Speaker
Description
We study the Coulomb-nuclear interference (CNI), a kinematical region of very low 4-momentum transfer squared, $-t$, where the single-spin asymmetry $A_N(t)$ is measured.
The measurement of the analyzing power $A_N(t)$ offers in particular a way of how polarimeters can determine the beam polarization e.g. in the RHIC spin program.
The current theoretical approaches assume that the proton non-flip to (single) spin-flip ratio, $r_5$, is the same for proton-proton as well as for proton-nucleus collisions.
Unfortunately, this approach is not able to describe newer data on analyzing power for heavy ions, particularly $p-Au$ measurements in the PHENIX experiment.
However, as we demonstrate, $r_5^{pA}$ is subject to strong nuclear effects and considerable differs from $r_5^{pp}$.
This new approach is compared with all available proton-nucleus data for analyzing power including $p-C, p-Al$ and $p-Au$ measurement at different energies.
