The Study Of Higher Moments Of Net Charge Fluctuation In High Energy AA Collisions

In standard model, hadrons is made up of quarks and anti-quarks. In ordinary circumstance, quarks and anti-quarks is confined in hadrons, there is no free quarks and anti-quarks. In a circumstance with very high temperature and very high energy density hadronic matter can undergo a thermodynamic transition to a color decofined state, which is called Quark-Gluon Plasma (QGP). Quarks and gluons who are confined in the scope of hadrons decofine to freedom QGP matter. In today's experimental condition, the critical point of temperature and energy density to produce QGP can be reached. Through high energy AA collision this condition can be reached. In collision region, huge kinetic energy of particles changes to heat energy, and then the circumstance with very high temperature and very high energy density is formed. In this circumstance, quarks and gluons deconfine to QGP.The topic of studying QGP is the common target both for theoretical and experimental. One of the target of building RHIC, which is located in BNL, is to explore QGP matter, and some discovery has been got. LHC, which will be run in Europe, has the probability to obtain new results in the exploration of QGP. The studying of QGP has significant meaning in the field of understanding the structure of matter and universe, because the earlier evolvement of universe has such a period with very high temperature and very high energy density.Net charge fluctuation of quark-anti-quark system is quite different of that of hadron system because of the fractional charge of quarks and anti-quarks. This properties is used to study the problem of underlying degree of freedom in e~+e~- annihilation in 1980s. Recently, physicists point out it can be used to high energy AA collision, to study the QGP. In experiment, net charge fluctuation is measured as well.This dissertation is based on the summarization of works by some other physicist. We deduce higher moments of net charge fluctuation from twice moments of it. The meaning to do this is significant: The original signal carried by final state particles is covered up because of the complexity of the reaction process due to the more and more higher collider energy. twice moments of net charge fluctuation can not reflects original information due to the interaction of final state particles and the border effect. Higher moments of net charge fluctuation can save more original information to final states than twice moments of it, so it is meaningful to study it deeply. The method we use is based on statistical mechanics. Reasonable assumption is made in our work. Using the concept of generating function, we calculate higher moments fluctuation of net charge in different underlying degree of freedom. The result of higher moments is also derived, the comparison between hadron system and quark-anti-quark system is made, this conclusion can guide experiment in future.