STAR Flow, Chirality and Vorticity PWG

[Prithwish Tribedy <ptribedy AT rcf.rhic.bnl.gov>]

Dear FCV folks,
 Here is an abstract on the first attempt to search for collectivity in 
photonuclear events from STAR.
Best,
Prithwish


Title: Search for collectivity in photon-nucleus collisions using 
ultra-peripheral Au+Au collisions from STAR
PAs: Nicole Lewis/Prithwish Tribedy

The remaining years of RHIC running and analyses of already collected 
data provide a unique opportunity to understand the origin of 
collectivity in small collision systems. One possible way to address 
this outstanding problem is to study colliding systems of various sizes 
at RHIC. We propose a key addition to such an initiative and propose the 
search for collectivity in inclusive photon-ion (γ+Au) interactions. 
This will push the boundaries of the recent system size scan at RHIC. 
The photonuclear γ+Au interactions occur in ultra-peripheral collisions 
(UPC) of Au+Au for which the CGC calculations predict a clean signature 
of long-range collectivity that can also be explored in e+Au collisions 
at the Electron-Ion Collider (EIC) [1]. This study will focus on the 
analysis of γ + Au interactions using the Au+Au 54 GeV UPC dataset from 
STAR. The events are triggered by requiring ZDC east (ZDCE) detector 
restricted to have a single neutron hit, while no restriction is placed 
on the ZDC west (ZDCW) for γ + Au candidates with east going photons, 
and vice versa. The pseudorapidity distribution of particles is strongly 
asymmetric in these interactions and the wide acceptance coverage of the 
STAR detector using TPC, BBC and VPD is exploited to improve the purity 
of the γ + Au-rich samples. We will present measurements on long-range 
di-hadron correlations and harmonic anisotropy coefficients in high 
activity γ + Au-rich events. In order to address non-flow effects we use 
template subtraction method using correlation measurements from low 
activity γ + Au events. We also compare peripheral Au+Au collisions for 
baseline studies.

[1] Y. Shi et al, e-Print: 2008.03569 [hep-ph]