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Quadrupole spectra derived from 2.76-TeV Pb-Pb identified-hadron v2(pt) data

Thomas A. Trainor

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Phys. Rev. C 114, 034911 – Published 14 September, 2026

DOI: https://doi.org/10.1103/sw4r-4nxr

Abstract

pt-differential quantity v2(pt) is meant to measure elliptic flow manifested by a dense QCD medium formed in high-energy nucleus-nucleus collisions. Elliptic flow may be referred to more neutrally as a cylindrical quadrupole component of the transverse motion of particle sources within a collision. As defined, v2(pt) relies on an implicit assumption that almost all produced particles emerge from a single source. This article describes a detailed study of the algebraic structure of v2(pt). A procedure is developed to derive a common monopole boost (“radial flow”) value and quadrupole pt spectra for several hadron species. The method is applied to v2(pt) data for four hadron species from 2.76-TeV Pb-Pb collisions. According to available v2(pt) data the assumption of a single dominant particle source within A−A collisions is unjustified. Combined with a previous study of quadrupole amplitude variation for 200-GeV p−p collisions these results demonstrate that quadrupole structure is related to a novel QCD process separate from projectile-nucleon dissociation and jet production. Given quadrupole evolution it is unlikely that a hydrodynamic description is relevant to that process.

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Phys. Rev. C 114, 034911– Published 14 September, 2026
  • Received 13 December 2025
  • Revised 26 February 2026
  • Accepted 12 August 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.

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