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arXiv · 2604.07005

Measurement of inclusive $J/\psi$ polarization in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\rm NN}}=200$ GeV at STAR

STAR Collaboration
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Abstract

The first measurement of inclusive J/psi polarization at mid-rapidity (|y^{J/psi}| < 0.8) in 200 GeV Ru+Ru and Zr+Zr collisions at sqrt(s_NN) = 200 GeV with the STAR experiment at RHIC is presented. J/psi mesons are reconstructed through their di-electron (e+e-) decay channel. The polarization parameters (lambda_theta, lambda_phi) are measured as a function of the J/psi transverse momentum (p_T) and collision centrality in both the helicity and the Collins-Soper frames. These polarization parameters are found to be consistent with zero across the measured J/psi p_T range of 0.2 < p_T < 10 GeV/c and across collision centralities within 0-80 percent in both frames. These results are consistent with corresponding measurements p+p collisions at the same collision energy and with transport-model calculations.

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STAR Collaboration. 2026-04-08. Measurement of inclusive $J/\psi$ polarization in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\rm NN}}=200$ GeV at STAR. https://arxiv.org/abs/2604.07005

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