Measurement of the proton scalar polarizabilities at MAMI
E. Mornacchi* on behalf of the A2 collaboration
Pre-published on:
February 19, 2018
Published on:
March 20, 2018
Abstract
The electric ($\alpha_{\text{E1}}$) and magnetic ($\beta_{\text{M1}}$) 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 $\alpha_{\text{E}1}$ and $\beta_{\text{M}1}$ were determined from the unpolarized differential cross-section of Compton scattering $\gamma p \rightarrow \gamma p$. The measurement of the beam asymmetry $\Sigma_3$ 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 4$\pi$ coverage. A new high precision measurement of both unpolarized cross-section and beam asymmetry $\Sigma_3$ will be performed in the near future and polarizabilities $\alpha_{\text{E}1}$ and $\beta_{\text{M}1}$ will be extracted with unprecedented precision.
DOI: https://doi.org/10.22323/1.310.0235
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