arXiv subjects

Ludovic Scyboz

Publications and source records attributed to Ludovic Scyboz.

At least 19 recordsLinked to original sources

arXiv2026

Higgs Boson Pair Production via Gluon Fusion: Higher-Order Corrections and Theoretical Uncertainties

In this contribution, the higher-order QCD and electroweak corrections to Standard Model Higgs boson pair production via the gluon-fusion mechanism, $gg\to hh$, are summarized and the different sources of theoretical uncertainty are assessed. The discussion includes finite top quark mass effects, matching to parton showers, approximate NNLO and N$^3$LO QCD corrections, NLO electroweak effects, and uncertainties associated with the top quark mass scheme and perturbative scale choices. In addition, we provide an updated state-of-the-art recommendation for the inclusive gluon-fusion Higgs boson pair production cross section and the corresponding Higgs boson pair invariant-mass distribution.

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arXiv2026

Timelike showers with jet recoils

We propose a new way to impose four-momentum conservation on timelike parton-shower branchings, allowing for recoil to be imparted not only to individual partons but also to groups of partons, "jets". In this work we present an explicit realisation of this idea for a dipole parton-shower, using angular ordering to decide which partons are grouped into jets in a way that does not require explicit jet clustering at each stage of the evolution. We verify that the algorithm satisfies next-to-leading logarithmic (NLL) accuracy criteria, from numerical fixed-order tests as well as resummation tests across a range of observables. Our conclusion is that jet recoils provide a viable path for adapting existing dipole/antenna-type showers to achieve NLL accuracy.

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arXiv2025

Logarithmically-accurate and positive-definite NLO shower matching

We present methods to achieve NLL+NLO accurate parton showering for processes with two coloured legs: neutral- and charged-current Drell-Yan, and Higgs production in $pp$ collisions, as well as DIS and $e^+e^-$ to jets. The methods include adaptations of existing approaches, as well as a new NLO matching scheme, ESME, that is positive-definite by construction. Our implementations of the methods within the PanScales framework yield highly competitive NLO event generation speeds. We validate the fixed-order and combined resummation accuracy with tests in the limit of small QCD coupling and briefly touch on phenomenological comparisons to standard NLO results and to Drell-Yan data. The progress reported here is an essential step towards showers with logarithmic accuracy beyond NLL for processes with incoming hadrons.

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arXiv2025

Matching Z $\to$ Hadrons at NNLO with Sector Showers

We present a detailed technical derivation of matching conditions at next-to-next-to-leading order in the sectorised VINCIA parton shower, by considering leading-colour 2-, 3- and 4-jet rates in hadronic Z-boson decays. In particular, we introduce a full subtraction-based calculation of the matching coefficient required to obtain the NLO 3-jet rate. This is achieved through a judicious choice of the counter-terms, which optimises the numerical evaluation of the subtracted double-real matrix element. We additionally give a consistent prescription for incorporating interference effects due to higher-order mixing between Born states with different flavour contents. Finally, we briefly comment on higher-order uncertainty estimates.

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arXiv2025

Flavoured jet algorithms: a comparative study

The accurate identification of heavy-flavour jets, those which originate from bottom or charm quarks, is crucial for precision studies of the Standard Model and searches for new physics. However, assigning flavour to jets presents significant challenges, primarily due to issues with infrared and collinear (IRC) safety. This paper aims to address these challenges by evaluating recently-proposed jet algorithms designed to be IRC-safe and applicable in high-precision measurements. We compare these algorithms across benchmark heavy-flavour production processes and kinematic regimes that are relevant for LHC phenomenology. Exploiting both fixed-order calculations in QCD as well as parton shower simulations, we analyse the infrared sensitivity of these new algorithms at different stages of the event evolution and compare to flavour-labelling strategies currently adopted by LHC collaborations. The results highlight that, while all algorithms lead to more robust flavour-assignments compared to current techniques, they vary in performance depending on the observable and energy regime. The study lays groundwork for robust, flavour-aware jet analyses in current and future collider experiments to maximise the physics potential of experimental data by reducing discrepancies between theoretical and experimental methods.

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arXiv2025

Sudakov evolution without unitarity

We present a method for sampling singular functions defined on (nested) multi-particle phase spaces, based on a generalisation of parton-shower phase-space generation techniques. At the heart of the method are three key ingredients: 1) the Sudakov sampling by which shower-style calculations sweep across phase space in an ordered manner, from hard to soft; 2) the sequential nesting of multiparticle phase spaces; and 3) the factorisations obeyed by singular multiparton amplitudes on the edges of these phase spaces. We demonstrate a C++ implementation of the proposed algorithm, dubbed Sunshine, for hadronic Z decays, and use it to test the tree-level accuracy of the Vincia sector shower through $\mathcal{O}(α_s^2)$.

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arXiv2025

A new standard for the logarithmic accuracy of parton showers

We report on a major milestone in the construction of logarithmically accurate final-state parton showers, achieving next-to-next-to-leading-logarithmic (NNLL) accuracy for the wide class of observables known as event shapes. The key to this advance lies in the identification of the relation between critical NNLL analytic resummation ingredients and their parton-shower counterparts. Our analytic discussion is supplemented with numerical tests of the logarithmic accuracy of three shower variants for more than a dozen distinct event-shape observables in $Z \to q \bar q$ and Higgs $\to gg$ decays. The NNLL terms are phenomenologically sizeable, as illustrated in comparisons to data.

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arXiv2024

Effective Field Theory descriptions of Higgs boson pair production

Higgs boson pair production is traditionally considered to be of particular interest for a measurement of the trilinear Higgs self-coupling. Yet it can offer insights into other couplings as well, since - in an effective field theory (EFT) parameterisation of potential new physics - both the production cross section and kinematical properties of the Higgs boson pair depend on various other Wilson coefficients of EFT operators. This note summarises the ongoing efforts related to the development of EFT tools for Higgs boson pair production in gluon fusion, and provides recommendations for the use of distinct EFT parameterisations in the Higgs boson pair production process. This document also outlines where further efforts are needed and provides a detailed analysis of theoretical uncertainties. Additionally, benchmark scenarios are updated. We also re-derive a parameterisation of the next-to-leading order (NLO) QCD corrections in terms of the EFT Wilson coefficients both for the total cross section and the distribution in the invariant mass of the Higgs boson pair, providing for the first time also the covariance matrix. A reweighting procedure making use of the newly derived coefficients is validated, which can be used to significantly speed up experimental analyses.

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arXiv2024

Subleading operators and gamma5-scheme dependence in SMEFT for Higgs boson pair production

The calculation of contributions from the chromomagnetic and four-top-quark-operators within Standard Model Effective Field Theory (SMEFT) to Higgs boson pair production in gluon fusion is presented, in combination with NLO QCD corrections. Here we focus on the $γ_5$-scheme dependence introduced by the four-top-quark-operators and the interplay with other operators contributing to this process in SMEFT.

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arXiv2023

Introduction to the PanScales framework, version 0.1

In this article, we document version 0.1 of the PanScales code for parton shower simulations. With the help of a few examples, we discuss basic usage of the code, including tests of logarithmic accuracy of parton showers. We expose some of the numerical techniques underlying the logarithmic tests and include a description of how users can implement their own showers within the framework. Some of the simpler logarithmic tests can be performed in a few minutes on a modern laptop. As an early step towards phenomenology, we also outline some aspects of a preliminary interface to Pythia, for access to its hard matrix elements and its hadronisation modules.

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arXiv2023

Flavoured jets with exact anti-$k_t$ kinematics and tests of infrared and collinear safety

We propose extensions of the anti-$k_t$ and Cambridge/Aachen hierarchical jet clustering algorithms that are designed to retain the exact jet kinematics of these algorithms, while providing an infrared-and-collinear-safe definition of jet flavour at any fixed order in perturbation theory. Central to our approach is a new technique called Interleaved Flavour Neutralisation (IFN), whereby the treatment of flavour is integrated with, but distinct from, the kinematic clustering. IFN allows flavour information to be meaningfully accessed at each stage of the clustering sequence, which enables a consistent assignment of flavour both to individual jets and to their substructure. We validate the IFN approach using a dedicated framework for fixed-order tests of infrared and collinear safety, which also reveals unanticipated issues in earlier approaches to flavoured jet clustering. We briefly explore the phenomenological impact of IFN with anti-$k_t$ jets for benchmark tasks at the Large Hadron Collider.

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arXiv2023

Two Higgs bosons, two loops, x+2 operators

We discuss the combination of NLO QCD corrections with operators of canonical dimension six within Standard Model Effective Field Theory (SMEFT), as well as within non-linear Effective Field Theory (HEFT) for Higgs-boson pair production in gluon fusion. Particular emphasis will be put on the identification of leading and subleading operators contributing to this process.

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arXiv2023

SMEFT predictions for $gg\to hh$ at full NLO QCD and truncation uncertainties

We present a calculation of the NLO QCD corrections for Higgs-boson pair production in gluon fusion including effects of anomalous couplings within Standard Model Effective Field Theory (SMEFT). We study effects of different truncation options of the EFT expansion in $1/Λ$ and of double operator insertions, both at total cross-section level as well as for the distribution of the invariant mass of the Higgs-boson pair, at $\sqrt{s}=13$ TeV. The NLO corrections are implemented in the generator $\texttt{ggHH_SMEFT}$ in the $\texttt{Powheg-Box-V2}$ framework.

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arXiv2023

Matching and event-shape NNDL accuracy in parton showers

To explore the interplay of NLO matching and next-to-leading logarithmic (NLL) parton showers, we consider the simplest case of $γ^*$ and Higgs-boson decays to $q\bar q$ and $gg$ respectively. Not only should shower NLL accuracy be retained across observables after matching, but for global event-shape observables and the two-jet rate, matching can augment the shower in such a way that it additionally achieves next-to-next-to-double-logarithmic (NNDL) accuracy, a first step on the route towards general NNLL. As a proof-of-concept exploration of this question, we consider direct application of multiplicative matrix-element corrections, as well as simple implementations of MC@NLO and POWHEG-style matching. We find that the first two straightforwardly bring NNDL accuracy, and that this can also be achieved with POWHEG, although particular care is needed in the handover between POWHEG and the shower. Our study involves both analytic and numerical components and we also touch on some phenomenological considerations.

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arXiv2023

Parton showering with higher-logarithmic accuracy for soft emissions

The accuracy of parton-shower simulations is often a limiting factor in the interpretation of data from high-energy colliders. We present the first formulation of parton showers with accuracy one order beyond state-of-the-art next-to-leading logarithms, for classes of observable that are dominantly sensitive to low-energy (soft) emissions, specifically non-global observables and subjet multiplicities. This represents a major step towards general next-to-next-to-leading logarithmic accuracy for parton showers.

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arXiv2022

Beyond dimension six in SM Effective Field Theory: a case study in Higgs pair production at NLO QCD

We present the NLO (two-loop) QCD corrections to Higgs boson pair production in gluon fusion within Standard Model Effective Theory (SMEFT), including also squared dimension-6 operators and double insertions of operators. The different options to truncate the EFT expansion are contrasted to a non-linear EFT approach (HEFT) and their effects are illustrated by several phenomenological examples.

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arXiv2021

Soft spin correlations in final-state parton showers

We introduce a simple procedure that resolves the long-standing question of how to account for single-logarithmic spin-correlation effects in parton showers not just in the collinear limit, but also in the soft wide-angle limit, at leading colour. We discuss its implementation in the context of the PanScales family of parton showers, where it complements our earlier treatment of the purely collinear spin correlations. Comparisons to fixed-order matrix elements help validate our approach up to third order in the strong coupling, and an appendix demonstrates the small size of residual subleading-colour effects. To help probe wide-angle soft spin correlation effects, we introduce a new declustering-based non-global spin-sensitive observable, the first of its kind. Our showers provide a reference for its single-logarithmic resummation. The work in this paper represents the last step required for final-state massless showers to satisfy the broad PanScales next-to-leading logarithmic accuracy goals.

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arXiv2021

Anomalous couplings in Higgs-boson pair production at approximate NNLO QCD

We combine NLO predictions with full top-quark mass dependence with approximate NNLO predictions for Higgs-boson pair production in gluon fusion, including the possibility to vary coupling parameters within a non-linear Effective Field Theory framework containing five anomalous couplings for this process. We study the impact of the anomalous couplings on various observables, and present Higgs-pair invariant-mass distributions at seven benchmark points characterising different $m_{hh}$ shape types. We also provide numerical coefficients for the approximate NNLO cross section as a function of the anomalous couplings at $\sqrt{s}=14$ TeV.

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