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

Abstract

Suppression of the J/ψ 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 ψ(2S) state in p/d+A collisions suggested the presence of final-state effects. Results of J/ψ and ψ(2S) measurements in the dimuon decay channel are presented here for p+p, p+Al, and p+Au collision systems at √ s N N = 200 GeV. The results are predominantly shown in the form of the nuclear-modification factor, RpA, the ratio of the ψ(2S) invariant yield per nucleon-nucleon collision in collisions of proton on target nucleus to that in p+p collisions. Measurements of the J/ψ and ψ(2S) nuclear-modification factor are compared with shadowing and transport-model predictions, as well as to complementary measurements at Large-Hadron-Collider energies.

Multiplicity dependence of σψ(2S)/σJ/ψ in pp collisions at $$ \sqrt{s} $$ = 13 TeV

“…In heavy-ion collisions, quarkonium production is affected by initial-state effects like modification of parton distribution function (PDF) [4] and energy losses through multi-particle scattering [5]. While comparing the production rates for excited quarkonium states to those of the ground states can mitigate the initial-state effects listed above, observations highlight a distinct suppression of excited charmonia (ψ(2S)) and bottomonia (Υ (2S), Υ (3S)) compared to their ground states J/ψ(1S) and Υ (1S), from collaborations at the SPS [6], RHIC [7] and LHC [8][9][10][11][12]. This difference points towards the necessity of considering additional effects.…”