Polarizing a stored proton beam by spin flip?

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.Comment: 18 pages, 6 figure

Measurement of the Spin–Dependence of the p‾−p\overline{p}-p Interaction at the AD–Ring

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin–dependent pbar-p cross sections σ1 and σ2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin–spin dependence of the nucleon–antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double–polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single– and double–spin observables, thereby opening a new window on QCD spin physics. A recent experiment at COSY revealed that ep spin–flip cross sections are too small to cause a detectable depolarization of a stored proton beam. This measurement rules out a proposal to use polarized positrons to polarize an antiproton beam by e+pbar spin–flip interactions. Thus, our approach to provide a beam of polarized antiprotons is based on spin filtering, using an internal polarized hydrogen gas target – a method that has been tested with stored protons. We expect to produce a polarized antiproton beam with at least ten orders of magnitude higher intensity than a secondary polarized antiproton beam previously available. Provided that antiproton beams with a polarization of about 15% can be obtained with the APR, the antiproton machine at FAIR (the High Energy Storage Ring) could be converted into a double–polarized asymmetric pbar-p collider by installation of an additional COSY–like ring. In this setup, antiprotons of 3.5 GeV/c collide with protons of 15 GeV/c at c.m. energies of √s ≈ √200 GeV with a luminosity in excess of 10^31 cm−2s−1. The PAX physics program proposed for FAIR has been highly rated, and would include, most importantly, a first direct measurement of the transversity distribution of the valence quarks in the proton, and a first measurement of the moduli and the relative phase of the time–like electric and magnetic form factors G_E,M of the proton.We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics

Spin-Filtering Studies at COSY

We propose to use an internal polarised target in the COSY ring to determine the polarisation build–up in a proton beam. Spin–filtering experiments at COSY would provide the necessary data to test our present understanding of spin–filtering processes in storage rings. Measurements of the polarisation build–up of stored protons are crucial to progress towards the PAX goal to eventually produce stored polarised antiproton beams. The availability of intense stored beams of polarised antiprotons will provide access to a wealth of single– and double–spin observables, opening a new window on QCD spin physics. It is planned to realise this experimental programme at the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. A recent experiment at COSY revealed that e~p spin–flip cross sections are too small to cause a detectable depolarisation of a stored proton beam. This measurement rules out a proposal to use polarised electrons to polarise a proton beam by ~ep spin–flip interactions. Thus, our approach to provide a beam of polarised protons is based on spin–filtering using an internal polarised gas target. In total 22 weeks of beam time are needed to complete the experimental program at COSY. We now ask for two weeks of beam time for commissioning of the low–β section and measuring the machine acceptance

Status Report and Beam-Time Request for COSY experiment #199 Spin–Filtering Studies at COSY

We report on the progress of the PAX experimental programme since the last PAC meeting. During summer shutdown 2009 four new quadrupole magnets and a modified vacuum system have been installed into the COSY ring to form a section with low β functions. With the successful commissioning of this low-β insertion in January 2010 it has also been discovered that intra-beam scattering effects are likely limiting the beam lifetime. In order to get these effects under control and to improve the lifetime, to commission a new detection system, and to finally perform a first series of spin–filtering measurements with transverse polarisation, we request ten weeks of beam time. Content

Beam Request Spin-Filtering Studies at COSY

Summary of experiment: We report on the progress of the PAX experimental program since the last PAC meeting. During two blocks of each three weeks beam development intercepted by two weeks of maintenance, systematic machine studies have been carried out. An effective procedure for setting up the machine with the low-β section and a target cell at the new PAX-IP in order to achieve high beam lifetimes has been developed. The effect of flow-limiters and one NEG-pump on the beam lifetime has been studied, as well as the effect of different beam emittances and beam intensities on the beam lifetime. Even though by increasing the beam emittance a reproducible maximum for the beam lifetime was achievable, no effect of the beam intensity was seen and therefore no clear observation of the so-called Touschek-effect was possible. Nevertheless, we learned how to gain a sufficient beam lifetime for spin-filtering studies at COSY and apply for 3 weeks of beam development followed by 4 weeks of beam time