19th International Workshop on Top Quark Physics (TOP2026)

5 Oct 2026, 08:30 → 9 Oct 2026, 14:00 Europe/Istanbul

Antalya, Türkiye 🇹🇷

Didar Dobur (Ghent University (BE))

The 19th International Workshop on Top Quark Physics (TOP2026) will be held from October 5 to 9, 2026 at the Belconti Hotel, Belek, in the Antalya Region of Türkiye.

TOP2026 brings together experimentalists and theorists to present and discuss the latest developments in top quark physics. This year's meeting is hosted by Ghent University (Belgium).

Recent editions of the TOP Workshop:

• TOP2025 (Korea)
• TOP2024 (France)
• TOP2023 (USA)

 

 

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Monday 5 October

Introductions + Keynote

1 Welcome

Speaker: Didar Dobur (Ghent University (BE))

2 Keynote presentation

Speakers: Uli Haisch, Ulrich Andreas Haisch (University of Oxford (GB))

3 Measurement of the top-quark production and charge asymmetry at LHCb

Speaker: Hang Yin (Central China Normal University CCNU (CN))

10:00 Coffee Break

Objects and Tools

4 Jet calibrations and flavor tagging (CMS)

Speaker: Francesco Romeo (Vanderbilt University)

5 Jet calibrations and flavor tagging (ATLAS)

Speaker: Carlo Schiavi (INFN e Universita Genova (IT))

6 How to unfold top decays

Speaker: Luigi Favaro (Universite Catholique de Louvain (UCL) (BE))

7 ML usage in statistical interpretation (ATLAS/CMS)

Speaker: Andrew Wildridge (Purdue University (US))

12:30 Lunch + Free time

Cross sections

8 tt measurements (ATLAS/CMS)

Speaker: Luca Martinelli (INFN Sezione di Roma (IT))

9 Single top measurements (ATLAS/CMS)

Speaker: Nils Faltermann (Karlsruher Institut für Technologie (DE))

10 3/4top measurements (CMS)

Speaker: Joscha Ahäuser (Karlsruher Institut für Technologie (DE))

17:00 Coffee Break

Cross sections: Associated Production

11 W/Z/gamma-associated measurements (ATLAS/CMS)

Speaker: Ethan Lewis Simpson (The University of Manchester (GB))

12 tt+bb/cc/light measurements (ATLAS/CMS)

Speaker: David Kavtaradze (Ghent University (BE))

13 Higgs-associated measurements (ATLAS/CMS)

Speaker: Ian Brock (University of Bonn (DE))

14 Evening lecture

Speaker: Ken Mimasu (University of Southampton)

Tuesday 6 October

ttbar Predictions and Generators

15 Modern MC generators (ATLAS/CMS)

Speaker: Teresa Barillari (Max Planck Society (DE))

16 Quantum observables in top physics

Speaker: Kun Cheng (University of Pittsburgh)

17 Towards NNLO QCD predictions for off-shell tt production and decays

Speaker: Luca Buonocore (CERN)

10:00 Coffee Break

Threshold production

18 Toponium with pNRQCD

Speaker: Benedikt Gurdon (RWTH Aachen)

19 Theshold/Toponium measurements (ATLAS)

Speaker: Annika Stein (Johannes Gutenberg Universitaet Mainz (DE))

20 Theshold/Toponium measurements (CMS)

Speaker: Beatriz Ribeiro Lopes (Ghent University (BE))

12:00 Lunch + Free time

Objects and Tools: ML/SBI

21 Proton Structure from Neural Simulation-Based Inference

Speaker: Elie Hammou (Nikhef National institute for subatomic physics (NL))

22 Simulation-based inference

Speaker: Ricardo Barrué (Marietta Blau Institute for Particle Physics)

Young Scientist Forum

23 Are quantum observables sensitive to CP-violation in $t\bar{t}$ pairs?

Within the framework currently adopted for the description of the fundamental interactions, the particles involved in high-energy collisions are expected to exhibit a basic quantum behaviour.
As a consequence of this statement, a novel class of "quantum" observables for collider studies naturally arises, whose physical interpretation is rooted in the characteristics of the underlying quantum states.

We present a study on the sensitivity of quantum observables to new sources of CP-violation in top-antitop pairs ($t\bar{t}$), taking into account different production mechanisms. We also investigate how the same additional sources would affect the quantum tomography protocol adopted for the reconstruction of quantum states in collider environments. The ability to discriminate the stage where new physics would modify the current theoretical predictions is also discussed.

Speaker: Olimpia Miniati

24 Top quark mass interpretation from simulation of top-flavoured mesons

The interpretation of the top quark mass measurements in terms of well-known field theory definitions has been the topic of a long-standing discussion. In this work we reconsider this issue and simulate fictitious top-flavoured mesons, whose mass can be related to any top mass definition, such as the pole mass, by means of Heavy Quark Effective Theory. We explore final-state observables for top-pair production in $e^{+}e^{-}$ and hadron collisions, and relate the top mass in standard $t\bar{t}$ events to the pole mass extracted from top-meson samples simulated with Pythia 8.3. Our results are in agreement with the expectation of an uncertainty about $200$-$300$ MeV, hence of the order of $\Lambda_{\rm QCD}$.

Speaker: Alexander Lind (INFN Laboratori Nazionali di Frascati (LNF))

25 Big Dipper, Help Me Find A Way -- Dip-hunting at hadron colliders

Machine-learning (ML) methods are increasingly important in collider searches, particularly in scenarios where conventional analysis strategies lose sensitivity. For instance, in searches for heavy top-philic scalar resonances, destructive interference between signal and Standard Model (SM) contributions can strongly distort the invariant-mass spectra and suppress the performance of traditional bump-hunting approaches. In these regimes, the resonance signature can manifest as a local peak-dip structure rather than an excess, complicating both discovery and interpretation.

In this work, we introduce dip-hunting, a ML-based framework designed to identify interference-dominated signatures [1]. As a proof-of-principle case study, we use a simplified CP-even scalar extension of the SM in the $gg\rightarrow S\rightarrow t\bar{t}$ channel. We formulate the problem as parameterised likelihood-ratio inference conditioned on event observables and theory parameters. To account for the quasi-probabilistic nature of the likelihood-ratio produced when including samples containing negative event weights, we employ the Ratio of Signed Mixtures Model (RoSMM) [2] together with parametric neural networks to learn mappings between SM and beyond-SM hypotheses across the parameter space.

Using parton-level $t\bar{t}$ observables, we demonstrate accurate extraction of resonance mass, and coupling parameters, including interpolation to unseen benchmark points and simultaneous multi-parameter inference. We study robustness beyond the nominal model assumptions and show sensitivity to moderate variations of resonance-width correlations not explicitly included during training.

These results establish dip-hunting as a complementary analysis paradigm for interference-dominated new physics searches and motivate future extensions toward detector-level studies and experimental deployment.

[1] Diego A. Baron Moreno, Christoph Englert, Yvonne Peters, Big Dipper, Help Me Find A Way -- Dip-hunting at hadron colliders, submitted to JEHP. [arXiv:2604.25407],
[2] M. Drnevich, S. Jiggins, J. Katzy, and K. Cranmer, Neural quasiprobabilistic likelihood ratio estimation with negatively weighted data, Mach. Learn. Sci. Tech. 6 (2025), no. 4 045023, [arXiv:2410.10216].

Speaker: Diego Baron (The University of Manchester (GB))

26 Toponium effects on quantum steering and Bell nonlocality of top quarks

Recent LHC measurements near the $t\bar{t}$ production threshold show a cross-section enhancement consistent with a toponium bound state. This work provides the first comprehensive assessment of how toponium affects advanced quantum correlations, specifically quantum steering and Bell nonlocality, in this kinematic region.

We model the continuum background ($pp \to b\bar{b}W^+W^-$) alongside a pseudoscalar toponium resonance ($\eta_t$) in the beamline basis. Following detector simulation of the dilepton decay channel, the $t\bar{t}$ system is reconstructed via $\chi^2$ minimization, and detector effects are mitigated using iterative D'Agostini unfolding. Toponium acts as a pure spin-singlet state, substantially strengthening the pair's spin-singlet component even at non-zero velocities. By targeting the threshold region with specific kinematic cuts (invariant mass $m_{t\bar{t}} \le 370$–$380$ GeV, lab velocity $\beta \le 0.9$), we evaluate steering and CHSH nonlocality witnesses and find:

• Quantum Steering: This correlation is highly accessible with current
  LHC data, reaching a statistical significance around 10σ.

• Bell Nonlocality: Violations become statistically significant (up to $\sim$9σ) under tighter mass cuts ($m_{t\bar{t}} \le 360$ GeV) when toponium is included. However, the feasibility of this measurement depends crucially on the control of systematic uncertainties, as our simulation primarily accounts for bin-migration effects.

Including these non-relativistic bound-state effects is vital for accurately interpreting future quantum information measurements at colliders.

This presentation is based on the recent work available at arXiv:2606.30768 [hep-ph].

Speaker: Sergio Rodríguez Benítez (Instituto de Física Teórica IFT-UAM/CSIC)

27 Recent updates on modelling of top-antitop production

Speaker: Nihad Hidic (Charles University (CZ))

16:30 Coffee Break + Posters

Young Scientist Forum

28 Modelling of $b$-jets in the $pp \to t\bar{t}b\bar{b}$ process in the $2\ell$ channel at the LHC

I present full off-shell predictions of the production of a top quark pair in association with flavoured jets in the $2\ell$ decay channel at the LHC. Thereby reporting results of the NLO QCD computation for the $pp\to e^+ \nu_e \, \mu^- \bar{\nu}_\mu + nb +X$ process, where $n=3,4$. This calculation includes all resonant and non-resonant diagrams as well as interferences and finite width effects of the top quark and $W$ boson. For the calculation with $n=4$ we compare our predictions in the 5- and 4-flavour schemes. The  calculation for $n=3$ is only provided in the 4FS. The modelling of the $b$-jets in these phase-space regions is studied in detail. These predictions are relevant for the $pp\to t\bar{t}H(H\to b\bar{b})$ process, for which the QCD $pp \to t\bar{t}b\bar{b}$  process is an important irreducible background.

Speaker: Manal Alsairafi

29 Quantum Observables and Their Sensitivity to Fundamental Interactions at Polarized Lepton Colliders

High-energy colliders probe fundamental interactions through direct searches and precision measurements. In the absence of direct signals for new physics, it is important to identify complementary observables that can enhance sensitivity to different underlying dynamics. Conventional observables such as total cross sections and asymmetries have been widely used for indirect searches, but they do not fully exploit the intrinsically quantum nature of multi-particle final states.

In this talk, I will discuss a density-matrix-based framework for defining and reconstructing quantum observables in collider experiments, with emphasis on spin density matrices and their measurable components. Different interaction structures, including scalar, vector, and tensor mediators, populate distinct entries of the density matrix, motivating the use of multiple observables. I will highlight quantum-information-theoretic quantities such as entanglement, Bell inequality violation, purity, and magic, and explain how they probe different features of scattering amplitudes.

As an example, I will focus on top-antitop production at future lepton colliders, presenting analytic results for the spin density matrix and showing how beam polarization can improve sensitivity to specific operator structures. These results demonstrate that quantum observables, combined with polarized beams, provide a systematic and complementary approach to probing new physics at colliders.

Speaker: Priyanka Lamba

30 Four-top-quark production at the LHC: NLO+NNLL predictions and uncertainties

The production of four top quarks is one of the rarest Standard Model processes accessible at the LHC, where it was observed in 2023. Studying this process offers valuable insights into the top-quark Yukawa coupling and may reveal new physics. Thus, comparing theoretical predictions with current and future measurements is a crucial test for the Standard Model.
I will present state-of-the-art predictions for four top-quark production, obtained at NNLL accuracy within the invariant-mass threshold resummation framework, and matched to the complete NLO. I will also discuss a detailed assessment of all the uncertainties entering the calculation. Results will be shown for both the total cross section and the invariant-mass distribution.

Speaker: Michele Lupattelli (Muenster University)

31 AI-enhanced Tops: Machine learning tasks, and their interplay, for advancing top quark measurements

Precision measurements in top-quark physics require accurate kinematic reconstruction, definition of interesting observables, and performant signal-to-background separation. This talk will introduce a supervised learning method for generic event reconstruction, highlighting its application to top-quark physics specifically in channels with multiple neutrinos. The approach will be contrasted with physics-inspired generative regression methods for specific top measurements, including quantum tomography. Additionally, we will explore model applicability in Beyond Standard Model (BSM) scenarios, Monte Carlo generator dependencies, as well as the role of reconstruction as an auxiliary task in signal-background discrimination.

Speaker: Ethan Lewis Simpson (The University of Manchester (GB))

32 Precise and Comprehensive Top Quark Reconstruction at the LHC

Precision measurements at LHC and HL-LHC require reconstruction of the full event kinematics to derive the observables of interest, a task complicated by two distinct source of ambiguity: the kinematics of neutrinos, which escape the detector undetected, and parton origin of the observed final states. We present VyPER, a Graph Neural Network that provides comprehensive event reconstruction with generative graph diffusion and hypergraph representation learning. It is designed to simultaneously reconstruct neutrino kinematics and identify the partonic origin of the final states, offering a unified alternative to traditional multi-step reconstruction pipelines. We present performance studies comparing VyPER against existing state-of-the-art approaches across a range of physics processes, and discuss its prospective role in precision top-quark and electroweak measurements at ATLAS and CMS.

Speaker: Zihan Zhang (The University of Manchester (GB))

33 Measurement of ttW production cross section at 13.6 TeV

Speaker: Miguel Obeso Menendez (Universidad de Oviedo (ES))

34 Measurements of single top t-channel production

Speaker: Jorge Ayllon Torresano (Universidad de Oviedo (ES))

35 Measurement of the CKM matrix element |V_cb|

Speaker: Emily Tsai (Northeastern University (US))

36 Search for Top-Philic Vector Resonances in Multi-Top Final States with ATLAS

Speaker: Zongpu Wang (University of Hong Kong (HK))

37 Search for charged lepton flavour violation in ATLAS using top events

Speaker: Thomas Thory-Rao (University of Birmingham (GB))

Poster Session

38 Toponium effects on quantum steering and Bell nonlocality of top quarks

Recent LHC measurements near the $t\bar{t}$ production threshold show a cross-section enhancement consistent with a toponium bound state. This work provides the first comprehensive assessment of how toponium affects advanced quantum correlations, specifically quantum steering and Bell nonlocality, in this kinematic region.

We model the continuum background ($pp \to b\bar{b}W^+W^-$) alongside a pseudoscalar toponium resonance ($\eta_t$) in the beamline basis. Following detector simulation of the dilepton decay channel, the $t\bar{t}$ system is reconstructed via $\chi^2$ minimization, and detector effects are mitigated using iterative D'Agostini unfolding. Toponium acts as a pure spin-singlet state, substantially strengthening the pair's spin-singlet component even at non-zero velocities. By targeting the threshold region with specific kinematic cuts (invariant mass $m_{t\bar{t}} \le 370$–$380$ GeV, lab velocity $\beta \le 0.9$), we evaluate steering and CHSH nonlocality witnesses and find:

• Quantum Steering: This correlation is highly accessible with current
  LHC data, reaching a statistical significance around 10σ.

• Bell Nonlocality: Violations become statistically significant (up to $\sim$9σ) under tighter mass cuts ($m_{t\bar{t}} \le 360$ GeV) when toponium is included. However, the feasibility of this measurement depends crucially on the control of systematic uncertainties, as our simulation primarily accounts for bin-migration effects.

Including these non-relativistic bound-state effects is vital for accurately interpreting future quantum information measurements at colliders.

This presentation is based on the recent work available at arXiv:2606.30768 [hep-ph].

Speaker: Sergio Rodríguez Benítez (Instituto de Física Teórica IFT-UAM/CSIC)

39 Top Quark Pair Production and Decay: The 1-Higgs-Singlet Model and Pseudoscalar Decay

The process of top quark pair production through the decay of the scalars in the 1 Higgs Singlet extension of the Standard Model is associated with large interference effects between the loop-induced 'SM-like' Higgs and heavy Higgs amplitudes, and the QCD continuum background. We attach leptonic decays to the di-top final state at NLO and study the effects of spin correlation in the process. We also make phenomenological predictions for the leptonic decays of the top quark pair produced by the decaying of a CP-odd pseudoscalar at the LHC at NLO accuracy, with the full spin correlation effects preserved in the decayed products. We attach Parton Showers and perform analyses of differential cross sections as functions of various parameters to study the significance of the results in searches for new scalars and pseudoscalars beyond the Standard Model.

Speaker: Vishakha Lingadahally

40 An Optimal Observable Machine for reinterpretable measurements in top quark physics

Precision measurements in top quark physics increasingly rely on machine-learning techniques, yet their outputs are often difficult to publish in a form that enables future reinterpretation. We present the Optimal Observable Machine (OOM), a machine-learning framework that constructs unfoldable generator-level observables optimized for the extraction of a parameter of interest. The training incorporates detector response, systematic uncertainties, and the unfolding procedure through a likelihood-based loss function, directly optimizing the expected measurement precision while reducing dependence on assumptions about the parameter itself. As a demonstration, the method is applied to the study of a pseudoscalar excess near the top quark pair production threshold. The resulting observable significantly enhances sensitivity compared to conventional approaches while retaining the long-term reinterpretability of a published differential measurement. This framework provides a general strategy for designing precision measurements that combine the performance of modern machine learning with the robustness and reusability required for future physics interpretations.

Speaker: Torben Mohr (Ghent University (BE))

41 Simultaneous measurement of tqγ and ttγ cross section

Speaker: Iakov Andreev (Deutsches Elektronen-Synchrotron (DE))

42 Search for the Charged Lepton Flavour Violation in the top quark interaction with a lepton (muon or electron) and a tau

Speaker: Yeonsu Ryou (Hanyang University (KR))

43 Search for heavy resonances decaying to top-quark pairs in single-lepton and dilepton channels with the full Run-2 ATLAS dataset

Speaker: Laura Pintucci (Universita degli Studi di Udine (IT))

44 Studies of recoil variations in ttbar events

Speakers: Matilde Uboldi (University of Sussex (GB)), Matilde Uboldi (Università degli Studi e INFN Milano (IT))

45 Studies of the MiNNLOPS ttbar process by ATLAS

Speakers: Shayma Wahdan, Shayma Wahdan (Bergische Universitaet Wuppertal (DE))

Wednesday 7 October

BSM: EFT

46 EFT interpretations (CMS)

Speaker: Niels Van den Bossche (MBI - Austrian Academy of Sciences (AT))

47 EFT interpretations (ATLAS)

Speaker: Lidia Dell'Asta (Università degli Studi e INFN Milano (IT))

48 ttH in the SMEFT framework

Speaker: Giuseppe Bevilacqua (Istituto Nazionale Fisica Nucleare (IT))

49 Loop-level sensitivities to four-quark operators

Speaker: Stefano Di Noi (KIT (ITP))

10:30 Coffee Break

BSM: Searches

50 FCNC+rare interpretations (CMS)

Speaker: Reza Goldouzian (University of Notre Dame (US))

51 Searches for rare processes (ATLAS)

Speaker: Farida Fassi (Universite Mohammed V (MA))

52 Multi-top signals of vectorlike quarks

Speaker: Bogdan Dobrescu

12:30 Lunch

53 Excursion

Thursday 8 October

Theory mini-workshop: CPV and Baryogenesis

54 Recent developments in Baryogenesis

Speaker: Oleksii Matsedonskyi (University of Cambridge)

55 A deepdive into Baryon Assymetry

Speakers: Rui Santos (University of Southampton and NExT Institute), Rui Santos (ISEL and CFTC-UL)

10:00 Coffee Break

Theory mini-workshop: CPV and Baryogenesis

56 CPV in top and EW Baryogenesis

Speaker: Dorival Gonçalves (Oklahoma State University)

57 CPV in top-Higgs coupling

Speaker: Dr Adil Jueid (Institute for Basic Science)

For the future

58 Resonance-aware PS matching for off-shell tt in e+e-

Speakers: Daniele Lombardi (Max-Planck Institut für Physik), Daniele Lombardi

12:00 Lunch + Free time

Properties / Rare processes

59 Top mass (ATLAS)

Speaker: Wolfgang Wagner (Bergische Universitaet Wuppertal (DE))

60 Rare SM measurements (ATLAS)

Speaker: James Alfred Mueller (University of Pittsburgh (US))

61 Flavor measurements (CMS)

Speaker: Luigi Marchese (ETH Zurich (CH))

16:30 Coffee Break

Joker talks

62 CMS Joker 1

Speaker: Osama Ragab Ahmed Dawood (Purdue University (US))

63 ATLAS Joker 1

Speaker: Lukas Kretschmann (Bergische Universitaet Wuppertal (DE))

64 ATLAS Joker 2

Speaker: Thomas James Stevenson (University of Sussex (GB))

65 CMS Joker 2

66 Q&A session with drinks

Friday 9 October

Threshold production

67 Top-quark spin entanglement and decoherence

Speaker: Dr Maria Moreno Llacer (Univ. of Valencia and CSIC (ES))

Summary

68 Theory summary

Speaker: Michelangelo Mangano (CERN)

For the future

69 Probing Top Quark - Electron Interactions at Future Colliders

Speaker: Luigi Bellafronte (Florida State University)

10:15 Coffee Break

70 Recent advances in top-quark physics studies at FCC-ee

Speaker: Christian Schwanenberger (Deutsches Elektronen-Synchrotron (DE))

Summary

71 Experimental summary

Speaker: Alexander Grohsjean (Hamburg University (DE))

72 Announcement of TOP2027

73 Closing

Speaker: Didar Dobur (Ghent University (BE))