Multiplicity Studies and Effective Energy in ALICE at the LHC

TL;DR

This paper investigates effective energy and multiplicity in high-energy collisions at the LHC, proposing a universal approach to predict charged particle production in proton-proton and heavy-ion collisions, with implications for understanding collision dynamics.

Contribution

It introduces a novel method to estimate charged multiplicity in heavy-ion collisions at the LHC using effective energy and limiting fragmentation scaling, extending universality concepts from lower energies.

Findings

Charged multiplicity in central Pb-Pb collisions is predicted to be 1000-2000 per rapidity unit.

The approach suggests lower multiplicities than many existing models.

Universality in particle production may extend from proton-proton to ion-ion collisions.

Abstract

In this work we explore the possibility to perform ``effective energy'' studies in very high energy collisions at the CERN Large Hadron Collider (LHC). In particular, we focus on the possibility to measure in $pp$ collisions the average charged multiplicity as a function of the effective energy with the ALICE experiment, using its capability to measure the energy of the leading baryons with the Zero Degree Calorimeters. Analyses of this kind have been done at lower centre--of--mass energies and have shown that, once the appropriate kinematic variables are chosen, particle production is characterized by universal properties: no matter the nature of the interacting particles, the final states have identical features. Assuming that this universality picture can be extended to {\it ion--ion} collisions, as suggested by recent results from RHIC experiments, a novel approach based on the scaling hypothesis for limiting fragmentation has been used to derive the expected charged event multiplicity in $AA$ interactions at LHC. This leads to scenarios where the multiplicity is significantly lower compared to most of the predictions from the models currently used to describe high energy $AA$ collisions. A mean charged multiplicity of about 1000-2000 per rapidity unit (at $\eta \sim 0$) is expected for the most central $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 5.5 TeV$.