Complete Electric Dipole Response and Neutron Skin in 208 Pb

RIKEN Seminar, September 8th, 2011

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Complete Electric Dipole Responseand Neutron Skin in 208Pb

A. TamiiResearch Center for Nuclear Physics, Osaka University


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Collaborators RCNP, Osaka UniversityA. Tamii, H. Matsubara, H. Fujita, K. Hatanaka,

H. Sakaguchi Y. Tameshige, M. Yosoi and J. Zenihiro

Dep. of Phys., Osaka UniversityY. Fujita

Dep. of Phys., Kyoto UniversityT. Kawabata

CNS, Univ. of TokyoK. Nakanishi,

Y. Shimizu and Y. Sasamoto

CYRIC, Tohoku UniversityM. Itoh and Y. Sakemi

Dep. of Phys., Kyushu UniversityM. Dozono

Dep. of Phys., Niigata UniversityY. Shimbara

IKP, TU-DarmstadtP. von Neumann-Cosel, A-M. Heilmann,

Y. Kalmykov, I. Poltoratska, V.Yu. Ponomarev,

A. Richter and J. Wambach

KVI, Univ. of GroningenT. Adachi and L.A. Popescu

IFIC-CSIC, Univ. of ValenciaB. Rubio and A.B. Perez-Cerdan

Sch. of Science Univ. of WitwatersrandJ. Carter and H. Fujita

iThemba LABSF.D. Smit

Texas A&M CommerceC.A. Bertulani

GSIE. Litivinova


Sn Sp

Illustrative View of E1 ResponseParticle （ neutron （ separation energy

0

PDR GDRg.s.

oscillation of neutron skin against core?

oscillation between neutrons and protons

E1

1-

core neutron skin

symmetry energy


Electric Pygmy Dipole Resonance (PDR)

PDR: resonance-like structure, typically close to neutron threshold

Strength related to neutron excessmeasure of neutron skin

symmetry energy

Strength distribution around neutron threshold relevant for nucleosynthesis (r-process)

Dipole oscillation between an isospin-saturated core and a neutron (proton) skin?


LAND exp. at GSI

dissociation c.s. photo-nuclear c.s.

P. Adrich et al., PRL95, 132501(2005)

Sn Isotopes


68NiO. Wieland et al. PRL102, 092502(2009)


Dipole oscillation between an isospin-saturated core and a neutron (proton) skin?

Pigmy Dipole Resonance

T. Aumann et al., NPA805, 198c(2008).


J. Zenihiro et al., PRC82, 044611 (2010).


Sn Sp


0

PDR GDRg.s.

oscillation of neutron skin against core?

oscillation between neutrons and protons

E1

1-

core neutron skin

symmetry energy


P.-G. Reinhard and W. Nazarewicz, Phys. Rev. C 81, 051303(R) (2010).

Self-consistent mean field theory in the energy density functional theory formulationn with SV-min interaction.- SV-min parameters were determined to reproduce binding energies, r.m.s. radii, pairing gap, ls-splitting, surface thickness, etc.


Sn Sp

(,’)

(,n)

Giant Resonances and ContinuumDiscrete States


(e,e’), (p,p’)

0

PDR GDRg.s.

(Coulomb Excitation) (Coulomb Dissociation) ← Unstable nuclei


Sn Sp

(,’)

(,n)

GR and Continuum (Main Strength)Discrete (Small Strength)


(e,e’), (p,p’)

0

PDR GDRg.s.

208Pb(,)M1 strength measured by

R.M. Laszewski et al, PRL61(1988)1710


p

q,

A A*

p’

Coulomb (or Strong) Interaction

detector

beam

A A*

Excited StateTarget Nucleus

real photon

Probing EM response of the target nucleus

Decay products and/or -rays are measured.

Select a low momentum transfer (q~0) kinematical condition,i.e. at zero degrees

Excited StateTarget Nucleus

detector

detector

Missing Mass Spectroscopy: Insensitive to the decay channel. Total strengths are measured.


Missing Mass Measurement - independent to the decay property of the excited states and decay threshold. - no feeding from upper excited states - measure of the total (not partial) width

At 0 deg, E1 excitation in dominated by Coulomb interaction and M1 by nuclear interaction

High-resolution (~20keV). High and uniform detection efficiency. Single shot measurement in an excitation energy region of 5-25MeV.

Uncertainty from reaction mechanism. Nuclear interaction and coulomb interaction.

Polarization transfer and angular distribution of the C.S. can be used for E1/M1 decomposition.

Proton Inelastic Scattering


Experimental Method

High-Resolution (p,p’) measurement at close to zero degrees

AT et al.,


High-resolution Spectrometer

Grand Raiden

High-resolution WS beam-line(dispersion matching)


Spectrometers in the 0-deg. experiment setup

Intensity : 3 ~ 8 nA

As a beam spot monitor in the vertical direction

Transport : Dispersive mode

Polarized Proton Beam at 295 MeV

Focal Plane Polarimeter


2006-Oct 2008-Nov

Spin Precession in the Spectrometer

bp

g )12

( p: precession angle with respect to the beam directionb: bending angle of the beamg: Lande’s g-factor: gamma in special relativity

162b 180b


I. Poltoratska, PhD thesis


E1/M1 Decomposition by Spin Observables

LLNNSS DDD

spinflip / non-spinflip separation*

(model-independent)

Polarization observables at 0°

-1 for S = 1, M1 excitations

3 for S = 0, E1 excitations

0ΔS

1ΔS

for

for

0

1TransferSpinTotal

4

)2(3

LLSS DD

E1 and M1 cross sections can be decomposed

T. Suzuki, PTP 103 (2000) 859

At 0° DSS = DNN


S

(p,p’) this work

J. Enders et al., NPA724(2003)243N. Ryezayeva et al., PRL27(2002)272502A. Veyssiere et al., NPA159(1970)561Z.W.Bell et al., PRC25(1982)791

Preliminary

ΔS=0 (~E1)


Multipole Decomposition

Neglect of data for >4: (p,p´) response too complex

Included E1/M1/E2 or E1/M1/E3 (little difference)


Comparison of Both Methods

Total

S = 1

S = 0


E1 Response in 208Pb

Quasiparticle Phonon Model3 phonons up to 8.2 MeV2 phonons in the GDR regionV.Yu. Ponomarev

Relativistic Quasiparticle Time-Blocking Approximation2QP×1 phononE. Litvinova et al., PRC 78 (2008) 014312,PRC 79 (2009) 054312

This Exp.



Relativistic Quasiparticle Time Blocking Approximation

Quasiparticle Phonon Model

up to 130 MeV20.1+-0.6 fm3/e2


Self-Consistent Mean Field Theory

(Nuclear) Energy Density Functional Theory

Skyrm Force: SV-min


- SV-min parameters were determined to reproduce binding energies, diffraction radii, surface thickness, r.m.s. radii, pairing gap, and ls-splitting.


AT, I. Poltoratsuka, et al., PRL107, 062502(2011)

[8] P.-G. Reinhard and W. Nazarewicz, PRC81, 051303(R) (2010).

0.156+0.025-0.021 fm

20.1+-0.6 fm3/e2



Self-consistent mean field theory in the energy density functional theory formulationn with SV-min interaction.- SV-min parameters were determined to reproduce binding energies, r.m.s. radii, pairing gap, ls-splitting, surface thickness, etc.



proton elastic scattering 0.211+0.054-0.063 fm

0.156+0.025-0.021 fm

(p,p’) with EDF SkM*

Antiproton Atoms0.18+-0.02 fm

PREX 0.34+0.15-0.17 fm



spin-M1 Strength Distribution in 208Pb


M. Sasano et al., PRC79, 024602(2009).

mb/sr9.1208ˆGT A

2Nmb/sr/72.0208ˆ A

Gamow-Teller unit cross section of (p,n) reactions at 297 MeV,

extrapolated to A=208:

Converted to B() unit cross section of (p,p’) reactions for A=208.

Extraction of spin-M1 strengh (After making extrapolation to q=0, with a help of

DWBA calc.


Preliminary


Summary• High-resolution (p,p’) measurement (inc. pol-transfer data) at forward angles

has been applied for extracting E1 response in 208Pb. • Special interest is placed on the E1/spin-M1 strength distribution in the region

of neutron separation energy.• Agreement on E1/spin-M1 decomposition is quite satisfactory between the two

methods using spin-transfer and multipole-decomposition.• The overall E1 response in 208Pb has been accurately determined.• The electric-dipole polarizability of 208Pb has been determined as 20.1+-0.6

fm3/e2. The polarizability is discussed to be sensitive to the neutron skin and nuclear symmetry energy.

• Refering a self consistent mean field calculation by P.-G. Reinhard and W. Nazarewicz, the polarizability corresponds to the neutron-skin thickness of 0.156+0.025-0.021 fm, although the number is model-dependent.

• With independent determination of the neutron-skin thickness, the electric dipole polarizability will much constrain the model parameters. PDR strength is also discussed to be sensitive to the neutron skin thickness.

• 120Sn, 154Sm (dcs and spin), 88Mo, 90Zr, 92Mo (dcs) : under analysis


END

Complete Electric Dipole Response and Neutron Skin in 208 Pb

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