Invariant-mass spectroscopy of neutron halo nuclei Takashi Nakamura 中村隆司 Tokyo Institute of Technology 東京工業大学 中日 NP 06, Shanghai

T.Nakamura, A.M. Vinodkumar,T.Sugimoto, N.Fukuda, M.Miura, Y.Kondo, N.Aoi, N.Imai, T.Kubo, T.Kobayashi, T.Gomi, A.Saito, H.Sakurai, S.Shimoura,D.Bazin, H.Hasegawa, H.Baba, T. Motobayashi, T.Yakushiji, Y. Yanagisawa, K.Yoneda, K. Watanabe, Y.X.Watanabe, M.Ishihara Collaborators Coulomb Breakup of 11 Li Submitted to Phys.Rev.Lett.

Invariant Mass Method (unbound excited states) Radioactive Ion beam Breakup Kinematic Focusing Well-defined Energy by Invariant Mass Thick Target Ex 12 Be vs. 14 Be 12 Be MeV Be Drip line 11 Be+n MeV MeV ? Be+2n Bound Region Inbeam  spectroscopy Unbound Region Invariant mass  spectroscopy

14 Be + 12 C  12 Be + n + n + 12 C E ex = S 2n + E rel = 1.56  0.13 MeV E rel (MeV) d  /dE rel (mb/MeV) T.Sugimoto, TN et al., (2006) 1.56MeV N=8 Magicity Loss

H He Li Be B C N O F Ne Neutron Dripline N =8 N =20 11 Be 19 C N Z Neutron halos Studied by Invariant Mass Method by our group 11 Li 11 Be 2n halo nucleus 1n halo nucleus Neutron Halo Nuclei– Nuclei at the stability limit 9Li9Li n n 10 Be n S n =504 keV S 2n =300 keV 14 Be

11 Li High-Z Target (Pb) 9 Li n  = N E1 (E x ) dB(E1) dE x d  CD dE x 9hc 16  3 Cross section = (Photon Number)x  Transition Probability) Invariant Mass Equivalent Photon Method 11 Li* n Coulomb Breakup of 11 Li

11 Be : E1 Response of one-neutron Halo ExEx 10~20MeV 1~2MeV N.Fukuda, TN et al., PRC70, (2004) TN et al.,PLB 331,296(1994) core n dB(E1) dE x 11 Be dB(E1) dE x  exp(iqr)| rY 1 m |  gs  | 2 Z A   -S n  ~   |exp(-r/ )/r| 2 Fourier Transform Low-lying E1 Strength Halo State  exp(iqr)| rY 1 m | s 1/2  | 2 Z A Direct Breakup Mechanism S n =504keV   = 0.72 

One neutron halo nucleus vs. Two neutron halo nucleus 9Li9Li n n 10 Be n Motion between core and 1 valence neutron Motion between 1.Core and neutron 2.Core and neutron 3.Two valence neutrons (neutron-neutron correlations) S 2n =300 keV S n =504 keV

Coulomb Dissocitaion of 11 Li (Summary of Previous Results) 43MeV/nucleon PLB348 (1995) 29. NPA 619 (1997) MeV/nucleon PRL 70 (1993) 730. PRC 48(1993) 118.

Primary Beam 18 O 100 AMeV Projectile Fragmentation Secondary Beam 11 Li ~70 AMeV ~20 kcps RIKEN Projectile-fragment Separator 18 O 100 AMeV 11 Li ~70 AMeV

11 Li 9 Li n n Experimental at RIKEN Pb Target NEUT HOD BOMAG DC DALI 70MeV/nucleon

Examine Different Wall Events t1t1 t2t2 11 22  12 Condition: Almost no bias E th =6MeVee to avoid any gamma related events Elimination of Cross-Talk events

Coulomb Dissociation Spectrum of 11 Li Angular Distribution

Calculation: H.Esbensen et al.,NPA542(1992)310. Private Communication “Soft dipole excitations in 11 Li” Present Result Comparison with the 3-body theory = N E1 (E x ) dB(E1) dE x d  CD dE x 9hc 16  3 B(E1) Distribution

Non-energy weighted E1 Cluster Sum Rule r1r1 r2r2 n 9 Li r c-2n (Extrapolated cluster strength) ~70% larger than non-correlated strength H.Esbensen et al.,NPA542(1992)310.

Experimental Result E(9Li-n) 1MeV Simulation (Phase-space decay) E(9Li-n) 1MeV Correlation?

Summary 11 Li(2n halo)+Pb (Coulomb Breakup) Low-lying B(E1) Strength Could be used to see the nn correlation & 9 Li-n correlation in 11 Li (E1 Non-energy weighted sum rule) Strong B(E1) at very low excitation energy c.f. B(E1)=1.05(6) e 2 fm 2 for 11 Be Invariant Mass Spectroscopy ----Powerful Spectroscopic tool