Measurement of the $\Upsilon$(1S) pair production cross section and search for resonances decaying to $\Upsilon$(1S)$\mu^+\mu^-$ in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam, Federico Ambrogi, Thomas Bergauer, Marko Dragicevic, Janos Erö, Alberto Escalante Del Valle, Martin Flechl, Rudolf Fruehwirth, Manfred Jeitler, Natascha Krammer (+2287 others)
Measurement of the Υ(1S) pair production cross section and search for resonances decaying to Υ(1S)µ + µ − in proton-proton collisions at √ s = 13 TeV The CMS Collaboration * Abstract The fiducial cross section for Υ(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Υ(1S) 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
more » ... responds to the uncertainty in the Υ(1S) 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 Υ(1S)µ + µ − in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks 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 Υ(1S) resonance are set as a function of the resonance mass. The event reconstruction is based on the particle-flow algorithm [30] , which identifies individual particle candidates using information from all the individual subdetectors. Muons are reconstructed by combining information from the silicon tracker and the muon system [17] . Events are selected with a trigger that requires the presence of three muons. Among these muons, two must have an invariant mass compatible with a Υ resonance (8.5 < m 2µ < 11.4 GeV) at trigger level, and the dimuon vertex fit probability, calculated using the χ 2 and the number of degrees of freedom of the fit, must be greater than 0.5%. Offline, we require each event to have four reconstructed muons with p T > 2 GeV and |η| < 2.4. These muons are required to satisfy the global or particle-flow muon identification criteria
doi:10.18154/rwth-2020-10525 fatcat:ci44enmqirc6fmasjbw3mgtlmu