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

## TL;DR

This study uses a multi-phase transport model to investigate how initial momentum anisotropy and collision geometry influence collective flow in small collision systems, revealing that initial anisotropy persists and affects final-state collectivity.

## Contribution

It demonstrates that initial-state momentum anisotropy can significantly impact final-state collectivity, challenging the assumption that collectivity solely arises from collision geometry effects.

## Key findings

- Initial momentum anisotropy may not be fully isotropized.
- Final-state collectivity correlates with initial anisotropy and geometry.
- Initial anisotropy influences event-by-event flow fluctuations.

## Abstract

A multi-phase 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 are 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 geometry response of the collective flow can not rule out the presence of large contributions from the initial state.