The Effect Of Bose-Einstein Condensation On The Chaoticity Parameter In Two-pion Interferometry In High Energy Heavy Ion Collisions

Hanbury-Brown-Twiss (HBT) intensity interferometry has been extensively used to study the space-time structure, the source coherence and the dynamic evolution in high energy heavy ion collisions. In HBT interferometry, the chaoticity parameter λ is defined by the momentum correlation function at zero relative momentum of the particle pair. Because of the HBT correlation is disappear in the completely coherent source, the chaotic parameter A in HBT interferometry is relative to the Bose-Einstein condensate which may occurs in the system of the identical boson. Base on the study of the isotropic static emission source, it studies the Bose-Einstein condensate, which occurs in the anisotropic and expending pion sources in high energy heavy ion collisions, and its impact on the chaoticity parameter λ in2π interferometry by this thesis.Using the quantum statistic theory to study the fugacity parameter Z, condensation fraction f0and the density distributions in spatial and momentum space with an anisotropic harmonic oscillator potential that arises either externally or from bosons’own mean fields in non-relativistic and relativistic conditions. The conditions which the Bose-Einstein con-densate occurs are discussed, and the two-particle HBT correlation function and chaoticity parameter λ are calculated for the system with different particle number and temperature. The results show that the condensation fraction f0decreases with increasing temperature in the mean-field intensity remains the same, and this leads to increase of the chaoticity param-eter λ value. Because the particles with larger momenta are averagely at the uncondensed high-energy states, the λ values for the larger momenta are larger for the fixed temperature. Besides, λ are sensitive to the frequencies of the potential in longitudinal and transverse di-rections, ωz and ωp. The λ value decreases with the increasing ratio, v=ωz/ωp when the ωp fixed.The particle source is expending evolution source in high energy heavy ion collisions. So, one firstly investigates the Bose-Einstein condensate and its influence on the HBT chaoticity parameter A for an expanding non-relativistic boson gas model within the time-dependent mean-field of harmonic oscillator by this thesis. Then, base on the expending relativistic identical boson gas model is established by relativistic hydrodynamics, one studies the Bose- Einstein condensate of the identical pions gas, which may appear in high energy heavy ion collisions, and its impact on the2π interferometry chaoticity parameter A. The results indi-cate that the sources with thousands of identical pions may appear a degree of Bose-Einstein condensation at the temperatures of the hadronic phase in relativistic heavy ion collisions. This finite condensation may decrease the chaoticity parameter λ in the two-pion interferom-etry measurements at low pion pair momenta, and influence little on the v value measured at high pion pair momentum. The identical pion multiplicity of event can reach to several in LHC Pb-Pb collisions. In this case, the effect of Bose-Einstein condensation for the identical particle on two-pion interferometry chaoticity parameter λ is worth of serious consideration.