Measurements of Compton scattering on the proton at 2-6 GeV
Danagoulian, Areg
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https://hdl.handle.net/2142/33760
Description
Title
Measurements of Compton scattering on the proton at 2-6 GeV
Author(s)
Danagoulian, Areg
Issue Date
2006-05
Director of Research (if dissertation) or Advisor (if thesis)
Nathan, Alan M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Nuclear
Real Compton Scattering (RCS)
Compton Scattering
Language
en
Abstract
Similar to elastic electron scattering, Compton Scattering on the proton at high momentum
transfers(and high p⊥) can be an effective method to study its short-distance structure. An
experiment has been carried out to measure the cross sections for Real Compton Scattering
(RCS) on the proton for 2.3-5.7 GeV electron beam energies and a wide distribution of
large scattering angles. The 25 kinematic settings sampled a domain of s = 5−11(GeV/c)2,
−t = 2−7(GeV/c)2 and −u = 0.5−6.5(GeV/c)2. In addition, a measurement of longitudinal
and transverse polarization transfer asymmetries was made at a 3.48 GeV beam energy
and a scattering angle of θcm = 120o. These measurements were performed to test the
existing theoretical mechanisms for this process as well as to determine RCS form factors.
At the heart of the scientific motivation is the desire to understand the manner in which
a nucleon interacts with external excitations at the above listed energies, by comparing
and contrasting the two existing models – Leading Twist Mechanism and Soft Overlap
“Handbag” Mechanism – and identify the dominant mechanism. Furthermore, the Handbag
Mechanism allows one to calculate reaction observables in the framework of Generalized
Parton Distributions (GPD), which have the function of bridging the wide gap between
the exclusive(form factors) and inclusive(parton distribution functions) description of the
proton. The experiment was conducted in Hall A of Thomas Jefferson National Accelerator Facility(Jefferson Lab). It used a polarized and unpolarized electron beam, a 6% copper
radiator with the thickness of 6.1% radiation lengths (to produce a bremsstrahlung photon
beam), the Hall A liquid hydrogen target, a high resolution spectrometer with a focal plane
polarimeter, and a photon hodoscope calorimeter. Results of the differential cross sections
are presented, and discussed in the general context of the scientific motivation.
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