Compton Scattering @ the High Intensity Gamma-ray Source
The Compton@HIGS collaboration will improve our knowledge of the strong nuclear force in protons and neutrons by Compton scattering mono-energetic gamma photons from hydrogen, deuterium, helium-4 and helium-3 nuclei at the unique HIGS facility of Triangle Universities Nuclear Laboratory (TUNL).
The measurements of these nano-barn-sized cross-sections processes will improve our determination of the electric and magnetic polarizabilities of protons and neutrons. For the latter, these are only known to 10 % and 30 %, respectively. [7] These ground-state properties are essential for testing Effective Field Theories and lattice Quantum Chromodynamics calculations. [8,9]
Chiral effective field theories (EFT) provide QCD descriptions of low-energy properties of hadrons in terms of effective degrees of freedom. The electromagnetic (EM) polarizabilities of nucleons are fundamental low-energy structure constants that constrain the parameters in yEFT and evaluate lattice QCD calculations. In the classical model, the polarizabilities measure the “stiffness” response of the nucleon to externally applied electric or magnetic fields. In addition to the scalar EM polarizabilities, there are spin-dependent polarizabilities. The spin-polarizabilities describe the stiffness of the internal degrees of freedom of the nucleon associated with the nucleon spin. The HIGS Compton collaboration is performing high precision Compton-scattering measurements on the proton, deuteron and light nuclei to determine the dynamical dipole electric and magnetic polarizabilities of the proton and neutron in the energy range from 60 to 100 MeV using the high intensity mono-energetic and polarized gamma-ray beam at HIGS. An increase in the energy capability of HIGS up to 120 MeV will create new opportunities for measurements of the spin polarizability parameters using Compton scattering of polarized gamma-rays from active polarized targets.
The Project Team: TUNL Faculty: Mohammad Ahmed, Ben Crowe, Calvin Howell, Haiyan Gao, Hugon Karwowski, Diane Markoff, Ying Wu, Kent Leung; TUNL Students: Xiaqing Li (Duke), D. Godagama (UKy); Post-Docs/Research Scientists: Mark Sikora, S. Mikhailov; Collaborators: J. Feldman, H. Grieshammer, E. Downie (GWU), M. Kovash (UKy), A. Banu, C.S. Whisnant (JMU), R. Pywell (USask), M. Spraker (GCSU); Technical Staff: Z. Zhao, G. Swift, M. Emamian, P. Wallace (DFELL)