Two-nucleon correlations in the decaysof unbound nuclei beyond the drip lines
Kouichi Hagino (Tohoku Univ.)
Hiroyuki Sagawa (Univ. of Aizu)

1. Di-neutron correlations in neutron-rich nuclei
2. Two-neutron decays of 26O: three-body model- decay energy spectrum- angular distribution of two neutrons- decay width
3. SummaryDi-neutron correlations in neutron-rich nuclei
Strong di-neutron correlations
in neutron-rich nuclei

 Borromean nuclei (3body calc.)
Bertsch-Esbensen (‘91)
Zhukov et al. (‘93)
Hagino-Sagawa (‘05)
Kikuchi-Kato-Myo (‘10)
 Heavier nuclei (HFB calc.)
Matsuo et al. (‘05)
Pillet-Sandulescu-Schuck (‘07)

11Li

K.H. and H. Sagawa,
PRC72(’05)044321

Di-neutron correlations in neutron-rich nuclei
Strong di-neutron correlations
in neutron-rich nuclei

How to probe it?

 Coulomb breakup
T. Nakamura et al.
cluster sum rule(mean value of nn)
 pair transfer reactions
 Borromean nuclei (3body calc.)
 two-proton decays
Bertsch-Esbensen (‘91)
Coulomb 3-body problem
Zhukov et al. (‘93)
 two-neutron decays
Hagino-Sagawa (‘05)
3-body resonance due to
Kikuchi-Kato-Myo (‘10)
a centrifugal barrier
16Be, 13Li, 26O)
MoNA( Heavier nuclei (HFB calc.)
26O)
SAMURAI(Matsuo et al. (‘05)26O)
GSI(Pillet-Sandulescu-Schuck (‘07)

Two-neutron emission decays of 26O (MoNA@MSU)
E. Lunderberg et al., PRL108 (‘12) 142503
Z. Kohley et al., PRL 110 (‘13)152501
27F (82 MeV/u) + 9Be  26O  24O + n + n

Edecay = 150 +50-150 keV
cf. Y. Kondo et al., (SAMURAI)
C. Caesar et al., PRC88 (‘13) 034313 (GSI exp.)

exp =1.0+0.34-0.25+/- 0.68
x 10-10 MeV

K.H. and H. Sagawa, PRC89 (‘14) 014331

3-body model analysis

cf. Expt. : 27F (82 MeV/u) + 9Be  26O  24O + n + n25FnV

Vn24O

n
V’suddenV’nremoval of proton

24Onn
spontaneous decayg.s. of 27F (bound)the same config. (non-eigenstate of 24O+n+n)
FSI

Green’s function method

25Fn24OVVnsudden
removal of protonnV’24OnV’nn24O + n potential
C.R. Hoffman et al.,Woods-Saxon potential
PRL100(‘08)152502
e2s1/2 = -4.09 (13) MeV,
e1d3/2 = + 770+20-10 keV, 1d3/2 = 172(30) keV

25F + n potential(24O + n) potential + Vls

pn tensor interaction
T. Otsuka et al., PRL95(‘05)232502

e1d3/2 (26F) = - 0.811 MeV
nn interaction (density-dependent zero-range interaction)
Eexp (27F) = -2.80(18) MeV

Decay energy spectrum

K.H. and H. Sagawa,
PRC89 (‘14) 014331

with final state nn interaction

 = 0.21 MeV

without final statenn interaction
cf. e1d3/2(25O)= 0.770 MeV

very narrow three-body resonance state (exp ~ 10-10 MeV)
Epeak = 0.14 MeV with this setup

Angular correlation of the two emitted neutrons
main contributions:s- and p-waves in three-bodywave function(no or low centrifugal barrier)2n correlations
enhancement ofback-to-back emission
dineutron correlation
r ＝ 0: enhanced
Fourier transformk ＝ : enhanced
cf. similar conclusion: L.V. Grigorenko et al., PRL111(‘13)042501

Decay width
two-potential method:
S.A. Gurvitz, PRL59 (‘87) 262

simple prescription:

K.H., G.F. Bertsch, H. Sagawa,preliminary

Another method: ACCC?

Summary2n emission decay of 26O

three-body model withdensity-dependent zero-range interaction

 Decay energy spectrum: strong low-energy peak
 Energy distribution of 2 neutrons: three-body resonance Angular distributions: enhanced back-to-back emission
dineutron emission

open problems
Analyses for 16Be, 13Li (especially angular distributions)Decay width?
similarities and differences in 2n- and 2p- decays