Spin-orbit potential in 6He
studied with
polarized proton target
2007/6/5, INPC2007
Satoshi SakaguchiCenter for Nuclear Study, Univ. of Tokyo
Spin-orbit Coupling in Nuclei
Spin-orbit coupling Strong spin-orbit interaction
→ Magic number, shell model
Spin-orbit coupling brought us
dawn of nuclear structure physics
Spin-orbit coupling in unstable nuclei Quenching of spin-orbit coupling in n-rich region
→ Effects on shell structure
J. Dobaczewski et al., Phys. Rev. Lett. 72 (1994) 981.
G. A. Lalazissis et al., Phys. Lett. B 418 (1998) 7.
B. S. Pudliner et al., Phys. Rev. Lett. 76 (1996) 2416.
Dependence of spin-orbit coupling on excess neutrons
spin-orbitcoupling
?
N
Spin-orbit Potential in n-rich Nuclei
Spin-orbit potential Sensitive to surface structure Neutron skin/halo nuclei :
Different surface of proton/neutron
→ Shape of spin-orbit potential
in neutron skin/halo nuclei is …
Proton elastic scattering on n-rich nuclei Vector analyzing power
→ Direct information on
spin-orbit potential
No data exists due to the lack
of polarized probe !
Differential cross sectionp+6He 71 MeV/u @RIKEN
41.6 MeV/u @GANIL
25.3 MeV/u @Dubna
p+8He 71 MeV/u @RIKEN
・ High mag. field ~2.5T
・ Low temperature <1K
Polarized Proton Target for RI-Beam Exp.
RI12Cp
12Cp
pRI
p×
Cryostat
p
RI
~ 10 MeV
RI
RI-beam
Solid pol. proton target in 0.1T, 100K has been constructed @CNS.
→ Polarization study of unstable nuclei !
Recoiled p cannot be detected.
Conventional pol. p target Boltzmann polarization in extreme conditions
Ref.・ Poster (QT325), Today・ T. Wakui et al., NIM A 526 (2004) 182.
Ay Measurement for p+6He
6He beam (71 MeV/u)
Pol. p target
RIPS facility @RIKEN
Recoiled pScattered 6He
14 mm
1 mmt
naphthalene+ pentacene
Py ~ 14% @100K, 0.09T
Theoretical prediction G-matrix folding model
Effective NN interaction Density distribution
Successful in p+stable nuclei
Experimental Data
Differential cross section Reasonably reproduced
Analyzing power Large discrepancy
What is responsible for this discrepancy?
Large discrepancy!
S.P.Weppner et al.,Phys. Rev. C 61 (2000) 044601.
Vp-Vp-n
6He
Spin-orbit Potential in 6He
Progress in folding calculation Standard folding +2n cluster folding (Y. Iseri et al.)
Better description
→ Importance of p- int.
Phenomenological analysis Reproduction of the data with
phenomenological optical pot. Comparison of LS pot.
To reproduce Ay data, spin-orbit
potential in 6He should have
“long tail” in r > 2fm region.
6He(p,p) 71MeV
Possible origin of “long-tail” Density distribution Effective interaction Coupling with continuum states
6He: weakly bound nucleus
Spin-orbit Potential in n-rich nuclei
Experimental approachSystematic study of He isotopes
4He
stable
6He
2 valence n
8He
4 valence n
→ Excess neutron effects on spin-orbit pot.
Summary
Polarization study of unstable nuclei has been initiated with new solid polarized proton target.
Spin-orbit potential in n-rich nucleiAnalyzing power measurement for p+6,8He @71MeV/uData could not be reproduced by folding calc.Phen. analysis → “Long tail” of LS pot.
→ Polarization phenomena in n-rich nuclei looks different from what we expected before.
Polarization study of unstable nuclei will reveal new aspects of nuclei
Collaborators
CNS, Univ. of Tokyo
T. Uesaka, T. Kawabata, K. Suda,
Y. Maeda, Y. Sasamoto
Univ. of Tokyo
H. Sakai, K. Yako, H. Kuboki,
M. Sasano, Y. Takahashi,
H. Iwasaki, Y. Ichikawa,
D. Suzuki, T. Nakao
Toho Univ. T. Kawahara
Saitama Univ. K. Itoh
RIKEN
K. Sekiguchi, N. Aoi,
M. Yamaguchi, N. Sakamoto
Tokyo Institute of Technology
Y. Satou, Y. Hashimoto,
M. Shinohara
CYRIC, Tohoku Univ.
T. Wakui, H. Okamura, M. Itoh,
R. Matsuo, M. Ichikawa
RCNP, Osaka Univ.
A. Tamii