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

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, 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.

The RHIC polarized H⁻ ion source.

A novel polarization technique had been successfully implemented for the Relativistic Heavy Ion Collider (RHIC) polarized H(-) ion source upgrade to higher intensity and polarization. In this technique, a proton beam inside the high magnetic field solenoid is produced by ionization of the atomic hydrogen beam (from external source) in the He-gaseous ionizer cell. Further proton polarization is produced in the process of polarized electron capture from the optically pumped Rb vapor. The use of high-brightness primary beam and large cross sections of charge-exchange cross sections resulted in production of high intensity H(-) ion beam of 85% polarization. The source very reliably delivered polarized beam in the RHIC Run-2013 and Run-2015. High beam current, brightness, and polarization resulted in 75% polarization at 23 GeV out of Alternating Gradient Synchrotron (AGS) and 60%-65% beam polarization at 100-250 GeV colliding beams in RHIC.

Charge neutralized low energy beam transport at Brookhaven 200 MeV linac.

The H(-) magnetron source provides about 100 mA H(-) beam to be match into the radio-frequency quadrupole accelerator. As H(-) beam traverses through low energy transport, it ionizes the residual gas and electrons are repelled and positive ions are trapped in the beam, due to negative potential of the beam, providing charge neutralization for the H(-) beam. The neutralization time for the critical density depends upon the background gas and its pressure. Critical density for xenon gas at 35 keV is about 43 times smaller than that of hydrogen and stripping cross section is only 5 times than that of hydrogen gas. We are using xenon gas to reduce neutralization time and to improve transmission through the 200 MeV linac. We are also using pulse nitrogen gas to improve transmission and stability of polarized H(-) beam from optically pumped polarized ion source.

Production, formation, and transport of high-brightness atomic hydrogen beam studies for the relativistic heavy ion collider polarized source upgrade.

The RHIC polarized H(-) ion source had been successfully upgraded to higher intensity and polarization by using a very high brightness fast atomic beam source developed at BINP, Novosibirsk. In this source the proton beam is extracted by a four-grid multi-aperture ion optical system and neutralized in the H2 gas cell downstream from the grids. The proton beam is extracted from plasma emitter with a low transverse ion temperature of ∼0.2 eV which is formed by plasma jet expansion from the arc plasma generator. The multi-hole grids are spherically shaped to produce "geometrical" beam focusing. Proton beam formation and transport of atomic beam were experimentally studied at test bench.

Review of polarized ion sources (invited).

Recent progress in polarized ion sources development is reviewed. New techniques for production of polarized H(-) ion (proton), D(-) (D(+)), and (3)He(++) ion beams are discussed. Feasibility studies of these techniques are in progress at BNL and other laboratories. Polarized deuteron beams will be required for the polarization program at the Dubna Nuclotron and at the deuteron electric dipole moment experiment at BNL. Experiments with polarized (3)He(++) ion beams are a part of the experimental program at the future electron ion collider.

Optical beam profile monitor and residual gas fluorescence at the relativistic heavy ion collider polarized hydrogen jet.

A gas fluorescence beam profile monitor has been implemented at the relativistic heavy ion collider (RHIC) using the polarized atomic hydrogen gas jet, which is part of the polarized proton polarimeter. RHIC proton beam profiles in the vertical plane of the accelerator are obtained as well as measurements of the width of the gas jet in the beam direction. For gold ion beams, the fluorescence cross section is sufficiently large so that profiles can be obtained from the residual gas alone, albeit with long light integration times. We estimate the fluorescence cross sections that were not known in this ultrarelativistic regime and calculate the beam emittance to provide an independent measurement of the RHIC beam. This optical beam diagnostic technique, utilizing the beam induced fluorescence from injected or residual gas, offers a noninvasive particle beam characterization and provides visual observation of proton and heavy ion beams.

Overcoming depolarizing resonances with dual helical partial Siberian snakes.

Acceleration of polarized protons in the energy range of 5 to 25 GeV is challenging. In a medium energy accelerator, the depolarizing spin resonances are strong enough to cause significant polarization loss but full Siberian snakes cause intolerably large orbit excursions and are also not feasible since straight sections usually are too short. Recently, two helical partial Siberian snakes with double pitch design have been installed in the Brookhaven Alternating Gradient Synchrotron (AGS). With a careful setup of optics at injection and along the energy ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances otherwise encountered during acceleration to maintain a high intensity polarized beam in medium energy synchrotrons. The observation of partial snake resonances of higher than second order will also be described.

Polarized proton collisions at 205 GeV at RHIC.

The Brookhaven Relativistic Heavy Ion Collider (RHIC) has been providing collisions of polarized protons at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during acceleration from injection to 100 GeV. However, the intrinsic spin resonances beyond 100 GeV are about a factor of 2 stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were first accelerated to the record energy of 205 GeV in RHIC with a significant polarization measured at top energy in 2005. This Letter presents the results and discusses the sensitivity of the polarization survival to orbit distortions.

Parity violation in proton-proton scattering at 221 MeV.

The parity-violating longitudinal analyzing power, A(z), has been measured in pvectorp elastic scattering at an incident proton energy of 221 MeV. The result obtained is A(z) = [0.84+/-0.29(stat)+/-0.17(syst)]x10(-7). This experiment is unique in that it selects a single parity violating transition amplitude (3P2 - 1D2) and consequently directly constrains the weak meson-nucleon coupling constant h(pp)(rho). When this result is taken together with the existing pvectorp parity violation data, the weak meson-nucleon coupling constants h(pp)(rho) and h(pp)(omega) can, for the first time, both be determined.