# Quasi equilibrium state of expanding quantum fields and two-pion Bose-Einstein correlations in $pp$ collisions at the LHC

## TL;DR

This paper investigates how two-pion Bose-Einstein correlations in high-multiplicity proton-proton collisions at the LHC reveal the ground state structure of an expanding quantum field, highlighting the role of different emission scales and their dependence on transverse momentum.

## Contribution

It introduces a novel interpretation of two-particle correlations as signals of a quasi equilibrium ground state in an expanding quantum field in high-energy collisions.

## Key findings

- Suppression of Bose-Einstein correlations increases with pion pair transverse momentum.
- Two emission scales are identified: one from local equilibrium and one from ground-state condensate.
- Correlation functions reflect the ground state structure of the expanding quantum field.

## Abstract

We argue that the two-particle momentum correlation functions of high-multiplicity $p+p$ collisions at the LHC provide a signal for a ground state structure of a quasi equilibrium state of the longitudinally boost-invariant expanding quantum field which lies in the future light cone of a collision. The physical picture is that pions are produced by the expanding quantum emitter with two different scales approximately attributed to the expanding ideal gas in local equilibrium state and ground-state condensate. Specifically, we show that the effect of suppressing the two-particle Bose-Einstein momentum correlation functions increases with increasing transverse momentum of a like-sign pion pair due to different momentum-dependence of the corresponding particle emission regions.