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HK: Fachverband Hadronen und Kerne

HK 35: Hadron Structure and Spectroscopy II

HK 35.1: Group Report

Tuesday, March 17, 2009, 16:30–17:00, H-ZO 30

Towards polarized Antiprotons — •Frank Rathmann — Institut für Kernphysik, Forschungszentrum Jülich, Germany

We present a short overview of the PAX physics case for polarized antiprotons. The recent measurement of the depolarizing pe cross section settled a long–standing controversy about the role of electrons in the polarization buildup of a stored beam by spin-filtering. The depolarization study sheds light on the ep spin–flip cross sections when the target electrons are unpolarized. The experimental finding rules out the practical use of polarized leptons to polarize a beam of antiprotons with present–day technologies. This leaves us with the only proven method to polarize a stored beam in situ, namely spin filtering by the strong interaction. At present, we are lacking a complete quantitative understanding of all underlying processes, therefore the PAX collaboration is aiming at high–precision polarization buildup studies with transverse and longitudinal polarization using stored protons in COSY. The polarized internal target required for these investigations is presently set up to be installed together with a large–acceptance detector system for the determination of target and beam polarizations in a dedicated low β section at COSY. In contrast to the pp system, the experimental basis for predicting the polarization buildup in a stored antiproton beam by spin filtering is practically non–existent. Therefore, it is of high priority to perform, subsequently to the COSY experiments, a series of dedicated spin–filtering experiments using stored antiprotons at the AD ring at CERN.