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

We present measurements of the cross section and double-helicity asymmetry ALL of direct-photon production in p ⃗ + p ⃗ collisions at ffis ffi p = 510 GeV. The measurements have been performed at midrapidity (I & eta;I < 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 ffiffistrong force at leading order. Therefore, at p 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.

Automated summary

We have performed measurements of the cross section and double-helicity asymmetry ALL of direct-photon production in polarized proton-proton collisions at a center of mass energy of 510 GeV. These measurements provide clean and direct access to the gluon helicity in the polarized proton, with sensitivity to the sign of the gluon contribution.