We examine the characteristic quantities of pion-emitting sources extracted by model-independent imaging analysis in relativistic heavy ion collisions. The moments of the spatial separation of pion pair emission can provide the characteristic information about the source geometry and coherence. They are better for describing the non-Gaussian sources with granular and core-halo structures. An improved granular source model of quark-gluon plasma droplets can reproduce the main characteristics of the two-pion correlation functions and source functions in the experiment of √ sNN = 200GeV Au+Au collisions. The transverse-momentum dependence of the normalized first-order moments of the separation for the granular source is consistent with that of the usual interferometry results of source radii, after taking into account the Lorentz contraction in the direction of transverse momentum of pion pair.PACS numbers: 25.75.-q, 25.75.Gz

In many simulations of high-energy heavy-ion collisions on an event-by-event analysis, it is known that the initial energy density distribution in the transverse plane is highly fluctuating. Subsequent longitudinal expansion will lead to many longitudinal tubes of quark-gluon plasma which have tendencies to break up into many spherical droplets because of sausage instabilities. We are therefore motivated to use a model of quark-gluon plasma granular droplets that evolve hydrodynamically to investigate pion elliptic flows and Hanbury-Brown-Twiss interferometry. We find that the data of pion transverse momentum spectra, elliptic flows, and HBT radii in √ sNN = 200 GeV Au + Au collisions at RHIC can be described well by an expanding source of granular droplets with an anisotropic velocity distribution.

We examine the evolution of quark-gluon plasma (QGP) droplets with viscous hydrodynamics and analyze the pion transverse-momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in a granular source model consisting of viscous QGP droplets. The shear viscosity of the QGP droplet speeds up and slows down the droplet evolution in the central and peripheral regions of the droplet, respectively. The effect of the bulk viscosity on the evolution is negligible. Although there are viscous effects on the droplet evolution, the pion momentum spectrum and elliptic flow change little for granular sources with and without viscosity. On the other hand, the influence of viscosity on HBT radius Rout is considerable. It makes Rout decrease in the granular source model. We determine the model parameters of granular sources using the experimental data of pion transversemomentum spectrum, elliptic flow, and HBT radii together, and investigate the effects of viscosity on the model parameters. The results indicate that the granular source model may reproduce the experimental data of pion transverse-momentum spectrum, elliptic flow, and HBT radii in heavy-ion collisions of Au-Au at √ sNN = 200 GeV and Pb-Pb at √ sNN = 2.76 TeV in different centrality intervals. The viscosity of the droplet leads to an increase in the initial droplet radius and a decrease of the source shell parameter in the granular source model.

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 √ sNN = 200 GeV Au-Au and √ sNN = 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 Rout, 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 small ratios of the transverse HBT radii Rout/R side .PACS numbers: 25.75.Gz Hanbury-Brown-Twiss (HBT) interferometry is a useful tool to probe the space-time geometry of the particleemitting sources in high energy heavy ion collisions [1][2][3][4]. The experimental results of the HBT measurements for the Au-Au collisions at the high energies of the Relativistic Heavy Ion Collider (RHIC) indicate that it is hard to describe the source space-time by a simple evolution model [5][6][7][8]. HBT interferometry data provide strong constraints for the models of source space-time. Recently, the HBT measurement for the √ s N N = 2.76TeV Pb-Pb most central collisions at the Large Hadron Collider (LHC) is performed [9]. A consistent explanation to the HBT data of the LHC and RHIC experiments is required naturally for the source models, which will be helpful to understand the initial condition, source evolution, and particle freeze-out in ultrarelativistic heavy ion collisions. In Refs. [10,11], the granular source model of quarkgluon plasma (QGP) droplets [12] is developed to explain the RHIC HBT data [7,8]. In this work we investigate the two-pion HBT interferometry in ultrarelativistic heavy ion collisions in the granular source model of QGP droplets. Our results indicate that the granular source for the LHC Pb-Pb collisions may have the same initial droplet temperature and velocity formula as those for the RHIC Au-Au collisions, but a larger initial system breakup time. The consistent granular source model reproduces the pion transverse momentum spectra and HBT radii in the most central collisions of the RHIC [8,13,14] and LHC [9, 15] experiments.In ultrarelativistic heavy ion collisions, the system at central rapidity may reach a local equilibrium at a very short time τ 0 , then fast expand in the beam direction (z-axis). Because of the initial fluctuation, the local- * wnzhang@dlut.edu.cn equilibrium system is not uniform in space [16,17]. It may form many tubes along the beam direction during the fast longitudinal expansion, and finally fragment into many droplets (see Fig.1 of Ref.[10]) due to the "sausage" instability and surface tension [10]. On the other hand, the rapidly increased bulk viscosity in the QGP near the phase transition may also leads to the system breakup [18].We assume that the system fragments and forms a granular source of many QGP droplets at a time t 0 (> τ 0 ). On the basis of the Bjorken hypothe...

We develop a method for detecting the inhomogeneity of the pion-emitting sources produced in ultra-relativistic heavy ion collisions, through event-by-event two-pion Bose-Einstein correlations.The root-mean-square of the error-inverse-weighted fluctuations between the two-pion correlation functions of single and mixed events are useful observables for the detection. By investigating the root-mean-square of the weighted fluctuations for different impact parameter regions people may hopefully determine the inhomogeneity of the particle-emitting in the coming Large Hadron Collider (LHC) heavy ion experiments. 25.75.Nq, 25.75.Gz