Weakly bound and unbound nuclei Takashi Nakamura Department

Weakly bound and unbound nuclei Takashi Nakamura Department of Physics, Tokyo Institute of Technology The 9 th Japan-China Joint Nuclear Physics Symposium (JCNP 2015), 7 -12/Nov/2015, Osaka Univ.

Contents Introduction: Drip Lines and Barely bound/unbound nuclei Probes: Coulomb and Nuclear Breakup at intermediate energies SAMURAI Facility at RIBF at RIKEN Coulomb/Nuclear Breakup of Borromean 2 n-Halo 22 C Spectroscopy of 25 O, 26 O -- @ SAMURAI at RIBF Summary and Outlook

Characteristic Nuclear structure near neutron-drip line? Neutron Drip-line b-Stable 1 n separation energy Sn=8 Me. V p n More n-rich Sn<1 Me. V Beyond -1 Me. V<Sn<0 Me. V continuum p n Neutron Drip Line Fermi levels between n and p—Very Different Valence neutron – Loosely-Bound/Unbound Neutron Halo/Skin (Neutron-matter surface) Continuum Strong cluster-like correlation dineutron?

Dineutron? A. B. Migdal Strongly correlated “dineutron” on the surface of a nucleus Sov. J. Nucl. Phys. 238(1973). n n Unbound a= -18 fm n n S=1 M. Matsuo PRC 73, 044309(2006). A. Gezerlis, J. Carlson, PRC 81, 025803(2010) Electric-Dipole (E 1) Response of 11 Li Dineutron: @ Low-dense neutron skin/halo? /surface of neutron star? q 12 n n T. N. et al. PRL 96, 252502(2006). n-star core Dineutron Correlation Strongly Polarized Strong E 1 Excitation Indirect Hint of Dineutron Correlation

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 K Deformation? Ar Cl Halo? S Drip Line? Si P N=28 Continuum? Al He H C B Be Li O N Mg Na Ne F N=20 N=16 37 Mg 21 C N=8 18 B 19 B 25 O 26 O 28 22 C 31 Ne O 1 n halo known 2 n halo known 4 n halo/skin

Probes– Nuclear and Coulomb breakup of drip-line nuclei at intermediate energies

Probe-1: Nuclear Breakup – Case of 1 n Halo e. g. 1 n knockout reaction of 31 Ne (TN et al. , PRL 112, 142501 (2014). ) 31 Ne 240 Me. V/u 31 Ne* 30 Ne n C Target 30 Ne (g) p f g ray in coincidence 30 Ne(2+) / 30 Ne(0+) Contribution of valence n, configuration s-1 n and P// distribution Theory: Eikonal Approximation

New 1 n Halo Systems 31 Ne and 37 Mg: 31 Ne 30 Ne core p-wave halo neutron Deformation b~0. 5 (~ 3: 2) Strongly deformed although it is N=21 (close to 20) 37 Mg: N. Kobayashi, TN et al. , PRL 112, 242501, 2014

Probe-1 Nuclear Breakup – Case of 2 n Halo e. g. 22 C* 20 C 22 C 12 C ds/d. Erel Inelastic scattering n n 2+ (? ) 21 C* 20 C 22 C n C P//(20 C) s ds/d. Erel Knockout reaction 12 12 C d N. Kobayashi, TN, PRC 2012

Probe-2: Coulomb Breakup Photon absorption of a fast projectile 22 C* g(virtual photon) b>0. 3 High-Z Target (Pb) Equivalent Photon Method ds. CB 16 p 3 d. B(E 1) = N (E ) d. Ex 9 hc E 1 x d. Ex Cross section = (Photon Number)x(Transition Probability) C. A. Bertulani, G. Baur, Phys. Rep. 163, 299(1988). Halo Soft E 1 Excitation (E 1 Concentration at Ex<1 Me. V) Invariant Mass 20 C n n Di-neutron Correlation Single particle state (Halo)

SAMURAI Facility at RIBF at RIKEN

RIKEN RI Beam Factory (RIBF) Completed in 2007 New-Generation RI-beam facility SCRIT 2013 SLOWRI 2014 ZDS 2008 SAMURAI 2012 SRC Big. RIPS 2007 Rare RI RING 2014 SHARAQ 2009 SRC: World Largest Cyclotron (K=2500 Me. V) Heavy Ion Beams up to 238 U at 345 Me. V/u (Light Ions up to 440 Me. V/u) eg. Increasing Year by Year! 48 Ca beam (345 Me. V/nucleon) ~200 pn. A (250 pn. A max. ) 48 Ca: ~500 pn. A 2014 238 U beam (345 Me. V/nucleon) ~12 pn. A (15 pn. A max. ) 238 U: ~ 30 pn. A 2015

SAMURAI Superconducting Analyzer for MUlti-particle from RAdio Isotope Beam Kinematically Complete measurements by detecting multiple particles in coincidence RI beam from Big. RIPS Superconducting Magnet (3 T, 2 m dia. Pole 80 cm gap) Large momentum acceptance Brmax / Brmin ~ 2 – 3 Good Momentum Resolution Dp/p~ 1/1500 Large Bending Angle (~60 deg) +4 Tracking Detectors T. Kobayashi NIMB 317, 294 (2013) Target rotatable Proton Large angular acceptance for n Neutron(s) Heavy Ion +-8. 8 deg (H) x +-4. 4 deg(V) (~50% coverage < Erel ~ 5 Me. V) Moderate Erel Resolution DE = 200 ke. V (s) at Erel=1 Me. V Stage: Rotatable (-5 -- 95 degrees) Variety of Physics Opportunities

SAMURAI Superconducting Analyzer for MUlti-particle from RAdio Isotope Beam March 2012

Breakup Experiments at SAMURAI -- Results from Day-One campaign experiments at SAMURAI Coulomb Breakup of 19 B and 22 C, Nakamura et al. Study of 18 B, 21 C, and excited states of 19 B, 22 C, Orr et al. Structure of Unbound Oxygen Isotopes 25 O, 26 O, Kondo et al. He H C B Be Li O N F 21 C N=8 18 B 19 B 25 O 26 O 28 O 22 C

22 C (Z=6, N=16) (<rm 2>)1/2=5. 4(9) fm c. f. ~3. 5 fm 11 Li K. Tanaka et al. , PRL 104, 062701(2010). S 2 n= -0. 14(46) Me. V L. Gaudefroy et al. PRL 109, 202503(2012). 22 C s. R(mb) p Prominent 2 n-Halo? Reaction cross section measurements Z=8 19 C 20 C p N=16 Magicity? 20 16 A 1 d 3/2 2 S 1/2 1 d 5/2 A. Ozawa et al. , PRL 84, 5493 (2000). p Heaviest s-wave dominant 2 n Halo within reach? c. f. 3 s 1/2 Halo: Far away for the current and near-future RIB facilities N~60 -70

SAMURAI Experiment May/2012 First Full Exclusive Coulomb/Nuclear Breakup Measurement of 22 C and 19 B 22 N DE 23 N ~10 cps RIBF (~10 cph RIPS) 20 C 22 C Pb 3. 26 g/cm 2 2 C 1. 79 g/cm 19 C 17 B 19 B n 22 C+C AZ+X n 2. 8 3 3. 2 3. 4 3. 6 3. 8 7 4 A/Z 240 Me. V/nucleon 22 C 6 Z 22 C 19 C 20 C 5 20 C 4 17 B 19 B 14 Be 3 2. 4 2. 6 2. 8 3 3. 2 3. 4 3. 6 3. 8 4 A/Z

Heavy Ion + 1 neutron : 22 C(22 N)+C 21 C* 20 C+n 22 F 23 F 26 F 24 F 25 F 27 F 28 F 29 F 30 F 21 O 22 O 23 O 24 O 22 N 21 C* 20 C+n 20 N 21 N 22 N 23 N 19 C 20 C 21 C 18 B 19 B Spokesperson: N. A. Orr, J. Gibelin 31 F S. Leblond Preliminary 22 C 22 N 21 C* 20 C+n S. Mosby et al. (MSU) NPA 909, 69(2013). N=16 s 20 16 22 C 21 C* 20 C+n 1 d 3/2 Preliminary 2 S 1/2 1 d 5/2 Erel(Me. V) 8 2 2 22 C s d 1 p 1/2 1 p 3/2 1 s 1/2 0 0 1 2 3 Edecay(Me. V) 4 5 Spectra 1 2 Edecay(Me. V) Spectra from S. Leblond/N. A. Orr 3

Coulomb Breakup of 22 C (20 C+n+n Spectrum) Spokesperson: T. Nakamura 22 C+Pb 22 C* 20 C+n+N R. Minakata (Tokyo Tech) counts y ! r a in m i l re P y r Ve 0 1 2 3 4 5 Erel(Me. V) 6 7 8 9 10

Study of unbound nuclei 25 O and 26 O at SAMURAI Spokesperson Yosuke Kondo Experimental study of unbound oxygen isotopes towards the possible double magic nucleus 28 O T. Otsuka et al. , PRL 105, 032501 (2010). 24 Ne 25 Ne 26 Ne 27 Ne 28 Ne 29 Ne 30 Ne 31 Ne 32 Ne 23 F 24 F 25 F 26 F 27 F 22 O 23 O 24 O 25 O 26 O 21 N 22 N 23 N 20 C 21 C 19 B 22 C N=16? 28 F 29 F 30 F 27 O 28 O Drip line 31 F Z=8 N=20 Oxygen Anomaly 3 N force: significant at N>16 G. Hagen et al. , PRL 108, 242501(2012). H. Hergert et al. , PRL 110, 242501(2013). S. K. Bogner et al. , PRL 113, 142501(2014). Continuum Effect: A. Volya, V. Zelevinski, PRL 94, 052501(2005). nn correlations: L. V. Grigorenko et al. , PRL 111, 042501(2013) K. Hagino, H. Sagawa PRC 89, 014331(2014).

~770 ke. V 2 n radioactivity of 26 O? E. Lunderberg et al. PRL 108, 142503 (2012) 25 O+n 26 O: 24 O(0+) ⊗ (nd 3/2)2 24 O+2 n L. V. Grigorenko et al. PRC 84, 021303 (2011) Th ? x 26 O C. Caesar et al. PRC 88, 034313 (2013) eo ry Er < 200 ke. V Z. Kohley et al, PRL 110, 152501 (2013) T 1/2=4. 5+1. 1 -1. 5 ps (3 ps systematic error) 2 n radioactivity? Usual 1 n decay G~Me. V or ke. V Er < 120 ke. V (95% CL) t < 5. 7 ns Excite state at 4. 2 Me. V? 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 26 O?

Experimental Setup at SAMURAI at RIBF C target Ionization (1. 8 g/cm 2) Chamber 2 Plastics 2 MWDCs MWDC Superconducting Dipole Magnet (B=3. 0 T) NEBULA n n 27 F ~210 Me. V/u (from Big. RIPS) DALI 2 MWDC Hodoscope 24 O

Decay energy spectrum of 25 O Edecay=750 ke. V 26 F+C 25 O* 24 O+n 25 O gs 24 O+n Kondo et al. Edecay=749(10) ke. V G= 88(6) ke. V C. R. Hoffman et al. , (MSU) PRL 100, 152502 (2008) Previous Works (GSI) C. Caesar, PRC 2013 (MSU) Hoffman, PRL 2008

Decay energy spectrum of 26 O (24 O+2 n, 24 O+n) 26 O gs 24 O+n+X Counts /20 ke. V Counts /50 ke. V 27 F+C 26 O 24 O+2 n 26 O 1 st New! 27 F+C 26 O, 25 O 26 O 1 st+ 25 O gs Edecay(24 O+n) Edecay(24 O+n+n) =Edecay(24 O+n)+Edecay(25 O+n) Edecay(24 O+n+n) Finite Value! n Most likely 2+ No peak at ~4. 2 Me. V 24 O n

Barely unbound nucleus 26 O Present Results on 25 O and 26 O 1. 27(11) Me. V (2+) 749(10) ke. V 25 O+n 24 O+n+n 18(5) ke. V 25 O+n 26 O Centrifugal Barrier Extremely weakly UNBOUND state! E 0+ • N=16 shell closure is confirmed • USDB fail to describe E(2+) of 26 O Effect of pf shell? 3 N-forces, pf shell, continuum Submitted to PRL Next step: Study of 27 O and 28 O in Nov. -Dec

Summary and Outlook Coulomb and Nuclear Breakup Useful tool to probe weakly-bound states (HALO) near/beyond the drip-line 31 Ne TN, N. Kobayashi, PRL 2014, 37 Mg N. Kobayashi, TN, PRL 2014. SAMURAI Facility at RIBF (since 2012) Powerful equipment for various experiments using RI beams Coulomb/Nuclear Breakup of 22 C at SAMURAI S. Leblond, J. Gebelin, M. Marques, N. Orr, R. Minakata, S. Ogoshi, TN, et al. 21 C spectrum pin down s and d 1 hole state of 22 C Large Coulomb breakup cross sections Spectroscopy of 25 O, 26 O at SAMURAI Y. Kondo, J. Tsubota, TN et al. 26 O(0+gs): Very weakly unbound 2 n states Correlation? Continuum? 26 O(2+): Found for the first time at E =1. 28(11) Me. V Shell Evolution? rel Keys to understand Oxygen drip-line anomaly, Shell Evolution Near Future: Variety of unbound states along n-drip line 28 O (Possible unbound doubly magic nucleus, 24 O+4 n)

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, IN 2 P 3 -CNRS: M. Vandebrouck

Backup

Mass identification@SAMURAI Counts 22 O 21 O 27 F+C AO @SAMURAI ~13 s separation! 23 O @GSI 22 O C. Caesar et al. PRC(2013). 23 O 24 O A Clear Particle identification! A/DA=310 (1 s) High resolving power of the SAMURAI spectrometer

Eg=1. 6 Me. V gated