Nuclear Physics Seminars at BNL

# Measurements of long-range correlations in photonuclear collisions and prospects for small-system longitudinal decorrelation

## by Blair Seidlitz (University of Colorado Boulder)

US/Eastern
Description

The ultra-peripheral collisions of relativistic heavy-ion beams lead to a preva-lent and diverse set of photon-nucleus interactions. Measurements of particlesproduced in photonuclear collisions and their interactions can shed light onthe QCD dynamics of EM-induced, extremely asymmetric colliding systems,with energies between those available at RHIC and the LHC. In addition, un-derstanding the hadronic fluctuation spectrum of the photon in this fashion iscritical for maximizing the precision of measurements at the future Electron IonCollider facility. This talk presents a measurement of two-particle long-rangeazimuthal correlations in photonuclear collisions using 5.02 TeV Pb+Pb col-lision data. Candidate photonuclear events are selected using a combinationof single-sided zero-degree calorimeter activity and reconstructed pseudorapid-ity gaps. Correlation functions are constructed and non-collective contributionsare removed. The resulting elliptic and triangular flow coefficients are presentedwhere significant non-zero values are observed and compared to proton–protonand proton–lead collisions in similar multiplicity ranges.The results in this highly-asymmetric system could be sensitive the longi-tudinal structure of the initial state (i.e. event-plane twist) of which little hasbeen explored in small systems. This talk will also present the prospect forunderstanding the relevant sub-nucleonic structure leading to small-system lon-gitudinal decorrelation and how it relates to previous studies in large systems.