A twisted emission geometry in non-central Pb+Pb collisions measurable via azimuthally sensitive HBT

TL;DR

This paper investigates a novel twisted emission geometry in non-central Pb+Pb collisions, using simulations and proposing experimental measurement via azimuthally sensitive HBT correlations, revealing a tilt dependent on measurement scale.

Contribution

It introduces the concept of a twist in the emission geometry and proposes a method to measure it experimentally, linking it to the source evolution.

Findings

The emission zone exhibits a tilt away from the beam axis.

The tilt magnitude depends on the measurement scale.

The twist relates to particle emission timing during source evolution.

Abstract

We use the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model to simulate Pb+Pb collisions. In the freeze out geometry of non-central Pb+Pb collisions we observe a tilt of the particle emission zone in the collision plane away from the beam axis. We find that the magnitude of this tilt depends on the scale at which the distribution is measured. We quantify this "twisting" behavior with a parameterization and propose to measure it experimentally via azimuthally sensitive Hanbury-Brown Twiss correlations. Additionally we show that the twist is related to the emission of particles from different times during the evolution of the source. A systematic comparison between the theoretically observed twist in the freeze out position distribution and a mock experimental analysis of the model calculations via HBT correlations is shown.