HBT interferometry relative to the triangular flow plane in heavy-ion collisions

TL;DR

This paper investigates the origins of third-order harmonic oscillations in HBT radii relative to the triangular flow plane in heavy-ion collisions, proposing models with geometric deformation and flow anisotropy.

Contribution

It introduces a simple Gaussian source model to distinguish between geometric deformation and flow anisotropy as sources of third-order oscillations in HBT radii.

Findings

Third-order oscillations can originate from geometric deformation or flow anisotropy.

The phase of oscillations helps distinguish the underlying cause.

Models show how triangular flow influences HBT measurements.

Abstract

The PHENIX Collaboration has reported third-order harmonic oscillations of the source radius parameters when measuring the Hanbury Brown-Twiss correlation function for charged hadrons relative to the triangular flow angle. We explore possible origins of such third-order oscillations with a simple Gaussian source featuring both a triangular geometric deformation and triangular flow. Third-order oscillations of the HBT radii can arise from a purely geometric triangular deformation superimposed on an azimuthally symmetric radial flow, or from a radially symmetry spatial distribution which expands anisotropically with a triangular component in the flow velocity profile. In both cases the final particle momentum distribution features triangular flow. We show that the two alternatives can be distinguished experimentally through the phase of the azimuthal oscillations of the HBT radii relative to the triangular flow plane.