Polarizing a stored proton beam by spin flip?

TL;DR

This study measures the spin flip cross section in low-energy electron-proton scattering to evaluate its effectiveness in polarizing stored proton beams, finding it too small for practical use and invalidating related proposals.

Contribution

The paper provides the first experimental measurement of the spin flip cross section in low-energy electron-proton scattering, challenging previous theoretical predictions.

Findings

Measured spin flip cross sections are too small for effective polarization.

Results invalidate proposals using co-moving polarized positrons for antiproton polarization.

Experimental data contradict recent conflicting calculations.

Abstract

We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin flip cross section in low-energy electron-proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.