Measuring the Charged Particle Multiplicity with ALICE

TL;DR

This paper discusses the measurement of charged particle multiplicity in ALICE, highlighting the methods for unfolding the data and the detector's capabilities for high-multiplicity physics, essential for understanding background and validating models.

Contribution

It presents two unfolding methods for charged particle multiplicity and demonstrates the SPD fast OR trigger's ability to study high-multiplicity events.

Findings

Unfolding methods based on chi2 minimization and Bayes' theorem are described.

The SPD fast OR trigger enables physics at very high multiplicities.

The measurement aids in tuning Monte Carlo generators and understanding background processes.

Abstract

The charged particle multiplicity distribution is one of the first measurements that ALICE will be able to perform. The knowledge of this basic property at a new energy is needed to configure Monte Carlo generators correctly with the aim of understanding the background of other, especially rare, processes including new physics. It allows to study the scaling behaviour and to verify model predictions. The unfolding of the measurement is a non-trivial task due to the finite precision and acceptance of the detector. Solutions are based on chi2 minimization or iteratively using Bayes' theorem. Both approaches to unfold the spectrum are presented. Furthermore, the capabilities of the SPD fast OR trigger are shown that enable physics at very high multiplicities.