Abstract
Exploring the shape of the pair-source function for particles such as pions or kaons has been an important goal of heavy-ion physics, and substantial effort has been made in order to understand the underlying physics behind the experimental observations of non-Gaussian behavior. In experiments, since no direct measurement of the source function is possible, quantum-statistical momentum correlations are utilized to gain information about the space-time geometry of the particle emitting source. Event generators, such as EPOS, however, provide direct access to the freeze-out coordinates of final state particles, and thus the source function can be constructed and investigated. The EPOS model is a sophisticated hybrid model where the initial stage evolution of the system is governed by Parton-Based Gribov–Regge theory, and subsequently a hydrodynamic evolution is utilized, followed by hadronization and hadron dynamics. EPOS has already proven to be successful in describing several different experimental observations for systems characterized by baryon chemical potential close to zero, but so far the source shape has not been explored in detail. In this paper we discuss an event-by-event analysis of the two-particle source function in = 200 GeV Au+Au collisions generated by the EPOS model. We find that when utilizing all stages of the model, Lévy-shaped distributions (unlike Gaussian distributions) provide a good description of the source shape in the individual events. Hence it is clear that it is not the event averaging that creates the non-Gaussian features in the pair distributions. Based on this observation, we determine Lévy-parameters of the source as a function of event centrality and particle momentum.
Highlights
A long-standing goal of high-energy nuclear physics has been to understand and explore the space-time geometry of the particle emitting source created in heavy-ion collisions [1]
There is a whole sub-field of high-energy nuclear- and particle-physics called femtoscopy, which deals with such measurements of lengths and time intervals on the femtometer scale [2]
In this√paper we present a detailed event-by-event analysis of the two-pion source distribution in sNN = 200 GeV Au+Au collisions generated by EPOS
Summary
A long-standing goal of high-energy nuclear physics has been to understand and explore the space-time geometry of the particle emitting source created in heavy-ion collisions [1]. One main observable that is of great interest is the two-particle source function, sometimes called spatial correlation function or pair-separation distribution Detailed investigation of this quantity is important for a multitude of reasons (connected to hydrodynamic expansion, critical behavior, etc.), it is not something that is easy to reconstruct experimentally. There is a whole sub-field of high-energy nuclear- and particle-physics called femtoscopy, which deals with such measurements of lengths and time intervals on the femtometer (fm) scale [2] Source imaging studies [13,14] on the other hand suggest that the two-particle source function of pions has a long-range component, obeying a power-law behavior It was shown recently by various experimental measurements, that a generalization of the Gaussian source shape, the Lévy distribution can provide a much more suitable description of the observed sources [15,16].
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