Speaker
Description
A possibility to precisely measure absolute vertical polarization of the EIC ${}^3\mathrm{He}$ beams using the polarized hydrogen gas jet target (HJET) is discussed. By concurrent measurement of $a_h$ and $a_p$, the beam $h^\uparrow p$ and jet $p^\uparrow h$ spin asymmetries for the detected recoil protons, the He3 beam polarization can be approximated by $P_\mathrm{beam}=P_\mathrm{jet}\times a_h\kappa_p/a_p\kappa_h$, where $\kappa_p=1.793$ and $\kappa_h = -1.398$ are derived from the magnetic moments $\mu_p$ and $\mu_h$, and $P_\mathrm{jet}\approx0.957$ is the jet polarization determined by a conventional Breit-Rabi polarimeter. The result does not depend on the actual parameters of $hp$ scattering: total cross-section $\sigma_\mathrm{tot}$, forward real-to-imaginary ratio $\rho$, or Coulomb phase $\delta_C$.
Corrections of a few percent to the value of $P_\mathrm{beam}$ due to the term $\sim m^2/s$ in the electromagnetic spin-flip amplitude and due to hadronic spin-flip amplitudes $r_5^{hp}$ and $r_5^{ph}$ are well determined. Since the ${}^3\mathrm{He}$ ground state is mostly fully space-symmetric $S$ state, the $hp$ spin-flip amplitudes can be readily related with sufficient accuracy, $r_p^{hp}=r_5^{pp}/3$ and $r_5^{ph}=r_5^{pp}$, to the amplitude measured in elastic $pp$ scattering. Considering the experimental uncertainty in the value of $r_5^{pp}$ as well as the uncertainties in the measurement of $a_h/a_p$, we can expect $\sigma_P^\mathrm{syst}\leq0.9\,\%$ accuracy for the absolute ${}^3\mathrm{He}$ beam polarization at EIC.
Since only the recoil proton is detected in HJET measurements, the acquired data may be contaminated by inelastic (${}^3\mathrm{He}$ break-up) events. However, since only low energy protons in the small solid angle at 90 degree are counted, the inelastic component is strongly suppressed. Analyzing Run 16 data with a deuteron beam, we found that data contamination by the break-up events should not exceed a few percent. In addition, the inelastic corrections are significantly canceled in the $a_h/a_p$ ratio. Thus, the anticipated alteration of the measured $P_\mathrm{beam}$ due to ${}^3\mathrm{He}$ break-up can be neglected.
