Transverse Single Spin Asymmetry for Forward Direct Photon Production in $\sqrt{s}=200$ GeV $p^{\uparrow}+p$ Collisions at STAR

Experimental results for large transverse single spin asymmetries, $A_{N}$, continue to challenge our understanding of QCD. One important test of the current theoretical framework is the sign reversal of $A_{N}$ from SIDIS to Drell-Yan channels, a topic closely linked to QCD factorization. Theoretical models based on initial state effects predict the sign of $A_{N}$ for jets and prompt photons in hadron collisions to be the same as Drell-Yan, but opposite of what is observed for mesonic final states, such as previous STAR results for $\pi^0$ and $\eta$. The $A_{N}$ for direct photons (prompt + fragmentation) may serve as an indirect test of this model, especially if final state effects (Collins asymmetry) are small for fragmentation photons. We present the status update for the STAR measurement of $A_{N}$ for direct photon production at average pseudorapidity of 3.65. All data were collected for polarized p+p collisions at RHIC energies of $\sqrt{s}$ = 200 GeV. The integrated luminosity was 6.8 pb$^{-1}$, and the average polarization was 56\%.