Darmstadt 2016 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 6: Structure and Dynamics of Nuclei II
HK 6.1: Gruppenbericht
Montag, 14. März 2016, 14:00–14:30, S1/01 A04
Beam normal single-spin asymmetry measurements at MAMI — •Michaela Thiel for the A1 collaboration — Institut für Kernphysik, Johannes Gutenberg-Universität Mainz
Reaching new precision frontiers in nuclear physics brings up new experimental challenges as well as the demand for more sophisticated theoretical calculations. Especially in parity violating electron scattering experiments the contribution from higher order processes, such as two-photon exchange, is comparable in size with the observed asymmetry Apv. Hence, a precise knowledge of this contribution is mandatory to determine the systematic uncertainties.
The beam normal single-spin asymmetry An is a direct probe of the imaginary part of the two-photon exchange amplitude in the elastic scattering of transversely polarized electrons from unpolarized nucleons. Up to now, there is significant disagreement between experiment and theory for 208Pb, which motivates more measurements to study the Q2 and Z dependence. Therefore a new experimental campaign started at the Mainz Microtron (MAMI) using the spectrometer setup of the A1 collaboration. Within three weeks of beam time An was measured as a function of Q2 for 12C. First results for four different 4-momentum transfer values, ranging from 0.02 to 0.05 (GeV/c)2, will be presented in this talk.