Narrow Results

By exploiting the chiral Ward identities based on the QCD Lagrangian for pion weak production, we derive a transition amplitude by the weak current and show analytical results of relevant multipole amplitudes without any expansion. Their physical implications and numerical results are also discussed.

Preliminary results are presented of the reaction γ*N→Δ→πN that was studied at the Jefferson Laboratory for transferred four momentum of 1.0 (GeV/c)². Angular distributions of the cross sections and polarizations were measured over much of the available phase space. Out of the eighteen response functions involved in this reaction, fourteen separate responses and two additional response combinations were extracted. All resonant and background multipole amplitudes were decomposed for s- and p-waves as well as several of the d-wave multipole amplitudes. The responses and multipoles were compared to model calculations. Significant differences were observed between the experimental values and those of the models for several of the responses and multipoles. The ratios of the electric and longitudinal quadrupole amplitudes to the magnetic dipole amplitude were extracted. These values are different from previously reported values.

Following the model independent approach to deuteron photodisintegration with linearly polarized γ-rays, we show that the measurements of the tensor analyzing powers on aligned deuterons along with the differential cross-section involve five different linear combinations of the isovector ; j = 0, 1, 2 amplitudes interfering with the isoscalar M1_s and E2_s amplitudes. This is of current interest in view of the recent experimental finding [M. A. Blackston et al., Phys. Rev. C78 (2008) 034003] that the three amplitudes are distinct and also the reported experimental observation [B. D. Sawatzky, Ph.D. thesis, University of Virginia (2005)] on the front–back (polar angle) asymmetry in the differential cross-section.