Studies of hypernuclei with the AMD method Masahiro ISAKA Institute of Physical and Chemical Research (RIKEN) Focusing on 25  Mg, based on M. Isaka, M. Kimura, A. Dote and A. Ohnishi, PRC 87, (R) (2013)

Hypernuclear physics  hypernucleus Normal nucleus As an impurity + Interaction: knowledge of B-B interactions 2 body interaction between baryons hyperon – nucleon (YN) hyperon – hyperon (YY) A major issue in hypernuclear physics Structure: baryon many-body system Structure change caused by hyperon(s) No Pauli exclusion between N and Y YN interactions are different from NN one “Hyperon as an impurity in nuclei”  Hypernuclei Nuclei with hyperon(s) Examples:  Grand challenges of hypernuclear physics (Single)  hypernuclei  particle s d u  hypernuclei

Structure of  hypernuclei  has no Pauli blocking to nucleons  N attraction (different from NN) 6 Li (  + d) 7  Li (  + d +  ) 8 Be (unbound)   Be (bound) “Shrinkage effect” [1-3] “Glue-like role” of  [4] Structure change: A unique probe:  can penetrate into nuclear interior ground state Genuine hypernuclear state [6] (Super-symmetric state [5] ) Unique states in hypernuclei: 9 Be analog 9  Be [1] T. Motoba, et al., PTP 70, 189 (1983). [2] E. Hiyama, et al., PR C59 (1999), [3] K. Tanida, et al., PRL 86 (2001), [4] H. Bando, et. al., PTP 69 (1982) 913. [5] R.H. Dalitz, A. Gal, PRL36 (1976) 362 [6] H. Bando, NPA 450 (1986) 217c Unique phenomena

Toward heavier  hypernuclei Experiments at J-PARC, JLab and Mainz etc. Various  hypernuclei will/can be produced –p-sd shell  hypernuclei –neutron-rich  hypernuclei etc. O. Hashimoto and H. Tamura, PPNP 57 (2006), 564. Structure study of such hypernuclei becomes one of interesting topics p-sd shell region neutron-rich region

Structure of sd shell nuclei Ex) 24 Mg  Various deformations  Coexistence of structures Ex) 20 Ne (deformed) mean-field  + 16 O cluster Coexistence in low-lying region Candidate of triaxially deformed nuclei But its identification is not easy Structure changes by  are different ?  can be a probe to identify ? Today’s talk K. Ikeda, et al., PTPS 52,(1972) M. Kimura, PRC69, (2004) R. Batchelor, et al., NP16, 38 (1960).

Deformation of nuclei Many nuclei manifests various quadrupole deformation –Most are prolately or oblately deformed (axially symmetric) Parameterized by quadrupole deformation parameters  and  Triaxial deformed nuclei are not many and its (direct) identification is not easy. Prolate Oblate Triaxial  = 0 ◦  ≈ 30 ◦ Spherical  = 60 ◦   0 0◦0◦ 60 ◦ Candidate: Mg isotope Long Middle Short “  in p orbit can be a probe to study nuclear (triaxial) deformation”

Example: p-states (  in p-orbit) in 9  Be 9  Be: axially symmetric 2  clustering [1] R.H. Dalitz, A. Gal, PRL 36 (1976) 362. [2] H. Bando, et al., PTP 66 (1981) 2118.; H. Bando, et al., IJMP 21 (1990) [3] O. Hashimoto et al., NPA 639 (1998) 93c. Anisotropic p orbit of  hyperon Axial symmetry of 2  clustering  in p-orbit generates two bands as p-states [1,2] p-orbit parallel to/perpendicular to the 2  clustering parallel perpendicular

Splitting of p-states in 9  Be  9  Be with 2  cluster structure [1] R.H. Dalitz, A. Gal, PRL 36 (1976) 362. [2] H. Bando, et al., PTP 66 (1981) 2118.; H. Bando, et al., IJMP 21 (1990) Lowest: p orbit parallel to 2  (long axis) 2nd: p orbit perpendicular to 2  (short axes) Large overlap Deeply bound Shallowly bound Split corresponding to long/short axes Small overlap p-states splits into 2 bands depending on the direction of p-orbits

Triaxial deformation If 24 Mg is triaxially deformed nuclei Large overlap leads deep binding Middle Small overlap leads shallow binding cf. prolate deformation Ex.) 9  Be p orbit parallel to 2  (long axis) p orbit perpendicular to 2  (short axes) Large overlap Deeply bound Split corresponding to long/short axes Small overlap Shallowly bound Triaxial deformation Prolate deformation p-states split into 3 different state

Triaxial deformation If 24 Mg is triaxially deformed nuclei Large overlap leads deep binding Middle Small overlap leads shallow binding Triaxial deformation Prolate deformation G.S. Excitation Energy 25  Mg 24 Mg ⊗  s-orbit) 24 Mg ⊗  p-orbit) Split into 3 states? Observing such 3 different states is strong evidence for triaxial deformation of 24 Mg p-states split into 3 different state

Purpose  Purpose and problem To reveal triaxial deformation of 24 Mg, we will predict the level structure of the p-states in 25  Mg 25  Mg –p-states will split into 3 different states, if 24 Mg is triaxially deformed  Method HyperAMD (Antisymmetrized Molecular Dynamics for hypernuclei) –No assumption on symmetry of nuclei YNG-NF interaction

Theoretical framework: HyperAMD We extended the AMD to hypernuclei  Wave function Nucleon part ： Slater determinant Spatial part of single particle w.f. is described as Gaussian packet Single particle w.f. of  hyperon: Superposition of Gaussian packets Total w.f. ： [1] Y. Yamamoto, T. Motoba, H. Himeno, K. Ikeda and S. Nagata, Prog. Theor. Phys. Suppl. 117 (1994), 361.  N ： YNG interaction (Central force) [1] NN ： Gogny D1S  Hamiltonian HyperAMD (Antisymmetrized Molecular Dynamics for hypernuclei)

Theoretical framework: HyperAMD  Procedure of the calculation Variational Calculation Imaginary time development method Variational parameters: Energy variation ClusterShell Initial w.f. nucleons (Described by Gaussian wave packets)  hyperon

Theoretical framework: HyperAMD  Procedure of the calculation Variational Calculation Imaginary time development method Variational parameters: Angular Momentum Projection Generator Coordinate Method(GCM) Superposition of the w.f. with different configuration Diagonalization of and

Results and Discussions  single particle energy of the different p-orbit directions 2.Excitation spectra of the p-states

Results ： Single particle energy of  hyperon   single particle energy on  plane Single particle energy of  hyperon is different from each p state –This is due to the difference of overlap between  and nucleons 25 Mg (AMD,  in p orbit) 3 p-states with different spatial distributions of   Lowest p state2nd lowest p state3rd lowest p state

Results ： Single particle energy of  hyperon   single particle energy in axial/triaxial deformed nucleus Lowest p state 2nd lowest p state 3rd lowest p state I II III  s. p. energy is different from each other with triaxial deformation split into 3 p-orbit states I II III I II III I II III 25 Mg (AMD)  (Parallel to long axis) (Parallel to middle axis) (Parallel to short axis)

Results: Excitation spectra 3 bands are obtained by  hyperon in p-orbit – 24 Mg ⊗  p(lowest), 24 Mg ⊗  p(2nd lowest), 24 Mg ⊗  p(3rd lowest) Lowest threshold : in between 8.3 and 12.5 MeV Ne + 21   Splitting of the p states

Summary  Summary Knowledge of YN interaction will allow us to reveal structure of hypernuclei –Structure change and modification of nuclear properties by adding a hyperon –Bounding unbound systems by using hyperons as a glue –Probing nuclear structure (deformation) by using hyperon Combination of the modern YN interaction with nuclear models –Antisymmetrized molecular dynamics + effective YN interaction Probing nuclear deformation by using  –By looking at the orbit of  in hypernuclei, it is possible to use a  as a probe Example: Splitting of the p orbits in 25  Mg due to triaxial deformation  Future plans (Mg hypernucleus) To reveal how to observe the splitting of the p-state in hypernuclei

Triaxial deformation of 26 Mg Constraint Hartree-Fock-Bogoliubov + Local QRPA (CHFB + LQRPA) approach They solve the collective Schroedinger eq. and obtain the excitation spectra, and they calculate the vibrational w.f. squared to analyze each state N. Hinohara and Y. Kanada-En'yo, Phys. Rev.C 83, (2011) The 26 Mg ground state has a  -soft character 26 Mg 24 Mg The p states of 27  Mg should split into three, if 26 Mg is triaxially deformed

Genuine hypernuclear (super symmetric) state 9  Be:  +  +  structure Genuine hypernuclear states cannot be formed in ordinary 9 Be Example:  Be 9 R.H. Dalitz, A. Gal, Phys. Rev. Lett. 36 (1976) 362 H. Bando, Nuclear Phys. A 450 (1986) 217c Genuine hypernuclear states 9 Be analog states n n In case of 9 Be (  +  + n) allowed Forbidden by Pauli principle H. Bando, Nuclear Phys. A 450 (1986) 217c

Backup: 25  Mg with  in p orbit

Backup ： Deformation change due to  in p-orbit 2nd 2 + state of 24 Mg Deformation changes are different depending on the direction of each p-orbit Peak positions of the GCM overlap –Lowest p: unchanged –2nd lowest: –3rd lowest: GCM overlap: (  =0.48,  =21 ∘ ) (  =0.43,  =15 ∘ ) (  =0.48,  =21 ∘ ) (  =0.53,  =27 ∘ )

Backup ： Deformation change due to  in p-orbit 2nd 2 + state of 24 Mg Deformation changes are different depending on the direction of each p-orbit Peak positions of the GCM overlap –Lowest p: –2nd lowest: unchanged GCM overlap: (  =0.48,  =21 ∘ ) (  =0.53,  =27 ∘ )

Backup ： Density distributions of 25  Mg Intrinsic wave functions corresponding to the peak of GCM overlap Lowest p state (  =0.48,  =21 ∘ ) 2nd lowest p state (  =0.43,  =15 ∘ ) 3rd lowest p state (  =0.53,  =27 ∘ )       

Results: Excitation spectra

Back up: p-states in 9  Be [1] H. Bando, et al., PTP 66 (1981) [2] H. Bando, et al., IJMP 21 (1990) K  = 0  band K  = 1  band

Backup: Constraint on the  single particle w.f. The constraint potential on the  single particle w.f. In actual calculation, Total w.f.  single particle w.f.

Backup: 25  Mg with  in s orbit Positive parity bands associated with the triaxial deformation Examples: 25  Mg How does  modify the nuclear properties of triaxial deformed (hyper)nuclei ? M. Isaka, M. Kimura, A. Dote and A. Ohnishi, PRC 85 (2012),

Structure of 24 Mg Large deformation ・・・ Candidate of triaxial deformed nuclei Excitation energy of K  =2  band depends on the triaxial deformation [1,2] [1] M. Bender and P-H. Heenen, Phys. Rev. C78, (2008). [2] M. Kimura, R. Yoshida and M.Isaka, Prog. Theor. Phys. 127, 287(2011).

Structure of 24 Mg Large deformation ・・・ Candidate of triaxial deformed nuclei Excitation energy of K  =2  band depends on the triaxial deformation [1,2] [1] M. Bender and P-H. Heenen, Phys. Rev. C78, (2008). [2] M. Kimura, R. Yoshida and M.Isaka, Prog. Theor. Phys. 127, 287(2011). How does  modify triaxial deformation of 24 Mg ? Ex K  = 2  band is rigid against the exclusion of the triaxial deformation

Results: Excitation spectra of 25  Mg Excitation energy of K  =2  ⊗  s band is shifted up by about 200 keV 200keV

Results: Reasons for the shift up  Difference of the  binding energy B  B  for the K  =0  ⊗  s band is larger than that for the K  =2  ⊗  s band Energy shift of the K  =2  ⊗  s band Mg  Mg B  = MeV B  = MeV 5.31 MeV 5.53 MeV             (K  =0  ⊗  s ) (K  =2  ⊗  s ) (K  =0   (K  =2  

Color plots: GCM overlapContour lines: energy surface K  =0  band: Energy surface is soft (flat) against the ( ,  ) reduction K  =2  band: rigid against the deformation change Results: Deformation change by  hyperon (  =0.48,  =21 ∘ ) (  =0.43,  =15 ∘ ) By adding  to K  = 0 + Unchanged: (  =0.48,  =21 ∘ ) By adding  to K  = 2 + Changes of GCM overlap

Backup: Excitation spectra of 25  Mg

Backup: application of HyperAMD to light hypernuclei

Backup

Application to 9  Be hypernucleus [1] Bando et al., PTP 66 (1981) [2] M. May et al., PRL 51 (1983) 2085; H. Akikawa et al., PRL 88 (2002) [3] O. Hashimoto et al., NPA 639 (1998) 93c [1] [2] [3]

 binding energy  Reasons for the variation of the  binding energies Overlap between  and nucleons  in s-orbit: large overlap with small deformation  in p-orbit: large overlap with large deformation Large distribution of  reduces the kinetic energy 12 C(Pos)⊗  (p) 12 C(Pos.)⊗  (s) 12 C(Neg)⊗  (s)  binding energy [MeV]  = 0.30  = 0.00

Backup: Structure study of sd shell  nuclei  A typical example: 21  Ne Coexistence of structures in a hypernucleus Their modifications by  21 Ne (Neg., AMD) M. I, et al., PRC83 (2011), Ne (Neg.,  + 16 O +  ) T. Yamada, et al., PTP71 (1984), 985. T. Yamada, et al., PTP71 (1984), 985.  + 16 O +  model calc. Various  + 16 O +  states B(E2) reduction in cluster band M. I., et al., PRC83 (2011), AMD calc. (Deformed) mean-field states appear as well as cluster states B(E2) reduction is different between the structures