Ar+sc Collisions at SPS Energies: Lévy Sources in Ultra-Relativistic Molecular Dynamics Monte-Carlo Simulations

Understanding the very early stages of heavy-ion collisions requires detailed knowledge of the emitting source of particles created in these events, and recent research confirms that these sources often follow Lévy alpha-stable distributions. Barnabas Porfy and Mate Csanad, from ELTE Eötvös Loránd University, now present a comprehensive investigation into these distributions, specifically examining two-pion pair sources produced in Argon plus Scandium collisions. Their work utilises the Ultra-Relativistic Molecular Dynamics Monte-Carlo event generator to simulate these collisions, allowing them to fit the resulting pair sources with Lévy-stable distributions and extract key parameters. By determining the spatial scale, shape and strength of these sources, this research advances our understanding of particle production mechanisms in extreme conditions and provides valuable insights into the properties of matter created in these collisions.

New measurements underpin current research into particle emissions. Recent experiments confirm that the two-particle pion emitting source aligns well with Lévy alpha-stable distributions. To facilitate theoretical interpretation, scientists conduct simulations at relevant energies, utilising various heavy-ion collision models.

Lévy-Stable Function Describes Pion Emission Sources

This research paper investigates two-particle Bose-Einstein correlations, a technique known as HBT interferometry, in heavy-ion collisions. The study focuses on using the Lévy-stable distribution to model the particle-emitting source, aiming to understand the spatiotemporal characteristics of particle emission by analysing correlations between identical bosons, specifically pions. Scientists utilise the UrQMD model to simulate the heavy-ion collisions and generate event data, analysing HBT radii, parameters that characterise the size and shape of the emitting source, extracted from the two-particle correlations. The study confirms that the Lévy-stable distribution provides a better description of the emitting source compared to Gaussian models, especially in capturing fluctuations and long-range correlations. Researchers observe that the HBT radii change with the collision centrality, reflecting the degree of overlap in the collision, exploring the relationship between the Lévy parameters and the collision dynamics, providing insights into how the source evolves. The work focuses on understanding the space-time geometry of particle emission in high-energy heavy-ion collisions, employing a Lévy-stable distribution to model the pair source. Researchers generated simulations for beam momenta ranging from 13 to 150A GeV/c, corresponding to center of mass energies per nucleon pair of approximately 5 to 17 GeV, and analysed 10,000 events for each energy within a 0-10% centrality range. The team fitted the reconstructed two-particle source functions with three-dimensional Lévy distributions, extracting parameters that describe the spatial scale, shape, and strength of the source.

Analysis revealed that the Lévy stability index, α, remains consistent throughout the simulations, indicating the preservation of the distribution’s shape under convolution, a key property of Lévy-stable distributions. Measurements confirm that the pair source is well described by a Lévy-stable distribution, allowing for the extraction of parameters defining the source’s spatial extent. The UrQMD model provides direct access to the source function, enabling detailed investigation of simulated events and uncovering hidden properties of experimental data.

Lévy Sources Characterise Heavy-Ion Collisions

This research presents a detailed investigation of particle-emitting sources created in heavy-ion collisions, utilising data generated by the UrQMD microscopic transport model. Scientists successfully mapped the spatial distribution of particle pairs, specifically pions, produced in these collisions, employing Lévy-stable distributions to characterise the source. The analysis reveals how the properties of this source, its size, shape, and strength, depend on the mass of the particle pairs and the collision energy. The study demonstrates that Lévy-stable distributions accurately describe the observed particle sources, offering a more comprehensive approach than traditional Gaussian models, particularly in capturing the power-law tails observed in the data. This refined understanding of the source characteristics contributes to a more accurate picture of the space-time geometry of particle production in heavy-ion collisions.