Separation of Pygmy Dipole and M1 Resonances in Zr-90 by a High-Resolution Inelastic Proton Scattering Near 0 degrees

Abstract

A high-resolution measurement of inelastic proton scattering off Zr-90 near 0 degrees 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 +/- 0.18 MeV with Gamma(PDR) = 2.91 +/- 0.64 MeV and at E-M1 = 9.53 +/- 0.06 MeV with Gamma(M1) = 2.70 +/- 0.17 MeV in the Lorentzian function, respectively. The B(E1) up arrow value for pygmy dipole resonance over 7-11 MeV is 0.75 +/- 0.08 e(2) fm(2), which corresponds to 2.1 +/- 0: 2% of the Thomas-Reiche-Kuhn sum rule.