核子第一正宇称激发态结构的研究

Study of first excited states of nucleon with positive parity

利用几种夸克和手征场耦合模型讨论了核子第一正宇称激发态N*(1440)的结构,分析了各种介子交换效应对能量的影响。结果表明,引入π、σ介子场后可以使激发态能量降低,但比实验值还要高110MeV。在手征SU(3)夸克模型下,由于η,η'和σ'介子提供排斥作用,计算结果增加了50 MeV。最后考虑了矢量介子场耦合,由于ρ介子提供的吸引作用,可以使计算结果改进,更加接近实验值。

We calculate the energy of the lowest excited state of nucleon with positive parity in several quark models. The effects of various kinds of meson exchange on energy are analyzed. The results show that the energy of excited state can be reduced considering the σ and π mesons exchange but even 110 MeV is higher than experimental value. In the chiral SU（3 ） quark model, the result is increased 50 MeV because of the repulsion from η,η＇ and σ＇ mesons exchange. After considering the vector meson exchange, the result can be improved a lot and more closer to the experimental value, because of the attraction from p meson exchange.