Structures of light halo nuclei

Creative Research Institute “Sousei”, Hokkaido Univ. M. Kimura Meme Media Laboratory, Hokkaido Univ.

N. FurutachiHigh energy Accelerator Research organization (KEK) 　 　　　　　　　　　 A. DoteYukawa Institute for Theoretical Physics Y. Kanada-En'yo

Introduction

Two-neutron halo

One-neutron halo

One-proton halo

Importance of core excitation in halo nuclei8B: one-proton halo nucleus

　－ From the measurements of 12C(8B,7Be+γ)X and 208Pb(8B,7Be+γ)X reactions

13% of 7Be* (Jπ=1/2+ at 429 kev) componet

11Be: one-neutron halo nucleus

D. Cortina-Gil et al, Nucl. Phys. A 720 (2003), 3

18% of 10Be* (Jπ=2+ at 3.34 MeV) componet

　－ From the measurements of 9Be(11Be,10Be+γ)X reaction

19C: one-neutron halo nucleus

Core enlargement has been proposed from systematic analysis ofinteraction cross section and ligitudinal momentum distribution measurements

R. Kanungo, I. Tanihata, A. Ozawa, Phys.Lett. B512 (2001), 261

T. Aumann et al, Phys. Rev. Lett. 84 35, (2000)

Theoretical model for investigation of halo nuclei involving core excitation is proposed

Multiple-width Gaussian basis AMD (MAMD)

Nucleon wave function of AMD is improved

－ Superposition of Gaussian wave packets that have different width parameters

　　　 　 　・ Core excitation is naturally described as same as ordinary AMD　 　 　 　　・ Description of halo structure is improved over that of ordinary AMD

Two-dimensional generator coordinate method (GCM) is introduced

Introduction

Efficiency of MAMD in describing halo structure is demonstrated

Application to He isotopes － Core excitation is not expected in He isotopes. Description of halo structure in MAMD is discussed in detail

Application to 8B and 9C

Investigation of halo structure involving core excitation

－ α+3He+p and α+3He+p+p structures are expected in these nuclei. 　 　 Structures of these nuclei are investigated focusing on their halo structure and core clustering

Introduction

MAMD AMD wave function

Improvement of nucleon wave function

Ordinary AMD

MAMD

Framework

α=2　for　|N-Z|　neutron-(proton-)　wave　functions　in　neutron　(proton)rich　nuclei,　and　α=1　for　other　nucleon　wave　functions　

Multiple-width Gaussian basis AMD( )

Variational function

Hamiltonian

Energy variation； Volkov No.2+G3RS force

Angular momentum projection

Framework

GCM

Generator coordinate; proton and neutron radius (in He isotopes, generator coordinate is matter radius)

MAMD AMDEXP.

4He6He 8He

10He

Efficiency of MAMD Results

Binding energy of He isotopes

Density distribution of 6,8He

Efficiency of MAMD: 6He

Wave function of 6He

Width parameter 　： 1.39 fm 2.13 fm (AMD: 1.54 [fm])

Spatial extension of neutron density distribution is described

Description of shell-like structure is improved

Efficiency of MAMD: 8He

Wave function of 8He

Width parameter 　： 1.41 fm 2.50 fm (AMD: 1.54 [fm])

E [MeV] rm [fm] r

p [fm] r

n [fm] Q [e fm2] μ[μ

n]

8B(2+) MAMD -35.7 2.50 2.64 2.24 4.3 0.95 AMD -34.7 2.48 2.60 2.26 4.2 0.96 Exp. -37.38 2.55 6.45 1.04 9C(3/2-) MAMD -39.2 2.40 2.54 2.08 -3.2 -1.73 AMD -36.1 2.26 2.35 2.07 -2.7 -1.72 Exp. -39.72 2.42 -1.39(Sch. -1.91)

Results of 8B and 9CDensity distributions

Energy, radii, electric and magnetic moments

8B 　 　 　の計算結果

Energy surface

(a)

(b)

(c)

E [MeV] rm [fm] Q [e fm2] μ[μ

n]

(a) -32.1 2.26 2.9 0.77 (b) -31.8 2.35 2.2 0.72 (c) -31.7 2.55 4.7 1.11GCM -35.7 2.50 4.3 0.95Exp. -37.38 2.55 6.45 1.04

Importance of core clustering in 8B

(c)

Energy surface

E [MeV] rm [fm] Q [e fm2] μ[μ

n]

(d) -35.6 2.36 -2.7 -1.43 (e) -34.7 2.21 -1.9 -1.94 (f) -34.2 2.27 -2.5 -1.11GCM -39.2 2.40 -3.2 -1.72Exp. -39.72 2.42 -1.39 (Sch. -1.91)

Importance of core clustering in 9C

(d)

(e)

(f)

Summary

8B

Core has α+3He structure. Described as weakly bound α+3He+p three-body system

Core clustering is important to explain large experimental value of electric quadrupole moment.　 － Electric quadrupole moment is sensitive to relative distance 　 　 between α and 3He clusters, but insensitive to development of proton halo

Investigation of halo structure involving core excitation

Efficiency of MAMD in describing halo structure was demonstrated

Simultaneous description of spatial extension and shell-like structure of valence neutrons　 →　 Binding energies and radii of 4,6,8He are systematically reproduced

9CBoth of α+3He cluster structure and shell-like structure in coreare important for binding of 9C

Development of core clustering is important to explain experimental value of magnetic dipole moment that have large deviation from Schmidt value

He isotopes