Heavy quarkonium in saturated environment of high-multiplicity pp collisions

TL;DR

This paper investigates heavy quarkonium production in high-multiplicity proton-proton collisions, revealing nonlinear saturation effects that better explain experimental data and show similar suppression patterns for J/psi and Upsilon at forward rapidities.

Contribution

It introduces a parameter-free nonlinear correction model for quarkonium production, improving agreement with high-multiplicity collision data and unifying suppression patterns across different quarkonia.

Findings

Nonlinear saturation effects explain high-multiplicity J/psi production data.

J/psi and Upsilon show similar suppression at forward rapidities.

Model aligns well with data across multiple pT intervals.

Abstract

High-multiplicity pp collisions exhibit features, traditionally associated with nuclear effects. Coherence motivates to treat high-multiplicity pp, pA and AA collisions on an equal footing. We rely on the phenomenological parametrization for mean multiplicities of light hadrons and J/psi, assuming their linear dependence on N_{coll} in pA collisions. The results of this approach underestimate the recently measured production rate of J/psi at very high hadronic multiplicities. The linear dependence of J/psi multiplicity on N_{coll} is subject to predicted nonlinear corrections, related to mutual boosting of the saturation scales in colliding dense parton clouds. A parameter-free calculation of the non-linear corrections allows to explain data for pT-integrated yield of J/psi at high hadronic multiplicities. Calculations are in a good accord with data binned in several pT-intervals as well. As was predicted, Upsilon and J/psi are equally suppressed at forward rapidities in pA collisions. Consequently, their fractional multiplicities at forward rapidities in pp collisions are equal as well, and their magnitude agrees with data.