Measurement of theB(E2)ofΛ7Liand Shrinkage of the Hypernuclea

Abstract

We report on the first measurement of a hypernuclear gamma-transition probability. gamma rays emitted in the E2(5/2(+)-->1/2(+)) transition of (7)(Lambda)Li were detected by a large-acceptance germanium detector array (Hyperball), and the lifetime of the parent state ( 5/2(+)) was determined by the Doppler shift attenuation method. The obtained result, 5.8(+0.9)(-0.7)+/-0.7 ps, was then converted into the reduced transition probability [ B(E2)] to be B(E2;5/2(+)-->1/2(+)) = 3.6+/-0.5(+0.5)(-0.4) e(2) fm(4). Compared with the B(E2) of the corresponding E2(3(+)-->1(+)) transition in the 6Li nucleus, our result gives evidence that the size of the 6Li core in (7)(Lambda)Li is smaller than the 6Li nucleus in the free space.

Effect of different baryon impurities

“…Note that Λ, Ξ − and Ξ 0 are different particles from proton and neutron, they are all not constrained by the Pauli exclusion. It is obviously that the common explanation [1] for the Λ shrinkage does not suit the case of Ξ − and Ξ 0 . Otherwise, both Λ and Ξ 0 hyperon are neutral, hence the origin of the above difference can not be attributed to the Coulomb potential.…”

“…Since a Λ does not suffer from Pauli blocking in Λ hypernuclei, it can locate at the center of a nucleus, then Λ attracts surrounding nucleons (Λ has the additional attraction provided by -stronger net attraction -induced attraction) and makes the nucleus shrink [1,2]. Recently, the experiment KEK-PS E419 has found clear evidence for this shrinkage of 7 Λ Li hypernucleus [1,2]. In-medium hyperon interactions have been studied non-relativistically and relativistically by several groups, e. g. Hjorth-Jensen et al [3], Lenske et al [4], Ring and Vretenar.…”

Modification of triaxial deformation and change of spectrum inΛ25Mg caused by theΛhyperon

“…[2,16], and compare the B(E2) values of 25 Mg with the corresponding E2 transitions of 24 Mg. Here, we assume that the initial (final) state with angular momentum J i (J f ) of the hypernucleus consists of a core state with angular momentum j …”

“…Development of hypernuclear gamma-ray spectroscopy has enabled us to obtain precise excitation energies [1][2][3]. By analyzing these hypernuclear spectra theoretically and experimentally, most of the central part of the N effective interaction has been clarified [3][4][5][6][7][8][9][10].…”

Splitting of theporbit in triaxially deformedΛ25Mg

“…Since a hyperon is unaffected by the Pauli principle governing the nucleons, it can be regarded as an impurity in nuclei and modifies nuclear properties such as clustering and deformation. For example, a hyperon in s orbit reduces the intercluster distance between α and d in 7 Li, which was confirmed from the reduction of B(E2) [1][2][3][4]. Furthermore, many authors have predicted the deformation change in p-sd shell hypernuclei by adding the hyperon in s orbit [1,2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”