Influence of initial-state momentum anisotropy on the final-state collectivity in small collision systems

A multiphase transport model is used to understand the origin of long-range collective azimuthal correlations in small-system collisions. To disentangle between collectivity associated with initial-state intrinsic momentum anisotropy and the collectivity arising as a final-state response to the collision geometry, we studied the development of collectivity in 5.02-TeV p+Pb collisions with both initial-state and final-state effects included. We find that the initial momentum anisotropy may not be fully isotropized through parton interactions, and the final-state partonic collectivity in general is correlated with both the initial momentum anisotropy and the shape of the collision geometry. The initial momentum anisotropy also influences the event-by-event fluctuation of collective flow. Therefore, the mere evidence of the geometry response of the collective flow cannot rule out the presence of large contributions from the initial state.