Spin-orbit potential in 6 He studied with polarized proton target 2007/6/5, INPC2007 Satoshi Sakaguchi Center 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) Dependence of spin-orbit coupling on excess neutrons spin-orbit coupling ? 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 section p+ 6 He p+ 8 He 71

・ High mag. field ~2.5T ・ Low temperature <1K Polarized Proton Target for RI-Beam Exp. RI 12 C p p p RI p × Cryostat p RI ~ 10 MeV RI RI-beam Solid pol. proton target in 0.1T, 100K  has been → 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.

A y Measurement for p+ 6 He 6 He beam (71 MeV/u) Pol. p target RIPS Recoiled p Scattered 6 He 14 mm  1 mm t naphthalene + pentacene P y ～ 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)

Vp-  Vp-n 6 He  Spin-orbit Potential in 6 He 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 A y data, spin-orbit potential in 6 He should have “long tail” in r > 2fm region. 6 He(p,p) 71MeV

Possible origin of “long-tail”  Density distribution  Effective interaction  Coupling with continuum states 6 He: weakly bound nucleus Spin-orbit Potential in n-rich nuclei Experimental approach Systematic study of He isotopes 4 He stable 6 He 2 valence n 8 He 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 nuclei Analyzing power measurement for p+ 6,8 Data 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