Isovector soft dipole mode in 6Be

By using the 1H(6Li, 6Be)n charge-exchange reaction, population of continuum states in 6Be was observed up to ET=16MeV, ET being the 6Be energy above its three-body decay threshold. In kinematically complete measurements performed by detecting α+p+p coincidences, an ET spectrum of high statistics was obtained, containing approximately ∼5×106 events. The spectrum provides detailed correlation information about the well-known 0+ ground state of 6Be at ET=1.37MeV and its 2+ state at ET=3.05MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by ΔL=1 angular momentum transfer without other significant contributions. This structure can be interpreted as a novel phenomenon, i.e. the isovector soft dipole mode associated with the 6Li ground state. The population of this mode in the charge-exchange reaction is a dominant phenomenon for this reaction, being responsible for about 60% of the cross-section obtained in the measured energy range.