Invariant mass spectroscopy of 23O via the (p,p’) reaction in

inverse kinematics

HHe

LiBeBC

NO

FNe

Neutron drip line

N=8

N=20

23O

Y.SatouSeoul National University

The Fifth Asia-Pacific Conference on Few-Body Problems in Physics 2011 (APFB2011)22-26 August 2011, Seoul, Republic of Korea

1. Introduction2. Experiment3. Results4. Discussion5. Summary

• Seoul National University– Y.Satou, K.Tshoo, H.C.Bhang, S.H.Choi

• Tokyo Institute of Technology– T.Nakamura, Y.Kondo,Y.Nakayama, N.Kobayashi, K.N.Tanaka,

S.Deguchi, Y.Kawada, N.Tanaka• RIKEN

– T.Motobayashi, H.Sakurai, H.Otsu, N.Aoi, S.Takeuchi, K.Yoneda, Y.Togano, M.Ishihara

• Center of Nucelar Study (CNS) University of Tokyo– S.Shimoura

• Tohoku University– T.Kobayashi

• Rikkyo University– M.Matsushita, T.Honda

• Tokyo University of Science– T.Sumikama, Y.Miyashita, K.Yoshinaga

• Caen– N.A.Orr, F.M.Marques, J.Gibelin, F.Delaunay

• ATOMKI– D.Sohler

• Pekin University – T.Zheng, Z.H.Li, Z.X.Cao

Collaboration: 　― RIKEN, R405n

Three-body forces in nucleiT.Otsuka et al., PRL105(2010)032501.

∆ SPE=𝑛 𝑗 ′ ∙∑𝑚 ,𝑚 ′

⟨ 𝑗𝑚 𝑗 ′𝑚′|𝑉| 𝑗𝑚 𝑗 ′𝑚 ′ ⟩ / ∑𝑚 ,𝑚 ′

1

Next step:Three-body force effects on unbound states in neutron rich oxgen isotopes.

1. Introduction

Spectroscopic study of 23O

Ground state configuration of 23O Jπ(gnd.)E.Sauvan et al., PLB491(2000)1. 23O→22O 1/2+

R.Kanungo et al., PRL(2002)142502. 23O→22,21O 5/2+

D.Cortina-Gil et al., PRL93(2004)062501.

23O→22O+ 1/2+

Spectroscopic studies of excited states of 23O Ex (MeV)M.Stanoiu et al., PRC69(2004)034312. 26Ne→23O+ No statesZ.Elekes et al., PRL98(2007)102502. 22O(d,p)22O+n 4.0, 5.3A.Shiller et al., PRL99(2007)112501. 26Ne→22O+n 2.8

This study 23O(p,p’)22O+n ?

Experimental purposes

1. Clarification of the ground state configuration of 23O2. Spectroscopic study of excited states

23O

24O: K.Tshoo, Aug.23 Parallel 4C

Existing studies on excited states in 23O

Z.Elekes et al., PRL98(2007)102502. A.Shiller et al., PRL99(2007)112501.

26Ne→23O+n22O(d,p)22O+n4.0 MeV

5.3 MeVErel=45(2) keV, Ex=2.79(13) MeV

Experimental methodInvariant mass method in inverse kinematics

These features validate use of this method for spectroscopy.

Projectile

Target

θ Erel

Neutron(E1,P1)

Ejectile (E2,P2) Detectors

1. Kinematical focusing of reaction products at forward angles2. Coincidence detection of multi particles3. No need for incident beam momentum4. Drastic gain in Erel resolution

10Be+n at Ei(i=1,2)=50 AMeV, ΔPi/Pi=0.01 => ΔErel=0.1 MeV at Erel=1 MeV

c.f.) ΔE～ 10 MeV for 10Be ΔE～ 1 MeV for neutron

Features:

2. Experiment

23O

22O

n

LH2 Target

NEUT

HOD

BOMAG

DALI

63.5 MeV/nucleon

Primary beam 40Ar@95 AMeV

Secondary beam 23O@63.5 AMeV

⊿P/P ±3%

Intensity 40 cps

Secondary Target LH2 : 160 mg/cm2

DC

Experimental setup at RIKEN RIPS facility

Good acceptance near threshold

Particle identification

TOF

Z (B

eam

)

Incident beam

O❑23 → O+𝑛❑

22

O❑22

F❑24

F❑25

N❑21

A (Fragment)

O❑23O❑

22O❑21

O❑23

Relative energy (MeV)Invariant mass spectrum

Z (Fragment)

Outgoing fragment

ONC

He

Invariant mass spectrum

𝐸 rel=42±6 keV

c.f. ) A.Shiller et al., PRL99(2007) 112501.N.Frank et al., NPA813 (2008) 199.

3. Results

Differential cross section

• Optical model potential (OMP): Bruyeres potential (JLMB)

E.Bauge et al., PRC63(2001)024607.

• Effective interaction: M3Y (ALTSO parameter) G.Bertsch et

al.,NPA284(1977)399.• One body transition density:

USDb shell model interaction (sd model space) B.A.Brown et al.,

PRC74(2006)034315.

• Single particle wave function: Harmonic oscillator well the b parameter (b=2.05)

constrained by the experimental rms matter radius

A.Ozawa et al.,NPA693(2001)32.

• Shell model code: Nushell@MSU

B.A.Brown and W.D.M.Rae• DWBA code:

DW81 J.R.Comfort extended version.

𝑑𝜎𝑑Ω=

𝑚𝑎𝑚𝑏

(2𝜋ℏ2 )2𝑘𝑏

𝑘𝑎¿¿

Microscopic DWBA analysis4. Discussion

Experimental and DWBA cross sections

1/2¿ ¿

Analysis with different assumption on

𝐽𝜋 (gs)=5 /2+¿¿

Narrow resonances observed slightly above the neutron threshold

12B 16B23O

14C ① Universal phenomenon?② What is the underlining mechanism?③ Astrophysical implications?

Summary• (p,p) reaction on 23O at 63.5 MeV/nucleon in

inverse kinematics– Invariant mass method– A narrow state at Erel=42(6) keV (Ex=2.78 MeV)

• DWBA analysis for the differential cross section– The normalization factor close to unity

=> Spherical nature of 23O Decoupled valence neutrons from the 16O core– The possibility of J(gs)=5/2+ was examined

=> Excluded• Possible universal appearance of narrow

neutron resonances

5. Summary

Analysis with different OMPs: JLMB & KD02

1/2¿ ¿

Analysis for different excited states

𝐽𝜋 (gs)=5 /2+¿¿

19C(p,p’)19C reaction study

Y.Satou et al., PLB660 (2008) 320.

𝑑𝜎𝑑Ω ∝ ¿¿

1999@RIKENH.Sakurai et al., PLB448(1999)180.

2002@RIKEN/GANILM.Notani et al., PLB542(2002)49.S.M.Lukyanov et al., J.Phys.G28(2002)L41.

2007@MUSO.Tarasov et al., PRC75(2007)064613.T.Baumann et al., Nature 449(2007)1022.

•New isotopes

•New magic number N=16A.Ozawa et al., PRL84(2000)5493.

•Neutron halosI.Tanihata et al., PRL55(1985)2676.

•Disappearance of magicity at N=8H.Iwasaki et al., PLB491(2000)8.

•Disappearance of magicity at N=20T.Motobayashi et al., PLB346(1995)9.

• To map out the neutron drip line for larger Z• To accumulate spectroscopic information and explore unexpected structures

Challenges in the physics of rare isotopes

Introduction

Neutron drip-line

•Three body forces in nucleiT.Otsuka et al., PRL105(2010)032501.

23O22O

neutron