Separation of pygmy dipole and M1 resonances in Zr90 by a High-resolution inelastic proton scattering near 0°

A high-resolution measurement of inelastic proton scattering off Zr90 near 0° was performed at 295 MeV with a focus on a pronounced strength previously reported in the low-energy tail of giant dipole resonance. A forest of fine structure was observed in the excitation energy region 7-12 MeV. A multipole decomposition analysis of the angular distribution for the forest was carried out using the ECIS95 distorted-wave Born approximation code with the Hartree-Fock plus random-phase approximation model of E1 and M1 transition densities and inclusion of E1 Coulomb excitation. The analysis separated pygmy dipole and M1 resonances in the forest at E PDR=9.15±0.18MeV with Γ PDR=2.91±0.64MeV and at E M1=9. 53±0.06MeV with Γ M1=2.70±0.17MeV in the Lorentzian function, respectively. The B(E1) value for pygmy dipole resonance over 7-11 MeV is 0.75±0.08e2fm2, which corresponds to 2.1±0.2% of the Thomas-Reiche-Kuhn sum rule. © 2012 American Physical Society.