Multiplicity-dependent modification of $\chi_{c1}(3872)$ and $\psi{(2S)}$ production in $pp$ collisions at $\sqrt{s}$= 8 TeV

In $pp$ collisions at $\sqrt{s}$ = 8 TeV, $\chi_{c1}(3872)$ and $\psi{(2S)}$ states are produced promptly at the primary collision vertex or in decays of $b$~hadrons. We study their relative production rates as a function of particle multiplicity. The fraction of promptly produced states is found to decrease with multiplicity for both $\chi_{c1}(3872)$ and $\psi{(2S)}$. This evolution differs between the two species: the ratio of cross-sections for promptly produced particles, $\sigma_{\chi_{c1}(3872)}$/$\sigma_{\psi{(2S)}}$, is found to decrease with increasing multiplicity. By contrast, no significant dependence on multiplicity is observed for the equivalent ratio for $\chi_{c1}(3872)$ and $\psi{(2S)}$ produced in $b$-hadron decays. This behaviour is consistent with the interpretation of the $\chi_{c1}(3872)$ as a weakly bound state, such as a $ D^0 \bar{D}^{*0}$ hadronic molecule.