Single Spin Asymmetry $A_N$ in Polarized Proton-Proton Elastic Scattering at $\sqrt{s}=200$ GeV

TL;DR

This study presents a high-precision measurement of the single spin asymmetry in polarized proton-proton elastic scattering at 200 GeV, providing insights into the hadronic spin-flip amplitude and Pomeron exchange effects.

Contribution

The paper offers the first precise measurement of $A_N$ at 200 GeV in the specified $t$ range, constraining the hadronic spin-flip amplitude and Pomeron exchange contributions.

Findings

Measured $A_N$ is consistent with zero, indicating negligible hadronic spin-flip amplitude.

Results constrain the ratio of single spin-flip to non-flip amplitudes in elastic scattering.

Supports the dominance of Pomeron exchange with minimal spin-flip effects.

Abstract

We report a high precision measurement of the transverse single spin asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant 0.035$ $\GeVcSq$, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of $A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.