1 / 19

低密度原子核体系中的双中子关联现象

低密度原子核体系中的双中子关联现象. 孙保元 (Bao Yuan SUN) 兰州大学核科学与技术学院. Introduction Di-neutron Spatial Correlations in Nuclear Matter Di-neutron Spatial Correlations in Giant Halo Nuclei Summary. 第十四届全国核结构大会 浙江湖州 , 13 April 2012. Di-neutron Spatial Correlations.

flo
Download Presentation

低密度原子核体系中的双中子关联现象

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 低密度原子核体系中的双中子关联现象 孙保元 (Bao Yuan SUN) 兰州大学核科学与技术学院 • Introduction • Di-neutron Spatial Correlations in Nuclear Matter • Di-neutron Spatial Correlations in Giant Halo Nuclei • Summary 第十四届全国核结构大会 浙江湖州, 13 April 2012

  2. Di-neutron Spatial Correlations • Pairing correlations play a crucial role in the fermion systems. • J. Bardeen, L. N. Cooper, J. R. Schrieffer, Phys. Rev. 108 (1957) 1175. • A. Bohr, B. R. Mottelson, D. Pines, Phys. Rev. 110 (1958) 936. • In nuclear physics, it is expected that di-neutron correlations in low-density nuclear systems should be significant. • A large scattering length for the 1S0 neutron-neutron interaction • G.F.d. Téramond, B. Gabioud, Phys. Rev. C 36 (1987) 691. • A large value of the 1S0 pairing gap at low densities • M. Baldo, J. Cugmon, A. Lejeune, U. Lombardo, Nucl. Phys. A 515 (1990) 409. • T. Takatsuka, R. Tamagaki, Prog. Theor. Phys. Suppl. 112 (1993) 27. • Enhancement of cross sections in two-neutron transfer reactions • W. von Oertzen, A. Vitturi, Rep. Prog. Phys. 64 (2001) 1247. • Small emission angle between 2n in di-neutron decay • A. Spyrou, Z. Kohley, T. Baumann et al., Phys. Rev. Lett. 108 (2012) 102501. (2n emission in 16Be) • Recently, experimental and theoretical progress on halo structure of weakly bound neutron-rich nuclei and possible BCS–BEC crossover of di-neutron pairs at low densities has stimulated lots of interests in di-neutron spatial correlations. • I. Tanihata:1985, G. F. Bertsch:1991, J. Meng:1996,1998,2006, J. Dobaczewski:1996 • M. Matsuo, Phys. Rev. C 73 (2006) 044309. B. Y. Sun, H. Toki and J. Meng, Phys. Lett. B 683 (2010) 134. • K. Hagino, H. Sagawa, J. Carbonell, P. Schuck, Phys. Rev. Lett. 99 (2007) 022506.

  3. Typical Experimental Evidence of Di-neutron Correlations in Nuclei The “di-neutron” configuration of 6He make the dominant contribution to the cross sections of two-neutron transfer reactions. Yu.Ts. Oganessian et al., PRL 82 (1999) 4996. A three-body model including a strong di-neutron correlation can well reproduce a strong low-lying E(1) distribution observed in 11Li. T. Nakamura et al., PRL 96 (2006) 252502. H. Esbensen et al., PRC 76 (2007) 024302. T. Myo et al., PRC 76 (2007) 024305.

  4. Di-neutron Coherence Length in Nuclei Cooper pair rms radius, measure of the pairing size: small sized Cooper pairs in the surface In light halo nuclei: The minimal value of coherence length in surface is essentially determined by the pairing strength. K. Hagino et al., Phys. Rev. Lett. 99 (2007) 022506. Comment: N. T. Zinner and A. S. Jensen (2008). Reply: K. Hagino et al. (2008). In medium or heavy superfluid nuclei: HFB M. Matsuo:2005,N. Pillet:2007, 2010. The small value of coherence length in the surface is essentially determined by the finite size properties of single-particle states in the vicinity of the chemical potential and has very little to do with enhanced pairing correlations in the nuclear surface. spatially compact Quite unique and exceptional situation: 11Li and 6He K. Hagino: JPG 37 (2010) 064040.

  5. Motivations and Goals Whether further similar cases to 11Li and 6He exist in the heavier nuclei on nuclear chart? How does pairing correlations account for the small sized Cooper pairs in the surface? • Explore the di-neutron correlations in nuclear matter based on microscopic calculation (RMF) with a realistic bare nucleon-nucleon interaction (Bonn-B) • Study BCS-BEC crossover phenomenon at low-density nuclear matter • B. Y. Sun, H. Toki and J. Meng, Phys. Lett. B 683, 134 (2010). • T. T. Sun, B. Y. Sun, J. Meng, H. Toki, submitted to Phys. Rev. C. Prediction for giant halo： N³82 140Zr N>40 66Ca Meng & Ring, PRL80, 460 (1998) Meng et al., PRC65,041302R (2002) • Study the di-neutron spatial correlations in giant halo nuclei with Relativistic Continuum Hartree–Bogoliubov(RCHB) theory • J. Meng et al., Prog. Part. Nucl. Phys. 57 (2006) 470. • Spatial distribution of pairing tensor • Coherence length of neutron Cooper pairs • B. Y. Sun, Y. Zhang, J. Meng, in preparation.

  6. BCS-BEC Crossover Phenomenon crossover BCS (weak coupling) BEC (strong coupling) • Weakly interacting fermions • Correlation in p space • Large coherence length • Bosonic bound state • Correlation in r space • Small coherence length The transition takes place continuously: BCS-BEC crossover • Excitonic semiconductors: D. M. Eagles, Phys. Rev. 186, 456 (1969). • Ordinary superconductors: A. J. Leggett, J. Phys. Colloq. 41, 7 (1980). • Attractive Fermion gas: P. Nozieres and S. Schmitt-Rink, J. Low Temp. Phys. 59, 195 (1985). • Color superconductivity: Y. Nishida and H. Abuki, Phys. Rev. D 72, 096004 (2005). • Nuclear matter: M. Matsuo: PRC2006; J. Margueron: PRC2007; B. Y. Sun: PLB2010.

  7. BCS-BEC Crossover Phenomenon crossover BCS (weak coupling) BEC (strong coupling) • Weakly interacting fermions • Correlation in p space • Large coherence length • Bosonic bound state • Correlation in r space • Small coherence length The transition takes place continuously: BCS-BEC crossover • Excitonic semiconductors: D. M. Eagles, Phys. Rev. 186, 456 (1969). • Ordinary superconductors: A. J. Leggett, J. Phys. Colloq. 41, 7 (1980). • Attractive Fermion gas: P. Nozieres and S. Schmitt-Rink, J. Low Temp. Phys. 59, 195 (1985). • Color superconductivity: Y. Nishida and H. Abuki, Phys. Rev. D 72, 096004 (2005). • Nuclear matter: M. Matsuo: PRC2006; J. Margueron: PRC2007; B. Y. Sun: PLB2010.

  8. BCS Approximation and Pairing Gap Equation

  9. Cooper Pair Wave Function in Nuclear Matter • The relativistic pairing theory • ph:RMF with PK1 W. Long (2004) • pp: Realistic bare NN force Bonn-B BCS Cooper pair wave function • As the density decreases, the spatial structure evolves continuously from BCS-type to BEC-type. • BCS-type: oscillating attenuation • BEC-type: compact, no oscillation • Proper treatment of the short-range repulsion of nuclear force leads to suppressed amplitude around r = 0 Crossover B. Y. Sun, H. Toki and J. Meng, Phys. Lett. B 683, 134 (2010).

  10. Probability Density of Neutron Pairs in Nuclear Matter S=0 A two-dimensional plot for the probability density r2|Ψpair(r)|2 of the neutron Cooper pair as a function of the relative distance r between the pair partners and the neutron Fermi momentum kFn in SNM. B. Y. Sun, H. Toki and J. Meng, PLB 683(2010)134 K. Hagino et al., PRL 99(2007)022506

  11. BCS-BEC Crossover in Nuclear Matter No evidence for the appearance of a true BEC bound state of neutron pairing at any density ？ B. Y. Sun, H. Toki and J. Meng, PLB 683(’10)134 BCS-BEC crossover region: 0.05 fm-1 < kFn < 0.7 (0.75) fm-1 for the symmetric (neutron) nuclear matter Coherence Length: The coherence length in infinite NM strongly depends on the pairing strength and approximate inverse proportionality between the gap and the coherence length could be established.

  12. Relativistic Continuum HartreeBogoliubov Theory J. Meng, H. Toki, S.G. Zhou et al., Prog. Part. Nucl. Phys. 57 (2006) 470. • Bogoliubov Transformation: • Quasi-particle Wave Function: • Relativistic Hartree-Bogoliubov Equations: effective interaction NLSH • Pairing Force: V0 = −670 MeV fm3

  13. Probability Density Distribution of Cooper Pairs: |κ(r, R)|2r2R2 Different Parity To grasp the full physics of nuclear pairing it is very important to work in a large configuration space, comprising several shells below and above the Fermi surface. NLSH Rm = 5.20 fm Rn = 5.47 fm Rp = 4.51 fm Contrasted with infinite matter: Different number of levels in the range of the gap value Coulomb barrier: low-j levels

  14. WF: Similarity to BCS-BEC Crossover Phenomenon

  15. Effects of the Parity Mixing The strong concentration of small sized pairs in the surface of nuclei can be treated as a feature of halo nuclei. The parity mixing induced by the pairing force leads to a short range di-neutron space correlations in the surface of the nuclei. The concentration only shows up when even and odd parity states are mixed. Same conclusion in: F. Catara:1984, L. Ferreira:1984, Tischler:1998, N. Pillet:2007.

  16. Influence of the Strength of Pairing Force Whether concentration of small sized pairs in the surface is due to pairing correlation? V0 = −670 MeV fm3 V0 = −460 MeV fm3 -0.53 Pairing Energy -13.6 In giant halo nucleus 134Zr: The small coherence length of Cooper pairs in the surface of nuclei is essentially determined by the pairing strength.

  17. Evolution in Zr Isotope

  18. Summary The di-neutron spatial correlations is studied in both nuclear matter and giant halo nuclei with the relativistic bogoliubov theory. • Di-neutron spatial correlations in nuclear matter • A strong concentration of the probability density is revealed for the neutron pairs in the fairly small relative distance. • BCS-BEC crossover region: 0.05 fm-1 < kFn < 0.7 (0.75) fm-1 • The coherence length of Cooper pairs in infinite nuclear matter strongly depends on the intensity of pairing correlations. • Di-neutron spatial correlations insuperfluid nuclei • Similar cases to 11Li and 6He exist in the heavier nuclei. • BCS-BEC crossover phenomenon is displayed by WF of Cooper pairs. • Parity mixing in large configuration space leads to a strong concentration of small sized Cooper pairs in the nuclear surface. Low-j level is important! • Pairing correlations have effects on small sized pairs in the surface: 134Zr. • Evolution of pairing in Zr isotope:possible criterion of BCS-BEC crossover Thank you for your attention !

  19. Collaborators 北京大学物理学院： 孟杰 教授 孙亭亭 博士 张颖 博士 大阪大学RCNP： Hiroshi Toki 教授

More Related