1. Spectroscopy of weakly bound and unbound nuclei
Takashi Nakamura
Department of Physics,
Tokyo Institute of Technology
“Physics beyond the limits of stability : exploring the continuum”, 17-21,Oct.,2016, ECT*, Trento, Italy

2. --Weakly Bound and Unbound Nuclei --Dineutron, Oxygen Anomaly
Contents
Introduction
--Weakly Bound and Unbound Nuclei
--Dineutron, Oxygen Anomaly
Spectroscopy of 2n Halo Nuclei (11Li,6He,22C)
Spectroscopy of Barely unbound 2n emitter (26O)
Summary and Perspectives

3. Weakly Bound and Unbound Nuclei
Strong nn Correlations
Barely Unbound Nulclei
Fermi Level
Halo Nuclei
paring gap
(~2MeV at A=30)
J. Dobaczewski et al., Prog. Part. Nucl. Phys. 59, 432 (2007).

4. Dineutron? Unbound a= -18 fm q~1/l n-star Possible dineutron site: n
A.B.Migdal
Strongly correlated “dineutron”
on the surface of a nucleus
Sov.J.Nucl.Phys.238(1973). n
S=0 n n
Dineutron:
@ Low-dense neutron skin/halo?
/surface of neutron star?
S=0
Unbound
a= -18 fm
M.Matsuo
PRC73,044309(2006). A.Gezerlis, J.Carlson, PRC81,025803(2010)
n-star
(s)2
q~1/l
(s)2 +(p)2 +(d)2+…
Possible dineutron site:
2n Halo Nuclei?
2n barely-unbound nuclei?
9Li
11Li n
S2n=0.37MeV
24O n
26O
S2n= (5) MeV
Kondo et al., PRL2016

5. Evolution Towards the Stability Limit
Where is the neutron drip line?
What are characteristic features of drip-line nuclei?
How does nuclear structure evolve towards the drip line?
Shell? Ca
Deformation? K Ar
Halo? Cl S
Drip Line?
Continuum? P Si
N=28 Al
Deformation
Driven Halo Mg
N=20 Na Ne
N.Kobayashi et al.,
PRL 112, (2014).
N=16
37Mg F O
31Ne
TN et al., PRL 112, (2014). N
29Ne
N.Kobayashi et al.
PRC 93, (2016). C B
25O
26O
28O
Oxygen Anomaly Be
16Be
21C Li
13Li
1n halo known
22C He
10He
2n halo known H
6He
Dineutron?
4n halo/skin 5

6. Spectroscopy of 2n Halo Nuclei (11Li,6He,22C)
---Probed (mainly) by Coulomb Breakup
T.N.
Sun Yelei
S. Leblond, J.Gieblin, N.A.Orr
R. Minakata
et al.

7. Probe of weakly bound states--Heavy target
Coulomb Breakup
22C
22C*
20C n
g(virtual photon) n
High-Z Target
(Pb)
Di-neutron Correlation
Single particle state (Halo)
Equivalent Photon Method
dsCB
16p3
dB(E1)
dEx
= NE1(Ex)
dEx
9hc
Cross section = (Photon Number)x(Transition Probability)
C.A. Bertulani, G. Baur, Phys. Rep. 163,299(1988).
Halo  Soft E1 Excitation
(E1 Concentration at Ex<1MeV) 7

8. Soft E1 Excitation of 2n-halo  dineutron-like correlation
Coulomb Breakup of 2n Halo
 Probe of Dineutron Correlation n
11Li T.Nakamura et al. PRL96,252502(2006).
rc-2n r2 n r1
9Li
Correlation in the Ground State of 11Li
Soft E1 Excitation of 2n-halo
 dineutron-like correlation

9. 6He 6He Sun Yelei (Saclay), TN et al. in preparation rc-2n
Present Preliminary Results
6He
70MeV/nucleon
T.Aumann et al.,
PRC59, 1252 (1999).

10. 22C (Z=6,N=16) Prominent 2n-Halo? ? N=16 Magicity?
Huge Reaction Cross Section
(<rm2>)1/2=5.4(9) fm c.f. ~3.5 fm11Li
K.Tanaka et al., PRL 104, (2010).
sR(mb)
S2n= -0.14(46) MeV
L.Gaudefroy et al. PRL109,202503(2012). A
Narrow Momentum Distribution ~73MeV/c
N.Kobayashi et al. PRC86,054604(2012). ?
N=16 Magicity? 20
1d3/2 16
2S1/2
1d5/2
A.Ozawa et al., PRL 84, 5493 (2000).
M.Stanoiu et al., PRC78, (2008).

11. RI Beam Factory at RIKEN
SRC
IRC
fRC
RRC
RILAC
ECR
CSM
GARIS &
GARIS2
AVF
RILAC2
RIPS
BigRIPS
ZeroDegree
SAMURAI
SHARAQ
SCRIT
KISS
SLOWRI
Rare RI Ring
2007~
In-Flight RI Separator
with large acceptance
SRC: World Largest Cyclotron (K=2500 MeV)
Heavy Ion Beams up to 238U at 345MeV/u (Light Ions up to 440MeV/u)
eg. 48Ca: ~500pnA (~3x1012pps) ~10 times compared to 2008
238U: ~30pnA (~2x1011 pps) ~103 times compared to 2007

12. Superconducting Analyzer for MUlti-particle from RAdio Isotope Beam
SAMURAI
Superconducting Analyzer for MUlti-particle from RAdio Isotope Beam
Kinematically Complete measurements by detecting multiple particles in coincidence
Large momentum acceptance
Brmax / Brmin ~ 2 – 3
Good Momentum Resolution
Dp/p~ 1/1000
A/DA>100 (>5s)
Large Bending Angle (~60deg)
+4 Tracking Detectors
T.Kobayashi NIMB 317, 294 (2013)
Large angular acceptance for n
+-8.8 deg (H) x deg(V)
(~50% coverage < Erel ~ 5MeV)
TN, Y.Kondo, NIMB 376, 156 (2016).
Moderate Erel Resolution
DE = 200 keV (s) at Erel=1MeV
Stage: Rotatable ( degrees)
Variety of Physics Opportunities
Superconducting
Magnet
(3T, 2m dia. Pole
80cm gap)
RI beam
from BigRIPS
Target
rotatable
Neutron(s)
Proton
Heavy Ion

13. SAMURAI Experiment May/2012
22C
19B
17B
20C
19C
23N
22N DE 3
3.6 4
3.8
3.4
3.2
2.8
A/Z
SAMURAI Experiment May/2012
~10cps RIBF
(~10cph RIPS)
First Full Exclusive Coulomb/Nuclear Breakup Measurement of 22C and 19B
Pb3.26g/cm2
C 1.79g/cm2 n n
20C
22C
240MeV/nucleon

14. Coulomb Breakup of 22C (20C+n+n Spectrum)
R. Minakata, T.Nakamura
counts
Erel(MeV) 10 1 2 3 4 5 6 7 8 9
R.Minakata (Tokyo Tech)
22C+Pb22C* 20C+n+n
Very Preliminary !
~1b
Strong Soft E1 Excitation  Evidence of Halo

15. Reaction Cross Section of 22C
Y.Togano, TN, Y.Kondo et al.,
Phys.Lett.B 761, 412 (2016).
22C+CAZ+X
2.4
2.6
2.8 3
3.2
3.4
3.6
3.8 4 5 6 7 Z
A/Z
22C
20C
19C
19B
17B
14Be
B.Abu-Ibrahim et al.,
PRC77, (2008).
22C
19C
20C
sR=1.280(23)b : rrms=3.44(8) fm
Smaller than the previous result (~2s):
c.f. K.Takaka et al, MeV)
rrms=5.4(9) fm

16. Ex Ex INVARIANT MASS SPECTROSCOPY OF 21C: C(22N / 22C,20C+n) …
Slide: N.A. Orr, Ph.D thesis of Sylvain Leblond
INVARIANT MASS SPECTROSCOPY OF 21C: C(22N / 22C,20C+n) …
… SAMURAI04 Sylvain
C(22N,20C+n)
C(22C,20C+n)
Er=0.900.10 MeV
Er=0.750.20 MeV
Er=1.500.10 MeV
l=0
l=0
l=2 Ex Ex
S Leblond et al., NP1106-SAMURAI04
JA Tostevin
S Leblond, PhD Thesis LPC/UCN Dec 2015

17. of Barely Unbound 2n emitter 26O
Spectroscopy
of Barely Unbound 2n emitter 26O
(& Other studies on unbound oxygen isotopes)
Yosuke Kondo
et al.

18. Study of unbound nuclei 25O and 26O at SAMURAI
Spokesperson Yosuke Kondo
Experimental study of unbound oxygen isotopes towards the possible double magic nucleus 28O
T. Otsuka et al., PRL105, (2010).
Drip line
3N force: significant at N>16
24Ne
25Ne
26Ne
27Ne
28Ne
29Ne
30Ne
31Ne
32Ne
23F
24F
25F
26F
27F
28F
29F
30F
31F
22O
23O
24O
25O
26O
27O
28O
Z=8
21N
22N
23N
N=20
G. Hagen et al., PRL108, (2012).
H. Hergert et al., PRL110, (2013).
S.K.Bogner et al., PRL113, (2014).
Again, this is the nuclear chart.
One of the important problem of nuclear physics is the location of the drip line, which is strongly affected by the nuclear structure.
The neutron drip line regularly evolves with increase of proton number like this dashed line.
But anomalous behavior can be seen at Z=8.
This anomalous behavior may be due to the shell evolution.
So, it is very interesting to investigate towards 28O, which has Z=8 and N=20.
Oxygen Anomaly
20C
21C
22C
19B
N=16?
Continuum Effect:
A.Volya, V.Zelevinski, PRL94,052501(2005).
K. Tsukyiyama, T. Otsuka, PTEP2015, 093D01 (2015).
nn correlations:
L.V. Grigorenko et al., PRL111,042501(2013).
K. Hagino, H. Sagawa PRC89,014331(2014).

19. 2n radioactivity of 26O? x 25O+n 26O 24O+2n 7５0keV ?
E. Lunderberg et al.
PRL108, (2012)
Er < 200keV
26O: 24O(0+) ⊗ (nd3/2)2
26O
24O+2n
L.V. Grigorenko et al. PRC 84, (2011)
Theory
Usual 1n decay
G~MeV or keV
C. Caesar et al.PRC88, (2013)
Excite state at 4.2MeV?
Er < 120keV (95% CL)
t < 5.7ns
T1/2= ps
(3ps systematic error)
2n radioactivity?
Z. Kohley et al,PRL110, (2013)
Large uncertainty of experimental study
Only upper limit is given for the ground state energy
Large systematic error in the lifetime measurement
Excited State of 26O?

20. Experimental Setup at SAMURAI at RIBF
C target
(1.8g/cm2)
MWDC
Ionization
Chamber
Superconducting
Dipole Magnet
(B=3.0T)
NEBULA n
2 MWDCs
2Plastics n
27F ~210MeV/u
(from BigRIPS)
DALI2
MWDC
24O
Hodoscope

21. Decay energy spectrum of 25O
24O+n
Edecay
Edecay=749(10)keV
25Ogs
26F+C 25O*24O+n
Kondo et al. PRL2016
Edecay=749(10) keV
= 88(6) keV
C.R.Hoffman et al.,(MSU)
PRL100, (2008)
Previous Works
(GSI) C.Caesar, PRC 2013
(MSU) Hoffman, PRL 2008

22. Study of 26O (SAMURAI02) 27F+C26O24O+2n Decay Energy (MeV)
Ground state (0+)
5 times higher statistics than previous study
18±3(stat)±4(syst)keV
Finite value is determined for the first time
1st excited state (2+)
Observed for the first time
MeV
N=16 shell closure is confirmed USDB cannot describe 2+ energy at 26O effects of pf shell?, continuum? 2n Correlations?, 3N force?
Y. Kondo et al., Phys. Rev. Lett. 116, , (2016)

23. Spectra of 25O and 26O 25O (2+) 25O+n 0+ 24O+2n 25O+ n 26O 26O 24O
1.28(11) MeV
18(5) keV
749(10) keV
(2+)
Extremely weakly
UNBOUND state!
25O+n 0+
24O+2n
25O+ n
26O
26O E
Centrifugal
Barrier
24O n
Strong 2n correlation?
Hagi16: K.Hagino,H.Sagawa,PRC93,034330(2016).
Voly06: A.Volya,V.Zelevinsky,PRC74,064314(2006).
Tsuk15: K. Tsukyiyama, T. Otsuka, PTEP2015, 093D01 (2015).

24. Dineutron correlation in 26O?
1. Mixture of different L (parities)  Develop Dineutron n
(0d3/2)2+ (s)2+(p)2+…
1S0
Hagino et al.
2. Spatially compact  Large width in Momentum n
P1~ -P2
Can we see the dineutron correlation by 2n decay?
3. Effect of Final State Interactions (inc. Tunneling Effect)
 Hagino’s talk
N.B. Opposite correlation? In 13Li, 16Be
13Li: Z.Kohley et al., PRC87, (R)(2013).
16Be: A.Spyrou et al., PRL108, (2012).
: Both observed 2n emitted in the same direction in c.m.
They call it “dineutron”
 Rather “Non-localized nn correlation”

25. 13Li 26O Angular Correlations in 13Li and 26O
Z.Kohley et al., PRC 87, (R) 2013.
13Li n
26O
Z.Kohley et al.,
PRC 91, (2015).

26. Masses of Oxygen Isotopes Beyond the dripline
Doubly Magic
Or not?
1.28(11) MeV
18(5) keV
749(10) keV
(2+) ?
Extremely weakly
UNBOUND state!
Weakly Unbound 4n
Emitter or not?
25O+n 0+
24O+2n
25O+ n
26O
27O+n
28O
24O+4n
25O+3n
26O+2n E
Centrifugal
Barrier E
24O n
24O n
S2n= (5) MeV
Kondo et al., PRL2016
Strong 4n correlation?
Or 2x 2n correlation?
Strong 2n correlation?

27. 27,28O measurements in 2015 (SAMURAI21)
Slides: Y.Kondo
MINOS
Superconducting
Dipole Magnet
(B=2.9T)
MWDC
NeuLAND
NEBULA
2Plastics n
2 MWDCs
DALI2 n
NeuLAND
MINOS n
29F
(from BigRIPS)
MWDC n
Hodoscope
24O

28. High intense beam of 29F Z 29F 90cps A/Z High intense 29F beam
31Ne
30Ne Z
High intense 29F beam
(48Ca intensity > 500pnA)
+ thick LH2 target (15cm)
highest luminosity for 28O
Analysis: Under Progress

29. Summary and Outlook Barely bound and unbound nuclei
Strong neutron-neutron correlation (dineutron correlation) expected
Dineutron Correlation in 2n Halo nuclei
11Li, 6He, 22C
SAMURAI: Useful Facility for Drip Line Nuclei
Reaction Cross Section of 22C
Y.Togano, TN, Y.Kondo et al., PLB 761, 412 (2016).
Spectroscopy of 21C
S.Leblond, J.Gebelin, M.Marques, N.Orr,
21C spectrum  pin down s and d 1hole state of 22C
Barely unbound 2n emitter 26O
Y. Kondo et al., PRL 116, , (2016) .
26O(0+gs): Very weakly unbound 2n states  Correlation? Continuum?
26O(2+): Found for the first time at Erel=1.28(11) MeV  Shell Evolution?
 27,28O : Experiment Successfully Done, Nov-Dec, 2015.
Near Future: Variety of spectroscopies along n-drip line

30. Day-one Collaboration
Tokyo Institute of Technology: Y.Kondo, T.Nakamura, N.Kobayashi, R.Tanaka, R.Minakata, S.Ogoshi, S.Nishi, D.Kanno, T.Nakashima, J. Tsubota, A. Saito LPC CAEN: N.A.Orr, J.Gibelin, F.Delaunay, F.M.Marques, N.L.Achouri, S.Leblond, Q. Deshayes Tohoku University : T.Koabayshi, K.Takahashi, K.Muto RIKEN: K.Yoneda, T.Motobayashi ,H.Otsu, T.Isobe, H.Baba,H.Sato, Y.Shimizu, J.Lee, P.Doornenbal, S.Takeuchi, N.Inabe, N.Fukuda, D.Kameda, H.Suzuki, H.Takeda, T.Kubo Seoul National University: Y.Satou, S.Kim, J.W.Hwang Kyoto University : T.Murakami, N.Nakatsuka GSI : Y.Togano Univ. of York: A.G.Tuff GANIL: A.Navin Technische Universit¨at Darmstadt: T.Aumann Rikkyo Univeristy: D.Murai Universit´e Paris-Sud, IN2P3-CNRS: M.Vandebrouck

31. SAMURAI21 collaboration—27,28O
Y.Kondo, T.Nakamura, N.L.Achouri, H.Al Falou, L.Atar, T.Aumann, H.Baba, K.Boretzky, C.Caesar, D.Calvet, H.Chae, N.Chiga, A.Corsi, H.L.Crawford, F.Delaunay, A.Delbart, Q.Deshayes, Zs.Dombrádi, C.Douma, Z.Elekes, P.Fallon, I.Gašparić, J.-M.Gheller, J.Gibelin, A.Gillibert, M.N.Harakeh, A.Hirayama, C.R.Hoffman, M.Holl, A.Horvat, Á.Horváth, J.W.Hwang, T.Isobe, J.Kahlbow, N.Kalantar-Nayestanaki, S.Kawase, S.Kim, K.Kisamori, T.Kobayashi, D.Körper, S.Koyama, I.Kuti, V.Lapoux, S.Lindberg, F.M.Marqués, S.Masuoka, J.Mayer, K.Miki, T.Murakami, M.A.Najafi, K.Nakano, N.Nakatsuka, T.Nilsson, A.Obertelli, F.de Oliveira Santos, N.A.Orr, H.Otsu, T.Ozaki, V.Panin, S.Paschalis, A.Revel, D.Rossi, A.T.Saito, T.Saito, M.Sasano, H.Sato, Y.Satou, H.Scheit, F.Schindler, P.Schrock, M.Shikata, Y.Shimizu, H.Simon, D.Sohler, O.Sorlin, L.Stuhl, S.Takeuchi, M.Tanaka, M.Thoennessen, H.Törnqvist, Y.Togano, T.Tomai, J.Tscheuschner, J.Tsubota, T.Uesaka, H.Wang, Z.Yang, K.Yoneda
Tokyo Tech, Argonne, ATOMKI, CEA Saclay, Chalmers, CNS, Cologne, Eotvos, GANIL, GSI, IBS, KVI-CART, Kyoto Univ., Kyushu Univ., LBNL, Lebanese-French University of Technology and Applied Science, LPC-CAEN, MSU, Osaka Univ., RIKEN, Ruđer Bošković Institute, SNU, Tohoku Univ., TU Darmstadt, Univ. of Tokyo
88 Participants 25 Institutes

32. Backup

33. N=16 22C(2+) SAMURAI04 – DAYONE: C(23N,20C+n+n) … … SAMURAI + NEBULA
J.Gibelin, N.A.Orr
<23N|22C>
SHELL MODEL- WBP
EX [MeV] Jp C2S
BEAMTIME = 1.4 DAYS
< 23N >  45 pps
C TARGET = 2 g/cm2

34. Decay energy spectrum of 26O (24O+2n, 24O+n)
26Ogs
Counts /20keV
Edecay(24O+n)
Edecay(24O+n+n)
=Edecay(24O+n)+Edecay(25O+n)
24O n
26Ogs
26O1st+25Ogs
27F+C26O,25O
24O+n+X
27F+C26O24O+2n
26O1st
New!
Counts /50keV
Edecay(24O+n+n)
Finite Value!
Most likely 2+
No peak at ~4.2MeV

35. MINOS at the RIBF Slide by Obertelli, CEA SACLAY, Obertelli et al.
mm liquid hydrogen target
Vertex resolution : < 5 mm FWHM
Detection efficiency > 90%
Vertex tracker
proton
Target e-
Project started in November 2010
In use at the RIBF since 2014
DALI2: S. Takeuchi et al., Nucl. Instr. Meth. A 763, 596 (2014)
MINOS: A. Obertelli et al., Eur. Phys. Jour. A 50, 8 (2014)

36. Deformation Driven p-wave Halo --- 31Ne, 37Mg, 29Ne
Sn (31Ne)=-0.06(0.42) MeV
L.Gaudefroy et al., PRL(2012)
Coulomb breakup
σ(E1;0+g.s.) (b)
|31Neg.s. 〉 : 3/2-
|30Ne(0+g.s.) ⊗ p3/2〉 component
Exp. σ-1n(E1;0+g.s.) = 448(108) mb
Theoretical calc. for
|31Neg.s. 〉 = |30Ne(0+g.s.) ⊗ p3/2〉
(C2S = 1)
Nuclear breakup
σ(C;0+g.s.) (b)
Exp. σ-1n(C;0+g.s.) = 33(15) mb
68%C.L.
31Ne: 3/2- p-wave
C2S
Deformed in spite of N=21
[321 3/2]
b~0.5
Sn (31Ne) (MeV)
31Ne: TN, N.Kobayashi et al., PRL 112, (2014). 3/2- Sn=150(16)keV
37Mg: N.Kobayashi, TN et al., PRL 112, (2014). 3/2-/1/2- Sn=220(12)keV
29Ne: N.Kobayashi, TN et al., PRC 93, (2016). 3/2- Sn=960(140) keV

37. Courtesy of N. Fukunishi
RIBF Performance Summary
11.4 kW
320 AMeV 4He
18O
294 AMeV 18O
1000
13.1 kW
78Kr
48Ca
1012 pps
70Zn
100
Graphite-sheet stripper
86Kr
124Xe
4.0 kW
(pnA) 10
He-gas stripper / Be-disk stripper / fRC upgrade
Variable energy
238U
Fixed energy
SC-ECRIS with 28-GHz RILAC2
AVF injection 1
SC-ECRIS with 18-GHz RILAC (test operation)
18-GHz
0.1
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
(year)
Beam energies of the beams without explicitly indicated are 345 AMeV.
Courtesy of N. Fukunishi

38. Probe of weakly (un) bound states--Light target
e.g. 22C, 21C
22C
12C
20C n
22C*
Inelastic scattering
2+ (?)
ds/dErel
22C
20C
21C* n
Knockout reaction
12C
12C
P//(20C)
ds/dErel s d
N.Kobayashi,TN,PRC2012