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arXiv · 2202.08158

Measurement of Direct-Photon Cross Section and Double-Helicity Asymmetry at $\sqrt{s}=510$ GeV in $\vec{p}+\vec{p}$ Collisions

PHENIX Collaboration·N. J. Abdulameer·U. Acharya·A. Adare·C. Aidala·N. N. Ajitanand·Y. Akiba·R. Akimoto·M. Alfred·N. Apadula·Y. Aramaki·H. Asano·E. T. Atomssa·T. C. Awes·B. Azmoun·V. Babintsev·M. Bai·N. S. Bandara·B. Bannier·K. N. Barish·S. Bathe·A. Bazilevsky·M. Beaumier·S. Beckman·R. Belmont·A. Berdnikov·Y. Berdnikov·L. Bichon·D. Black·B. Blankenship·J. S. Bok·V. Borisov·K. Boyle·M. L. Brooks·J. Bryslawskyj·H. Buesching·V. Bumazhnov·S. Campbell·V. Canoa Roman·C. -H. Chen·M. Chiu·C. Y. Chi·I. J. Choi·J. B. Choi·T. Chujo·Z. Citron·M. Connors·R. Corliss·Y. Corrales Morales·M. Csanád·T. Csörgő·A. Datta·M. S. Daugherity·G. David·C. T. Dean·K. DeBlasio·K. Dehmelt·A. Denisov·A. Deshpande·E. J. Desmond·L. Ding·A. Dion·V. Doomra·J. H. Do·A. Drees·K. A. Drees·J. M. Durham·A. Durum·H. En'yo·A. Enokizono·R. Esha·B. Fadem·W. Fan·N. Feege·D. E. Fields·M. Finger, Jr.·M. Finger·D. Firak·D. Fitzgerald·S. L. Fokin·J. E. Frantz·A. Franz·A. D. Frawley·P. Gallus·C. Gal·P. Garg·H. Ge·M. Giles·F. Giordano·A. Glenn·Y. Goto·N. Grau·S. V. Greene·M. Grosse Perdekamp·T. Gunji·H. Guragain·Y. Gu·T. Hachiya·J. S. Haggerty·K. I. Hahn
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Abstract

We present measurements of the cross section and double-helicity asymmetry $A_{LL}$ of direct-photon production in $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=510$ GeV. The measurements have been performed at midrapidity ($|\eta|<0.25$) with the PHENIX detector at the Relativistic Heavy Ion Collider. At relativistic energies, direct photons are dominantly produced from the initial quark-gluon hard scattering and do not interact via the strong force at leading order. Therefore, at $\sqrt{s}=510$ GeV, where leading-order-effects dominate, these measurements provide clean and direct access to the gluon helicity in the polarized proton in the gluon-momentum-fraction range $0.02<x<0.08$, with direct sensitivity to the sign of the gluon contribution.

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PHENIX Collaboration, N. J. Abdulameer, U. Acharya, A. Adare, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, M. Alfred, N. Apadula, Y. Aramaki, H. Asano, E. T. Atomssa, T. C. Awes, B. Azmoun, V. Babintsev, M. Bai, N. S. Bandara, B. Bannier, K. N. Barish, S. Bathe, A. Bazilevsky, M. Beaumier, S. Beckman, R. Belmont, A. Berdnikov, Y. Berdnikov, L. Bichon, D. Black, B. Blankenship, J. S. Bok, V. Borisov, K. Boyle, M. L. Brooks, J. Bryslawskyj, H. Buesching, V. Bumazhnov, S. Campbell, V. Canoa Roman, C. -H. Chen, M. Chiu, C. Y. Chi, I. J. Choi, J. B. Choi, T. Chujo, Z. Citron, M. Connors, R. Corliss, Y. Corrales Morales, M. Csanád, T. Csörgő, A. Datta, M. S. Daugherity, G. David, C. T. Dean, K. DeBlasio, K. Dehmelt, A. Denisov, A. Deshpande, E. J. Desmond, L. Ding, A. Dion, V. Doomra, J. H. Do, A. Drees, K. A. Drees, J. M. Durham, A. Durum, H. En'yo, A. Enokizono, R. Esha, B. Fadem, W. Fan, N. Feege, D. E. Fields, M. Finger, Jr., M. Finger, D. Firak, D. Fitzgerald, S. L. Fokin, J. E. Frantz, A. Franz, A. D. Frawley, P. Gallus, C. Gal, P. Garg, H. Ge, M. Giles, F. Giordano, A. Glenn, Y. Goto, N. Grau, S. V. Greene, M. Grosse Perdekamp, T. Gunji, H. Guragain, Y. Gu, T. Hachiya, J. S. Haggerty, K. I. Hahn. 2022-02-16. Measurement of Direct-Photon Cross Section and Double-Helicity Asymmetry at $\sqrt{s}=510$ GeV in $\vec{p}+\vec{p}$ Collisions. https://doi.org/10.1103/physrevlett.130.251901

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