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 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
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. S n Neutron threshold Core Protons Response function GDR PDR Neutrons Neutron Skin 0 0 5 10 15 20 25 30 Excitation Energy
The correlation between D and neutron skin thickness • It is appeared from the study for 208 Pb that symmetry energy term of the EOS and neutron skin information closely related to the dipole polarizability D . The D is an inversely energy-weighted sum value of the B(E1). ( 1 ) : E1 transitio n probabilit y B E 8 ( 1 ) c dB E : Photoabsor ption cross section abs abs 2 2 D 2 9 0 0 : Excitation energy Nuclear equation of state (EOS) • E E 2 ( , ) ( , 0 ) ( ) , S A A Symmetry energy term • L ( ) ( ) , S J 0 3 0 J : the nuclear symmetry energy , n p , n p at saturation energy n p : the saturation density L : slope parameter X. Roca-Maza et al., PRC 88, 024316 (2013). 0
The correlation between D and neutron skin thickness Systematical data of D is expected to narrow the parameters of the neutron EOS etc… X. Roca-Maza et al., inarXiv:1510.01874v1
The study of the structure of PDR To focus on the correlation between PDR structure and excess neutron. • 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 208 Pb(p, p’) E p =80MeV B(E1) = 0.3 e 2 fm 2 n – skin mode p – n mode n – skin mode V. Ponomarev, Private Comminication
The correlation between the PDR and the neutron number T. Inakura et al. Phys. Rev. C 84, 021302(R) (2011) The evolution is predicted in lower energy region by the increase of the valence neutrons occupied a orbit of low- For example – stable Zr isotopes – Spherical nuclear • Proton subshell closer • ↓ : by the valence neutrons occupied 1g9/2 → The role of the neutron number ↓ : by the valence neutrons occupied 2d5/2 can be separated out T. Inakura, Private Communication
Previous experiment of E1 and M1 component in Zr isotopes G. M. Crawley et al., PRC 26, 87 (1982). 90 Zr(p, p’) 0 < < 0.5 degree 2 Blue: E1 1.8 Preliminary Red: Spin M1 Differenctial cross section 1.6 1.4 [mb/sr/0.1MeV] 1.2 1 0.8 Excitation Energy (MeV) 0.6 0.4 0.2 0 5 7 9 11 13 15 17 Excitation Energy [MeV] 20 16 10 8 4 Excitation Energy (MeV)
Experimental Setup At Research Center for Nuclear Physics of Osaka University(RCNP) • Setting angles of Grand Raiden ： 0deg, 2.5 deg, 4.5 deg (Range of measured angular distribution) ： 0deg ‐ 5.5 deg ) High resolution magnetic spectrometer Foil target (~4 mg/cm 2 ) Grand Raiden 90 Zr (97.65 %) 92 Zr (94.57 %) 94 Zr (96.28 %) Focal Plane Detectors 96 Zr (57.36 %) DSR+ mode Ex range : 4 – 23 MeV Large Acceptance Spectrometer (LAS) Beam Dump for 2.5deg, 4.5deg Beam Dump for 0deg Blank target, 0deg., Faint beam Angular resolution: 0.14 deg. • Proton Beam Energy Resolution: 80 – 60 keV • 295 MeV
Energy spectra integrated over 0 – 0.5 degree 600 GDR 90 Zr 92 Zr 94 Zr 96 Zr GDR GDR GDR PDR PDR PDR PDR 400 200 Counts/50keV 0 16 16 16 4 8 12 20 4 8 12 20 4 8 12 16 20 4 8 12 20 300 200 100 0 6 10 12 4 8 6 8 10 12 6 10 12 6 8 10 12 8 E x [MeV] ※ Very Preliminary ※ normalized by beam intensity and target thickness ※ do NOT separate E1 component and spin-M1 component ※ target thickness and detection efficiency are almost same. ※ show a one-tenth of the whole data
Comparison with previous ( , ’) and ( , n) data 1.0E+03 1.0E+02 abs [mb] ( , abs) [1, 2] (g, abs) 1.0E+01 ( , ’ ) [3] (g,g) [3] (Corrected ※ 4) (Preliminary) Present Data 1.0E+00 系列 6 Energy Weighted Sum Value in 90 Zr SkM* [5] Inakura Skm* 1.0E-01 6 MeV < Ex < 28 MeV 5 10 15 20 25 = 129 ± 11 fm 2 MeV (Preliminary) 1.0E+02 (97 % of TRK Sum rule ) 1.0E+01 6-18MeV : Present data : ( , abs) data [1, 2] 18-28 MeV abs [mb] 1.0E+00 1.0E-01 5 6 7 8 9 10 11 12 Ex [MeV] [1] B. L. Berman et al., PR 162, 1098 (1967). ※ 1 Present data is normalized to ( , abs) cross section at 16.5 MeV [2] D. Brajnik et al., PRC 13, 1852 (1976). ※ 2 ( , abs) = ( , n) + ( , n+p) + ( , 2n) + ( , p) [3] R. Schwengner et al., PRC 78,064314 (2008). ��� � ※ 3 � � ��� � � �� � � � ∑ � � ���1� � [4] R. M. Laszewski et al., PRL 59, 431 (1987). � � [5] T. Inakura, Private Communication. ※ 4 In Ref [3], they perform a correction for branching transitions
Dipole Polarizability in 90Zr Dipole Polarizability in 90 Zr 6 MeV < Ex < 28 MeV D = 4.3 ± 0.2 fm 3 (Preliminary) 6-18MeV : Present data : ( , abs) data [1, 2] 18-28 MeV X. Roca-Maza et al., inarXiv:1510.01874v1
Summary High resolution inelastic proton scattering experiment was performed. • Energy spectra of scattered protons in Zr isotopes were obtained. • In 92 Zr, 94 Zr and 96 Zr, We can find strength that was not found in 90 Zr • 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…
Collaborators of RCNP-E326 and RCNP-E421 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 Konan University H. Utsunomiya, H. Akimune, T. Yamagata, A. Okamoto, T. Kondo, Y. Matsuda, K. Heguri, F. Hattori, TU - Darmstadt S. Bassauer, M. Singer, G. Steinhilber, M. Hilcker, M. Zweidinger, P. von Neumman-Cosel Institute for Basic Science Chiba University T. Hashimoto H. Nakada Kyoto University Okayama University M. Tsumura, T. Nanamura M. Sakuda, T. Mori, T. Izumi, I. Ou H. Fujioka, N. Nakatsuka, T. Kawabata Istanbul University Miyazaki University B. Bilgire, H. C. Kozer T. Yamamoto, Y. Maeda Texas A&M University RIKEN Nishina Center Y.-W. Lui J. Zenihiro Tokyo University National Institute of Radiological Science Y.N. Watanabe H. Matsubara Tokyo Instit. of Tech. Niigata University Y. Togano T. Inakura, Y. Shimbara, M. Nagashima
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