An inversion-asymmetric source function for HBT analysis in relativistic   heavy ion collisions
  The inversion-asymmetry of the emission source in relativistic heavy ion collision under the Bertsch-Pratt convention is discussed and explicitly exhibited by a Monte Carlo model. The Gaussian source function popularly used in the HBT analysis of relativistic heavy ion collisions is invalid in this case. An inversion-asymmetric source function is suggested. A method for extracting the inversion-asymmetry degree of the source together with the source size from experimental data is proposed. 
Liu Lianshou, Shi Shusu, Du Jiaxin