Double isobaric analog of 11Li in 11B

Abstract

The ground state of 11Li is the preeminent example of a two-neutron-halo nucleus and is part of an isobaric sextet. Another member of this sextet, the double isobaric analog of 11Lig .s. in 11B, has been identified in the 12Be(p,2n)11B reaction. The state was discovered through its two-proton decay branch. From detected 2p+9Li events, its excitation energy was determined to be 33.57(8) MeV using the invariant mass method. With the known masses of 11Li and its isobaric analog state in 11Be, three members of the same sextet have measured masses for the first time, permitting the masses of the remaining members to be extrapolated using the isobaric multiplet mass equation. All members of this multiplet are expected to have a two-nucleon halo structure and this was found consistent with the evolution of the mass across the sextet. The momentum correlations of the detected protons were found to have both "diproton" and "cigar" components. © 2012 American Physical Society.