UCLA

Measurements of mass and Λ binding energy of Λ 4 H and Λ 4 He in Au+Au collisions at s NN = 3 GeV are presented, with an aim to address the charge symmetry breaking (CSB) problem in hypernuclei systems with atomic number A = 4. The Λ binding energies are measured to be 2.22 ± 0.06 (stat.)±0.14(syst.) MeV and 2.38 ± 0.13 (stat.)±0.12(syst.) MeV for Λ 4 H and Λ 4 He, respectively. The measured Λ binding-energy difference is 0.16 ± 0.14 ( stat . ) ± 0.10 ( syst . ) MeV for ground states. Combined with the γ-ray transition energies, the binding-energy difference for excited states is − 0.16 ± 0.14 ( stat . ) ± 0.10 ( syst . ) MeV, which is negative and comparable to the value of the ground states within uncertainties. These new measurements on the Λ binding-energy difference in A = 4 hypernuclei systems are consistent with the theoretical calculations that result in Δ B Λ 4 ( 1 exc + ) ≈ − Δ B Λ 4 ( 0 g.s. + ) < 0 and present a new method for the study of CSB effect using relativistic heavy-ion collisions.