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

A A Poblaguev,D Svirida,Y Makdisi,I Alekseev,W B Schmidke,K O Eyser,A Zelenski,E Aschenauer,N H Buttimore,H Huang,G Atoian

doi:10.1103/physrevlett.123.162001

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_{beam}=100 GeV) and 2017 (255GeV) 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 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.

Highlights

In this Letter, we report new measurements of the single spin ANðtÞ and double spin ANNðtÞ analyzing powers in the small angle elastic collision of Relativistic Heavy Ion Collider (RHIC)’s polarized proton beams with (HJET) [12]
HJET publications [9,10] and this has allowed us to isolate hadronic spin-flip amplitudes and to incorporate spin dependence in a Regge pole analysis. It appears that forward elastic pp scattering has nonvanishing single and double spin-flip hadronic amplitudes at high energy where the Pomeron dominates
A crucial part of the analysis relates to an accurate determination of the background event rate in every Si detector as a function of the measured energy and the spins of the jet and beam

Summary

Introduction

In this Letter, we report new measurements of the single spin ANðtÞ and double spin ANNðtÞ analyzing powers in the small angle elastic collision of RHIC’s polarized proton beams with (HJET) [12] It appears that forward elastic pp scattering has nonvanishing single and double spin-flip hadronic amplitudes at high energy where the Pomeron dominates.

Results

Conclusion