Testing hydrodynamic response to initial-state geometry in Pb+d^↑ collisions

¹ Department of Physics, University of Jyväskylä, P.O. Box 35, 40014 University of Jyväskylä, Finland
² Helsinki Institute of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
³ Physics Department, Brookhaven National Laboratory, Upton, NY 11973, USA
⁴ Department of Physics and Astronomy, Wayne State University, Detroit, Michigan 48201, USA
⁵ Physics Department, University of California, Berkeley, California 94720, USA
⁶ Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^* Speaker; e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 17 April 2026

Abstract

Deuterons with different polarization states have distinct shapes for their wavefunctions. This offers a unique opportunity to experimentally control the initial-state collision geometry with the polarization of the light-ion targets in relativistic heavy-ion experiments. We study the charged hadron elliptic flow coefficients with respect to the polarization angle of deuterons in Pb + polarized deuteron collisions using a hydrodynamics + hadronic transport model. Hydrodynamic response to initial-state geometry predicts a distinct sign of v₂ correlated with the deuteron's polarization states, providing a clean test case for elucidating the collective origin in small collision systems.