arXiv · 2608.02787
Elliptic flow of $\pi^0$ mesons in Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and U$+$U at $\sqrt{s_{_{NN}}}=193$ GeV
Abstract
The second-order azimuthal anisotropy coefficients ($v_2$) of neutral $\pi$ mesons ($\pi^0$) have been measured as a function of the transverse momentum ($p_T$) and centrality of Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$~GeV and U$+$U at $\sqrt{s_{_{NN}}}=193$ GeV at the Relativistic Heavy Ion Collider. The analysis used experimental data collected by the PHENIX experiment at midrapidity $|\eta|<0.35$ over a broad $p_T$ range up to $\approx10$~GeV/$c$, and the obtained results are compared with previous PHENIX measurements in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$~GeV. In all three collision systems, the $\pi^0$~$v_2$ values follow the scaling with the second-order participant eccentricity and the cube root of the number of participating nucleons ($\varepsilon_2 N_{\rm part}^{1/3}$) up to $\approx4$~GeV/$c$. Furthermore, the behavior of the azimuthal-dependent $\pi^0$ nuclear-modification factors and associated fractional parton-energy losses are evaluated from measured nonzero $v_2$ values of $\pi^0$ at $p_T>5$ GeV/$c$ and found to be approximately the same for similar values of $N_{\rm part}^{1/3}$ in these collision systems. These findings demonstrate that the mechanism of $\pi^0$ $v_2$ generation exhibits a high degree of universality across different initial geometries of heavy-ion collisions.
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PHENIX Collaboration, N. J. Abdulameer, U. Acharya, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, J. Alexander, D. Anderson, S. Antsupov, K. Aoki, N. Apadula, H. Asano, E. T. Atomssa, T. C. Awes, B. Azmoun, V. Babintsev, M. Bai, X. Bai, B. Bannier, E. Bannikov, K. N. Barish, S. Bathe, V. Baublis, C. Baumann, S. Baumgart, A. Bazilevsky, M. Beaumier, R. Belmont, A. Berdnikov, Y. Berdnikov, L. Bichon, D. Black, B. Blankenship, D. S. Blau, J. S. Bok, V. Borisov, K. Boyle, M. L. Brooks, J. Bryslawskyj, H. Buesching, V. Bumazhnov, S. Butsyk, S. Campbell, P. Chaitanya, C. -H. Chen, D. Chen, M. Chiu, C. Y. Chi, I. J. Choi, J. B. Choi, S. Choi, P. Christiansen, T. Chujo, V. Cianciolo, B. A. Cole, M. Connors, R. Corliss, N. Cronin, N. Crossette, M. Csanád, T. Csörgő, L. D'Orazio, A. Datta, M. S. Daugherity, G. David, K. Dehmelt, A. Denisov, A. Deshpande, E. J. Desmond, L. Ding, V. Doomra, J. H. Do, O. Drapier, A. Drees, K. A. Drees, J. M. Durham, A. Durum, T. Engelmore, A. Enokizono, R. Esha, K. O. Eyser, B. Fadem, D. E. Fields, M. Finger Jr., M. Finger, D. Firak, D. Fitzgerald, F. Fleuret, S. L. Fokin, J. E. Frantz, A. Franz, A. D. Frawley, Y. Fukao, T. Fusayasu, K. Gainey, C. Gal, P. Garg, A. Garishvili, I. Garishvili. 2026-08-03. Elliptic flow of $\pi^0$ mesons in Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and U$+$U at $\sqrt{s_{_{NN}}}=193$ GeV. https://arxiv.org/abs/2608.02787
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