Flow plus coalescence explain hadron nuclear modification and high-pT anisotropy
Abstract
It has long been a puzzle why the nuclear modification factor in relativistic pPb collisions is consistent with unity, while the high-pT elliptic flow is significantly positive. The latter is traditionally interpreted as path-length-dependent energy loss, whereas the former is consistent with zero energy loss. In this Letter, we propose that even at high pT a hard parton coalesces with a boosted thermal medium parton whose energy is correlated with the angle-dependent radial flow. We compare this flow for pp, pPb, pO, OO and PbPb collision systems and conclude in particular that the pPb flow is large and anisotropic. The collective medium pushes out the hard partons, and more so in pPb, or in-plane, than in pp collisions, or out-of-plane. The mechanism qualitatively agrees with experiment and predicts a significantly smaller elliptic flow signal for jets than for hadrons.
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BibTeX
@misc{schee2026flow,
title = {{Flow plus coalescence explain hadron nuclear modification and high-$p_T$ anisotropy}},
author = {Wilke van der Schee and Isobel Kolbé},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.24762},
eprint = {2609.24762},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.24762},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Flow plus coalescence explain hadron nuclear modification and high-p_T anisotropy
AU - Wilke van der Schee
AU - Isobel Kolbé
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.24762
UR - https://arxiv.org/abs/2609.24762
AB - It has long been a puzzle why the nuclear modification factor in relativistic pPb collisions is consistent with unity, while the high-p_T elliptic flow is significantly positive. The latter is traditionally interpreted as path-length-dependent energy loss, whereas the former is consistent with zero energy loss. In this Letter, we propose that even at high p_T a hard parton coalesces with a boosted thermal medium parton whose energy is correlated with the angle-dependent radial flow. We compare this flow for pp, pPb, pO, OO and PbPb collision systems and conclude in particular that the pPb flow is large and anisotropic. The collective medium pushes out the hard partons, and more so in pPb, or in-plane, than in pp collisions, or out-of-plane. The mechanism qualitatively agrees with experiment and predicts a significantly smaller elliptic flow signal for jets than for hadrons.
ER -