Shell Model Studies of the Quark-Antiquark Excitations in the Nucleon

High energy physics, Nuclear physics and radiation

Malik, Sirajuddin

University:University of Glasgow

关键词: High energy physics, Nuclear physics and radiation;   

Others  :  http://theses.gla.ac.uk/77971/1/10999289.pdf

来源: University of Glasgow

【 摘 要 】

The calculation of the nucleon-nucleon interaction from quantum chromodynamics is a problem which has been received a great deal of attention in recent years. Many studies have been made on the assumption that nucleons are composed of exactly three quarks bound in colourless triplets and that the N-N interaction arises from the exchange of gluons between quarks in different nucleons. It is now clear that this model can not account for the long range attractive part of the interaction which is responsible for nuclear binding and these long range forces arise from the exchange of colourless mesons, namely quark-antiquark pairs. As a first step we have extended the simple 3q-model of the nucleon to include the presence of quark-antiquark pairs. Antiquarks are viewed in our model, as excitations from a filled sea of quarks. The numerous interactions between particles are handled by a version of the Glasgow nuclear shell model with colour and intrinsic parity added. We first obtain values of the model parameters which reproduce the observed mass of the nucleon and give a quite reasonable value of the N-A mass-difference in the present extended quark model. We then calculate the magnetic moment, root mean squared mass and charge radii and charge density of the proton and neutron. The present model predicts that the components of the internal wavefunction of the nucleon with configuration (q4q) contribute 13-14 % and 4.1-5.3% to the total values of the magnetic moment and root mean squared radii of the nucleon respectively. The charge density of the neutron calculated in the present model predicts the charge mean square radius of the neutron to be negative.