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MEASUREMENT OF THE GENERALIZED POLARIZABILITIES OF THE PROTON IN VIRTUAL COMPTON SCATTERING
Li, Ruonan
Li, Ruonan
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Thesis/Dissertation
Date
2022
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Physics
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http://dx.doi.org/10.34944/dspace/8296
Abstract
Understanding how the visible matter in the universe arises from its elementary quark andgluon constituents is a central question for science. The visible world is founded on the
proton, the only composite building block of matter that is stable in nature. Consequently,
understanding the formation of matter relies on explaining the dynamics and the properties
of the proton’s bound state. A fundamental property of the proton involves the system’s
response to an external electromagnetic (EM) field. It is characterized by the EM polarizabilities
that describe how easily the charge and magnetization distributions inside the
system are distorted by the EM field. When the polarizabilities are generalized to finite
momentum transfer, their Fourier transform can map out the spatial distribution of the polarization
densities in a proton subject to an EM field.
This thesis focuses on the measurement of the proton generalized polarizabilities (GPs)
at low four-momentum transfer in experimental Hall C at the Thomas Jefferson National
Accelerator Facility (TJNAF). Among the six independent GPs, we will focus on the electric
(aE1) and the magnetic (bM1) scalar GPs. The GPs can be accessed through measurements
of the Virtual Compton Scattering reaction, by replacing the incoming real photon of
the Compton scattering process with a space-like virtual photon. The outgoing real photon
provides the EM perturbation to the system. In addition, the Dispersion Relation Formalism
is used for generalized polarizability extraction. In this work, the two scalar GPs measured
with unprecedented precision, and the measurements help explore a momentum transfer
region where an anomalous enhancement of the electric GP that contradicts the predictions
of nuclear theory has been observed.
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