Experimental Study of Double-Λ Hypernuclei with Nuclear Emulsion

Our experimental knowledge concerning double strangeness system is summarized, briefly. Latest numerical values of energies are given for Λ-Λ interaction and binding of two Λ hyperons in several nuclei. A double-Λ hypernucleus of 6ΛΛHe (“Lambpha ” / NAGARA event) strongly suggested an weak attractive Λ-Λ interaction with ΔBΛΛ = 0.67±0.16 MeV, and the lower mass limit of the H-dibaryon to be 2223.7 MeV/c2 (90 % C.L.). A probable candidate of 10ΛΛBe ∗ nucleus was observed with its excitation energy of 2.8 ± 0.4 MeV. §1. Experimental status for double strangeness nuclei Double strangeness (S = −2) nucleus (double hypernucleus) is understood to be double-Λ hypernucleus, conventionally, where two Λ hyperons stay in ground state. However it is not obvious due to very little knowledge of the mass of the H-dibarycon predicted by Jaffe1) and Ξ-nucleon interaction, even though many experiments have been carried out.2)–4) Therefore, information from double strangeness nuclei is quite important for unified understanding of baryon-baryon interaction in a framework of the SU(3)flavor symmetry.