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