A new polarized target using HD in the solid phase has been developed for studies of the nucleon spin structure at Q(2) = 0 using pion photo-production. In combination with the high quality LEGS photon beam and a large solid angle spectrometer this target allows practically background-free measurements on the proton and on the neutron. The first beam-target double-polarization data taken with this target are reported here.

We report preliminary results of pi photo-production using polarized gamma beams and a polarized HD target. Four observables can be extracted simultaneously from the data, the cross section, the beam asymmetry Sigma, and the double-polarization observables G and E. The latter determines the GDH sum rule integral.

A solid, polarized HD target has been developed for the measurement of double-polarization observables in the Delta resonance region. We report here the inaugural data obtained with this target. This new polarized target technology, combined with the high quality LEGS photon beam and the large acceptance spectrometer, SASY, provides a unique facility for studying the spin structure of the nucleon below 500 MeV. Pion production data collected on a longitudinally polarized target with six gamma-ray polarization states provides the first simultaneous measurement of d sigma/d Omega, as well as the Sigma, G and E asymmetries. With the future addition of magnetic analysis to SASY, a complete set of pion production observables on the proton and the deuteron (neutron) will be obtained.

Cross sections are presented for the {sup 16}O({gamma}(vector sign),{pi}{sup -}p) reaction at incident photon energies between 290 and 325 MeV. The data are presented for specific proton and pion angles as a function of proton energy, which are compared with calculations in a local distorted wave impulse approximation model. The results are in agreement at most kinematics, although at some kinematics the data and calculations disagree by a factor of 2 or more. These data do not support the conclusion of a large modification to the mass of the {delta} resonance in the nucleus. (c) 2000 The American Physical Society.

Cross sections are presented for the O-16(<(gamma)over right arrow>, pi(-) p) reaction at incident photon energies between 290 and 325 MeV. The data are presented for specific proton and pion angles as a function of proton energy, which are compared with calculations in a local distorted wave impulse approximation model. The results are in agree ment at most kinematics, although at some kinematics the data and calculations disagree by a factor of 2 or more. These data do not support the conclusion of a large modification to the mass of the Delta resonance in the nucleus.

Cross sections are presented for the {sup 16}O({gamma}(vector sign),{pi}{sup -}p) reaction at incident photon energies between 290 and 325 MeV. The data are presented for specific proton and pion angles as a function of proton energy, which are compared with calculations in a local distorted wave impulse approximation model. The results are in agreement at most kinematics, although at some kinematics the data and calculations disagree by a factor of 2 or more. These data do not support the conclusion of a large modification to the mass of the {delta} resonance in the nucleus. (c) 2000 The American Physical Society.

The (γ↘,π−p) reaction was measured for 16O at photon energies of 200 to 320 MeV, and angles ranging from about 20° to 160° for the proton and 32° to 135° for the pion. The photon asymmetry data are compared with calculations in a DWIA framework. The agreement between the present data and calculations is reasonable at quasifree kinematics, but disagree as the momentum transfer to the residual nucleus becomes large.

Energy weighted integrals of the difference in helicity-dependent photo-production cross sections ({sigma}{sub {1/2}} - {sigma}{sub 3/2}) provide information on the nucleon`s Spin-dependent Polarizability ({gamma}), and on the spin-dependent part of the asymptotic forward Compton amplitude through the Drell-Hearn-Gerasimov (DHG) sum rule. (The latter forms the Q{sup 2}=0 limit of recent spin-asymmetry experiments in deep-inelastic lepton-scattering.) There are no direct measurements of {sigma}{sub {1/2}} or {sigma}{sub 3/2}, for either the proton or the neutron. Estimates from current {pi}-photo-production multipole analyses, particularly for the proton-neutron difference, are in good agreement with relativistic-l-loop Chiral calculations ({chi}PT) for {gamma} but predict large deviations from the DHG sum rule. Either (a) both the 2-loop corrections to the Spin-Polarizability are large and the existing multipoles are wrong, or (b) modifications to the Drell-Hearn-Gerasimov sum rule are required to fully describe the isospin structure of the nucleon. The helicity-dependent photo-reaction amplitudes, for both the proton and the neutron, will be measured at LEGS from pion-threshold to 470 MeV. In these double-polarization experiments, circularly polarized photons from LEGS will be used with SPHICE, a new frozen-spin target consisting of {rvec H} {center_dot} {rvec D} in the solid phase. Reaction channels will be identified in SASY, a large detector array covering about 80% of 4{pi}. A high degree of symmetry in both target and detector will be used to minimize systematic uncertainties.