Polarized $^3$He ABS for an Absolute Hadron Polarimeter at the EIC
ORAL
Abstract
A polarized $^3$He$^{++}$ beam is a core capability envisioned for the Electron-Ion Collider (EIC), where $^3$He would serve as an effective polarized neutron probe. Realizing the EIC spin program thus requires precise, absolute $^3$He beam polarimetry. We present an absolute polarimeter based on $^3$He-$^3$He elastic scattering in the Coulomb-nuclear interference region, employing a polarized $^3$He atomic beam source (ABS) as the target. We also evaluated using an optically polarized $^3$He target.
The upgraded ABS, originally developed for the cryogenic neutron Electric Dipole Moment experiment at Oak Ridge National Laboratory, delivers a near-collinear, $\sim$1 K $^3$He atomic stream with flux of $\gtrsim10^{14}/\mathrm{s}$, with a beam diameter of $\sim1~$cm, and polarization $\approx95\%$ achieved with the help of a magnetic field gradient of $\sim$1 T cm$^{-1}$ provided by an array of permanent magnets. The source is vertically mountable and includes $2$-axis beam steering. Target polarization is measured in-situ by an analyzer quadrupole with reversed gradients. Comparing post-polarizer and post-analyzer transverse profiles with a residual-gas-analyzer yields the transmitted-fraction and thus the ABS polarization.
To reach H-jet-like target thickness, we plan to couple the ABS to a cylindrical cryogenic internal storage cell, with perforated conical Wakefield suppressors, thin aluminum windows, and differential pumping. This increases the effective target thickness to $\sim6.8\times10^{12}/\mathrm{cm^2}$. The dual left-right asymmetries of scattered target and scattered beam particles are expected to be measured using silicon strip sensors for scattered target particles, and radiation-hard diamond strips with QDC-based fragment veto capability for scattered-beam detection. The demonstrated ABS flux and the expected storage-cell density allows us to achieve $\sim1\%/\sqrt{\rm hour}$ statistical precision on the $^3$He$^{++}$ beam polarization for practical detector acceptances. As an ancillary physics effort, we exploit the same ABS to test $^4$He electrical neutrality via deflection in a reversible electric field.
The upgraded ABS, originally developed for the cryogenic neutron Electric Dipole Moment experiment at Oak Ridge National Laboratory, delivers a near-collinear, $\sim$1 K $^3$He atomic stream with flux of $\gtrsim10^{14}/\mathrm{s}$, with a beam diameter of $\sim1~$cm, and polarization $\approx95\%$ achieved with the help of a magnetic field gradient of $\sim$1 T cm$^{-1}$ provided by an array of permanent magnets. The source is vertically mountable and includes $2$-axis beam steering. Target polarization is measured in-situ by an analyzer quadrupole with reversed gradients. Comparing post-polarizer and post-analyzer transverse profiles with a residual-gas-analyzer yields the transmitted-fraction and thus the ABS polarization.
To reach H-jet-like target thickness, we plan to couple the ABS to a cylindrical cryogenic internal storage cell, with perforated conical Wakefield suppressors, thin aluminum windows, and differential pumping. This increases the effective target thickness to $\sim6.8\times10^{12}/\mathrm{cm^2}$. The dual left-right asymmetries of scattered target and scattered beam particles are expected to be measured using silicon strip sensors for scattered target particles, and radiation-hard diamond strips with QDC-based fragment veto capability for scattered-beam detection. The demonstrated ABS flux and the expected storage-cell density allows us to achieve $\sim1\%/\sqrt{\rm hour}$ statistical precision on the $^3$He$^{++}$ beam polarization for practical detector acceptances. As an ancillary physics effort, we exploit the same ABS to test $^4$He electrical neutrality via deflection in a reversible electric field.
*P. M. is supported by US-Dept. of Energy grants \#DE-SC0019768, \#DE-SC0014448, and \#DE-SC0018229, and BNL award \#460913.
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Presenters
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Prajwal T MohanMurthy
- Massachusetts Institute of Technology