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arXiv · 2507.16355

Energy Independence of the Collins Asymmetry in $p^{\uparrow}p$ Collisions

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·P. Barik·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·Y. S. Chang·Z. Chang·A. Chatterjee·D. Chen·J. H. Chen·Q. Chen·W. Chen·Z. Chen·J. Cheng·Y. Cheng·W. Christie·X. Chu·S. Corey·H. J. Crawford·M. Csanád·G. Dale-Gau·A. Das·D. De Souza Lemos·I. M. Deppner·A. Deshpande·A. Dhamija·A. Dimri·P. Dixit·X. Dong·J. L. Drachenberg·E. Duckworth·J. C. Dunlop·Y. S. El-Feky·J. Engelage·G. Eppley·S. Esumi·O. Evdokimov·O. Eyser·B. Fan·R. Fatemi·S. Fazio·H. Feng·Y. Feng·E. Finch·Y. Fisyak·F. A. Flor·C. Fu·T. Fu·C. A. Gagliardi·T. Galatyuk·T. Gao·Y. Gao·G. Garcia·F. Geurts·A. Gibson·A. Giri·K. Gopal·X. Gou·D. Grosnick·A. Gu·J. Gu·A. Gupta·W. Guryn·A. Hamed·R. J. Hamilton·J. Han·X. Han·S. Harabasz·M. D. Harasty·J. W. Harris·H. Harrison-Smith·L. B. Havener·X. H. He
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Abstract

The STAR experiment reports new, high-precision measurements of the transverse single-spin asymmetries for $\pi^{\pm}$ within jets, namely the Collins asymmetries, from transversely polarized ${p^{\uparrow}p}$ collisions at $\sqrt{s}$ = 510 GeV. The energy-scaled distribution of jet transverse momentum, $x_{\mathrm{T}} = 2p_{\mathrm{T,jet}}/\sqrt s$, shows a remarkable consistency for Collins asymmetries of $\pi^{\pm}$ in jets between $\sqrt{s}$ = 200 GeV and 510 GeV. This indicates that the Collins asymmetries are nearly energy independent with, at most, a very weak scale dependence in $p^{\uparrow}p$ collisions. These results extend to high-momentum scales ($Q^2 \leq 3400$ GeV$^2$) and enable unique tests of evolution and universality in the transverse-momentum-dependent formalism, thus providing important constraints for the Collins fragmentation functions.

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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, P. Barik, 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, Y. S. Chang, Z. Chang, A. Chatterjee, D. Chen, J. H. Chen, Q. Chen, W. Chen, Z. Chen, J. Cheng, Y. Cheng, W. Christie, X. Chu, S. Corey, H. J. Crawford, M. Csanád, G. Dale-Gau, A. Das, D. De Souza Lemos, I. M. Deppner, A. Deshpande, A. Dhamija, A. Dimri, P. Dixit, X. Dong, J. L. Drachenberg, E. Duckworth, J. C. Dunlop, Y. S. El-Feky, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, O. Eyser, B. Fan, R. Fatemi, S. Fazio, H. Feng, Y. Feng, E. Finch, Y. Fisyak, F. A. Flor, C. Fu, T. Fu, C. A. Gagliardi, T. Galatyuk, T. Gao, Y. Gao, G. Garcia, F. Geurts, A. Gibson, A. Giri, K. Gopal, X. Gou, D. Grosnick, A. Gu, J. Gu, A. Gupta, W. Guryn, A. Hamed, R. J. Hamilton, J. Han, X. Han, S. Harabasz, M. D. Harasty, J. W. Harris, H. Harrison-Smith, L. B. Havener, X. H. He. 2025-07-22. Energy Independence of the Collins Asymmetry in $p^{\uparrow}p$ Collisions. https://doi.org/10.1103/jgsw-zhny

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