Precision Small Scattering Angle Measurements of Elastic Proton-Proton Single and Double Spin Analyzing Powers at the RHIC Hydrogen Jet Polarimeter

TL;DR

This paper reports precise measurements of elastic proton-proton spin asymmetries at RHIC, utilizing upgraded detectors and analysis to isolate spin-flip amplitudes and distinguish Pomeron and Regge contributions at high energies.

Contribution

First reliable isolation of hadronic spin-flip amplitudes at high energies and momentum transfers, with separation of Pomeron and Regge contributions using improved experimental methods.

Findings

Reduced uncertainties in spin asymmetry measurements.

First separation of Pomeron and Regge contributions to spin-flip amplitudes.

Evidence that spin components may persist at high energies.

Abstract

The Polarized Atomic Hydrogen Gas Jet Target polarimeter is employed by the Relativistic Heavy Ion Collider (RHIC) to measure the absolute polarization of each colliding proton beam. Polarimeter detectors and data acquisition were upgraded in 2015 to increase solid angle, energy range and energy resolution. These upgrades and advanced systematic error analysis along with improved beam intensity and polarization in RHIC runs 2015 ($E_\textrm{beam}=100\,\text{GeV}$) and 2017 ($255\,\text{GeV}$) allowed us to greatly reduce the statistical and systematic uncertainties for elastic spin asymmetries, $A_N(t)$ and $A_NN(t)$, in the Coulomb-nuclear interference momentum transfer range $0.0013<-t<0.018\,\text{GeV}^2$. For the first time hadronic single spin-flip $r_5$ and double spin-flip $r_2$ amplitude parameters were reliably isolated at these energies and momentum transfers. Measurements at two beam energies enable a separation of Pomeron and Regge pole contributions to $r_5(s)$ and $r_2(s)$, indicating that the spin component may persist at high energies.