Magnetic Dipole Transition in Ca 48

The magnetic dipole transition strength B(M1) of Ca48 is dominated by a single resonant state at an excitation energy of 10.23 MeV. Experiments disagree about B(M1) and this impacts our understanding of spin flips in nuclei. We performed ab initio computations based on chiral effective field theory and found that B(M1: 0+→1+) lies in the range from 7.0 to 10.2 μN2. This is consistent with a (γ,n) experiment but larger than results from (e,e′) and (p,p′) scattering. Two-body currents yield no quenching of the B(M1) strength and continuum effects reduce it by about 10%. For a validation of our approach, we computed magnetic moments in Ca47,49 and performed benchmark calculations in light nuclei.