Probing Highly-fragmented Giant Resonances: Coincidence Experiments in the New Millennium

Abstract

Electric isoscalar and isovector giant resonances are excited strongly by inelastic electron and hadron scattering. In particular, the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant quadrupole resonance (ISGQR) have been found both experimentally and theoretically to be highly fragmented in medium mass nuclei. The use of a coincidence technique to measure the angular correlations of decay products after inelastic excitation of the target nucleus is a powerfull tool for determining the multipolarity of the resonance excited. Only recently with the advent of continuous wave electron accelerators has this been possible for the (e,e’x) reaction. Results will be presented on experiments done at the National Accelerator Centre for40Ca(p,p’x=p,α) and 48Ca(p,p’n)., This work compliments similar experiments performed using electrons at S-DALINAC (Darmstadt) and MAMI A (Mainz) in Germany. It will be shown that decay by a non-zero spin particle to a non-zero spin state in the residual nucleus leads to simple angular correlations from which the relative strengths of the various multipoles excited can be extracted unambiguously. This is unexpected since up to now a-particle decay has been studied, where channel spin plays no role.