arXiv subjects

Hua-Sheng Shao

Publications and source records attributed to Hua-Sheng Shao.

At least 19 recordsLinked to original sources

arXiv2026

Complete electroweak corrections to diphoton production via gluon fusion at the LHC

We present a complete calculation of the next-to-leading order (NLO) electroweak corrections to the loop-induced gluon-fusion process $gg\toγγ$ at the LHC, including the full third-generation quark and the Higgs boson contributions for the first time. To efficiently evaluate the large number of multi-scale two-loop Feynman integrals, we employ a numerical approach based on differential equations with an optimized basis. Our results show that, although the NLO electroweak corrections to the phase-space-integrated cross section remain at the sub-percent level, they can reach about $-10\%$ in the tails of the diphoton invariant-mass and photon transverse-momentum distributions. Moreover, the diphoton invariant-mass distribution exhibits rich and intriguing structures, including a dip-bump structure in the Higgs-threshold region and a mild enhancement near the top-quark pair threshold. These features make the electroweak corrections indispensable for future precision studies of diphoton production at the LHC.

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arXiv2026

Bound-state production in MadGraph5_aMC@NLO

I present the first implementation in MadGraph5_aMC@NLO for bound-state production, including quarkonium, leptonium, and B(c) mesons within Non-Relativistic Quantum Chromo-Dynamics (NRQCD) and Non-Relativistic Quantum Electro-Dynamics (NRQED). In these proceedings, I focus on the extension of MadGraph5_aMC@NLO to quarkonium states and describe the capabilities of the new framework for inclusive and associated S-wave quarkonium production in a wide variety of experimental environments at Leading Order (LO). These developments provide the community with a unified, automated, and efficient framework for bound-state production in QED and QCD, and establish a solid foundation for our future Next-to-Leading-Order (NLO) extension.

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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

Automated NRQCD and NRQED simulations of quarkonium and leptonium production with P-wave states and physical-mass effects

We present the $\texttt{MadSONS}$ module, which extends the $\texttt{MadGraph5_aMC@NLO}$ framework by providing a fully automated solution for the simulation of arbitrary tree-level production processes involving non-relativistic bound states. More specifically, we focus on the production of quarkonia and leptonia in non-relativistic QCD and QED, respectively. This work constitutes the next step in the programme initiated in arXiv:2510.26773, where the colour and spin projectors required for S-wave states were first incorporated into $\texttt{MadGraph5_aMC@NLO}$. In the present development, we implement the remaining projectors associated with orbital and total angular momentum, thereby enabling the event generation of processes involving P-wave states. The derivatives required for the orbital-angular-momentum projection are evaluated using dual numbers. In addition, we implement a momentum-reshuffling procedure that accounts for physical bound-state mass effects in the phase space. The resulting framework applies to a wide range of collider environments while remaining compatible with standard multi-purpose Monte Carlo event generators for parton showering and hadronisation. As a first phenomenological application, we revisit $J/ψ+ ψ(2{\rm S})$ production at the LHC and obtain an improved description of the LHCb data.

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arXiv2026

Soft Contributions Stabilize NNLO QCD Corrections to Quarkonium Production and Decay

Next-to-next-to-leading order (NNLO) QCD corrections to quarkonium production and decay are known to exhibit perturbative instabilities within non-relativistic QCD. We identify the origin of this problem and propose a simple remedy. Applying our approach to $S$-wave color-singlet quarkonium processes, we achieve substantially improved perturbative convergence and agreement with experimental data.

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arXiv2026

Fully differential Higgs boson pair production at N$^3$LO with top quark mass effects

Higgs-boson pair production is of fundamental importance for probing the Higgs potential. At hadron colliders, the dominant production channel proceeds via gluon-gluon fusion (ggF) mediated by a top-quark loop. We report the first fully differential predictions for Higgs-boson pair production through ggF at next-to-next-to-next-to-leading order (N$^3$LO) in the strong coupling $α_s$ in the heavy-top-quark limit (HTL). Fiducial cross section and selected differential distributions are presented at a center-of-mass energy of $\sqrt{s}$ = 14 TeV, under realistic experimental selection cuts. The N$^3$LO QCD corrections reduce the scale uncertainties of the next-to-next-to-leading order fiducial and differential predictions by approximately a factor of three, bringing the theoretical uncertainty to the percent level in the HTL. After incorporating top-quark-mass effects at next-to-leading order in $α_s$, we provide one of the most precise parton-level differential predictions to date for ongoing experimental searches for Higgs-boson pair production at the LHC.

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arXiv2026

Prospects for discovering strongly decaying doubly heavy $T_{bc}$ tetraquark states at LHCb

We investigate the discovery potential of the $T_{bc}$ state with $J^P = 0^+$ in proton-proton ($pp$) collisions at LHCb at a center-of-mass energy of $\sqrt{s} = 13~\mathrm{TeV}$. The study focuses on the decay channel $T_{bc} \to B^- D^+$. A phenomenological approach is employed to construct the background model based on the associated production of $B$ and $D$ mesons, incorporating previously published LHCb results. Background processes are simulated using $\texttt{MadGraph5\_aMC@NLO}$ and $\texttt{Pythia8.3}$. We explore the parameter space of the $T_{bc}$ mass, width, production cross section, and the effective double-parton scattering cross section ($σ_{\mathrm{eff}}$) relevant for the $B D$ meson background. The integrated luminosity required for a $5σ$ discovery at LHCb is evaluated under various assumptions. In particular, we consider three representative $T_{bc}$ production cross section scenarios: an optimistic estimate of $103~\mathrm{nb}$, an intermediate value of $18~\mathrm{nb}$ obtained by scaling from the $T_{cc}^+$ production cross section, and a conservative lower bound of $0.3~\mathrm{nb}$. We find that a $5σ$ observation is achievable for a production cross section of $103~\mathrm{nb}$, which is expected to be within reach during Run~4. In contrast, the more realistic cross section estimate of $18~\mathrm{nb}$ requires the full Run~5 dataset ($300~\mathrm{fb}^{-1}$) under the most favorable parameter choices. For the conservative scenario, no significant signal would be observable even with $300~\mathrm{fb}^{-1}$. In addition, we estimate the minimum observable $σ(T_{bc}) \times BR(T_{bc} \to B^- D^+)$ for a $5σ$ discovery under different luminosity scenarios, providing guidance for future experimental searches at LHCb.

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arXiv2026

Light-by-light scattering: asymptotic expansions, Coulomb resummation and NLO corrections

Light-by-light (LbL) scattering is one of the earliest predictions of quantum electrodynamics (QED). Interest in this process has been renewed following its experimental observation at the LHC and the prospects of future measurements at free-electron laser facilities. In this paper, we refine theoretical predictions for LbL scattering by improving the full fermion-mass-dependent two-loop QCD and QED helicity amplitudes using high- and low-energy asymptotic expansions, and by performing Coulomb resummation in the threshold region. We present state-of-the-art predictions for LbL cross sections in the Standard Model and provide a new event generator, LbLatNLO, for Monte Carlo simulations of LbL scattering.

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arXiv2026

NNLO QCD corrections to $γγ\rightarrow Q\bar{Q}$ from Local Unitarity combined with Coulomb resummation and NLO EW effects

The Local Unitarity (LU) formalism provides a constructive, integrand-level realisation of the Kinoshita-Lee-Nauenberg (KLN) theorem, by combining loop and phase-space integrals appearing in scattering cross-sections in such a way that their final-state infrared singularities cancel before integration. Supplemented with localised ultraviolet renormalisation, it enables the direct Monte Carlo integration of cross sections at arbitrary perturbative order in four-dimensional spacetime. In this paper, we present its application to the next-to-next-to-leading order (NNLO) QCD total cross sections for heavy-quark pair production in direct photon fusion, involving the contribution from 138 distinct forward-scattering diagrams where external photons couple only to heavy quarks. By combining NNLO QCD with next-to-leading order (NLO) electroweak (EW) corrections and next-to-leading power (NLP) Coulomb resummation, we obtain state-of-the-art predictions for top-, bottom-, and charm-quark production in ultraperipheral hadron collisions and at $e^+ e^-$ colliders.

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arXiv2026

Automated event generation for S-wave quarkonium and leptonium production in NRQCD and NRQED

We present an extension of the MadGraph5_aMC@NLO framework that enables the automated calculation of leading-order cross sections for S-wave quarkonium and leptonium production within the non-relativistic QCD (NRQCD) and non-relativistic QED (NRQED) factorisation formalisms. The framework has been validated against a variety of benchmark processes, demonstrating robustness and flexibility for phenomenological studies. A key advantage of this implementation is its seamless integration with existing MadGraph5_aMC@NLO features, allowing computations not only within the Standard Model but also in a wide range of Beyond the Standard Model or Effective Field Theory scenarios via a modified Universal Feynman Output (UFO) interface. Furthermore, the framework maintains compatibility with standard Monte Carlo event generators for parton showering and hadronisation. Through numerous examples, we highlight that theoretical studies of quarkonium processes require careful consideration: the impact of subleading contributions is often difficult to predict using simple counting arguments based solely on the hierarchy of couplings and velocity-scaling rules.

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arXiv2025

Analytic NNLO transverse-momentum-dependent soft function for heavy quark pair hadroproduction at threshold

The transverse-momentum-dependent (TMD) soft function for non-relativistic heavy quark pair production at hadron colliders is analytically computed at next-to-next-to-leading order (NNLO) in the strong coupling expansion. We present the details of our computational approach and analyze the general two-loop structure of the soft function. The final result, which takes a particularly simple form, provides the last missing ingredient for a complete NNLO calculation of color-octet $S$-wave quarkonium hadroproduction--including charmonium, bottomonium, and toponium--using the $q_T$-slicing formalism. It also enables next-to-next-to-next-to-leading-logarithmic (N$^3$LL) resummation at small transverse momentum for the same process.

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arXiv2025

Progress in NLO Calculations for gamma-gamma Physics

With the advent of precision measurements of photon-fusion processes in ultraperipheral collisions (UPCs) at facilities, such as RHIC and the LHC, the inclusion of higher-order corrections has become essential. While automated frameworks already make NLO corrections feasible for parton-parton scattering processes, no comparable tools had previously been available for UPC processes in two-photon collisions. In these proceedings, we review some recent explicit NLO computations and present the updated gamma-UPC+MadGraph5_aMC@NLO framework, the first automated software that enables NLO-accurate predictions for photon-photon processes in UPCs.

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arXiv2025

One-loop transverse-momentum-dependent soft function at higher orders in the dimensional regulator

The transverse-momentum-dependent (TMD) soft function for a generic hadroproduction process involving massive colored particles is analytically calculated at the one-loop level, extended to higher orders in the dimensional regulator $ε$. We present both the azimuthal-angle-averaged and azimuthal-angle-dependent soft functions in impact-parameter space, making them suitable for small $q_T$ resummation calculations. Their analytic expressions are provided in terms of multiple polylogarithms. Our results offer essential ingredients for a complete higher-order perturbative calculation of the TMD soft function.

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arXiv2025

Automated next-to-leading order QCD and electroweak predictions of photon-photon processes in ultraperipheral collisions

We present automated next-to-leading order QCD and/or electroweak (EW) predictions for photon-photon processes in ultraperipheral high-energy collisions of protons and ions, extending the capabilities of the MadGraph5_aMC@NLO framework together in combination with the gamma-UPC code. Key aspects of this extension are discussed. We compute QCD and/or EW quantum corrections for several phenomenologically interesting processes at LHC and FCC-hh energies.

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arXiv2025

Dimuon and ditau production in photon-photon collisions at next-to-leading order in QED

Next-to-leading-order (NLO) quantum electrodynamics (QED) corrections to the production of muon and tau pairs in photon-photon collisions, $γγ\toμ^{+}μ^{-},τ^{+}τ^{-}$, are calculated in the equivalent photon approximation. We mostly consider $γγ$ processes in ultraperipheral collisions of hadrons at the LHC, but the $γγ\toτ^{+}τ^{-}$ process in $\mathrm{e}^+\mathrm{e}^-$ collisions at LEP is also discussed. The NLO terms are found to modify the total fiducial cross sections by up to 5%, increasing the tails of the dilepton acoplanarity and transverse momentum distributions, and depleting by up to 15% the yields at high masses, with respect to the leading-order predictions including the very small virtuality of the colliding photons. At the LHC, the calculations obtained with the charge form factor for protons and lead ions including the NLO QED corrections improve the data--theory agreement for all measured differential distributions, and prove an indispensable ingredient for the extraction of precision quantities in photon-photon processes, such as the anomalous magnetic moment of the tau lepton.

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arXiv2025

Automation of Electroweak Corrections

This dissertation addresses a topic that I have worked on over the past decade: the automation of next-to-leading order electroweak corrections in the Standard Model of particle physics. After introducing the basic concepts and techniques of next-to-leading order QCD calculations that underpin the MadGraph5_aMC@NLO framework, I present a few key features relevant to the automated next-to-leading order electroweak contributions to short-distance cross sections, with an emphasis on the mixed QCD and electroweak coupling expansions. These include the FKS subtraction, the renormalization and electroweak input parameter schemes, and the complex mass scheme for dealing with unstable particles. Issues related to the initial or final photons and leptons are also discussed. Two remaining challenges are highlighted if one wishes to go beyond next-to-leading order computations. Some phenomenological applications at the LHC are given to demonstrate the relevance of electroweak corrections at colliders. Finally, an outlook on future studies concludes the dissertation.

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arXiv2024

Improved modeling of $γγ$ processes in ultraperipheral collisions at hadron colliders

The CERN LHC is not only the current energy-frontier collider for parton-parton collisions, but has proven a powerful photon collider providing photon-photon ($γγ$) collisions at center-of-mass energies and luminosities never reached before. The latest theoretical developments implemented in the gamma-UPC Monte Carlo (MC) event generator, which can calculate arbitrary exclusive final state produced via $γγ$ fusion in ultraperipheral collisions (UPCs) of protons and/or nuclei at the LHC, are presented. These include azimuthal modulations of dilepton pairs produced in the $γγ\to\ell^+\ell^-$ process, and neutron emission probabilities for photoexcited lead ions in PbPb UPCs. A few comparisons of the results of the updated gamma-UPC v.1.6 code to relevant RHIC and LHC data are presented.

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arXiv2024

FKS subtraction for quarkonium production at NLO

We extend the local infrared-divergence subtraction formalism, originally proposed by Frixione, Kunszt and Signer (FKS), to calculate short-distance (differential) cross section for any inclusive process involving a quarkonium particle in non-relativistic QCD (NRQCD) factorisation at next-to-leading order (NLO) accuracy in the strong coupling constant $α_s$. The new formulas are generally applicable to the production of an S- or P-wave quarkonium state in association with any number of elementary particles. The main new ingredients derived in this paper are the local and integrated soft counterterms for the colour-singlet and colour-octet P-wave bound states. It, therefore, paves the way to the automation of the NLO calculations for heavy quarkonium inclusive and associated production processes.

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