Pion transverse-momentum spectrum and elliptic anisotropy of partially coherent source

TL;DR

This study models pion momentum distribution in peripheral Pb-Pb collisions, showing how partial coherence affects the transverse-momentum spectrum and elliptic anisotropy, aligning well with experimental data.

Contribution

It introduces a partially coherent source model combining viscous hydrodynamics and a coherent emission component to explain pion observables.

Findings

Coherent emission influences pion spectra and anisotropy based on source size and shape.

Partially coherent model with 33% coherence matches experimental pion data.

Interference effects are significant, while source evolution has minor impact.

Abstract

In this letter, we study the pion momentum distribution of a coherent source and investigate the influences of coherent emission on the pion transverse-momentum ($p_T$) spectrum and elliptic anisotropy. With a partially coherent source, constructed by a conventional viscous hydrodynamics model (chaotic part) and a parameterized expanding coherent source model, we reproduce the pion $p_T$ spectrum and elliptic anisotropy coefficient $v_2(p_T)$ in the peripheral Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. It is found that the influences of coherent emission on the pion $p_T$ spectrum and $v_2(p_T)$ are related to the initial size and shape of the coherent source, largely due to the interference effect. However, the effect of source dynamical evolution on coherent emission is relatively small. The results of the partially coherent source with 33% coherent emission and 67% chaotic emission are consistent with the experimental measurements of the pion $p_T$ spectrum, $v_2(p_T)$, and especially four-pion Bose-Einstein correlations.