Measurement of $\psi (2S)$ nuclear modification at backward and forward rapidity in p0p, p1+Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

Suppression of the $J\mathrm{/}\psi$ nuclear-modification factor has been seen as a trademark signature of final-state effects in large collision systems for decades. In small systems, the nuclear modification was attributed to cold-nuclear-matter effects until the observation of strong differential suppression of the $\psi (2S)$ state in $p\mathrm{/}d$$+$$A$ collisions suggested the presence of final-state effects. Results of $J\mathrm{/}\psi$ and $\psi (2S)$ measurements in the dimuon decay channel are presented here for $p$$+$$p$, $p$$+$Al, and $p$$+$Au collision systems at $\sqrt{s_{{}_{NN}}}=200$ GeV. The results are predominantly shown in the form of the nuclear-modification factor, $R_{pA}$, the ratio of the $\psi (2S)$ invariant yield per nucleon-nucleon collision in collisions of proton on target nucleus to that in $p$$+$$p$ collisions. Measurements of the $J\mathrm{/}\psi$ and $\psi (2S)$ nuclear-modification factor are compared with shadowing and transport-model predictions, as well as to complementary measurements at Large-Hadron-Collider energies.