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A Study of QCD Radiation in VBF Higgs Production with Vincia and Pythia

by Stefan Höche, Stephen Mrenna, Shay Payne, Christian T Preuss, Peter Skands

This is not the latest submitted version.

This Submission thread is now published as SciPost Phys. 12, 010 (2022)

Submission summary

As Contributors: Christian Tobias Preuss
Preprint link: scipost_202106_00039v2
Date submitted: 2021-08-18 18:49
Submitted by: Preuss, Christian Tobias
Submitted to: SciPost Physics
Academic field: Physics
  • High-Energy Physics - Phenomenology
Approaches: Computational, Phenomenological


We discuss and illustrate the properties of several parton-shower models available in Pythia and Vincia, in the context of Higgs production via vector boson fusion (VBF). In particular, the distinctive colour topology of VBF processes allows to define observables sensitive to the coherent radiation pattern of additional jets. We study a set of such observables, using the Vincia sector-antenna shower as our main reference, and contrast it to Pythia's transverse-momentum-ordered DGLAP shower as well as Pythia's dipole-improved shower. We then investigate the robustness of these predictions as successive levels of higher-order perturbative matrix elements are incorporated, including next-to-leading-order matched and tree-level merged calculations, using Powheg Box and Sherpa respectively to generate the hard events.

Current status:
Has been resubmitted

List of changes

1. Changed title and abstract to be more descriptive of its content.
2. Reworded statements about coherence in Vincia.
3. Replaced "unique colour flow of the VBF process" by "distinct colour flow of the VBF process at leading order (LO)" in the introduction.
4. Fixed reference pointing to the wrong entry and added further references on studies of Pythia's default shower in VBF/VBS.
5. Added a new paragraph to section 2.1 discussing further details of the modelling of the VBF process.
6. Added remark on the scale treatment in Pythia to section 2.1
7. Added further references on truncated showers to section 2.3
8. Added remark on the treatment of soft radiation in angular-ordered showers to the conclusion.
9. Clarified some terminology.

Reports on this Submission

Anonymous Report 1 on 2021-10-3 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:scipost_202106_00039v2, delivered 2021-10-03, doi: 10.21468/SciPost.Report.3613


The authors have improved on the clarity of the manuscript and did address almost all of my criticism, which removes several possible misunderstandings. I still feel that the sentences involving "amount of coherent radiation" need clarification.

I also insist on the change to "parton shower model". Parton showers approximate QCD cross sections in extreme kinematic limits. As such they are exact calculations, and one can (at least in principle, though recently extensively demonstrated in the literature) unambiguously check, if a given algorithm provides an accurate approximation, or not.

Ambiguities arise in terms of subleading origin, and amount to a choice of scheme in the approximate calculation. To this extend (as opposed to the genuine neccessity of modeling in the absence of first-principles calculations) parton showers are a quantitative component of an event generator and hence solely deserve the term "algorithm".

  • validity: -
  • significance: -
  • originality: -
  • clarity: -
  • formatting: -
  • grammar: -

Author:  Christian Tobias Preuss  on 2021-10-13  [id 1843]

(in reply to Report 1 on 2021-10-03)

We appreciate that we have addressed most of the referee's criticism with our updated manuscript.

Following the referee's suggestions, we have replaced the phrase "amount of coherent radiation" by "amount of radiation". We believe that this rewording makes it unambiguous that the observable we introduce serves the purpose of measuring the total radiative deposit in the defined pseudorapidity regions. Furthermore, we have replaced all occurences of the phrase "shower model" by "shower algorithm".

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