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

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 (255 GeV) allowed us to greatly reduce the statistical and systematic uncertainties for elastic spin asymmetries, AN(t) and ANN(t), in the Coulomb-nuclear interference momentum transfer range 0.0013 < −t < 0.018 GeV 2 . For the first time hadronic single spin-flip r5 and double spin-flip r2 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 r5(s) and r2(s), indicating that the spin component may persist at high energies.PACS numbers: 24.70.+s, 25.40.Cm, 29.25.Pj.Introduction.-Study of the spin-averaged elastic pp hadronic amplitude at high energies has a more than 50 year history [1] and is continuing at the Large Hadron Collider. An essential contribution to this study relates to forward scattering for which the optical theorem and Coulomb-nuclear interference (CNI) provide an opportunity to separate the real and imaginary parts of an amplitude. Regge theory, based on the analyticity of a scattering amplitude, is a recognized method of understanding the energy dependence of amplitudes [2].An explanation of the unexpected discovery in the seventies of a growing pp cross section at high energies [3] was found [4] in the Pomeron concept, which is now associated with the exchange of nonperturbative QCD gluons [5]. Currently, the Pomeron and Regge pole picture of unpolarized elastic pp scattering is commonly considered as well established in the √ s = 5 GeV-13 TeV c.m. energy range [1], though some new results, e.g. from the TOTEM experiment [6], call for a revision [7]. However, the accuracy of existing polarized high energy experimental data [8][9][10][11] was insufficient to identify a Pomeron contribution, if any, to the pp spin-dependent amplitudes.In this Letter, we report new measurements of the single spin A N (t) and double spin A NN (t) analyzing powers in the small angle elastic collision of RHIC's polarized proton beams with Polarized Atomic Hydrogen Gas Jet Target [15](HJET) at √ s = 13.76 and 21.92 GeV. The precision has been significantly improved compared to previous HJET publications [9,10] and this has allowed us to not only isolate hadronic spin-flip amplitudes but also to incorporate spin dependence in a Regge pole anal-

The prospects on the absolute proton beam polarimetry at EIC

“…The complete system of EIC polarimeters (e.g. including the polarization profile control, 3 He beam polarimeters, etc.) will be discussed elsewhere.…”

“…(2.3) Asymmetry (2.1), measured as function of the momentum transfer t = −2m p T R , allowed us to precisely determine [3] the elastic pp analyzing power for two proton beam energies, 100 and 255 GeV. The obtained results are displayed in Fig.…”

“…The accuracy achieved in the determination of A N (t) [3] allows one to use a higher density unpolarized hydrogen jet target in a high precision absolute polarimeter, e.g., at EIC.…”

“…At RHIC, the absolute proton beam polarization, which is about P beam ∼ 55 -60%, can be determined [3] with low systematic uncertainties of σ syst P /P 0.5%. (1.1) This result well satisfies the EIC requirements.…”

Corrections to the elastic proton-proton analyzing power parametrization at high energies

“…1) on the vertically polarized target (the jet) with well-determined polarization |P j | = 0.957 ± 0.001 and the beam and jet spin correlated asymmetries of the recoil protons [Eq. (20)] are studied.…”