Measurement of HΛ4 and HeΛ4 binding energy in Au+Au collisions at s_NN = 3 GeV

Measurements of mass and Λ binding energy of _Λ⁴H and _Λ⁴He 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 _Λ⁴H and _Λ⁴He, 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 ΔB_Λ⁴(1_exc⁺)≈−ΔB_Λ⁴(0_g.s.⁺)<0 and present a new method for the study of CSB effect using relativistic heavy-ion collisions.