A surprising method for polarising antiprotons

TL;DR

This paper introduces a novel method to polarize antiprotons using a polarized positron beam at specific velocities, achieving significant spin-flip cross sections and promising practical source options, with potential advantages over existing techniques.

Contribution

It proposes a new approach for antiproton polarization via polarized positron beams, including detailed calculations and feasible source designs, improving efficiency over previous methods.

Findings

Spin-flip cross section reaches about 2×10^{13} barns at v/c ≈ 0.002.

Feasible polarized positron sources with high flux density are presented.

The method offers a tenfold improvement in figure-of-merit compared to existing proposals.

Abstract

We propose a method for polarising antiprotons in a storage ring by means of a polarised positron beam moving parallel to the antiprotons. If the relative velocity is adjusted to $v/c \approx 0.002$ the cross section for spin-flip is as large as about $2 \cdot 10^{13}$ barn as shown by new QED-calculations of the triple spin-cross sections. Two possibilities for providing a positron source with sufficient flux density are presented. A polarised positron beam with a polarisation of 0.70 and a flux density of approximately $1.5 \cdot 10^{10}$/(mm$^2$ s) appears to be feasible by means of a radioactive $^{11}$C dc-source. A more involved proposal is the production of polarised positrons by pair production with circularly polarised photons. It yields a polarisation of 0.76 and requires the injection into a small storage ring. Such polariser sources can be used at low (100 MeV) as well as at high (1 GeV) energy storage rings providing a time of about one hour for polarisation build-up of about $10^{10}$ antiprotons to a polarisation of about 0.18. A comparison with other proposals show a gain in the figure-of-merit by a factor of about ten.