Decorrelation of participant and spectator angular momenta in heavy-ion collisions

High-energy heavy-ion collisions contain enormous angular momentum, vertical bar(J) over right arrow vertical bar which is O(10(3)-10(6)(h) over bar over bar ) in the range of collision energy, root s(NN), spanned experimentally by the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). A fraction of (J) over right arrow is transferred to the overlapping collision region, which is indispensable for measuring observables such as vorticity-driven hadron spin alignment with (J) over cap. Experiments estimate the orientation of (J) over cap of the participant nucleons within the collision overlap region, (J) over cap (part), by using that of the forward-and backward-going spectating nucleons (J) over cap (spec). Using two models, we study the decorrelation between (J) over cap (part) and (J) over cap (spec), driven both by angular-momentum conservation and event-by-event fluctuations, as well as by the decorrelation between the orientation of the elliptic overlap region and the (J) over cap (part). root s(NN)-dependent decorrelation is observed in both of these cases and is large enough to be an important corrective factor used when experimentally observing phenomena driven by (J) over right arrow.

Automated summary

High-energy heavy-ion collisions transfer angular momentum to the collision region, which is essential for measuring observables. Experimental estimations of angular momentum direction in the collision region show correlation with the observed angular momentum direction. Two models demonstrate significant correlation, serving as an important corrective factor in experimental observations.