Transverse spin asymmetry at the A4 experiment

Abstract

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 _⊥(Q ² = 0.106 (GeV/c)²) = (−8.59 ± 0.89_stat ± 0.75_syst) · 10⁻⁶ and A _⊥(Q ² = 0.230 (GeV/c)²) = (−8.52 ± 2.31_stat ± 0.87_syst) · 10⁻⁶. A _⊥ arises from the imaginary part of the 2γ-exchange amplitude. Our experimentally determined values of A _⊥ show that in the intermediate hadronic state not only the ground state of the proton, but also excited states contribute to the asymmetry.

comprises part of PhD thesis