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

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

N. J. Abdulameer et al. (PHENIX Collaboration)

Phys. Rev. Lett. 130, 251901 – Published 21 June 2023

Abstract

We present measurements of the cross section and double-helicity asymmetry $A_{L L}$ of direct-photon production in $\vec{p} + \vec{p}$ collisions at $\sqrt{s} = 510 GeV$ . The measurements have been performed at midrapidity ( $| η | < 0.25$ ) 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.

Received 17 February 2022
Revised 4 November 2022
Accepted 28 April 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.251901

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Published by the American Physical Society