Frankfurt 2014 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 52: Hadronenstruktur und -spektroskopie
HK 52.1: Group Report
Friday, March 21, 2014, 11:00–11:30, HZ 1+2
Measurement of the Proton Polarizabilities at MAMI — •Vahe Sokhoyan for the A2 collaboration — The George Washington University, Washington D.C., USA — Institut für Kernphysik, Universität Mainz, Germany
Polarizabilities are fundamental properties related to the internal dynamics of the nucleon. They play a crucial role not only in our understanding of the nucleon, but also in other areas such as precision atomic physics and astrophysics. Recent analyses of unpolarized Compton scattering data have indicated significant model dependence in the extraction of the scalar polarizabilities of the proton, resulting in a gross underestimation of the errors. The four spin polarizabilities of the proton have never been separated and only two linear combinations of those are known.
A program performed by the A2 Collaboration at the MAMI accelerator facility in Mainz aims for the first individual extraction of the nucleon scalar and spin polarizabilities using Compton scattering on the nucleons. The Crystal Ball and TAPS 4π spectrometer setup is used for the corresponding measurements. To extract the proton scalar polarizabilities independently, the beam asymmetry Σ3 has been measured below pion production threshold. For the determination of the spin polarizabilities the beam asymmetry Σ3 and the beam-target asymmetry Σ2x were measured at higher energies, where the sensitivity to the spin polarizabilities increases.
In this talk the current results and the plans for the upcoming measurements will be presented.