at s=13TeV

Abstract The fiducial cross section for Y ( 1 S ) pair production in proton-proton collisions at a center-of-mass energy of 13TeVin the region where both Y ( 1 S ) mesons have an absolute rapidity below 2.0 is measured to be 79 ± 11 (stat) ± 6 (syst) ± 3 ( B )  pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y ( 1 S ) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb − 1 . This process serves as a standard model reference in a search for narrow resonances decaying to Y ( 1 S ) μ + μ − in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two bquarks and two b ‾ antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y ( 1 S ) resonance are set as a function of the resonance mass.