Spectroscopy of Single-Particle Statesin Oxygen Isotopes via (p, 2p) Reaction

Shoichiro KAWASE
Center for Nuclear Study, the University of Tokyo

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

(p,2p) reaction as a spectroscopic tool
Simple reaction mechanism

Spin-parity determinability

Ay(spin assymmetry)

DWIAcalc.

easy ID ofp1/2 & p3/2!
d3σdΩ1dΩ2dE

Fermi momentum

a powerful probe for the study ofsingle particle/hole state
S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

2Spin-orbit splitting

spinorbitsplitting

Woods-Saxon!

+ spin-orbit!

energy difference between g7/2-h11/2 (MeV)!

For the understanding of the nuclear structure,
it is necessary to know how the spin-orbit splitting changes with Z, N.

Sn Isotopes!

N - Z!
J. P. Schiffer et al. Phys. Rev. Lett., 92, 162501 (2004).!

Goal of this study:

Determine 1p proton spin-orbit splittingsin oxygen isotopes
as a function of neutron number
S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

318Previous experiment: O(p,2p)
S.K. et al.
Facility

Ring Cyclotron, RCNP, Osaka U

Reaction(p,2p) in normal kinematics

Beam

Polarized proton @ 200 MeV/u

TargetH218O ice target ~20 mg/cm2spin-orbit splitting
16O > 18O

Effectiveness of (p,2p) was clearly demonstrated
S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

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14,22,24
SHARAQ04 experiment:O(p,2p)
Facility

RIKEN RIBF

Reaction(p,2p) in inverse kinematics

Beam

14O, 22O, 24O @ ~250 MeV/u

TargetPolarized proton target ~100 mg/cm2Beam line
MWDC

Polarized
ProtonTargetRecoil MWDC

pp

ScatteringAngle

Recoil
MWDC
Plastic

TOF
from target

RecoilMomentumQ

Plastic
Scinti.

Separationenergy(Excitationenergy)
DThe first (p,2p) reaction measurementwith polarized target!
S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

Plastic
Scinti.

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SHARAQ04 Setup

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

614
Reaction Identification for O runp
Incident

Residualp

14ONCBBeLiHep

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

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13N Excitation Energy Spectra
Ground and excited states
can be distinguished bychoosing residual nuclei.

13N(g.s.)!

Residual = N!

13N*!

Residual = C!

1.9

0.0
13N

12C + pBackground is coming from…
•

14O(12C,2p) in the target• surrounding materials

Residual = B!
Excitation energy (MeV)!

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

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Cross section
Assume …
• smooth background distribution• the same peak width for every stateResidual = N!

• excited states mainly consists of 3/2components and includes 2 known states• 3.5 MeV (3/2-)• 15 MeV (3/2-) (IAS of 13O g.s.)cf.) 14C(p,d)13C: M.Yasue et al., Nucl.Phys. A509, 141 (1990)

statecounts

σexpg.s.

443(25)251(14)

3.5 MeV576(38)326(22)15 MeV

111(31)63(18)

Residual = C!

13N*→12C + p!

Excitation energy (MeV)!
The strength of 15 MeV state is unignorable

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

9Spectroscopic factor• σDWIA was calculated by using DWIA calculation code THREEDEE
N. S. Chant et al., Phys. Rev. C 15, 57 (1977).!

• optical potential: Energy-dependent atomic-mass dependent global Dirac potential
E. D. Cooper et al., Phys. Rev. C 47, 297 (1993).!

• NN scattering amplitude by Arndt
state

σexp (µb) σDWIA (µb)

R. A. Arndt et al., Phys. Rev. D 35, 128 (1987).!
C 2S

C2S / Shell Limit
0.76(4)g.s. (1/2-)

251(14)166

1.51(8)

3.5 MeV (3/2-)

326(22)161

2.02(14)0.51(4)0.65(6)15 MeV (3/2-)

63(18)

97.1

0.65(19)

Consistent with
quenching effect0.14(5)

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

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Spin-orbit splitting
Effective Single particle energy (ESPE)⇒ C2S-weighted mean of excitation energy
spin-orbit splitting = ESPE(3/2-) - ESPE(1/2-)= 6.3(6) MeV• sd-shell mixture in 14O ground state
Untested"• background distribution
Factors"• optical potential in cross section calc.

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

11Summary & Outlook• Goal: determine the proton 1p spin-orbit splitting in oxygen isotopes• (p,2p) reaction is a powerful tool to the study of single-particle orbit• A (p,2p) reaction experiment with 14,22,24O have been carried out• Reasonable amount of spectroscopic factors for ground and excited statesof 13N were obtained• 1p proton spin-orbit splitting of 14O, 6.2(6) MeV was obtained• Further analysis is needed …
• Improvement of resolution• Momentum distribution analysis-> sd mixing ratio• Spin polarization observable-> spin assignment• Calculation with more realistic optical potential
S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

12Collaborators
CNS, U Tokyo

S. Shimoura, K. Yako, S. Ota, S. Michimasa, H. Tokieda, H. Miya,
T.L. Tang, K. Kisamori, M. Takaki, Y. Kubota, C.S. Lee,R. Yokoyama, T. Fujii, M. Kobayashi

RIKEN Nishina Center

T. Uesaka, M. Sasano, J. Zenihiro, H. Matsubara, M. Dozono,H. Sakai, T. Kubo, K. Yoshida, N. Inabe, Y. Yanagisawa,
H. Takeda, K. Kusaka, N. Fukuda, D. Kameda, H. Suzuki

Toho U.

T. Kawahara

Tohoku U.

T. Wakui

Kyushu U.

T. Noro, T. Wakasa, S. Sakaguchi, J. Yasuda, T. Fukunaga

U. Miyazaki

Y. Maeda

Kyungpook Natʼl U., Korea

W. Kim, S.H. Hwang, S.S. Stepanyan

CEA Saclay, France

A. Obertelli

ORNL, USA

A. Galindo-Uribarri

ICN-UNAM, Mexico

E. Padilla-Rodal

IPN Orsay, France

D. Beaumel

S. Kawase (Center for Nuclear Study, U Tokyo) @ ARIS 2014, U Tokyo, June 2014!

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