Speaker
Description
The longitudinal spin decomposition of the proton provides key information about its structure. While the quark spin contribution was well constrained by the polarized deep inelastic scattering (DIS), the gluon spin contribution remains less known. Direct photon, jet, and charged pion production in the longitudinally polarized proton ($\vec{p}+\vec{p}$) collisions can probe the gluon spin at leading order. Compared with hadron production, direct photon production is the most ``clean'' channel since there is little fragmentation involved. The Relativistic Heavy Ion Collider (RHIC) is the only collider that is capable of producing two longitudinal polarized proton beams. The RHIC run of year 2013 provides the largest integrated luminosity (155 pb$^{-1}$) in $\vec{p}+\vec{p}$ collisions. The Electromagnetic Calorimeter at PHENIX has fine granularity to separate the two $\pi^0$ decay photons up to $\pi^0$ transverse momentum $p_T$ of 12 GeV/c. The shower profile analysis further extends the $\gamma/\pi^0$ discrimination up to 30 GeV/c. In this talk, I will present the direct photon cross section and double helicity asymmetry ($A_{LL}$) for photon $p_T$ of 6--30 GeV/c and 6--20 GeV/c, respectively. When included in future global analyses, our results will provide an independent constraint on the gluon spin contribution to the proton spin.
| Submitted on behalf of a Collaboration? | Yes |
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