Polarization effects in non-relativistic ep scattering

Abstract

The cross section which addresses the spin-flip transitions of a proton (antiproton) interacting with a polarized non-relativistic electron or positron is calculated analytically. In the case of attraction, this cross section is greatly enhanced for sufficiently small relative velocities as compared to the result obtained in the Born approximation. However, it is still very small, so that the beam polarization time turns out to be enormously large for the parameters of e ± beams available now.This practically rules out a use of such beams to polarize stored antiprotons or protons.

A surprising method for polarising antiprotons

“…[1]. Whereas we get σ (λ = ±) for antiproton and proton electron scattering as a function of the proton lab kinetic energy T h for b = 10 10 fm in PW and DW.…”

“…Milstein, S.G. Salnikov and V.M. Strakhovenko [1] we have searched for the reason of the dramatic difference of our triple-spin transfer cross-section in the scattering of spin-1/2 hadrons from leptons [2]. We found a numerical problem in our calculation of the spin-dependent cross-sections [3,4].…”

Coulomb effects in polarization transfer in elastic antiproton and proton electron scattering at low energies

“…In view of the criticism raised recently by Milstein et al [1] our code for the numerical evaluation, based on an integral representation, has been checked against the analytic evaluation of [1] based on a partial-wave expansion. It turned out that, besides a minor error, the main reason for the overestimation of the polarisation transfer crosssection for elastic electron proton scattering at low energies is caused by the fact that for larger positive values of the Coulomb parameter η (η ≥ 1.5), corresponding to a proton kinetic energy T h ≤ 0.01 MeV, the tensor D ij of the hyperfine interaction…”

PAX - The Road towards Polarized Antiprotons

“…In recent years, a paper claiming a very high cross section for the polarization transfer from polarized electrons (positrons) to protons (antiprotons) at small relative energy has received a lot of attention [13] (see however [14,15]. Since it is an elaborate task to perform a test with antiprotons and polarized positrons, we essentially turned the reaction around and made a depolarization measurement with polarized protons, interacting with unpolarized electrons (see sect.…”