Multiplicity dependence of ϒ production at forward rapidity in pp collisions at s=13 TeV

The measurement of ϒ(1S), ϒ(2S), and ϒ(3S) yields as a function of the charged-particle multiplicity density, $\text{d}{N}_{\text{ch}}/\text{d}\eta$, using the ALICE experiment at the LHC, is reported in pp collisions at $\sqrt{s}=$ 13 TeV. The ϒ meson yields are measured at forward rapidity ($2.5<y<4$) in the dimuon decay channel, whereas the charged-particle multiplicity is defined at central rapidity ($\left|\eta \right|<1$). Both quantities are divided by their average value in minimum bias events to compute the self-normalized quantities. The increase of the self-normalized ϒ(1S), ϒ(2S), and ϒ(3S) yields is found to be compatible with a linear scaling with the self-normalized $\text{d}{N}_{\text{ch}}/\text{d}\eta$, within the uncertainties. The self-normalized yield ratios of excited-to-ground ϒ states are compatible with unity within uncertainties. Similarly, the measured double ratio of the self-normalized ϒ(1S) to the self-normalized J/ψ yields, both measured at forward rapidity, is compatible with unity for self-normalized charged-particle multiplicities beyond one. The measurements are compared with theoretical predictions incorporating initial or final state effects.