Ab initio Calculations of Charge Symmetry Breaking in the A=4 Hypernuclei

We report on ab initio no-core shell model calculations of the mirror. hypernuclei H-4(Lambda) and He-4(Lambda), using the Bonn-Julich leadi-order chiral effective field theory hyperon-nucleon potentials plus a charge symmetry breaking Lambda - Sigma(0) mixing vertex. In addition to reproducing rather well the 0(g.s.)(+) and 1(exc)(+) binding energies, these four-body calculations demonstrate for the first time that the observed charge symmetry breaking splitting of mirror levels, reaching hundreds of keV for 0(g.s.)(+), can be reproduced using realistic theoretical interaction models, although with a non-negligible momentum cutoff dependence. Our results are discussed in relation to recent measurements of the H-4(Lambda)(0(g.s.)(+)) binding energy at the Mainz Microtron [A. Esser et al. (A1 Collaboration), Phys. Rev. Lett. 114, 232501 (2015)] and the He-4(Lambda)(1(exc)(+)) excitation energy [T. O. Yamamoto et al. (J-PARC E13 Collaboration), Phys. Rev. Lett. 115, 222501 (2015)]