Abstract.
We report on new measurements of the electric Generalized Polarizability (GP) of the proton \( \alpha_{E}\) in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have found that \( \alpha_E = (5.3 \pm 0.6_{stat} \pm 1.3_{sys}) 10^{-4}\) fm3 at \( Q^{2}=0.20\) (GeV/c)2. The new measurements, when considered along with the rest of the world data, suggest that \( \alpha_E\) can be described by either a local plateau or by an enhancement in the region \( Q^2=0.20\) (GeV/c)2 to 0.33 (GeV/c)2. The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the \( N \rightarrow \Delta\) transition through the exploration of the \( p(e,e'p)\gamma\) reaction. The new measurement gives \( CMR = (-4.4 \pm 0.8_{stat} \pm 0.6_{sys})\%\) at \( Q^2=0.20\) (GeV/c)2 and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties.
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Communicated by N. Kalantar
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This manuscript has no associated data or the data will not be deposited. [Authors’ comment: The data related to this publication, in their raw and filtered format, are stored in data disks currently at the Temple University Physics Department and they are available upon request. The data related to this publication are further described in the thesis of A. Blomberg (A. Blomberg, PhD Thesis, Temple University (2016)).]
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Blomberg, A., Atac, H., Sparveris, N. et al. Virtual Compton scattering measurements in the nucleon resonance region. Eur. Phys. J. A 55, 182 (2019). https://doi.org/10.1140/epja/i2019-12877-0
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DOI: https://doi.org/10.1140/epja/i2019-12877-0