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Temperature and Density Effect on the Pentaquark Theta+ Mass and Width

Temperature and Density Effect on the Pentaquark Theta+ Mass and Width. Xuguang Huang Xuewen Hao Pengfei Zhuang Physics Department Tsinghua University. Outline. Motivations Methods Numerical Results Conclusions. Motivations. Known : M=1540 MeV, <25MeV , B=+1, S=+1, Q=+1

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Temperature and Density Effect on the Pentaquark Theta+ Mass and Width

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  1. Temperature and Density Effect on the Pentaquark Theta+ Mass and Width Xuguang Huang Xuewen Hao Pengfei Zhuang Physics Department Tsinghua University

  2. Outline • Motivations • Methods • Numerical Results • Conclusions

  3. Motivations Known: M=1540 MeV, <25MeV, B=+1, S=+1, Q=+1 Decay channels: Unknown: Spin, Isospin, Parity

  4. Motivations • In medium, the mass and width of a particle would change. • For example. Considering chiral symmetry restoration at finite temperature and density, the effective nucleon mass can be determined through the gap equation of NJL model in the mean field approximation:

  5. Motivations • Temperature dependence and chemical potential dependence of the effective nucleon mass: • Questions: Why so narrow? How to determine its parity? Can it be formed easily in RHIC? • What are the medium effect on the pentaquark characteristics? Can the Temperature and Density Effects help us to solve these questions?

  6. Effective Lagrangians[PLB579(2004)43-51 & hep-ph/0402141]: Methods Here, P=+1 is assumed. For the case P=-1, there is no i in the Lagrangians. The coupling constants are fixed to reproduce the decay width =15MeV at zero temperature and zero density. At tree level one has:

  7. Methods The propagator reads: where , is the lowest-order self-energy calculated from the following Feynman diagram

  8. Methods • The complex mass is obtained by • In the rest frame of Theta+: • For negative parity, the only difference is

  9. Numerical Results • Temperature dependence of the medium modification to Theta+ mass:

  10. Numerical Results • Chemical potential dependence of the medium modification to Theta+ mass:

  11. Numerical Results • Temperature dependence of the medium modification to Theta+ width:

  12. Numerical Results • Chemical potential dependence of the medium modification to Theta+ width:

  13. Numerical Results • The medium modifications to Theta+ mass without considering effect of chiral symmetry restoration on mucleon mass: • The medium modifications to Theta+ mass including the effect of chiral symmetry restoration on mucleon mass:

  14. Numerical Results • The temperature modifications to Theta+ width without considering effect of chiral symmetry restoration on mucleon mass: • The temperature modifications to Theta+ width including the effect of chiral symmetry restoration on mucleon mass:

  15. Mumerical Results • Temperature and density effect on Theta+ mass and width at RHIC energy region, where T=200MeV and is determined by

  16. Analyses on the numerical results • The mass and width of Theta+ with positive parity are strongly affected by the medium, but weakly in the case with negative parity. • The density effect is much stonger than the temperature effect. • The width is much more sensitive to the medium effect compared with the mass. • Theta+ becomes light and unstable in the medium. • The effect of chiral phase transition plays an important role. If we neglect the effect of chiral phase transition , namely keeping the mucleon mass as a constant, the medium corrections are very small.

  17. Conclusions • It is more difficult to find Theta+ at RHIC region than to find it at zero temperature and density. • If the mass and width of Theta+ change substantially, one implies the positive parity of Theta+. If the mass and width of Theta+ change slightly, one implies the negative parity of Theta+.

  18. Thank you!

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