Investigation of the symmetry energy using electric dipole

response of neutron-rich nuclei

Yasuhiro Togano Tokyo Institute of Technology

Nuclear equation of state

δ=0

δ=1

L: large uncertaintyB. Tsang et al. PRC 86, 015803 (2012).

L. W. Chen et al. PRC72, 064309

E1 response of neutron-rich nuclei

• Pygmy dipole resonance (PDR) • Skin oscillation

• Giant dipole resonance (GDR) • Restoring force: symmetry energy

Excitation energy [MeV]

B(E

1) st

reng

thPygmy

Skin thickness Symmetry energy

J. Piekarewicz, EPJA 50, 25 (2014).

Sn

correlate

Light(γ)

Nucleus Core

Giant: Ex~80A-1/3 MeV

D. Rossi et al., PRL111, 242503

68Ni

Correlation of E1 response

Excitation energy [MeV]

B(E

1) st

reng

th

RPA calc. by Inakura-san

PDR strength

52Ca 52Ca

PDR strength of Ca isotopes• Ca: Rapid increase at N=28~34

T. Inakura et al., PRC84, 021302 (2011)

PDR

stre

ngth

[e2 f

m2 ]

E1 response of 48-52Ca →Evolution of PDR →Evolution of skin at 2p orbital →Restriction of L

Coulomb excitation and invariant mass method

β~0.6 virtual photon absorption

n

51Ca

52Ca52Ca

Eγ2

Pb

52Ca

51Ca+n

Eγ1

Erel

Eγ1Eγ2

Sn

RIKEN Nishina Center

SAMURAI

70Zn@ 345 MeV/nucleon (~5x1011 Hz) → 48,50,52Ca(102~104 Hz)@ 250 MeV/nucleon

70Zn

52Ca

Be target

SAMURAI setup

n

51Ca

52Ca

IC MWDCs

CATANA

Pb or C target

MWDC

MWDCIC

Plastic

NEBULA+NeuLANDplastic scinti. wall

B = 3 T

SAMURAI magnet

poster by J. Tsubota

CATANACAlorimeter for γ-ray Transitions in

Atomic Nuclei at high isospin Asymmetry

• High detection efficiency: 56% for 1MeV, ~35% for 10 MeV • CsI(Na) • housing: 0.5 mm Al

prototype CsI(Na) crystals

Complete in 2015 summer

Beam

CATANACAlorimeter for γ-ray Transitions in

Atomic Nuclei at high isospin Asymmetry

• High detection efficiency: 56% for 1MeV, ~35% for 10 MeV • CsI(Na) • housing: 0.5 mm Al

prototype CsI(Na) crystals

Complete in 2015 summer

Ex reconstruction• B(E1)dist. : PDR + GDR

coun

t/200

keV

(e

ffici

ency

cor

rect

ed) 52Ca

Simulation

7 days beam time approved at RIKEN

Summary• E1 response of 48-52Ca

• Evolution of PDR and information on the symmetry energy

• CATANA construction is ongoing

• Design and specification finalized

• Experiment: late 2015