Investigation into the event-activity dependence of $\Upsilon$(nS) relative production in proton-proton collisions at $\sqrt{s} = $ 7 TeV
(2020) Journal of High Energy Physics — Vol. 11 (2020)
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- The ratios of the production cross sections between the excited ϒ(2S) and ϒ(3S) mesons and the ϒ(1S) ground state, detected via their decay into two muons, are studied as a function of the number of charged particles in the event. The data are from proton-proton collisions at $ \sqrt{s} $ = 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{−1}$, collected with the CMS detector at the LHC. Evidence of a decrease in these ratios as a function of the particle multiplicity is observed, more pronounced at low transverse momentum $ {p}_{\mathrm{T}}^{\upmu \upmu} $. For ϒ(nS) mesons with $ {p}_{\mathrm{T}}^{\upmu \upmu} $> 7 GeV, where most of the data were collected, the correlation with multiplicity is studied as a function of the underlying event transverse sphericity and the number of particles in a cone around the ϒ(nS) direction. The ratios are found to be multiplicity independent for jet-like events. The mean $ {p}_{\mathrm{T}}^{\upmu \upmu} $ values for the ϒ(nS) states as a function of particle multiplicity are also measured and found to grow more steeply as their mass increases.[graphic not available: see fulltext]
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Bruno, G., Caputo, C., David, P., Delaere, C., Delcourt, M., Giammanco, A., Lemaitre, V., Prisciandaro, J., Saggio, A., Vischia, P., Zobec, J., & et al. (2020). Investigation into the event-activity dependence of $\Upsilon$(nS) relative production in proton-proton collisions at $\sqrt{s} = $ 7 TeV. Journal of High Energy Physics, 11. https://doi.org/10.1007/JHEP11(2020)001 (Original work published 2020)