Correlation of $\Upsilon$ meson production with the underlying event in $pp$ collisions measured by the ATLAS experiment

The multiplicity and distributions of kinematic variables of charged particles produced in association with an $\Upsilon$ meson are measured in pp collisions using the data collected by the ATLAS experiment at the LHC. The analysis uses a full Run 2 data set at $\sqrt{s} = 13$ TeV, corresponding to the integrated luminosity of 139 fb$^{−1}$. The measurement is performed separately for the first three $\Upsilon(nS)$ states in several intervals of Υ transverse momenta. At $\Upsilon$ transverse momentum close to zero, the associated charged-particle multiplicity is measured to be smaller by $12\pm1$ % in collisions where $\Upsilon(2S)$ is observed compared to the collisions with $\Upsilon(1S)$ For $\Upsilon(3S)$ this difference is $17\pm4$ %. These differences decrease with the increasing momentum of the $\Upsilon$ states.