Electroexcitation of isoscalar and isovector magnetic dipole transitions in 12C and isospin mixing Original Research Article

The excitation of the Jπ;T=1+;0 and 1+;1 states at View the MathML source and 15.11 MeV in 12C 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 View the MathML source eV, View the MathML source fm and View the MathML source eV, View the MathML source fm, respectively. For the evaluation of View the MathML source and View the MathML source 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 View the MathML source 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 first time a unique determination of the sign of View the MathML source.