1. Invariant mass spectroscopy of 23 O via the (p,p’) reaction in inverse kinematics Y.Satou Seoul National University The Fifth Asia-Pacific Conference on Few-Body Problems in Physics 2011 (APFB2011) 22-26 August 2011, Seoul, Republic of Korea 1.Introduction 2.Experiment 3.Results 4.Discussion 5.Summary

2. 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

3. Three-body forces in nuclei T.Otsuka et al., PRL105(2010)032501. Next step: Three-body force effects on unbound states in neutron rich oxgen isotopes. 1.Introduction

4. Spectroscopic study of 23 O Ground state configuration of 23 OJ π (gnd.) E.Sauvan et al., PLB491(2000)1. 23 O→ 22 O 1/2 + R.Kanungo et al., PRL(2002)142502. 23 O→ 22,21 O 5/2 + D.Cortina-Gil et al., PRL93(2004)062501. 1/2 + Spectroscopic studies of excited states of 23 OEx (MeV) M.Stanoiu et al., PRC69(2004)034312. 26 Ne→ 23 O+  No states Z.Elekes et al., PRL98(2007)102502. 22 O(d,p) 22 O+n4.0, 5.3 A.Shiller et al., PRL99(2007)112501. 26 Ne→ 22 O+n2.8 This study 23 O(p,p’) 22 O+n? Experimental purposes 1.Clarification of the ground state configuration of 23 O 2.Spectroscopic study of excited states 23 O 24 O: K.Tshoo, Aug.23 Parallel 4C

5. Existing studies on excited states in 23 O Z.Elekes et al., PRL98(2007)102502.A.Shiller et al., PRL99(2007)112501. 26 Ne→ 23 O+n 22 O(d,p) 22 O+n 4.0 MeV 5.3 MeV Erel=45(2) keV, Ex=2.79(13) MeV

6. Experimental method Invariant mass method in inverse kinematics These features validate use of this method for spectroscopy. Projectile Target θ E rel Neutron (E 1,P 1 ) Ejectile (E 2,P 2 ) Detectors 1.Kinematical focusing of reaction products at forward angles 2.Coincidence detection of multi particles 3.No need for incident beam momentum 4.Drastic gain in E rel resolution 10 Be+n at E i (i=1,2)=50 AMeV, ΔP i /P i =0.01 => ΔE rel =0.1 MeV at E rel =1 MeV c.f.) ΔE ～ 10 MeV for 10 Be ΔE ～ 1 MeV for neutron Features: 2. Experiment

7. 23 O 22 O n LH2 Target NEUT HOD BOMAG DALI 63.5 MeV/nucleon Primary beam 40 Ar@95 AMeV Secondary beam 23 O@63.5 AMeV ⊿ P/P ±3% Intensity40 cps Secondary TargetLH 2 : 160 mg/cm 2 DC Experimental setup at RIKEN RIPS facility Good acceptance near threshold

8. Particle identification TOF Z (Beam) Incident beam A (Fragment) Relative energy (MeV) Invariant mass spectrum Z (Fragment) Outgoing fragment O N C He

9. Invariant mass spectrum 3. Results

10. Differential cross section

11. 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. Microscopic DWBA analysis 4. Discussion

12. Experimental and DWBA cross sections

14. Narrow resonances observed slightly above the neutron threshold 12 B 16 B 23 O 14 C ①Universal phenomenon? ②What is the underlining mechanism? ③Astrophysical implications?

15. Summary (p,p) reaction on 23 O 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 23 O Decoupled valence neutrons from the 16 O core – The possibility of J  (gs)=5/2 + was examined => Excluded Possible universal appearance of narrow neutron resonances 5. Summary

16. Analysis with different OMPs: JLMB & KD02

17. Analysis for different excited states

18. 19 C(p,p’) 19 C reaction study Y.Satou et al., PLB660 (2008) 320.

19. 1999@RIKEN H.Sakurai et al., PLB448(1999)180. 2002@RIKEN/GANIL M.Notani et al., PLB542(2002)49. S.M.Lukyanov et al., J.Phys.G28(2002)L41. 2007@MUS O.Tarasov et al., PRC75(2007)064613. T.Baumann et al., Nature 449(2007)1022. New isotopes New magic number N=16 A.Ozawa et al., PRL84(2000)5493. Neutron halos I.Tanihata et al., PRL55(1985)2676. Disappearance of magicity at N=8 H.Iwasaki et al., PLB491(2000)8. Disappearance of magicity at N=20 T.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 nuclei T.Otsuka et al., PRL105(2010)032501.

20. 23 O 22 O neutron