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$Ξ$ hypernuclei $^{15}_Ξ$C, $^{12}_Ξ$Be and $ΞN$ two-body interaction

We study the energy spectra of $Ξ$ hypernuclei $^{15}_Ξ$C and $^{12}_Ξ$Be with a relativistic mean field (RMF) model with meson exchange $ΞN$ interactions. The RMF parameters are optimized to reproduce the average energy of KINKA and IRRAWADDY events for the ground state and also the average energy of KISO and IBUKI events for the excited state in $^{15}_Ξ$C. The potential depth of average $ΞN$ mean field potential is found to be about $-12$ MeV in the nuclear matter limit. We further introduce the two-body $s$- and $p$-wave interactions between valence nucleons and $Ξ$ particle. We found that the $s$-wave interaction deduced from the HAL LQCD results is rather weak to obtain the energy difference between IRRAWADDY and KINKA events. The $p$-wave interaction is added and fitted to reproduce the energy difference. The resulting interaction together with the $s$-wave one gives a reasonable energy simultanously for the IBUKI event as an excited $Ξ_p$ state. The model is further applied to predict the energy spectrum of $^{12}_Ξ$Be.