Low-energy collective structure of $^{92,94}$Zr and $^{94}$Mo from ($e,e^{\prime}$) and ($p,p^{\prime}$) scattering II. Signatures of mixed-symmetry states and origin of collectivity

Abstract

This is the second of two papers discussing a new experimental signature of mixed-symmetry states (MSS) in the vibrational nuclei $^{92,94}$Zr and $^{94}$Mo based on proton and neutron transition densities. Quasiparticle-phonon model calculations for these nuclei are extensively tested by comparison to ground-state properties, energies and moments of excited states, transition probabilities between them, and the momentum transfer dependence in $(e,e^\prime)$ and $(p,p^\prime)$ reactions. The overall very good agreement permits the extraction of information on the wave functions of the MSS and their fully symmetric (FSS) counterparts. MSS can be identified by a sign change between the leading proton and neutron two-quasiparticle configurations compared to the FSS. Possible candidates for $2^+$, $3^-$, and $4^+$ MSS are identified. The modification of proton and neutron transition densities, which can be derived from a combined analysis of inelastic electron and proton scattering, by the sign change provide a new experimental signature of MSS. The collectivity of ground-state excitations of predominantly one-phonon FSS and MSS is generated to a large extent by the coupling to high-lying states forming giant resonances with the same spin and parity.