Measurements of mass and $\Lambda$ binding energy of $\rm ^4_{ \Lambda}H$ and $\rm ^4_{ \Lambda}He$ in Au+Au collisions at $\sqrt{ s_{ _{ \rm NN}}}=3$ GeV are presented, with an aim to address the charge symmetry breaking (CSB) problem in hypernuclei systems with atomic number A = 4. The $\Lambda$ binding energies are measured to be $\rm 2.22\pm0.06(stat.) \pm0.14(syst.)$ MeV and $\rm 2.38\pm0.13(stat.) \pm0.12(syst.)$ MeV for $\rm ^4_{ \Lambda}H$ and $\rm ^4_{ \Lambda}He$, respectively. The measured $\Lambda$ binding-energy difference is $\rm 0.16\pm0.14(stat.)\pm0.10(syst.)$ MeV for ground states. Combined with the $\gamma$-ray transition energies, the binding-energy difference for excited states is $\rm -0.16\pm0.14(stat.)\pm0.10(syst.)$ MeV, which is negative and comparable to the value of the ground states within uncertainties. These new measurements on the $\Lambda$ binding-energy difference in A = 4 hypernuclei systems are consistent with the theoretical calculations that result in $\rm \Delta B_{ \Lambda}^4(1_{ exc}^{ +})\approx -\Delta B_{ \Lambda}^4(0_{ g.s.}^{ +})<0$ and present a new method for the study of CSB effect using relativistic heavy-ion collisions.
Categories: nucl-ex
