The Study Of Nn∧∧ In Quark Model

In October 1952, Marion Danysz and Jerzy Pniewski firstly reported the discovery of hypernuclei at the meeting of the Polish Academy of Science. It was confirmed that the bound particle was a A hypernuclei finally. This event had broken up the traditional concept of the nucleus’constituents and developed a new degree of freedom "strangeness". For example, a A hyper-nuclei contains a special particleA particle in addition to protons and neutrons. After that, a series of work of hyper-nuclear physics had been studied by physicists.In the years after the discovery of the first A hyper-nuclei, the event was observed just from a high energy cosmic ray interaction on a heavy emulsion nucleus or bubble chambers because of the restrictions of technology. So the hyper-nuclear physics developed slowly. In the 1960’s, someone proposed that n(K-,π-)A reaction could generate the A hyper-nuclei. They found when the K- meson crash into a nucleus, the strangeness would be remained in the nucleus and made up of A particle. At the same time, π- meson would be released.In the 1970’s, K- beams was used at CERN and later at BNL and KEK. These accel-erated the development of the hyperon nuclear. (π+,K+), (π-,K+), (e,e’K+) reactions could also be studied the system. Except for the A hyper-nuclei, there are S hyper-nuclei, (?) hyper-nuclei and even innovative hyper-nuclei with charm quark or bottom quark. With the development of technology, more and more hyper-nuclei is discovered.Hyperon - nucleon scattering experiments can, in principle, provide basic data on the interactions but it is quite difficult to carry out such experiments, because hyperon life-times are quite short (10-10s) and hyperon beams suitable for the scattering experiments are not readily available. Spectroscopic investigations yield valuable information on the hyperon-nucleon and hyperon-hyperon interactions.In this work, we study the nnAA system. There are two main reasons. Firstly, In 2002. Marques et al. claimed the tetraneutron was observed. Our group also studied this system and found about 100 MeV binding energy. But tetraneutron suffer from Pauli blocking by each other. Therefore, we consider that two A particles replace two neutrons, namely, nnAA. The A hyperon does not suffer from Pauli blocking by the other nucleons, it can penetrate into the nuclear interior and form deeply bound hypernuclear states. Secondly, hyper-nuclear physics become a popular field at the recently years. Especially in 2001, after the "Nagara" event, the question whether lighter S= - 2 systems exist or not had been raised.nnAA system is a multi-quark states. We study the system at the quark level rather than at hadrons level, in this way the quark exchange effects are taken into account. The chiral quark model is employed to do the calculation. In the calculation, the system is divided into four sub-clusters. First the symmetry is used to reduced the coordinates to describe the structure of the system to 3, then the structure is checked by employing the Monte Carlo method. We obtained about-112 MeV attraction under adiabatic approxi-mation. The attraction is the necessary condition of existence of the bound state, but it is not enough. To estimate the binding energy of the system, we approximate the effective potential by simple harmonics, then the zero-point energy is obtained, The sum of the minimum of the effective potential and the zero-point energy gives us the binding energy. The present estimation is that no bound state exists. However, the estimation is rather tough, a more precision method is needed to find the binding energy of the system. To use gaussian expansion method to do the dynamical calculation is discussed at last.