Spontaneous Creation of Quark-Antiquark Pairs in Few-Quark Systems

[摘要] There are growing hopes that QCD can explain the basic nucleon-nucleon interaction. Many studies have been made on the assumption that nucleons are three-quark systems and that N-N interaction arises from the exchange of gluons between quarks in different nucleons. It is now clear that these models can not account for the medium- and long-range attractive part of the interaction. These long range forces arise from the creation of a meson from a gluon emanating from a quark in one nucleon, which is then absorbed by the other nucleon. A natural way to include these mesonic effects is to consider the One Gluon Exchange theory which includes qq pair creation terms. So the simple quark model extended to include these creation and annihilation terms is going to be very satisfactory for the study of the NN interaction. As a first step to fully understand the NN interaction, the structure of the nucleon will be studied where these qq pairs are explicitly added to the model space. Antiquarks are distinguished from quarks by their intrinsic parity. We choose the shell model as the working framework. A significant innovation in this work is our solution to the problem that arises because the number of particles is not conserved. As these qq effects are introduced at an off-shell level, the set of parameters that produces the observed properties of the nucleon in the simple quark model is no longer valid. Therefore, we choose a new set of parameters appropriate to our model space. Our model measures different configuration mixings. In the case of the nucleon, it predicts a dominance of the 3q component accounting 73% of the total wavefunction, 22% for the 4qq component and only 5% for the 5q2q2 one. It predicts hardly any strangeness in the wavefunction of the nucleon. It also predicts that members of the baryon octet with S=-1 are less cloudy than those with S=0: a confirmation of the fact that the hyperon- (nucleon-) hyperon interaction is less attractive than the NN one. Encouraging results on the collective nature of the pion are obtained.

[发布机构] University:University of Glasgow

[关键词] High energy physics, Nuclear physics and radiation