Final source eccentricity measured by HBT interferometry with the event shape selection

TL;DR

This paper measures the final source eccentricity in heavy-ion collisions using HBT interferometry with event shape selection, revealing enhanced oscillations and potential twisted source structures due to initial fluctuations.

Contribution

It introduces an event shape engineering approach to measure source eccentricity and explores the twist effect in the spatial source distribution with model comparisons.

Findings

Enhanced source eccentricity with higher flow vector selection

Observation of oscillation amplification in source radii

Indication of a twisted source due to initial longitudinal fluctuations

Abstract

Azimuthal angle dependence of the pion source radii has been measured applying the event shape engineering technique at the PHENIX experiment. When events with higher magnitude of second-order flow vector are selected, the oscillation of the source radii is enhanced as well as $v_2$ which leads to the enhancement of the measured final source eccentricity. The event twist effect in the spatial source distribution in the final state has been also explored with AMPT model. Results indicate a possible twisted source due to the initial longitudinal fluctuations.