Collider processes at the highest available partonic center-of-mass energies — 10 TeV and above — exhibit a new regime of electroweak interactions where electroweak gauge bosons mostly act as quasi-massless partons in vector boson fusion processes. We scrutinize these processes using the Equivalent Vector boson Approximation (EVA) based on its implementation in the Monte Carlo generator framework W . Using a variety of important physics processes, including top pairs, Higgs pairs, neutrino pairs, and vector boson pairs, we study the behavior of processes initiated by transverse and longitudinal vector bosons, both $\textit{W}$ and $\textit{Z}$ induced. By considering several distributions for each process, we conclude that: there is no universal, process-independent prescription which minimizes the discrepancies between EVA- and matrix-element-based predictions; even by resorting to process-by-process prescriptions, we typically observe significant observable-dependent effects; the uncertainties associated with parameter dependencies in the EVA can be as large as $$\mathcal{O}(100\%)$$ , and can only possibly be reduced by careful process-dependent kinematical selections.

Sweden

Benjamin Dahlén

Germany

Maximilian Löschner

Poland

Krzysztof Mękała

Jürgen Reuter

Panagiotis Stylianou

EVAluation of the Equivalent Vector boson Approximation at highest energy colliders

Both ATLAS and CMS have recently performed the first searches for a heavy new spin-0 resonance decaying into a lighter new spin-0 resonance and a $\textit{Z}$ boson, where the lighter spin-0 resonance subsequently decays into $$ t\overline{t} $$ pairs. These searches are of particular interest to probe Two Higgs doublet model (2HDM) parameter space regions that predict a strong first-order electroweak phase transition. In the absence of CP violation, the investigated decay is possible if the lighter and the heavier spin-0 particles have opposite CP parities. The analysis techniques employed by ATLAS and CMS do not distinguish between the two possible signatures $\textit{A}$ → $\textit{ZH}$ and $\textit{H}$ → $\textit{ZA}$, where $\textit{A}$ and $\textit{H}$ denote CP-odd and CP-even Higgs bosons, respectively, if both signals are predicted to have the same total cross sections. We demonstrate the capability of angular variables that are sensitive to spin correlations of the top quarks to differentiate between $\textit{A}$ → $\textit{ZH}$ and $\textit{H}$ → $\textit{ZA}$ decays, even in scenarios where both signals possess identical total cross sections. Focusing on masses of 600 GeV and 800 GeV as a representative 2HDM benchmark, we find that a distinction between the two possible channels is possible with high significance with the anticipated data from the high-luminosity LHC, if the invariant mass distribution of the $$ t\overline{t} $$ system is further binned in angular variables defined by the direction of flight of the leptons produced in the top-quark decays. Moreover, we find a moderate gain in experimental sensitivity due to the improved background rejection for both signals.

Francisco Arco

Spain

Thomas Biekötter

Georg Weiglein

Top-quark spin correlations as a tool to distinguish pseudoscalar $\textit{A}$ → $\textit{ZH}$ and scalar $\textit{H}$ → $\textit{ZA}$ signatures in $$ Zt\overline{t} $$ final states at the LHC

In this work, we explore the discovery potential of the Inert Doublet Model (IDM) via the vector boson fusion (VBF) channel at a muon collider with centre-of-mass energy of 10 TeV. The Inert Doublet Model is a two-Higgs-doublet model variant with an unbroken discrete $\textit{ℤ}$ symmetry, featuring new stable scalar particles that can serve as dark matter candidates. Current dark matter data constrain the phenomenologically viable parameter space of the IDM and render certain collider signatures elusive due to tiny couplings. However, VBF-type processes can still exhibit significant enhancements compared to the Standard Model, presenting a promising avenue to probe the IDM at a high-energy muon collider. We consider as our specific target process $$ {\mu}^{+}{\mu}^{-}\to {\nu}_{\mu }{\overline{\nu}}_{\mu } AA\to {\nu}_{\mu }{\overline{\nu}}_{\mu } jj\mathcal{ll} HH $$ , where $\textit{H}$ and $\textit{A}$ are the lightest and second-lightest new scalars and $\textit{ℓ}$ can be electrons or muons. We perform both cut-based and machine-learning improved sensitivity analyses for such a signal, finding a population of promising benchmark scenarios. We additionally investigate the impact of the collider energy by comparing sensitivities to the target process at 3 TeV and 10 TeV. Our results provide a clear motivation for a muon collider design capable of reaching a 10 TeV centre-of-mass energy. We furthermore discuss constraints stemming from new-physics corrections to the Higgs to di-photon decay rate as well as the trilinear Higgs coupling in detail, using state-of-the-art higher-order calculations.

Johannes Braathen

Martin Gabelmann

Croatia

Tania Robens

Probing the Inert Doublet Model via vector-boson fusion at a muon collider

We here report on the progress of the HHH Workshop, that took place in Dubrovnik in July 2023. After the discovery of a particle that complies with the properties of the Higgs boson of the Standard Model, all Standard Model (SM) parameters are in principle determined. However, in order to verify or falsify the model, the full form of the potential has to be determined. This includes the measurement of the triple and quartic scalar couplings.

Morocco

Hamza Abouabid

Abdesslam Arhrib

United States

Hannah Arnold

Duarte Azevedo

Vuko Brigljevic

United Kingdom

Maggie Chen

Daniel Diaz

Javier Duarte

Netherlands

Tristan Pree

Jaouad Falaki

Dinko Ferencek

Portugal

Pedro. Ferreira

France

Benjamin Fuks

India

Japan

Sanmay Ganguly

Osama Karkout

Marina Kolosova

Jacobo Konigsberg

Greg Landsberg

Canada

China

Bingxuan Liu

CERN

Switzerland

Brian Moser

Margarete Mühlleitner

Andreas Papaefstathiou

Roman Pasechnik

Rui Santos

Brian Sheldon

Gregory Soyez

Marko Stamenkovic

Tatjana Susa

Gilberto Tetlalmatzi-Xolocotzi

Giulia Zanderighi

Rui Zhang

HHH whitepaper

Experimental information on the trilinear Higgs boson self-coupling  $$\kappa _3$$  <math> <msub> <mi>κ</mi> <mn>3</mn> </msub> </math>   and the quartic self-coupling  $$\kappa _4$$  <math> <msub> <mi>κ</mi> <mn>4</mn> </msub> </math>   will be crucial for gaining insight into the shape of the Higgs potential and the nature of the electroweak phase transition. While Higgs pair production processes provide access to  $$\kappa _3$$  <math> <msub> <mi>κ</mi> <mn>3</mn> </msub> </math>  , triple Higgs production processes, despite their small cross sections, will provide valuable complementary information on  $$\kappa _3$$  <math> <msub> <mi>κ</mi> <mn>3</mn> </msub> </math>   and first experimental constraints on  $$\kappa _4$$  <math> <msub> <mi>κ</mi> <mn>4</mn> </msub> </math>  . We investigate triple Higgs boson production at the HL-LHC, employing efficient Graph Neural Network methodologies to maximise the statistical yield. We show that it will be possible to establish bounds on the variation of both couplings from the HL-LHC analyses that significantly go beyond the constraints from perturbative unitarity. We also discuss the prospects for the analysis of triple Higgs production at future high-energy lepton colliders operating at the TeV scale.

Constraints on the trilinear and quartic Higgs couplings from triple Higgs production at the LHC and beyond

We discuss axionlike particles (ALPs) within the framework of Higgs effective field theory, targeting instances of close alignment of ALP physics with a custodial singlet character of the Higgs boson. We tension constraints arising from new contributions to Higgs boson decays against limits from high-momentum transfer processes that become under increasing control at the LHC. Going beyond leading-order approximations, we highlight the importance of multitop and multi-Higgs production for the pursuit of searches for physics beyond the Standard Model extensions.

 Anisha

Supratim Das Bakshi

Christoph Englert

Higgs boson footprints of hefty ALPs

Many scenarios of beyond the Standard Model (BSM) physics give rise to new top-philic interactions that can be probed at proton machines such as the Large Hadron Collider through a variety of production and decay modes. On the one hand, this will enable a detailed determination of the BSM model’s parameters when a discovery is made and additional sensitivity in nondominant production modes can be achieved. On the other hand, the naive narrow width approximation in dominant production modes such as gluon fusion might be inadequate for some BSM parameter regions due to interference effects, effectively making less dominant production modes more relevant in such instances. In this work, we consider both these questions in the context of four top quark final states at the LHC. First, we show that the SM potential can be enhanced through the application of targeted graph neural network techniques that exploit data correlations beyond cut-and-count approaches. Second, we show that destructive interference effects that can degrade BSM sensitivity of top-philic states from gluon fusion are largely avoided by turning to four top final states. This achieves considerable exclusion potential, e.g., the two Higgs doublet model. This further motivates four top final states as sensitive tools for BSM discovery in the near future of the LHC.

Oliver Atkinson

Akanksha Bhardwaj

Wrishik Naskar

BSM reach of four-top production at the LHC

We consider the anomalous magnetic moment of the muon <math><msub><mi>a</mi><mi>μ</mi></msub></math>, which shows a significant deviation from the Standard Model expectation given the recent measurements at Fermilab and Brookhaven National Lab (BNL). We focus on Standard Model effective field theory (SMEFT) with the aim to identify avenues for the upcoming LHC runs and future experiments such as MUonE. To this end, we include radiative effects to <math><msub><mi>a</mi><mi>μ</mi></msub></math> in SMEFT to connect the muon anomaly to potentially interesting searches at the LHC, specifically Higgs decays into muon pairs and such decays with resolved photons. Our investigation shows that, similar to results for concrete UV extensions of the Standard Model, the Fermilab/BNL result can indicate strong coupling within the EFT framework and <math><msub><mi>a</mi><mi>μ</mi></msub></math> is increasingly sensitive to a single operator direction for high scale UV completions. In such cases, there is some complementarity between expected future experimental improvements, yet with considerable statistical challenges to match the precision provided by the recent <math><msub><mi>a</mi><mi>μ</mi></msub></math> measurement.

Implications of the muon anomalous magnetic moment for the LHC and MUonE

Constraints on quartic interactions of the Higgs boson with gauge bosons have been obtained by the experimental LHC collaborations focussing on the so-called κ framework of flat rescalings of SM-like interactions in weak boson fusion (WBF) Higgs pair production. While such approaches are admissible to obtain a qualitative picture of consistency with the SM when the statistical yield is low, once more statistics become available a more theoretically consistent framework of limit setting is desirable. Reviewing the constraints provided at the Large Hadron Collider, we first show that these limits are robust when considered in a leading order context. Turning to radiative corrections, we demonstrate the limitations of this approach in the SM, and by adopting Higgs effective field theory techniques, we clarify the sensitivity from single Higgs measurements to rescalings of quartic Higgs-gauge couplings. We then discuss avenues for sensitivity improvements of WBF analyses employing Graph Neural Networks to combat the large contributing backgrounds.

Quartic Gauge-Higgs couplings: constraints and future directions

We explore the potential of Graph Neural Networks (GNNs) to improve the performance of high-dimensional effective field theory parameter fits to collider data beyond traditional rectangular cut-based differential distribution analyses. In this study, we focus on a SMEFT analysis of pp →   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  production, including top decays, where the linear effective field deformation is parametrised by thirteen independent Wilson coefficients. The application of GNNs allows us to condense the multidimensional phase space information available for the discrimination of BSM effects from the SM expectation by considering all available final state correlations directly. The number of contributing new physics couplings very quickly leads to statistical limitations when the GNN output is directly employed as an EFT discrimination tool. However, a selection based on minimising the SM contribution enhances the fit’s sensitivity when reflected as a (non-rectangular) selection on the inclusive data samples that are typically employed when looking for non-resonant deviations from the SM by means of differential distributions.

Stephen Brown

David Miller

Improved constraints on effective top quark interactions using edge convolution networks