Pair momentum dependence of tilted source in heavy ion collisions

TL;DR

This paper investigates the tilt of the particle-emitting source in non-central heavy-ion collisions, demonstrating a momentum-dependent bias in measurements and proposing an extrapolation method to improve tilt estimation accuracy.

Contribution

It introduces an exponential extrapolation technique to accurately determine the source tilt from azimuthally sensitive femtoscopy data across all particle momenta.

Findings

Strong momentum dependence of the tilt parameter in asHBT measurements

Exponential extrapolation improves tilt estimation at low momenta

Proposes a method to better measure source tilt in experiments

Abstract

In non-central heavy-ion collisions, the particle-emitting source can be tilted away from the beam direction, an effect that becomes particularly significant at collision energies of a few GeV and lower. This phenomenon, manifest itself in many observables such as directed flow, polarization, and vorticity, is therefore important to investigate. In this paper, we study the consistency between the tilt extracted directly from the freeze-out distribution of pions and the tilt parameter obtained using the azimuthally sensitive femtoscopy (asHBT) method. Using the UrQMD model, we demonstrate a strong dependence of the tilt parameter extracted with asHBT on the momentum of the particle pair. Considering the experimental challenges in accessing low particle momenta - where the tilt parameter extracted with asHBT closely matches the tilt of the freeze-out distribution of pions - we propose an exponential extrapolation method to obtain the tilt of the entire freeze-out distribution. This approach aims to enhance the accuracy of experimental measurements of tilt in non-central heavy-ion collisions.