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arxiv: 2605.13953 · v1 · submitted 2026-05-13 · ✦ hep-ph

Recognition: no theorem link

Logarithmically-accurate showers with massive quarks

Melissa van Beekveld , Silvia Ferrario Ravasio , Alba Soto-Ontoso , Gregory Soyez , Rob Verheyen
Authors on Pith no claims yet

Pith reviewed 2026-05-15 02:41 UTC · model grok-4.3

classification ✦ hep-ph
keywords parton showersquark massesnext-to-leading logarithmic accuracyfinal-state radiationresummationLund observablesheavy flavor
0
0 comments X

The pith

PanScales final-state showers now include quark masses at next-to-leading logarithmic accuracy while preserving their original performance for massless observables.

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

The paper formulates versions of the PanScales final-state parton showers that incorporate the masses of quarks such as charm and bottom. These modified showers reach next-to-leading logarithmic accuracy for observables sensitive to those masses. The formulation ensures that the original accuracy is retained for any observable where the quark masses can be neglected. Validation proceeds through fixed-order comparisons up to second order in the strong coupling and all-order matches to analytic resummed results for quantities including Lund-tree shapes, non-global energy flows, and sub-jet multiplicities. The work also presents initial phenomenological comparisons against LEP data.

Core claim

We formulate PanScales final-state showers that account for quark masses and achieve next-to-leading logarithmic accuracy, while preserving the original accuracy of the showers for observables where the mass of the quarks is irrelevant.

What carries the argument

The PanScales shower algorithm with mass-dependent adjustments to splitting kernels and phase-space boundaries that maintain the required logarithmic ordering.

If this is right

  • The showers can simulate processes involving heavy quarks at the same logarithmic precision previously available only for light quarks.
  • Fixed-order tests up to second order in alpha_s confirm the local accuracy of the mass-dependent kernels.
  • All-order comparisons reproduce analytic resummations for Lund-tree shapes, non-global energy flows, and Lund sub-jet multiplicities.
  • Phenomenological runs against LEP data illustrate direct usability for bottom- and charm-quark fragmentation studies.

Where Pith is reading between the lines

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

  • The same mass-correction strategy could be applied to initial-state showers or to other parton-shower frameworks that aim for NLL accuracy.
  • Improved heavy-flavor modeling would directly benefit predictions for top-quark and bottom-quark production at the LHC.
  • Future work could test whether the approach extends to even higher logarithmic orders or to observables that mix massive and massless partons.

Load-bearing premise

The mass modifications can be introduced without degrading the logarithmic accuracy already achieved for observables that do not depend on quark mass.

What would settle it

A discrepancy between the new shower predictions and either O(alpha_s^2) fixed-order matrix elements or semi-analytic NLL resummed calculations for a massive-quark observable such as a Lund sub-jet multiplicity would disprove the claimed accuracy.

read the original abstract

We formulate PanScales final-state showers that account for quark masses and achieve next-to-leading logarithmic accuracy, while preserving the original accuracy of the showers for observables where the mass of the quarks is irrelevant. We validate the accuracy of the shower algorithms by performing fixed-order tests up to second order in the strong coupling constant, and all-order comparisons to (semi-)analytic resummed calculations for a series of observables, including Lund-tree shapes, non-global energy flows and Lund sub-jet multiplicities. We also include some phenomenological studies using LEP data.

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

1 major / 2 minor

Summary. The paper formulates modifications to the PanScales final-state parton showers that incorporate finite quark masses while achieving next-to-leading logarithmic (NLL) accuracy for massive-quark observables and preserving the original NLL accuracy for observables insensitive to quark masses. Validation consists of fixed-order comparisons up to O(α_s²) for relevant splitting processes together with all-order numerical tests against independent resummed calculations for Lund-tree shapes, non-global energy flows and sub-jet multiplicities; a brief phenomenological comparison to LEP data is also included.

Significance. If the NLL accuracy holds, the result supplies a practical, logarithmically accurate shower implementation for heavy-quark processes that is directly usable in collider phenomenology. The explicit construction of mass-dependent kernels that reduce to the massless PanScales limit, combined with both fixed-order and all-order tests, addresses a long-standing limitation in shower accuracy for massive quarks and strengthens the reliability of Monte Carlo predictions for observables such as heavy-flavour jet shapes and non-global logarithms.

major comments (1)
  1. [§4] §4 (fixed-order validation): the O(α_s²) tests for massive-quark splittings are stated to agree with matrix-element results, but the manuscript provides neither quantitative measures of agreement (relative differences, χ² values or error bands) nor the precise phase-space cuts employed; without these the support for the NLL claim remains only moderate.
minor comments (2)
  1. Figure captions should explicitly distinguish curves obtained with massive versus massless kernels so that the preservation of massless accuracy is immediately visible.
  2. A short appendix tabulating the exact massive correction terms added to the PanScales splitting kernels would improve reproducibility.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their positive assessment and constructive comment on the fixed-order validation. We address the point below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [§4] §4 (fixed-order validation): the O(α_s²) tests for massive-quark splittings are stated to agree with matrix-element results, but the manuscript provides neither quantitative measures of agreement (relative differences, χ² values or error bands) nor the precise phase-space cuts employed; without these the support for the NLL claim remains only moderate.

    Authors: We agree that quantitative measures of agreement and explicit phase-space cuts would strengthen the presentation of the fixed-order tests. In the revised manuscript we will add relative differences (shower minus matrix-element results, normalised to the matrix-element value) for the O(α_s²) massive-quark splittings, include Monte-Carlo statistical error bands, and state the precise cuts (minimum transverse momentum, angular separation, and invariant-mass thresholds) used in each comparison. These additions will make the numerical support for NLL accuracy more transparent while leaving the underlying algorithm unchanged. revision: yes

Circularity Check

0 steps flagged

No significant circularity; minor self-citations not load-bearing

full rationale

The derivation constructs massive-quark corrections to PanScales splitting kernels and kinematics, then validates NLL accuracy via explicit O(α_s²) fixed-order matching for splitting processes and all-order numerical comparisons against independent resummed calculations for Lund shapes, non-global flows and sub-jet multiplicities. These tests are external to the shower implementation itself. Self-citations to prior PanScales work exist but are not used to import unverified uniqueness theorems or to define the target accuracy by construction; the central claim remains independently testable and is supported by the supplied benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review yields no identifiable free parameters, axioms, or invented entities; the work appears to extend an existing algorithmic framework rather than introduce new postulates.

pith-pipeline@v0.9.0 · 5390 in / 1002 out tokens · 40201 ms · 2026-05-15T02:41:53.679262+00:00 · methodology

discussion (0)

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Reference graph

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