Single transverse spin asymmetry of prompt photon production

Understand

We study the single transverse spin asymmetry of prompt photon production in high energy proton-proton scattering.

• We include the contributions from both the direct and fragmentation photons.
• While the asymmetry for direct photon production receives only the Sivers type of contribution, the asymmetry for fragmentation photons receives both the Sivers and Collins types of contributions.
• We make a model calculation for quark-to-photon Collins function, which is then used to estimate the Collins asymmetry for fragmentation photons.