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Small systems and the single-hit approximation in the AMY parton cascade ALPACA

Törnkvist, Robin LU and Zapp, Korinna LU (2024) In Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 856.
Abstract

Understanding how momentum anisotropies arise in small collision systems is important for a quantitative understanding of collectivity in terms of QCD dynamics in small and large collision systems. In this letter we present results for small collision systems from the newly developed parton cascade ALPACA, which faithfully encodes the AMY effective kinetic theory. ALPACA reproduces quantitatively previously known results from a calculation in the single-hit approximation for small values of the coupling. We discuss in detail how such a comparison is to be carried out. Particularly at larger coupling a generic difference between the two approaches becomes apparent, namely that in parton cascades particles interact over a finite distance... (More)

Understanding how momentum anisotropies arise in small collision systems is important for a quantitative understanding of collectivity in terms of QCD dynamics in small and large collision systems. In this letter we present results for small collision systems from the newly developed parton cascade ALPACA, which faithfully encodes the AMY effective kinetic theory. ALPACA reproduces quantitatively previously known results from a calculation in the single-hit approximation for small values of the coupling. We discuss in detail how such a comparison is to be carried out. Particularly at larger coupling a generic difference between the two approaches becomes apparent, namely that in parton cascades particles interact over a finite distance while in direct integrations of the Boltzmann equation the interactions are local. This leads to quantitative differences in the extracted values for the elliptic flow coefficient. These discrepancies appear in situations where the mean free path is not large compared to the interaction time and the applicability of kinetic theory is thus questionable.

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publication status
published
subject
keywords
Elliptic flow, Kinetic theory, Small systems
in
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
volume
856
article number
138952
publisher
Elsevier
external identifiers
  • scopus:85201112117
ISSN
0370-2693
DOI
10.1016/j.physletb.2024.138952
language
English
LU publication?
yes
id
9c90f8f4-a3f1-4e6c-a8c9-ed901f6be12f
date added to LUP
2024-09-05 15:15:38
date last changed
2025-05-27 11:35:44
@article{9c90f8f4-a3f1-4e6c-a8c9-ed901f6be12f,
  abstract     = {{<p>Understanding how momentum anisotropies arise in small collision systems is important for a quantitative understanding of collectivity in terms of QCD dynamics in small and large collision systems. In this letter we present results for small collision systems from the newly developed parton cascade ALPACA, which faithfully encodes the AMY effective kinetic theory. ALPACA reproduces quantitatively previously known results from a calculation in the single-hit approximation for small values of the coupling. We discuss in detail how such a comparison is to be carried out. Particularly at larger coupling a generic difference between the two approaches becomes apparent, namely that in parton cascades particles interact over a finite distance while in direct integrations of the Boltzmann equation the interactions are local. This leads to quantitative differences in the extracted values for the elliptic flow coefficient. These discrepancies appear in situations where the mean free path is not large compared to the interaction time and the applicability of kinetic theory is thus questionable.</p>}},
  author       = {{Törnkvist, Robin and Zapp, Korinna}},
  issn         = {{0370-2693}},
  keywords     = {{Elliptic flow; Kinetic theory; Small systems}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics}},
  title        = {{Small systems and the single-hit approximation in the AMY parton cascade ALPACA}},
  url          = {{http://dx.doi.org/10.1016/j.physletb.2024.138952}},
  doi          = {{10.1016/j.physletb.2024.138952}},
  volume       = {{856}},
  year         = {{2024}},
}