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arXiv · 2509.13497

Transverse single-spin asymmetry of forward $\eta$ mesons in $p^{\uparrow}+ p$ collisions at $\sqrt{s} = 200$ GeV

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
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Abstract

Utilizing the 2012 transversely polarized proton data from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, the forward $\eta$-meson transverse single-spin asymmetry ($A_N$) was measured for $p^{\uparrow}+p$ collisions at $\sqrt{s}=200$ GeV as a function of Feynman-x ($x_F$) for $0.2<|x_F|<0.8$ and transverse momentum ($p_T$) for $1.0 =0.086 \pm 0.019$), agreeing well with previous measurements of $\pi^{0}$ and $\eta$ $A_N$, but with reach to higher $x_F$ and $p_T$. The contribution of initial-state spin-momentum correlations to the asymmetry, as calculated in the collinear twist-3 framework, appears insufficient to describe the data and suggests a significant impact on the asymmetry from fragmentation.

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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. 2025-09-16. Transverse single-spin asymmetry of forward $\eta$ mesons in $p^{\uparrow}+ p$ collisions at $\sqrt{s} = 200$ GeV. https://arxiv.org/abs/2509.13497

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