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arXiv · 2504.02531

Onset of Constituent Quark Number Scaling in Heavy-Ion Collisions at RHIC

STAR Collaboration·B. E. Aboona·J. Adam·L. Adamczyk·I. Aggarwal·M. M. Aggarwal·Z. Ahammed·A. K. Alshammri·E. C. Aschenauer·S. Aslam·J. Atchison·V. Bairathi·X. Bao·K. Barish·S. Behera·R. Bellwied·P. Bhagat·A. Bhasin·S. Bhatta·S. R. Bhosale·J. Bielcik·J. Bielcikova·J. D. Brandenburg·C. Broodo·X. Z. Cai·H. Caines·M. Calderón de la Barca Sánchez·D. Cebra·J. Ceska·I. Chakaberia·P. Chaloupka·B. K. Chan·Z. Chang·A. Chatterjee·D. Chen·J. Chen·J. H. Chen·Q. Chen·Z. Chen·J. Cheng·Y. Cheng·W. Christie·X. Chu·S. Corey·H. J. Crawford·M. Csanád·G. Dale-Gau·A. Das·I. M. Deppner·A. Deshpande·A. Dhamija·A. Dimri·P. Dixit·X. Dong·J. L. Drachenberg·E. Duckworth·J. C. Dunlop·J. Engelage·G. Eppley·S. Esumi·O. Evdokimov·O. Eyser·R. Fatemi·S. Fazio·Y. Feng·E. Finch·Y. Fisyak·F. A. Flor·C. Fu·T. Fu·C. A. Gagliardi·T. Galatyuk·T. Gao·F. Geurts·N. Ghimire·A. Gibson·K. Gopal·X. Gou·D. Grosnick·A. Gu·A. Gupta·A. Hamed·R. J. Hamilton·X. Han·S. Harabasz·M. D. Harasty·J. W. Harris·H. Harrison-Smith·L. B. Havener·X. H. He·Y. He·N. Herrmann·L. Holub·C. Hu·Q. Hu·Y. Hu·H. Huang·H. Z. Huang·S. L. Huang·T. Huang
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Abstract

Partonic collectivity is one of the necessary signatures for the formation of quark-gluon plasma in high-energy nuclear collisions. Number of constituent quarks (NCQ) scaling has been observed for hadron elliptic flow $v_2$ in top energy nuclear collisions at the Relativistic Heavy Ion Collider and the LHC, and this has been theoretically suggested as strong evidence for partonic collectivity. In this Letter, a systematic analysis of $v_2$ of $π^{\pm}$, $K^{\pm}$, $K^{0}_{S}$, $p$, and $Λ$ in Au+Au collisions at ${\sqrt{s_{_{\rm{NN}}}}}$ = 3.2, 3.5, 3.9, and 4.5 GeV, with the STAR experiment at the Relativistic Heavy Ion Collider, is presented. NCQ scaling is markedly violated at 3.2 GeV, consistent with a hadronic-interaction dominated equation of state. However, as the collision energy increases, a gradual evolution to NCQ scaling is observed. This beam-energy dependence of $v_2$ for all hadrons studied provides evidence for the onset of dominant partonic interactions by ${\sqrt{s_{_{\rm{NN}}}}}$ = 4.5 GeV.

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STAR Collaboration, B. E. Aboona, J. Adam, L. Adamczyk, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, A. K. Alshammri, E. C. Aschenauer, S. Aslam, J. Atchison, V. Bairathi, X. Bao, K. Barish, S. Behera, R. Bellwied, P. Bhagat, A. Bhasin, S. Bhatta, S. R. Bhosale, J. Bielcik, J. Bielcikova, J. D. Brandenburg, C. Broodo, X. Z. Cai, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, J. Ceska, I. Chakaberia, P. Chaloupka, B. K. Chan, Z. Chang, A. Chatterjee, D. Chen, J. Chen, J. H. Chen, Q. Chen, Z. Chen, J. Cheng, Y. Cheng, W. Christie, X. Chu, S. Corey, H. J. Crawford, M. Csanád, G. Dale-Gau, A. Das, I. M. Deppner, A. Deshpande, A. Dhamija, A. Dimri, P. Dixit, X. Dong, J. L. Drachenberg, E. Duckworth, J. C. Dunlop, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, O. Eyser, R. Fatemi, S. Fazio, Y. Feng, E. Finch, Y. Fisyak, F. A. Flor, C. Fu, T. Fu, C. A. Gagliardi, T. Galatyuk, T. Gao, F. Geurts, N. Ghimire, A. Gibson, K. Gopal, X. Gou, D. Grosnick, A. Gu, A. Gupta, A. Hamed, R. J. Hamilton, X. Han, S. Harabasz, M. D. Harasty, J. W. Harris, H. Harrison-Smith, L. B. Havener, X. H. He, Y. He, N. Herrmann, L. Holub, C. Hu, Q. Hu, Y. Hu, H. Huang, H. Z. Huang, S. L. Huang, T. Huang. 2025-08-11. Onset of Constituent Quark Number Scaling in Heavy-Ion Collisions at RHIC. https://doi.org/10.1103/2qhx-cp79

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