The VII-th International Conference on the Initial Stages of High-Energy Nuclear Collisions : Initial Stages 2023

AMY Lorentz invariant parton cascade

Not scheduled

20m

Copenhagen

Oral Collective dynamics from small to large systems

Speaker

Robin Törnkvist (Lund University)

Description

Recently observed signs of collectivity in small systems has highlighted the need for a better understanding of equilibration in small and large collisions systems. In search of this, the QCD effective kinetic theory formulated by Arnold, Moore and Yaffe (AMY) [1] has emerged as a promising candidate. In order to bridge the gap between theory and experiments we introduce ALPACA, a Lorentz invariant parton cascade encoding the AMY effective kinetic theory of QCD at high temperatures [2]. It solves the Boltzmann equation with the full AMY kernels (elastic scattering and splitting/merging processes) by explicitly simulating the evolution of parton ensembles corresponding to single events. It is constructed in a fully Lorentz invariant way by using a method pioneered in [3], which also underlies the parton cascade PCPC [4]. A complication arises from quantities like the screening mass, that enter the AMY kernels and are defined as integrals over the phase space densities. We develop a method for extracting these locally from the parton ensemble without the need for further information. We perform an extensive validation of the framework by showing that it reproduces the expected behaviour in thermal equilibrium. We also look at the harmonic flow response to initial geometry deformations for different generic initial gluon distributions.

[1] Peter Brockway Arnold, Guy D. Moore, and Laurence G. Yaffe. “Effective kinetic theory for high temperature gauge theories”. JHEP 01 (2003), p. 030. doi:10.1088/1126-6708/2003/01/030. arXiv:hep-ph/0209353.
[2] Aleksi Kurkela, Robin Törnkvist, and Korinna Zapp. “AMY Lorentz invariant parton cascade - the thermal equilibrium case”. arXiv:hep-ph/2211.15454.
[3] G. Peter, D. Behrens, and C. C. Noack. “Poincare covariant particle dynamics. 1: Intranuclear cascade model”. Phys. Rev. C 49 (1994), pp. 3253–3265. doi:10.1103/PhysRevC.49.3253.
[4] V. Borchers et al. “A Poincare covariant parton cascade model for ultra-relativistic heavy ion reactions”. Phys. Rev. C 62 (2000), p. 064903. doi:10.1103/PhysRevC.62.064903. arXiv:hep-ph/0006038.