Bose-Einstein momentum correlations at fixed multiplicities: Lessons from an exactly solvable thermal model for $pp$ collisions at the LHC

TL;DR

This paper investigates two-particle momentum correlations of identical bosons in a solvable thermal model for proton-proton collisions at the LHC, revealing multiplicity-dependent coherence effects.

Contribution

It introduces an exactly solvable thermal model in the quantum canonical ensemble to study boson correlations, highlighting multiplicity-dependent partial coherence effects.

Findings

Partial coherence observed in fixed multiplicity events

Coherence effects increase with multiplicity

Model demonstrates features seen in small LHC systems

Abstract

Two-particle momentum correlations of $N$ identical bosons are studied in the quantum canonical ensemble. We define the latter as a properly selected subensemble of events associated with the grand canonical ensemble which is characterized by a constant temperature and a harmonic-trap chemical potential. The merits of this toy model are that it can be solved exactly, and that it demonstrates some interesting features revealed recently in small systems created in $p+p$ collisions at the LHC. We find that partial coherence can be observed in particle emission from completely thermal ensembles of events if instead of inclusive measurements one studies the two-boson distribution functions related to the events with particle numbers selected in some fixed multiplicity bins. The corresponding coherence effects increase with the multiplicity.