Quantum local-equilibrium state with fixed multiplicity constraint and Bose-Einstein momentum correlations

TL;DR

This paper derives one- and two-boson momentum spectra within a quantum local-equilibrium canonical ensemble with fixed particle number, highlighting the impact of multiplicity constraints on two-particle correlations in high-energy collisions.

Contribution

It introduces a quantum canonical ensemble approach with fixed multiplicity constraints and compares it to grand-canonical models, revealing enhanced sensitivity in two-particle correlations.

Findings

Two-particle momentum correlations are more sensitive to fixed multiplicity constraints.

The canonical ensemble results differ significantly from grand-canonical predictions.

The analysis aids in interpreting multiplicity-dependent measurements in p+p collisions.

Abstract

The one- and two-boson momentum spectra are derived in the quantum local-equilibrium canonical ensemble of noninteracting bosons with a fixed particle number constraint. We define the canonical ensemble as a subensemble of events associated with the grand-canonical ensemble. Applying simple hydro-inspired parametrization with parameter values that correspond roughly to the values at the system's breakup in $p+p$ collisions at the LHC energies, we compare our findings with the treatment which is based on the grand-canonical ensembles where mean particle numbers coincide with fixed particle numbers in the canonical ensembles. We observe a significantly greater sensitivity of the two-particle momentum correlation functions to fixed multiplicity constraint compared to one-particle momentum spectra. The results of our analysis may be useful for interpretation of multiplicity-dependent measurements of $p+p$ collision events.