The missing mass spectroscopy of the HeΛ7 hypernucleus was performed using the Li7(e,e′K+)HeΛ7 reaction at the Thomas Jefferson National Accelerator Facility Hall C. The Λ-binding energy of the ground-state (1/2+) was determined with a smaller error than that of the previous measurement, being BΛ=5.55±0.10stat.±0.11sys.MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at BΛ=3.65±0.20stat.±0.11sys.MeV was observed and assigned as a mixture of 3/2+ and 5/2+ states, confirming the "gluelike" behavior of Λ, which makes an unstable state in He6 stable against neutron emission.
Bibliographical noteFunding Information:
The program at JLab Hall C is supported by JSPS KAKENHI Grants No. 12002001, No. 15684005, No. 16GS0201, and No. 24.4123 (Grant-in-Aid for JSPS fellow), JSPS Core-to-Core Program No. 21002, and JSPS Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation No. R2201. This work was supported by U.S. Department of Energy Contracts No. DE-AC05-84ER40150, No. DE-AC05-06OR23177, No. DE-FG02-99ER41065, No. DE-FG02-97ER41047, No. DE-AC02-06CH11357, No. DE-FG02-00ER41110, and No. DE-AC02-98CH10886, and U.S.-NSF Contracts No. 013815 and No. 0758095.