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Spin-orbit potential in 6 He studied with polarized proton target

This study explores the spin-orbit potential in N-rich nuclei and its effects on the shell structure. The quenching of spin-orbit coupling in the n-rich region and the discrepancy in the analyzing power measurements are investigated. The study utilizes a newly developed solid polarized proton target for polarization studies of unstable nuclei.

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Spin-orbit potential in 6 He studied with polarized proton target

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  1. Spin-orbit potential in 6Hestudied with polarized proton target 2007/6/5, INPC2007 Satoshi Sakaguchi Center for Nuclear Study, Univ. of Tokyo

  2. 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 ? N Spin-orbit Coupling in Nuclei spin-orbit coupling

  3. 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 • Differential cross section p+6He 71 MeV/u @RIKEN 41.6 MeV/u @GANIL 25.3 MeV/u @Dubna p+8He 71 MeV/u @RIKEN • Vector analyzing power → Direct information on spin-orbit potential No data exists due to the lack of polarized probe !

  4. RI 12C RI p p 12C RI p RI ~ 10 MeV p p × Cryostat Polarized Proton Target for RI-Beam Exp. • Conventional pol. p target • Boltzmann polarization in extreme conditions • Solid pol. proton target in 0.1T, 100K • has been constructed @CNS. → Polarization study of unstable nuclei ! ・ High mag. field ~2.5T ・ Low temperature <1K RI-beam Recoiled p cannot be detected. Ref. ・ Poster (QT325), Today ・ T. Wakui et al., NIM A 526 (2004) 182.

  5. 6He beam (71 MeV/u) Pol. p target 1 mmt naphthalene + pentacene 14 mmf Recoiled p Scattered 6He Ay Measurement for p+6He Py～14% @100K, 0.09T RIPS facility @RIKEN

  6. S.P.Weppner et al., • Phys. Rev. C 61 (2000) 044601. Experimental Data • Theoretical prediction • G-matrix folding model • Effective NN interaction • Density distribution • Successful in p+stable nuclei • Differential cross section • Reasonably reproduced • Analyzing power • Large discrepancy What is responsible for this discrepancy? Large discrepancy!

  7. Progress in folding calculation Standard folding a+2n cluster folding (Y. Iseri et al.) Better description → Importance of p-a int. Phenomenological analysis Reproduction of the data with phenomenological optical pot. Comparison of LS pot. Vp-n Vp-a a 6He Spin-orbit Potential in 6He 6He(p,p) 71MeV To reproduce Ay data, spin-orbit potential in 6He should have “long tail” in r > 2fm region.

  8. Possible origin of “long-tail” Density distribution Effective interaction Coupling with continuum states 6He: weakly bound nucleus 4He stable 6He 2 valence n 8He 4 valence n Spin-orbit Potential in n-rich nuclei • Experimental approach Systematic study of He isotopes → Excess neutron effects on spin-orbit pot.

  9. 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+6,8He @71MeV/u 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

  10. 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

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