Searching for QGP Signatures in PhotoNuclear Collisions with ATLAS

by Sruthy Jyothi Das (University of Illinois Chicago)

Tuesday 29 Apr 2025, 11:00 → 12:00 US/Eastern

Ultraperipheral collisions (UPCs) of relativistic heavy-ion beams produce highly asymmetric photon-nucleus (photonuclear) interactions. Measurements of particles produced in these interactions can provide insights into QCD dynamics at energies between those available at RHIC and the LHC. Previous ATLAS studies have observed elliptic and triangular flow coefficients in such events [1]. This talk presents new measurements of charged hadrons and identified hadrons ($K_S^0$, $\mathrm{\Lambda }$, and $\mathrm{\Xi }$) in high-multiplicity photonuclear collisions [2], using 5.02 TeV Pb+Pb data collected in 2018 by ATLAS with a dedicated photo-nuclear event trigger.

 

The yields of charged hadrons and identified strange hadrons are presented differentially in rapidity, transverse momentum, and event multiplicity. These new results shed light on potential QGP formation in photonuclear collisions through observables sensitive to radial flow, enhanced baryon-to-meson ratios, and strangeness enhancement.  The results are compared to 5.02 TeV p+Pb data collected by ATLAS in 2016, at the same event multiplicities. Comparisons are also made with calculations from DPMJET and hydrodynamic-based models predicting flow even in these photonuclear collisions.

 

[1] Phys. Rev. C 104, 014903 (2021) https://doi.org/10.1103/PhysRevC.104.014903

[2] arXiv:2503.08181 [nucl-ex] https://doi.org/10.48550/arXiv.2503.08181