UrQMD calculations of two-pion HBT correlations in p+p and Pb+Pb collisions at LHC energies

TL;DR

This study uses the UrQMD model to analyze two-pion HBT correlations in p+p and Pb+Pb collisions at LHC energies, revealing insights into particle emission dynamics and constraining formation times.

Contribution

It applies a combined UrQMD and correlation afterburner approach to analyze HBT radii at LHC energies, providing constraints on formation time and highlighting discrepancies in emission explosiveness.

Findings

Charged particle multiplicity constrains formation time to ≤ 0.8 fm/c.

R_out is overpredicted by nearly 50% in Pb+Pb collisions.

The model's R_out/R_side ratio exceeds experimental data, indicating less explosive emission.

Abstract

Two-pion Hanbury-Brown-Twiss (HBT) correlations for p+p and central Pb+Pb collisions at the Large-Hadron-Collider (LHC) energies are investigated with the ultra-relativistic quantum molecular dynamics model combined with a correlation afterburner. The transverse momentum dependence of the Pratt-Bertsch HBT radii $R_{long}$, $R_{out}$, and $R_{side}$ is extracted from a three-dimensional Gaussian fit to the correlator in the longitudinal co-moving system. In the p+p case, the dependence of correlations on the charged particle multiplicity and formation time is explored and the data allows to constrain the formation time in the string fragmentation to $\tau_f \leq 0.8$ fm/c. In the Pb+Pb case, it is found that $R_{out}$ is overpredicted by nearly 50%. The LHC results are also compared to data from the STAR experiment at RHIC. For both energies we find that the calculated $R_{out}/R_{side}$ ratio is always larger than data, indicating that the emission in the model is less explosive than observed in the data.