High multiplicity pp events and J/\psi\ production at LHC

TL;DR

This paper investigates how J/ production in high-energy proton-proton collisions at the LHC depends on charged particle multiplicity, highlighting a nonlinear increase linked to parton saturation and string interactions.

Contribution

It introduces the idea that J/ production scales nonlinearly with multiplicity due to saturation effects, providing a new perspective on hard process behavior in high-density pp collisions.

Findings

J/ production grows faster than linearly with multiplicity.

High multiplicity pp collisions exhibit saturation or string interaction effects.

The shape of the J/ production distribution can reveal coherence effects.

Abstract

We discuss the dependence of J/\psi\ production on the charged particle multiplicity in proton-proton collisions at LHC energies. We show that, in the framework of parton saturation or string interaction models, the hard J/\psi\ production exhibits a significant growth with the multiplicity, which is stronger than linear in the high density domain. This departure from linearity, that should affect any hard observable, applies for high multiplicity proton-proton collisions in the central rapidity region and is a consequence of the parton saturation or the strong interaction among colour ropes that take place at LHC energies. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, can also be checked by studying the particular shape of the probability distribution associated to the J/\psi\ production.