Polarization observables in virtual compton scattering
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Abstract
Virtual Compton Scattering (VCS) is an important reaction for understanding
nucleon structure at low energies. By studying this
process, the generalized polarizabilities of the nucleon can be
measured. These observables are a generalization of the already known
polarizabilities and will permit theoretical models to be challenged on a new level.
More
specifically, there exist six generalized polarizabilities
and in order to disentangle them all, a double polarization experiment
must be performed.
Within this work, the VCS reaction p(e,e p)gamma was measured at MAMI using
the A1 Collaboration three spectrometer setup with Q2=0.33 (GeV/c)2.
Using the highly polarized
MAMI beam and a recoil proton polarimeter, it was possible to measure
both the VCS cross section and the double polarization observables.
Already in 2000, the unpolarized VCS cross section was measured at MAMI. In this new
experiment, we could confirm the old data and furthermore the double polarization observables
were measured for the first time.
The data were taken in five periods between 2005 and 2006. In this work,
the data were analyzed to extract the cross section and the proton
polarization. For the analysis, a maximum likelihood algorithm was developed
together with the full simulation of all the analysis steps.
The experiment is
limited by the low statistics due mainly to the
focal plane proton polarimeter efficiency. To overcome this problem, a new
determination and parameterization of the carbon analyzing power was performed.
The main result of the experiment is the extraction of a new combination of the
generalized polarizabilities using the double polarization observables.