Abstract
A study is presented of central exclusive production of $\Upsilon(nS)$ states, where the $\Upsilon(nS)$ resonances decay to the $\mu^+\mu^-$ final state, using $pp$ collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range $2<y(\Upsilon)<4.5$ where the muons are reconstructed in the pseudorapidity range $2<\eta(\mu^\pm)<4.5$. The data sample corresponds to an integrated luminosity of 2.9 fb$^{-1}$ and was collected at centre-of-mass energies of $7$ TeV and $8$ TeV. The measured $\Upsilon(1S)$ and $\Upsilon(2S)$ production cross-sections are \begin{eqnarray} \sigma(pp \to p\Upsilon(1S)p) &=& 9.0 \pm 2.1 \pm 1.7\textrm{ pb and}\nonumber\\ \sigma(pp \to p\Upsilon(2S)p) &=& 1.3 \pm 0.8 \pm 0.3\textrm{ pb},\nonumber \end{eqnarray} where the first uncertainties are statistical and the second are systematic. The $\Upsilon(1S)$ cross-section is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95\% confidence level for the exclusive $\Upsilon(3S)$ production cross-section, including possible contamination from $\chi_b(3P)\to\Upsilon(3S)\gamma$ decays.
Highlights
Detector and simulationThe LHCb detector [14, 15] is a single-arm forward spectrometer, designed for the study of particles containing b or c quarks
A study is presented of central exclusive production of Υ(nS) states, where the Υ(nS) resonances decay to the μ+μ− final state, using pp collision data recorded by the LHCb experiment
The exclusive production cross-section of Υ(nS) resonances is measured in the μ+μ− final state where both muons lie in the pseudorapidity (η) range 2 < η(μ±)
Summary
The LHCb detector [14, 15] is a single-arm forward spectrometer, designed for the study of particles containing b or c quarks. It is fully instrumented in the pseudorapidity range 2 < η < 5 and has tracking capability in the backward direction, in the range −3.5 < η < −1.5. In the subsequent software trigger, both of the final-state muons are required to have pT > 400 MeV/c. Nine background samples of a similar size are prepared containing events where an exclusively produced χb0,1,2(1P, 2P, 3P ) meson decays to the Υ(nS)γ final states with Υ → μ+μ−.
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