Bochum 2018 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 16: Hadron Structure and Spectroscopy III
HK 16.5: Vortrag
Dienstag, 27. Februar 2018, 15:15–15:30, HZO 50
Measurement of the proton scalar polarizabilities at MAMI — •Edoardo Mornacchi for the A2 collaboration — Institut für Kernphysik, Universität Mainz
The electric (αE1) and magnetic (βM1) scalar polarizabilities are fundamental properties related to the internal structure of the nucleon. They play a crucial role not only in our understanding of the nucleon, but also in other areas such as atomic physics. In the past, the values of αE1 and βM1 were determined from the unpolarized differential cross-section of the Compton scattering γ p → γ p. The measurement of the beam asymmetry Σ3, provides an alternative approach to the extraction of the scalar polarizabilities, with different sensitivity and systematics compared to the unpolarized cross-section.
This asymmetry was measured for the first time below the pion photoproduction threshold by the A2 Collaboration with the Crystal Ball/TAPS experiment at MAMI (Mainz, Germany). A linearly polarized photon beam impinged on a liquid hydrogen target and the scattered photons were detected with the Crystal Ball/TAPS setup, providing almost 4π coverage. A new high precision measurement of both unpolarized cross-section and beam asymmetry Σ3 is ongoing at MAMI and polarizabilities αE1 and βM1 will be extracted with unprecedented precision. The impact of the recently obtained and expected results on the extraction of the scalar polarizabilities will be discussed in this talk.
Supported by DFG under contract SFB1044.