Abstract
We confront the theoretical result of single spin asymmetry (SSA) $A_N$ in forward $pA$ collisions $p^\uparrow A \to hX$ including the gluon saturation effect with the recent preliminary experimental data from the PHENIX and STAR collaborations at RHIC. While we find overall reasonable agreement with the STAR data, our results indicate that the strong nuclear suppression of the asymmetry $A_N\sim A^{-1/3}$ observed by the PHENIX collaboration cannot be explained within the present understanding of this problem.
Highlights
Transverse single spin asymmetries (SSAs), as measured in collisions of an unpolarized probe with a transversely polarized proton, are traditionally a venue to understand the spin structure of the proton [1,2,3]
We have made a numerical computation of SSA in p↑p and p↑A in the forward region including the gluon saturation effect of the nucleus
While the saturation-based description seems to describe well the overall magnitude of the STAR data, it fails to explain the scaling AN ∼ A−1=3 observed by the PHENIX Collaboration
Summary
Transverse single spin asymmetries (SSAs), as measured in collisions of an unpolarized probe with a transversely polarized proton, are traditionally a venue to understand the spin structure of the proton [1,2,3]. Recent measurements at the Relativistic Heavy Ion Collider (RHIC) considered collisions of polarized protons on nuclear targets and so a completely new interplay between spin physics and the physics of gluon saturation becomes a reality [4,5,6,7,8,9,10,11]. This is especially so, as gluon saturation is important in the forward region of the produced hadron where SSA is the largest. We investigate the reason of this failure and discuss what extra contributions are needed to fix this problem
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
