Two-Pion Interferometry for the Granular Sources in Ultrarelativistic Heavy Ion Collisions at the RHIC and the LHC

We investigate the two-pion interferometry in ultrarelativistic heavy ion collisions in the granular source model of quark-gluon plasma droplets. The pion transverse momentum spectra and HBT radii of the granular sources agree well with the experimental data of the most central Au-Au collisions at (s_NN)^1/2=200 GeV at the RHIC and Pb−Pb collisions at (s_NN)^1/2=2.76 TeV at the LHC. In the granular source model the larger initial system breakup time for the LHC collisions as compared to the RHIC collisions may lead to the larger HBT radii R_out, R_side and R_long. However, the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to slightly smaller ratios of the transverse Hanbury–Brown–Twiss radii R_out/R_side.