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arxiv: 1907.09441 · v1 · pith:DZS4GQYYnew · submitted 2019-07-22 · ✦ hep-ph

TMD parton distributions from parton showers

Melanie Schmitz , Francesco Hautmann , Hannes Jung , Sara Taheri Monfared This is my paper

Pith reviewed 2026-05-24 17:57 UTC · model grok-4.3

classification ✦ hep-ph
keywords tmd parton distributionsparton showersmonte carlo simulationstransverse momentumparton branchingqcd evolutionhigh energy collisions
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The pith

Effective TMD parton distributions can be extracted from Monte Carlo parton showers.

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

The paper determines transverse momentum dependent parton distributions by examining the outputs of Monte Carlo parton shower programs. It compares these effective distributions to those obtained from the parton branching approach. A sympathetic reader would care because this links widely used simulation tools to specialized TMD formalisms in collider physics. The work shows that the transverse momentum information generated during shower evolution can be reinterpreted as TMD distributions. This opens a route to TMD studies that does not require separate evolution codes.

Core claim

The paper presents the determination of Transverse Momentum Dependent (TMD) parton distributions from Monte Carlo parton showers. It investigates the effective TMD distributions obtained from the parton showers and compares them to the TMD distributions determined within the Parton Branching method.

What carries the argument

Effective TMD distributions obtained by reading out the transverse momentum generated during parton shower evolution.

If this is right

  • TMD distributions become available from existing event generators without dedicated TMD modules.
  • Consistency between shower-based and branching-based TMDs can be checked directly.
  • TMD effects can be studied inside standard Monte Carlo simulations of collider events.
  • The method supplies a new way to validate TMD models against shower predictions.

Where Pith is reading between the lines

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

  • The same extraction could be repeated on other shower implementations to test whether the resulting TMDs converge.
  • Discrepancies between the two sets of TMDs might reveal the impact of specific approximations used in each shower.
  • One could insert the extracted TMDs back into a calculation of a measurable cross section and compare to data.

Load-bearing premise

The parton showers must encode transverse momentum dependence in a form that permits consistent extraction of TMD distributions comparable across methods.

What would settle it

If transverse momentum spectra computed from the extracted TMD distributions fail to reproduce the spectra generated directly by the showers, the extraction procedure would not hold.

Figures

Figures reproduced from arXiv: 1907.09441 by Francesco Hautmann, Hannes Jung, Melanie Schmitz, Sara Taheri Monfared.

Figure 1
Figure 1. Figure 1: TMD parton density as a function of k⊥ for gluons at µ = 20 GeV and x = 0.01 obtained from final state events (blue curve) and obtained from the input TMD PB-Set2 (red curve). Left: Collinear PDF: PB-Set2, TMD PDF: PB-Set2. Right: Collinear PDF: PB-Set1, TMD PDF: PB￾Set2 µ = 20 GeV. The distribution obtained from the final state of the PS2TMD process is presented (blue curve) and compared to the PB-Set2 (r… view at source ↗
Figure 2
Figure 2. Figure 2: TMD parton density as a function of k⊥ for gluons at µ = 70 GeV at x = 0.01 (left) and at µ = 20 GeV at x = 0.2 (right) obtained from final state events (blue curve) and obtained from the input TMD PB-Set2 (red curve). Collinear PDF: PB-Set1, TMD PDF: PB-Set2 In [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: TMD parton density as a function of k⊥ for gluons at µ = 100 GeV obtained from final state events of the PYTHIA shower (blue curve) and obtained from the input TMD PB-Set2 (red curve). The collinear PDF PB-Set2 is used for the generation. Left: x = 0.001. Right: x = 0.01. [GeV] t k −1 10 1 10 2 10 ) µ, t xA(x,k −5 10 −4 10 −3 10 −2 10 −1 10 1 gluon, x = 0.001, µ = 100 GeV PB-NLO-HERAI+II-2018-set2 PS2TMD+H… view at source ↗
Figure 4
Figure 4. Figure 4: TMD parton density as a function of k⊥ for gluons at µ = 100 GeV obtained from final state events of the HERWIG shower (blue curve) and obtained from the input TMD PB-Set2 (red curve). The collinear PDF PB-Set2 is used for the generation. Left: x = 0.001. Right: x = 0.01. k⊥ they differ. 4. Conclusion A method was described to determine TMDs from final state events. The concept is proven by using TMDs, the… view at source ↗
read the original abstract

We present the determination of Transverse Momentum Dependent (TMD) parton distributions from Monte Carlo parton showers. We investigate the effective TMD distributions obtained from the PYTHIA8 and HERWIG6 parton showers and compare them to the TMD distributions determined within the Parton Branching method.

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

0 major / 1 minor

Summary. The manuscript claims to determine effective Transverse Momentum Dependent (TMD) parton distributions by analyzing the outputs of the PYTHIA8 and HERWIG6 Monte Carlo parton showers and to compare the resulting distributions directly to those obtained within the Parton Branching method.

Significance. If the extraction procedure is well-defined and the comparisons are robust, the work could provide a useful link between standard parton-shower implementations and the TMD formalism, potentially aiding the modeling of transverse-momentum spectra in collider phenomenology.

minor comments (1)
  1. [Abstract] Abstract: the abstract states the determination but supplies no outline of the extraction algorithm, the kinematic cuts employed, or the quantitative outcome of the comparison; a one-sentence summary of the method and main result would improve readability.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and for the positive assessment, which accurately summarizes our work on extracting effective TMD distributions from PYTHIA8 and HERWIG6 parton showers and comparing them to the Parton Branching method. The recommendation for minor revision is noted. No specific major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity; derivation is self-contained numerical extraction

full rationale

The paper performs a direct numerical extraction of effective TMD distributions from the outputs of established Monte Carlo parton showers (PYTHIA8 and HERWIG6) and compares them to those obtained via the Parton Branching method. No load-bearing step reduces by construction to a fitted parameter, self-definition, or self-citation chain; the central claim rests on explicit shower simulation and comparison rather than any renaming, ansatz smuggling, or uniqueness theorem imported from the authors' prior work. The work is therefore self-contained against external benchmarks (the shower codes themselves) and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review provides no information on any free parameters, axioms, or invented entities.

pith-pipeline@v0.9.0 · 5565 in / 1107 out tokens · 40290 ms · 2026-05-24T17:57:12.004473+00:00 · methodology

discussion (0)

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Reference graph

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