Measurement of the multiplicity dependence of $\mit\Upsilon$ production ratios in $pp$ collisions at $\sqrt{s}=13$ TeV

Abstract

The $\mit{\Upsilon}(\mathrm{2}S)$ and $\mit{\Upsilon}(\mathrm{3}S)$ production cross-sections are measured relative to that of the $\mit{\Upsilon}(\mathrm{1}S)$ meson, as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of $13$ TeV. The measurement uses data collected by the LHCb experiment in 2018 corresponding to an integrated luminosity of 2 $\text{fb}^{-1}$. Both the $\mit{\Upsilon}(\mathrm{2}S)$-to-$\mit{\Upsilon}(\mathrm{1}S)$ and $\mit{\Upsilon}(\mathrm{3}S)$-to-$\mit{\Upsilon}(\mathrm{1}S)$ cross-section ratios are found to decrease significantly as a function of event multiplicity, with the $\mit{\Upsilon}(\mathrm{3}S)$-to-$\mit{\Upsilon}(\mathrm{1}S)$ ratio showing a steeper decline towards high multiplicity. This hierarchy is qualitatively consistent with the comover model predictions, indicating that final-state interactions play an important role in bottomonia production in high-multiplicity events.