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arxiv: 2502.12333 · v5 · submitted 2025-02-17 · ✦ hep-ph

Impact of momentum-dependent drag coefficient on energy loss of charm and bottom quarks in QGP

Marjan Rahimi Nezhad , Fatemeh Taghavi-Shahri , Kurosh Javidan This is my paper

Pith reviewed 2026-05-23 02:29 UTC · model grok-4.3

classification ✦ hep-ph
keywords charm quarksbottom quarksquark-gluon plasmadrag coefficientenergy lossnuclear modification factorFokker-Planckheavy-ion collisions
0
0 comments X

The pith

Expressing energy loss coefficients as polynomial expansions in momentum provides a flexible framework to test sensitivity to momentum dependence for charm and bottom quarks in the quark-gluon plasma.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper establishes that a phenomenological extension using polynomial expansions of the drag and energy loss coefficients in momentum offers a way to incorporate additional momentum dependence beyond simplified treatments. Numerical evolution of initial distribution functions via the Fokker-Planck equation then yields the nuclear modification factor R_AA for charm and bottom quarks in Pb-Pb collisions at 5.02 TeV, which is compared to recent ALICE and ATLAS data. A sympathetic reader would care because this tests how sensitive heavy-quark observables are to the momentum dependence in transport coefficients and enables more accurate separation of radiative and collisional energy loss.

Core claim

The central claim is that the phenomenological extension of the drag coefficient by polynomial expansions in momentum allows the effects of particle momentum on radiative and collisional energy loss to be determined more accurately, with the resulting R_AA values for charm and bottom quarks compared against experimental data.

What carries the argument

Polynomial expansions of the energy loss coefficients as functions of momentum, which provide a flexible phenomenological framework to test the sensitivity of heavy-quark observables to additional momentum dependence in transport coefficients.

If this is right

  • The nuclear modification factor R_AA of charm and bottom quarks can be computed with better accounting for momentum effects.
  • Radiative and collisional energy losses are determined more accurately.
  • Comparisons with ALICE and ATLAS data from Pb-Pb collisions at 5.02 TeV become feasible under this extended model.
  • Initial distributions are evolved using the Fokker-Planck equation under the momentum-dependent coefficients.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This framework could be used to explore the minimal order of the polynomial needed to fit the data.
  • Application to other heavy flavors or energies might reveal patterns in the momentum dependence.
  • The approach may help bridge between phenomenological models and microscopic calculations of QGP transport.

Load-bearing premise

The polynomial expansion of the drag and energy-loss coefficients accurately captures the true momentum dependence of heavy-quark interactions in the QGP without introducing uncontrolled artifacts.

What would settle it

An observation that the R_AA predictions remain insensitive to the choice of polynomial order or functional form for the momentum dependence, or that they fail to improve agreement with data compared to constant-coefficient models, would falsify the utility of this extension.

Figures

Figures reproduced from arXiv: 2502.12333 by Fatemeh Taghavi-Shahri, Kurosh Javidan, Marjan Rahimi Nezhad.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p012_5.png] view at source ↗
read the original abstract

This paper investigates the influence of heavy-quark momentum on their interaction rate and the resulting drag coefficient in a quark-gluon plasma. To go beyond simplified treatments, we introduce a phenomenological extension of the drag coefficient by expressing the energy loss coefficients as polynomial expansions of momentum, thereby providing a flexible framework to test the sensitivity of heavy-quark observables to additional momentum dependence in transport coefficients. Furthermore, the effects of particle momentum on radiative and collisional energy loss are determined more accurately. The study focuses on calculating the nuclear modification factor ($R_{AA}$) of charm and bottom quarks in Pb-Pb collisions at $\sqrt{S_{NN}} = 5.02 \: TeV$. The initial distribution functions are evolved numerically using the Fokker-Planck equation. The results are compared with the latest experimental data from ALICE and ATLAS, collected in 2021 and 2022.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript investigates the momentum dependence of the drag coefficient for charm and bottom quarks in the QGP by introducing a phenomenological polynomial expansion of the energy-loss coefficients. It evolves initial heavy-quark distributions via the Fokker-Planck equation to compute the nuclear modification factor R_AA in 5.02 TeV Pb-Pb collisions and compares the results to ALICE and ATLAS data. The central claim is that the momentum-dependent extension supplies a flexible framework for testing sensitivity to additional momentum dependence in transport coefficients and thereby yields a more accurate determination of radiative versus collisional energy loss.

Significance. If the polynomial form is shown to capture genuine momentum dependence without uncontrolled artifacts, the approach would supply a practical tool for exploring how momentum-dependent transport coefficients affect heavy-quark suppression observables. The numerical Fokker-Planck evolution and direct comparison to recent experimental data are standard and reproducible elements of the analysis.

major comments (2)
  1. [Abstract] Abstract (phenomenological extension paragraph): the claim that the polynomial extension yields 'more accurate' energy loss is not accompanied by any explicit functional form, polynomial degree, basis choice, or fitting procedure. Without these specifications it is impossible to determine whether reported improvements arise from physical momentum dependence or from additional free parameters.
  2. [Abstract] Abstract (phenomenological extension paragraph): the drag and energy-loss coefficients are defined via polynomials whose coefficients are free parameters; any improvement in R_AA agreement is therefore achieved by fitting those coefficients to the same data used for validation, rendering the reported 'prediction' and 'more accurate determination' circular by construction.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed review and constructive feedback on our manuscript. We address the major comments point by point below, agreeing that the abstract requires clarification and revision to avoid ambiguity.

read point-by-point responses

  1. Referee: [Abstract] Abstract (phenomenological extension paragraph): the claim that the polynomial extension yields 'more accurate' energy loss is not accompanied by any explicit functional form, polynomial degree, basis choice, or fitting procedure. Without these specifications it is impossible to determine whether reported improvements arise from physical momentum dependence or from additional free parameters.

    Authors: We agree that the abstract as written does not provide the necessary technical details. In the revised version we will specify the polynomial form (e.g., a quadratic expansion in momentum p), the degree chosen, the basis functions employed, and the procedure used to fix the coefficients (comparison with measured R_AA supplemented by theoretical guidance on the relative strength of radiative and collisional contributions). This will make clear that the extension is a controlled phenomenological parameterization rather than an ad-hoc addition of free parameters. revision: yes

  2. Referee: [Abstract] Abstract (phenomenological extension paragraph): the drag and energy-loss coefficients are defined via polynomials whose coefficients are free parameters; any improvement in R_AA agreement is therefore achieved by fitting those coefficients to the same data used for validation, rendering the reported 'prediction' and 'more accurate determination' circular by construction.

    Authors: The referee correctly identifies a potential circularity if the abstract is read as claiming an independent prediction. The manuscript's intent is to introduce a flexible parameterization that allows systematic exploration of momentum dependence, not to predict R_AA from first principles. We will revise the abstract to remove the phrasing 'more accurate determination' and 'prediction', replacing it with language that emphasizes the framework's utility for testing sensitivity to momentum-dependent transport coefficients. The body of the paper already compares constant versus momentum-dependent cases to illustrate the effect; the revised abstract will align with that exploratory scope. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected; derivation remains self-contained.

full rationale

The paper introduces a phenomenological polynomial extension of the drag and energy-loss coefficients as a flexible framework, evolves initial distributions numerically via the Fokker-Planck equation to obtain R_AA for charm and bottom quarks, and compares the results to ALICE/ATLAS data. No quoted step in the provided text shows the polynomial coefficients being fitted to the same R_AA data used for validation, nor any self-definitional reduction, self-citation load-bearing premise, or renaming of a known result. The numerical evolution step is independent of the specific momentum-dependent form chosen, so the comparison to external data constitutes a genuine test rather than a tautology by construction.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The model rests on a domain assumption that the Fokker-Planck equation suffices and on free parameters introduced by the polynomial expansion; no new entities are postulated.

free parameters (1)
  • coefficients of the polynomial expansion of drag/energy-loss terms
    Introduced explicitly to make the drag coefficient momentum-dependent; their values are not fixed by first principles and must be chosen or fitted.
axioms (1)
  • domain assumption Fokker-Planck equation accurately describes the evolution of heavy-quark momentum distributions in an expanding QGP
    Invoked when the initial distributions are evolved numerically to obtain final spectra and R_AA.

pith-pipeline@v0.9.0 · 5693 in / 1386 out tokens · 29188 ms · 2026-05-23T02:29:05.587013+00:00 · methodology

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