Spectator shadowing as the source of the breaking of NCQ scaling at RHIC-FXT and FAIR energies

Abstract

The apparent scaling of the elliptic flow of identified hadrons with the number of constituent quarks indicates the presence of quark coalescence, and in turn suggests the presence of a deconfined state in heavy-ion collisions. Recent measurements at RHIC found a breaking of NCQ scaling at low energies and suggested that this marks the onset of partonic collectivity at higher energies. Here, we present a new framework embedding the effect of spectator shadowing into the flow scaling relations. Using a toy model with an idealized quark coalescence source and a ballistic Glauber model for the bypassing spectator, we demonstrate that the observed breaking is an effect of spectator shadowing.

Comments: 6 pages, 1 figure. Conference Proceedings: The 22nd International Conference on Strangeness in Quark Matter (SQM 2026)