2020 Impact factor 3.043
Hadrons and Nuclei
Open Access
Eur. Phys. J. A 24, s2.35-s2.38 (2005)
DOI: 10.1140/epjad/s2005-04-007-1

Transverse spin asymmetry at the A4 experiment

Sebastian Baunack

Johannes Gutenberg Universität Mainz, Institut für Kernphysik, J.J. Becherweg 45, 55299 Mainz, Germany

(Received 15 October 2004 / Published online 08 February 2005)


The A4 collaboration at the MAMI accelerator has measured the transverse spin asymmetry in the cross section of elastic scattering of transversely polarized electrons off unpolarized protons. An azimuthal dependence of the asymmetry has been observed, the amplitudes have been determined as A$\perp$(Q2=0.106 (GeV/c)2 $)=({-8.59}~\pm~{0.89}_{stat}\pm~{0.75}_{syst})~\cdot~10^{-6}$ and A$\perp$(Q2=0.230 (GeV/c)2 $)=({-8.52}~\pm~{2.31}_{stat}\pm~{0.87}_{syst})~\cdot~10^{-6}$ . A$\perp$ arises from the imaginary part of the 2γ-exchange amplitude. Our experimentally determined values of A$\perp$ show that in the intermediate hadronic state not only the ground state of the proton, but also excited states contribute to the asymmetry.

PACS: 13.40.Gp Electromagnetic form factors - 11.30.Er Charge conjugation, parity, time reversal, and other discrete - 13.40.-f Electromagnetic processes and properties - 14.20.Dh Properties of protons and neutrons

The Author, for the A4-collaboration. This paper comprises part of the author's PhD thesis.

© Società Italiana di Fisica, Springer-Verlag 2005