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) August 2011, Seoul, Republic of Korea 1.Introduction 2.Experiment 3.Results 4.Discussion 5.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 nuclei T.Otsuka et al., PRL105(2010) Next step: Three-body force effects on unbound states in neutron rich oxgen isotopes. 1.Introduction

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) O→ 22,21 O 5/2 + D.Cortina-Gil et al., PRL93(2004) /2 + Spectroscopic studies of excited states of 23 OEx (MeV) M.Stanoiu et al., PRC69(2004) Ne→ 23 O+  No states Z.Elekes et al., PRL98(2007) O(d,p) 22 O+n4.0, 5.3 A.Shiller et al., PRL99(2007) 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

Existing studies on excited states in 23 O Z.Elekes et al., PRL98(2007) A.Shiller et al., PRL99(2007) 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

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

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

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

Invariant mass spectrum 3. Results

Differential cross section

Optical model potential (OMP):  Bruyeres potential (JLMB) E.Bauge et al., PRC63(2001) 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) 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:  B.A.Brown and W.D.M.Rae DWBA code:  DW81 J.R.Comfort extended version. Microscopic DWBA analysis 4. Discussion

Experimental and DWBA cross sections

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?

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

Analysis with different OMPs: JLMB & KD02

Analysis for different excited states

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

H.Sakurai et al., PLB448(1999)180. M.Notani et al., PLB542(2002)49. S.M.Lukyanov et al., J.Phys.G28(2002)L41. O.Tarasov et al., PRC75(2007) 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)

23 O 22 O neutron