The l-forbidden M1 transitions in chlorine isotopes around N = 28 shell closure

The effect of meson exchange current in nuclei is studied via l-forbidden (△l=2, △J=1) M1 transitions. The M1 transitions are caused by the single-particle-like transition of valence nucleons, the core excitation, and the meson exchange current. In the l-allowed (△l=0, △J=1) M1 transition, the single-particle-like transition and the core excitation are the dominant effects and the meson exchange current is very small. On the other hand, in the l-forbidden M1 transition, the meson exchange current measurably affects the transition strengths. Therefore, information about the meson exchange current is extracted from the l-forbidden M1 transition strengths. To measure the l-forbidden M1 transition strengths, we carried out the in-beam gamma-ray spectroscopy experiments of chlorine isotopes at RCNP (CAGRA campaign) and RIBF (HiCARI campaign). The l-forbidden M1 transition strengths were obtained from the transition lifetimes measured by the Doppler shift attenuation method with Ge detectors. In this presentation, we will report the analysis results of experiments and the contribution of the meson exchange current in the l-forbidden M1 transition strengths.