Speaker
Description
At RHIC, the calibration of the absolute beam polarization is based on the elastic proton-proton scattering from a polarized hydrogen gas jet target (HJET) in the CNI region. The nuclear polarization of the HJET itself is determined with a Breit-Rabi polarimeter. Electron and hadron beam polarizations of 70% with 1% absolute error are to be provided for the EIC (Electron Ion Collider). This represents a challenge and requires a more precise polarization determination and a higher polarization transfer in the accelerator chain leading to the hadron storage ring (HSR) than presently achieved. About ten times more and shorter beam bunches will be stored at the EIC, and the total beam current will also be larger compared to the one at RHIC. As a result, the depolarizing effect at the HJET must be re-evaluated and the target and detector systems must be optimized to meet the goals at the EIC. Consideration is being given to improving the polarimetry capabilities for the HSR, aiming to determine all Cartesian components of the polarization vector at the specific position of the polarized jet target in the HSR, and not just the vertical component of the beam polarization as has been done so far.
The injection of other polarized species, such as vector- or tensor-polarized deuterons and vector-polarized 3He ions, is not included in the base physics program for the EIC but is technically feasible. To enable absolute beam polarimetry for these target species, the successful concept of scattering identical particles to transfer the measured nuclear target polarization from an atomic polarimeter to calibrate the beam polarization will also be applied. For polarized 3He ions, a new source has been developed for this purpose [1], which will be used to address this problem. Although the magnetic moment of the deuteron is small (G = -0.1426) and would normally prevent longitudinal beam polarization in the HSR, it has been shown that imperfect spin resonances in the HSR can be overcome by using the detector magnets as partial coils [2]. This has the advantage of ensuring longitudinal polarization at |Gγ| = 3×integer together with vertical orbit bumps. The HJET and the associated atomic polarimeter can be easily converted to generate polarized deuterium beams for determining the absolute polarization of deuterons.
The talk aims to highlight the challenges and the status regarding hadron beam polarimetry for the EIC.
References:
[1] Prajwal Mohan Murthy, Polarized 3He ABS for an Absolute Polarimeter at the EIC, abstract submitted to the PSTP2024.
[2] H. Huang, F. Meot, V. Ptitsyn, V. Ranjbar, and T. Roser, Polarization preservation of polarized deuteron beams in the electron ion collider at Brookhaven National Laboratory, Phys. Rev. Accel. Beams, (2020), 021001.
