Studies of Spin Excitations with Electromagnetic and Hadronic Probes

Abstract

Excitation of unnatural parity states, predominantly of high spin, using electromagnetic and hadronic probes, is discussed. Spectroscopic strengths are deduced from studies of (e,e’), (p,p’), (π,π’), and (p,n) for states whose “doorway” is the “stretched” particle-hole configuration. These levels are excited primarily through the isovector electromagnetic-nucleon magnetization coupling, nucleon-nucleon tensor coupling, and pion-nucleon spin-orbit coupling. The extracted isovector spectroscopic strength is typically 38% of the extreme single particle-hole model and about 66% of that predicted by more realistic nuclear structure calculations. The observed isoscalar strength is only about one half of the isovector strength. The results obtained with the three different probes are quite consistent. The primary conclusion is that the “missing strength” for these high spin excitations is at least as large as for the low spin Ml and GT excitations. This implies the existence of other important “quenching” mechanisms since the Δ-N-1 mechanism involved in the discussion of the low spin excitation affects only the isovector transitions and contributes little to high spin excitations. This implies the existence of other important “quenching” mechanisms since the Δ-N-1 mechanism involved in the discussion of the low spin excitation affects only the isovector transitions and contributes to high spin excitations. A method for using (e, e’) and π+/π- cross section ratios to separate and determine the absolute isoscalar and isovector spin densities for TO to TO transitions in N≠Z nuclei is also discussed and some comments on extracting information from (e,e’) and (p,p’) studies at high q on low spin 1+ and 2- levels are presented.