Damping of Spin Resonances

In this conference we are learning how the Gamow-Teller giant resonance (GTR), after being a rather elusive vibrational mode1,2, is becoming one of the best characterized resonant structures of the nuclear spectrum. It has quantum numbers λ=0, τ=1 and σ=1, and it displays a forward peaked angular distribution in (p,n) reactions induced by protons with Ep ~ 200 MeV. The ratio of peak to background of these modes is strongly energy dependent and is determined by the energy dependence of the spin-isospin term \( V\left( r \right)\left( {\vec \sigma \vec \sigma } \right)\left( {\vec \tau \vec \tau } \right) \) of the nucleon-nucleon interaction3. A basic difference between the GTR and other giant resonances is that only about 50% of the strength of the operator responsible for the excitation of the GT mode (i.e. στ-) is found in the main peak and low energy region of the spectrum4.