Electroexcitation of isoscalar and isovector magnetic dipole transitions in C-12 and isospin mixing

摘要

The excitation of the J(pi);T = 1(+) ;0 and 1(+);1 states at E-x = 12.71 and 15.11 MeV in C-12 has been studied at momentum transfers q < 0.5 fm(-1) in inelastic electron scattering. The corresponding ground state radiation widths and transition radii for the isoscalar and isovector transition are deduced as Gamma(gamma 0) = 0.32(2) eV, R-tr = 2.95(9) fm a nd Gamma(gamma 0) = 35.9(6) eV, R-tr = 2.63(4) fm, respectively. For the evaluation of Gamma(gamma 0) and R-tr for the transition to the 15.11 state (e,e'), data of the present work have been combined with older data from other low energy electron accelerators, The results support the strong isospin mixing of the two 1(+) states, and in the frame of a two-state model a Coulomb matrix element [HC] = 118(8) keV is derived. This value agrees with other experiments using electromagnetic or pionic probes but is much more accurate. Furthermore, the measured difference in the transition radii for the isoscalar and isovector transitions allows for the Dst time a unique determination of the sign of (Hc). (C) 2000 Elsevier Science B.V. All rights reserved. [References: 39]