Experimental Program Overview

Summary

The focus of the South Carolina Intermediate Energy Group is the study of nucleon and meson interactions using unpolarized and polarized photon beams. Our experimental photonuclear physics program is conducted at the Laser Electron Gamma Source (LEGS) located at Brookhaven National Laboratory and with the Large Acceptance Spectrometer (CLAS) at the Continuous Electron Beam Accelerator Facility (CEBAF) located at the Thomas Jefferson National Accelerator Facility (JLab). The proposed activities significantly impact three overlapping areas: the spin structure of the nucleon, the study of the NN and ND interactions, and meson production. Central to these investigations is the Strongly Polarized Hydrogen deuteride ICE (SPHICE) target. This novel polarized HD target permits measurement of asymmetries and, for the first time, absolute cross sections on the polarized proton, neutron, and deuteron.

From left to right:
Steve Whisnant (seated), David Tedeschi (seated), Chaden Djalali, and Barry Preedom

With SPHICE at LEGS, and in experiment E94-117 at JLab, the spin-dependent Compton amplitude for the nucleon will be studied. A direct determination of the forward spin-polarizability, g , and the Gerasimov-Drell-Hearn (GDH) sum rule integrals for both the proton and neutron will be made. The measurement of g provides a stringent test of modern chiral perturbation theory calculations. The combination of LEGS and JLab data is essential for a complete measurement of this fundamental quantity.

The photodisintegration of vector and tensor polarized deuterium at LEGS with linearly and circularly polarized photons will examine the nucleon-nucleon interaction in the region of the D resonance in unprecedented detail. Combined with the earlier, high-precision cross sections and beam asymmetries, these data will permit stringent tests of state-of-the-art NN and ND coupled-channels calculations.

Our meson production program at both laboratories investigates the photon-nucleon and meson-nucleon interactions. Because no complete set of data exists at any energy, all current multipole analyses of pion photoproduction are model dependent. Our efforts at LEGS will provide the first model-independent determination of the multipoles. At JLab, f meson production experiments will be performed with unpolarized and linearly polarized photons. Since the f is a nearly pure object, it is dominantly produced diffractively via pomeron exchange. The high statistics and the large kinematic coverage available with CLAS will extend this measurement into unmeasured regions close to threshold providing sensitivity to meson exchange and other recently predicted mechanisms. In experiment E94-002, the photoproduction of vector mesons from ²H, C, Fe and Pb will be used to measure the mass of vector mesons embedded in nuclear matter. Chiral symmetry restoration at high baryon density implies a shift of the vector meson mass of as much as 100 MeV. A simultaneous measurement of the mass shift for the r , w and f will be accomplished by observing the e⁺e^- decay.

Our group, presently consisting of four faculty members, one postdoctoral scientist, seven graduate students, and five undergraduates, has a leading role in data analysis and hardware development projects at both laboratories. On-campus and laboratory-resident activities in our complementary programs provide a well-rounded education for our students.

The photodisintegration of vector and tensor polarized deuterium at LEGS with linearly and circularly polarized photons will examine the nucleon-nucleon interaction in the region of the D resonance in unprecedented detail. Combined with the earlier, high-precision cross sections and beam asymmetries, these data will permit stringent tests of state-of-the-art NN and ND coupled-channels calculations.

Our meson production program at both laboratories investigates the photon-nucleon and meson-nucleon interactions. Because no complete set of data exists at any energy, all current multipole analyses of pion photoproduction are model dependent. Our efforts at LEGS will provide the first model-independent determination of the multipoles. At JLab, f meson production experiments will be performed with unpolarized and linearly polarized photons. Since the f is a nearly pure object, it is dominantly produced diffractively via pomeron exchange. The high statistics and the large kinematic coverage available with CLAS will extend this measurement into unmeasured regions close to threshold providing sensitivity to meson exchange and other recently predicted mechanisms. In experiment E94-002, the photoproduction of vector mesons from ²H, C, Fe and Pb will be used to measure the mass of vector mesons embedded in nuclear matter. Chiral symmetry restoration at high baryon density implies a shift of the vector meson mass of as much as 100 MeV. A simultaneous measurement of the mass shift for the r , w and f will be accomplished by observing the e⁺e^- decay.

Our group, presently consisting of four faculty members, one postdoctoral scientist, seven graduate students, and five undergraduates, has a leading role in data analysis and hardware development projects at both laboratories. On-campus and laboratory-resident activities in our complementary programs provide a well-rounded education for our students.