Two-pion interferometry for the granular sources in ultrarelativistic heavy ion collisions

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 $\sqrt{s_{NN}}=200$ GeV Au-Au and $\sqrt{s_{NN}}=2.76$ TeV Pb-Pb most central collisions. In the granular source model the larger initial system breakup time may lead to the larger HBT radii $R_{\mathrm{o}\mathrm{u}\mathrm{t}}$, $R_{\mathrm{s}\mathrm{i}\mathrm{d}\mathrm{e}}$, and $R_{\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}}$. However, the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to small ratios of the transverse HBT radii $R_{\rm out}/R_{\rm side}$.