Excited-State Giant Dipole Resonances in (p, γ): A New Probe of Single-Particle Strengths

The ($p, \gamma$) reaction populating highly excited states in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ is shown to be dominated by giant dipole resonances built upon one-particle, one-hole states. Each giant resonance is centered at $E_{\gamma }\approx 20$ MeV, with a width which increases with the energy of the one-particle, one-hole state, and with a strength that is simply related to the proton stripping strength to the same final state.