English

Energy loss predicts no $v_2$ in small systems

High Energy Physics - Phenomenology 2026-03-24 v1

Abstract

We present high-pTp_T RABR_{AB} and v2v_2 from a perturbative quantum chromodynamics-based energy loss model that includes event-by-event hydrodynamic evolution of the medium and small system size corrections to the energy loss. The model is calibrated on, and describes well, large system RAAR_{AA} and v2v_2 experimental data. The extrapolation of our model to Ne+Ne\mathrm{Ne}+\mathrm{Ne} and O+O\mathrm{O}+\mathrm{O} agrees quantitatively with recent experimental measurements of RAAR_{AA}. Surprisingly, at high-pTp_T our energy loss model predicts v20v_2\approx0 for all symmetric and asymmetric small systems when extracted using either hard-hard or hard-soft two-particle correlations. We argue that all energy loss models will in general predict v20v_2\approx0 when extracted using hard-soft correlations, which is the usual experimental method for measuring anisotropy in hadronic collisions, due to a generic geometric decorrelation between the hard and soft sector participant planes.

Keywords

Cite

@article{arxiv.2603.21861,
  title  = {Energy loss predicts no $v_2$ in small systems},
  author = {Ben Bert and Coleridge Faraday and W. A. Horowitz},
  journal= {arXiv preprint arXiv:2603.21861},
  year   = {2026}
}

Comments

12 pages, 5 figures

R2 v1 2026-07-01T11:33:09.275Z