Hanbury-Brown–Twiss search for new states of matter inA+Acollisions

Abstract

A method allowing studies of the hadronic matter at the early evolution stage in A+A collisions is developed. It is based on an interferometry analysis of approximately conserved values such as the averaged phase-space density (APSD) and the specific entropy of thermal pions. The plateau found in the APSD behavior vs collision energy at Super Proton synchroton (SPS) level is associated, apparently, with the deconfinement phase transition at low SPS energies; a saturation of this quantity at the energies available at BNL's-Relativistic Heavy Ion Collider (RHIC) indicates the limiting Hagedorn temperature for hadronic matter. It is shown that if the cubic power of the effective temperature of pion transverse spectra grows with energy similarly to the rapidity density (which is roughly consistent with experimental data), then the interferometry volume is inversely proportional to the pion APSD, which is nearly constant because of the limiting Hagedorn temperature. This sheds light on the Hanbury-Brown--Twiss puzzle.