Single spin asymmetries in ultra-peripheral p A collisions
Abstract
We suggest inclusive hadron production in ultra-peripheral proton-nucleus collisions (UPCs) p A h AX 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 A π A X at s = 200 GeV and find a few percent asymmetry in the forward region.
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