Imaging of granular sources in high energy heavy ion collisions

Abstract

We investigate the source imaging for a granular pion-emitting source model in high energy heavy ion collisions. The two-pion source functions of the granular sources exhibit a two-tiered structure. Using a parametrized formula of granular two-pion source function, we examine the twotiered structure of the source functions for the imaging data of Au+Au collisions at Alternating Gradient Synchrotron (AGS) and Relativistic Heavy Ion Collider (RHIC). We find that the imaging technique introduced by Brown and Danielewicz is suitable for probing the granular structure of the sources. Our data-fitting results indicate that there is not visible granularity for the sources at AGS energies. However, the data for the RHIC collisions with the selections of 40 < centrality < 90% and 0.20 < k T < 0.36 GeV/c are better described by the model with granular emission than that of one Gaussian. The model with granular source has more parameters than the simple Gaussian, hence can describe more complicated shapes. 25.75.Nq, 25.75.Gz

Fluctuations of pion elliptic flow, triangular flow, and HBT correlation functions in ultrarelativistic heavy ion collisions

“…The changes of the widths of the distributions dN/df v2 and dN/df v3 with impact parameter b and σ 0 reflect the variations of the fluctuation magnitudes with the granular inhomogeneity of the initial sources. In order to quantify the granular inhomogeneity of the initial source, we introduce a granularity length of the initial source as the product of the initial transverse radius R ⊥ and the transverse granularity parameter ξ ⊥ [43] of the initial source, Here, we replace R ⊥ approximately with the average transverse radius of the initial source {ρ}, and replace N d approximately with 1 2 ({ρ}/σ 0 ) 2 , considering approximately the same numbers of the hot spot and cold valley in the initial source. Clearly, the concept of granular source requires N d ≥ 2.…”

Characteristic quantities of pion-emitting sources extracted by model-independent analysis in relativistic heavy ion collisions

“…So these quantitative HBT results are model depended. Recently, many studies indicate that the particle-emitting sources produced in relativistic heavy ion collisions are far from Gaussian distributed [5,6,7,8,9,10,11,12,13,14,15,16,17]. For the non-Gaussian sources the conventional HBT method of the Gaussian fit is inappropriate [15,18,19,20,21].…”

“…The imaging technique introduced by Brown and Danielewicz [5,22,23] is a model-independent way to obtain the two-pion source function S(r), the probability for emitting a pion pair with spatial separation r in the pair center-of-mass system (PCMS), from the measured two-pion correlations. This technique has been developed and used in analyzing one-and multidimension source geometry in relativistic heavy ion collisions [5,6,7,8,9,10,11,12,24,25,26,27,28,29,30,31]. Recent imaging analyses for the pion-emitting sources produced in relativistic heavy ion collisions suggest that the sources may have a core-halo [6,7] or granular struc- * wnzhang@dlut.edu.cn ture [12].…”

Analysis of the image of pion-emitting sources in the source center-of-mass frame

“…In conventional HBT analysis, the corresponding HBT results are model dependent, because people have to introduce a Gaussian emission function before fitting the HBT parameters. If the particle-emitting sources produced in relativistic heavy ion collisions are far from Gaussian distributed [10,11,12,13,14,15,16,17,18,19,20,21], this conventional HBT method is inappropriate [6,19,22,23,24]. In contrast, the imaging technique is a model-independent method.…”

“…In contrast, the imaging technique is a model-independent method. It has been developed and used in analyzing oneand multi-dimensional source geometry in relativistic heavy ion collisions [9,10,11,12,13,14,15,16,25,26,27,28,29,30,31,32].…”