Measurement of Direct-Photon Cross Section and Double-Helicity Asymmetry at √{s }=510 GeV in p →+p → Collisions

We present measurements of the cross section and double-helicity asymmetry A_{L L} of direct-photon production in p →+p → collisions at √{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 √{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.