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The Study of the Pygmy Dipole Resonances via High-Resolution (p, p) reaction Chihiro Iwamoto Research Center for Nuclear Physics, Osaka University Out line 1. Introduction Pygmy Dipole Resonance and Dipole Polarizability Correlation

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SLIDE 1

Chihiro Iwamoto Research Center for Nuclear Physics, Osaka University

The Study of the Pygmy Dipole Resonances via High-Resolution (p, p’) reaction

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SLIDE 2

Out line

  • 1. Introduction
  • Pygmy Dipole Resonance and Dipole Polarizability
  • Correlation between the PDR and the valence neutron number
  • Previous Experimental Data of Zr isotopes
  • 2. Experiment : inelastic proton scattering
  • 3. Results and Analysis
  • Spectrum of Zr isotopes
  • E1 strength distributions and Dipole Polarizability in 90Zr
  • 4. Summary
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SLIDE 3

5 10 15 20 25 30

Response function Excitation Energy

GDR PDR Sn Neutron threshold Protons Neutrons Core Neutron Skin

What is the Pygmy Dipole Resonance ?

Pygmy Dipole Resonance…

  • the low-energy E1 strength around low-energy tail of GDR

in medium-heavy and heavy nuclei with N > Z.

  • predicted to have a structure like a dipole oscillation of the

neutron skin against the core nucleus. →the neutron skin thickness. the neutron matter equation of state and neutron star.

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SLIDE 4
  • It is appeared from the study for 208Pb that symmetry energy term
  • f the EOS and neutron skin information closely related to the

dipole polarizability D.

The correlation between D and neutron skin thickness

TheD is an inversely energy-weighted sum value of the B(E1). energy Excitation : section cross ption Photoabsor : y probabilit n transitio E1 : ) 1 (

abs

  E B

 

 

 

2 2

) 1 ( 9 8 2        E dB c

abs D

  • X. Roca-Maza et al., PRC 88, 024316 (2013).

, ) ( 3 ) (          L J S

density saturation the : , ,         

p n p n p n

    

  • Nuclear equation of state (EOS)
  • Symmetry energy term

, ) ( ) , ( ) , (

2

         S A E A E

J : the nuclear symmetry energy at saturation energy L : slope parameter

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SLIDE 5

Systematical data of D is expected to narrow the parameters of the neutron EOS etc…

The correlation between D and neutron skin thickness

  • X. Roca-Maza et al., inarXiv:1510.01874v1
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SLIDE 6

The study of the structure of PDR

To focus on the correlation between PDR structure and excess neutron.

  • V. Ponomarev, Private Comminication
  • The correlation between the PDR strength and the neutron number.

→The measurement of PDR strength in isotope chain. (RCNP-E421 for Zr isotopes) done on July 2015

  • Experimental investigation of the neutron skin oscillation

→The measurement of transition density by (p, p’) experiment (RCNP-E450 experiment)

p – n mode n – skin mode B(E1) = 0.3 e2fm2

208Pb(p, p’) Ep=80MeV

p – n mode n – skin mode

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SLIDE 7

↓ : by the valence neutrons occupied 1g9/2 ↓ : by the valence neutrons occupied 2d5/2

  • T. Inakura et al. Phys. Rev. C 84, 021302(R) (2011)

The correlation between the PDR and the neutron number

The evolution is predicted in lower energy region by the increase of the valence neutrons

  • ccupied a orbit of low-

For example – stable Zr isotopes –

  • Spherical nuclear
  • Proton subshell closer

→ The role of the neutron number can be separated out

  • T. Inakura, Private Communication
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SLIDE 8
  • G. M. Crawley et al., PRC 26, 87 (1982).

Excitation Energy (MeV)

Previous experiment of E1 and M1 component in Zr isotopes

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 5 7 9 11 13 15 17 Differenctial cross section [mb/sr/0.1MeV] Excitation Energy [MeV]

90Zr(p, p’) 0 <  < 0.5 degree

Blue: E1 Red: Spin M1

20 16 10 8 4 Excitation Energy (MeV)

Preliminary

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Experimental Setup

High resolution magnetic spectrometer Grand Raiden

At Research Center for Nuclear Physics of Osaka University(RCNP)

Focal Plane Detectors DSR+ mode Ex range : 4 – 23 MeV Beam Dump for 0deg

Proton Beam 295 MeV

Beam Dump for 2.5deg, 4.5deg

Large Acceptance Spectrometer (LAS)

Blank target, 0deg., Faint beam

  • Angular resolution: 0.14 deg.
  • Energy Resolution: 80 – 60 keV
  • Setting angles of Grand Raiden

：0deg, 2.5 deg, 4.5 deg (Range of measured angular distribution) ：0deg ‐ 5.5 deg )

Foil target (~4 mg/cm2)

90Zr

(97.65 %)

92Zr

(94.57 %)

94Zr

(96.28 %)

96Zr

(57.36 %)

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SLIDE 10

Energy spectra integrated over 0 – 0.5 degree

※ Very Preliminary ※ do NOT separate E1 component and spin-M1 component ※ show a one-tenth of the whole data

GDR Counts/50keV Ex [MeV]

4 6 8 10 12 6 8 10 12 6 8 10 12 6 8 10 12 90Zr 92Zr 94Zr 96Zr

※ normalized by beam intensity and target thickness ※ target thickness and detection efficiency are almost same.

GDR GDR GDR PDR PDR PDR PDR

600 200 400 200 100 300 4 8 12 16 20 4 8 12 16 20 4 8 12 16 20 4 8 12 16 20

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Comparison with previous (, ’) and (, n) data

※1 Present data is normalized to (, abs) cross section at 16.5 MeV ※2 (, abs) = (, n) + (, n+p) + (, 2n) + (, p) ※3

  • ∑ 1
  • ※4 In Ref [3], they perform a correction for branching transitions

Energy Weighted Sum Value in 90Zr 6 MeV < Ex < 28 MeV  = 129±11 fm 2 MeV (Preliminary) (97 % of TRK Sum rule)

6-18MeV : Present data 18-28 MeV : (, abs) data [1, 2]

[1] B. L. Berman et al., PR 162, 1098 (1967). [2] D. Brajnik et al., PRC 13, 1852 (1976). [3] R. Schwengner et al., PRC 78,064314 (2008). [4] R. M. Laszewski et al., PRL 59, 431 (1987). [5] T. Inakura, Private Communication. 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03

5 10 15 20 25 abs [mb] (g, abs) (g,g) [3] Present Data 系列6 Inakura Skm*

1.0E-01 1.0E+00 1.0E+01 1.0E+02

5 6 7 8 9 10 11 12

abs [mb]

Ex [MeV]

(Preliminary) SkM* [5] (, ’) [3] (, abs) [1, 2] (Corrected ※4)

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Dipole Polarizability in 90Zr

  • X. Roca-Maza et al., inarXiv:1510.01874v1

Dipole Polarizability in 90Zr 6 MeV < Ex < 28 MeV D = 4.3 ±0.2 fm 3 (Preliminary)

6-18MeV : Present data 18-28 MeV : (, abs) data [1, 2]

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Summary

  • High resolution inelastic proton scattering experiment was performed.
  • Energy spectra of scattered protons in Zr isotopes were obtained.
  • In 92Zr, 94Zr and 96Zr, We can find strength that was not found in 90Zr

Are they the evolution of the PDR ? → I have to decompose between E1 and M1 in the future.

  • The E1 strength distributions and Dipole polarizability in 90Zr was obtained
  • Dipole Polarizability in 90Zr is smaller than theoretical prediction

→ Under discussion…

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SLIDE 14

RCNP , Osaka University

  • C. Iwamoto, A. Tamii, T. Shima, Y. Fujita, H. Fujita, T. Suzuki, K. Hatanaka,

H.J. Ong, P.Y. Chan, S. Noji, S. Adachi, A. Inoue, G. Gey, T.H. Hoang

Collaborators of RCNP-E326 and RCNP-E421

Institute for Basic Science

  • T. Hashimoto

Kyoto University

  • M. Tsumura, T. Nanamura
  • H. Fujioka, N. Nakatsuka, T. Kawabata

Miyazaki University

  • T. Yamamoto, Y. Maeda

RIKEN Nishina Center

  • J. Zenihiro

National Institute of Radiological Science

  • H. Matsubara

Niigata University

  • T. Inakura, Y. Shimbara, M. Nagashima

Chiba University

  • H. Nakada

Okayama University

  • M. Sakuda, T. Mori, T. Izumi, I. Ou

Istanbul University

  • B. Bilgire, H. C. Kozer

Texas A&M University Y.-W. Lui Tokyo University Y.N. Watanabe Tokyo Instit. of Tech.

  • Y. Togano

TU - Darmstadt

  • S. Bassauer, M. Singer, G. Steinhilber, M. Hilcker, M. Zweidinger,
  • P. von Neumman-Cosel

Konan University

  • H. Utsunomiya, H. Akimune, T. Yamagata, A. Okamoto, T. Kondo,
  • Y. Matsuda, K. Heguri, F. Hattori,