R. Barday | Searcharxiv

arXiv2007

A surprising method for polarising antiprotons

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.

physics.acc-ph↗

arXiv2006

An effective method for polarising antiprotons

There exists an inconsistency in the value of the kinetic energies of the antiproton in the electron laboratory reference frame and of the electron in the antiproton laboratory reference frame taken wrongly both as 0.65 keV (see figure 1 and table 2) of the paper. The consequence of this mistake is that the relative velocity of the electron is not -0.0504 (see table 2) but -0.00118, i.e. a factor of \sqrt{m_{electron}/m_{proton}} = 1/43 smaller. The consequence of this factor is that the relative velocity β_{relative} in eq. (27) and κare smaller by this factor. This means that the time for polarisation build-up is longer by a factor 43. Though the principle idea is not put into question, the method is not effective "with todays technology" and we have to withdraw the paper and the proposal.

physics.acc-ph↗