1. Contents Breakup reactions of 14 Be on a proton target  Inelastic scattering ( 14 Be)  One-neutron removal reaction ( 13 Be) Contents Breakup reactions of 14 Be on a proton target  Inelastic scattering ( 14 Be)  One-neutron removal reaction ( 13 Be) Y. Kondo RIKEN Nishina Center

2. 2 Y. Kondo, T. Nakamura, Y. Satou, T. Matsumoto, N. Aoi, N. Endo, N. Fukuda, T. Gomi, Y. Hashimoto, M. Ishihara, S. Kawai, M. Kitayama, T. Kobayashi, Y. Matsuda, N. Matsui, T. Motobayashi, T. Nakabayashi, K. Ogata, T. Okumura, H. J. Ong, T. K. Onishi, H. Otsu, H. Sakurai, S. Shimoura, M. Shinohara, T. Sugimoto, S. Takeuchi, M. Tamaki, Y. Togano, Y. Yanagisawa  Tokyo Institute of Technology  RIKEN Nishina Center  Tohoku University  Rikkyo University  Kyushu University  University of Tokyo  Center for Nuclear Study (CNS), University of Tokyo

3.  Exotic structures ▷ Neutron halo ▷ Magicity loss ( 12 Be, 32 Mg) ▷ Di-neutron correlation? ( 6 He, 11 Li) ▷ Different deformation of proton/neutron density( 16 C) Neutron halo Magicity loss Different deformations of Protons and neutrons Different deformations of Protons and neutrons Di-neutron? 13 Be, 14 Be 3

4.  14 Be ▷ Drip-line nucleus ▷ Two neutron halo ▷ Borromean ( 12 Be+n, n+n systems are unbound) ▷ No bound excited states  excited states locate above the neutron separation energy (S 2n =1.26MeV)  13 Be ▷ Unbound nucleus ▷ Low-lying levels are not clarified Several experimental results are not consistent Breakup of 14 Be on proton 4

5.  Inelastic scattering  One-neutron removal reaction  14 Be ▷ Angular distribution  J  assignment ▷ cross section  collectivity  13 Be ▷ Momentum distribution of 13 Be system  J  assignment p 12 Be n n 14 Be 12 Be n n  n n 14 Be* ~ 70 MeV/u p 12 Be n n 14 Be 12 Be n  n 13 Be n ~ 70 MeV/u Coulomb breakup cross section is small 5

6. l=0l=1l=2 Momentum distribution  spin-parity assignment of 13 Be l =2 l =1 l =0 Example of momentum distribution  width of P distribution ▷ depends on the orbital angular momentum of a knocked-out neutron

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8. Primary beam 18 O 100 MeV/u Production target Be 6 mm Plastic scintillator 1 mm 14 Be Energy : ~ 70MeV/u Intensity : ~8,000 counts/s Purity : 90% 14 Be Energy : ~ 70MeV/u Intensity : ~8,000 counts/s Purity : 90% RIPS （ RIKEN Projectile-fragment Separator) 8

9. 14 Be PPAC Angle of 14 Be Dipole magnet Drift chamber (FDC) Particle Identification Drift chamber (MDC) Angle of 12 Be NaI(Tl) scintillator  ray from 12 Be Reaction Target Liquid H 2 (227 mg/cm 2 ) charged particle Hodoscope (plastic scintillator) Velocity of 12 Be Neutron counter (plastic scintillator) Veto counter 12 Be n Detect 12 Be and (a) neutron(s) in coincidence ~ 70 MeV/u 9

10. Dipole Magnet Target Drift Chamber He bag Hodoscope Neutron Detector RIPS Beam 10

11. Charged particle VETO (thin plastic scintillators) Neutron counter Beam direction ~2m Efficiency For 1n detection Neutron Counter 54bars 6x6x214cm 3 11

12. Relative energy spectrum ( 12 Be+n+n) Angular distribution p 12 Be n n 14 Be 12 Be n n  n n 14 Be(2 + )

13.  Inelastic scattering 14 Be+p  14 Be*  12 Be+n+n ▷ Select M n =2 (detection multiplicity)  crosstalk rejection (position, timing) Two neutron event Crosstalk One neutron is detected by two (or more) detectors Crosstalk events NEUT-BNEUT-A Same Wall event Different Wall event 13

14. p( 14 Be, 12 Be+n+n) 69 MeV/nucleon  neutron crosstalk events are eliminated  efficiency and acceptance are corrected Similar peak at around 0.3MeV was observed C( 14 Be, 12 Be+n+n) 68 MeV/nucleon (previous exp.) T. Sugimoto, T. Nakamura, Y. Kondo et al PLB 654,160 (2007) 14 Be(2 + ) E r =0.28(1)MeV  L=2 14

15. DWBA analysis Two optical potentials (A) A.A. Korsheninnikov et al. PLB343, 53 (1995) (B) R.L. Varner et al. Phys. Rep. 201, 57 (1991) (CH89)   =1.40(19) fm ( 14 Be+p) p( 14 Be, 12 Be+n+n) 69 MeV/nucleon 14 Be(2 + ) E rel ( 12 Be+n+n) (MeV) E rel =0.25(1) MeV  =12.5±0.2±1.6 mb (A) (B) p( 14 Be, 14 Be(2 + ) ) 69 MeV/nucleon Y. Kondo, T. Nakamura, Y. Satou et al.: to be submitted Width is dominated by the experimental resolution (~100keV (1  @ 0.25MeV) (1  ) 15

16. 2 + energy Lower than 12 Be Deformation length Smaller than 12 Be Proton/neutron collectivities can be deduced (now in progress) 16

17.  Phase space decay ▷ 14 Be(2 1 + )  12 Be+n+n  Sequential Decay ▷ 14 Be(2 1 + )  13 Be+n (E rel =0.1MeV)  12 Be+n+n (E rel =0.15MeV) sequential phase space 12 Be n n E c-n1 E n-n E c-n2 E c-(nn) 17

18. Relative energy spectrum ( 12 Be+n) Transverse momentum distributions p 12 Be n n 14 Be 12 Be n  n 13 Be n

19. M n =1 events Inelastic channel Estimated from M n =2 events One-neutron removal channel Corresponds to 14 Be(2 + ) One-neutron removal channel (one neutron is emitted) knocked out Inelastic channel (two neutrons are emitted) not detected  two cases in M n =1 events ▷ inelastic component should be subtracted 19 p( 14 Be, 12 Be+n+n) 69 MeV/nucleon 14 Be(2 + ) E rel ( 12 Be+n+n) (MeV) E rel =0.25(1) MeV  =12.5±0.2±1.6 mb

20. 13 Be  12 Be(1 - )+n (E  =2.7MeV) 13 Be  12 Be(2 + )+n (E  =2.1MeV)  =11(2)mb (E rel =0~4MeV)  =5.3(7)mb (E rel =0~4MeV) 12 Be+n  =89(6)mb  for 12 Be+n+  is small 20

21.  Two peaks at 0.5MeV, 2MeV  Transverse momentum distribution (not longitudinal) ▷ Width of momentum distributions are different between peak regions E rel ( 12 Be+n) (MeV) p( 14 Be, 12 Be+n)  =89(6)mb (E rel =0-4MeV) 0.25-0.75MeV2.0-2.5MeV P x resolution ~30MeV/c 21

22.  Relative energy spectrum ▷ p- and d-wave components  Breit-Wigner shape ▷ s-wave component  G.F. Bertsch et al: PRC 57, 1366 (1998)  Momentum distribution  CDCC calculation (by T. Matsumoto) 13 Be is assumed to be a core in 14 Be ▷ 13 Be-p interaction JLM interaction J. Jeukenne et al.: PRC16, 80 (1977) ▷ n-p interaction R.A. Malfliet and J.A.Tjon NPA127, 161 (1969) ▷ 13 Be-n potential Wood-Saxon form  Depth is adjusted to reproduce the separation energy a : Scattering length 22

23.  0.5 MeV peak  p-wave resonance  2 MeV peak  d-wave resonance p s d p s d E rel ( 12 Be+n) (MeV) p( 14 Be, 12 Be+n)  =89(6)mb (E rel =0-4MeV) 0.25-0.75MeV2.0-2.5MeV 23 p d s

24.  p-wave component ▷ E r =0.50(1) MeV ▷  =0.36(2) MeV consistent with  sp (l=1) ▷ J  =1/2-  d-wave component ▷ E r =2.48(7) MeV ▷  =2.4(2) MeV larger than  sp (l=2)  other state @ 2MeV? s component a s ~ -3fm d state E r =2.48(7) MeV Γ=2.4(2)MeV p state E r =0.50(1) MeV Γ=0.36(2)MeV single particle width p -wave @0.50MeV  sp ~0.5MeV d -wave @2.48MeV  sp ~1.4MeV 24

25. The 2 + state in 14 Be locates lower than the g.s. of 13 Be  Sequential decay process is energetically forbidden 25

26.  The low-lying negative parity state  Intruder state This work 26

27.  Shell model calculation ▷ PSDMK D.J. Millener et al.: NPA255, 315 (1975) Provides the shell closure at 12 Be ▷ SFO (spin-flip p-n monopole interaction) T. Suzuki et al.: PRC67, 044302 (2003) resonably reproduce the magicity loss at 12 Be  Shell model calculation ▷ PSDMK D.J. Millener et al.: NPA255, 315 (1975) Provides the shell closure at 12 Be ▷ SFO (spin-flip p-n monopole interaction) T. Suzuki et al.: PRC67, 044302 (2003) resonably reproduce the magicity loss at 12 Be  13 Be  PSDMK Higher excitation energy of 1/2   SFO Ground state of 1/2   good! several states at ~2MeV  13 Be  PSDMK Higher excitation energy of 1/2   SFO Ground state of 1/2   good! several states at ~2MeV Intruder 1/2- state  disappearance of N=8 magicity  explained by spin-flip p-n monopole interaction 12 Be 13 Be 27

28. ▷ energy gap between [220 ½] and [101 ½] orbitals disappears with large prolate deformation ▷ Large quadrupole deformation (  ~0.6) of 12 Be H. Iwasaki et al. PLB481, 7 (2000)  intruder 1/2- state of 13 Be  indicate large deformation? 28 Ref) A. Bohr and B.R. Mottelson Nuclear structure Vol.1

29. Breakup reactions ( 14 Be+p)  Inelastic scattering ▷ 2 + state of 14 Be ▷ Phase space decay of 2 + state  One-neutron removal reaction ▷ Low-lying p-wave (intruder) resonance of 13 Be Breakup reactions ( 14 Be+p)  Inelastic scattering ▷ 2 + state of 14 Be ▷ Phase space decay of 2 + state  One-neutron removal reaction ▷ Low-lying p-wave (intruder) resonance of 13 Be 29