Single spin asymmetries in ultra-peripheral $p^{\uparrow }A$ collisions

We suggest inclusive hadron production in ultra-peripheral proton-nucleus collisions (UPCs) $p^{\uparrow }A\to hAX$ as a new channel to investigate single spin asymmetries (SSAs), in particular, to test the assumed dominance of the contribution from twist-three fragmentation functions. The UPC cross sections are obtained by considering the photoproduction limit of semi-inclusive deep inelastic scattering (SIDIS). In particular, we find simple formulas for the polarized UPC cross sections in the collinear twist-three framework. We then numerically calculate the fragmentation contribution to SSA in $p^{\uparrow }A\to \pi AX$ at $\sqrt{s}=200$ GeV and find a few percent asymmetry in the forward region.