CZ+SK HEP Workshop 2026

10 Sept 2026, 00:01 → 11 Sept 2026, 23:18 Europe/Zurich

Academy of Science, Sál Dvořák (Prague)

Czech and Slovak HEP Workshop

 

A meeting of the Czech and Slovak high-energy physics community focused on CERN experiments, neutrino physics, and detector R&D.

The workshop provides a space to share recent results, discuss ongoing research activities, and strengthen collaboration across the CZ+SK particle physics community. We especially encourage participation and contributions from students and early-career researchers.

Topics included:

• CERN experiments: ATLAS, ALICE, AMBER, NA62, etc.
• Other HEP experiments, e.g. Belle II
• Neutrinos: theory and experiment
• Detector research and development activities

Thursday 10 September

09:00 → 10:30 Block 1

09:00 Welcome

Speaker: Tomas Davidek (Charles University (CZ))

09:15 ATLAS highlights

News from ATLAS experiment

Speaker: Jana Faltova (Charles University (CZ))

09:45 Differential Cross-Section Measurements of Higgs Production in Decays to Tauon Pair

The Higgs boson remains an object of key interest due to its unique position and role in the Standard Model framework. The cross-sections of three dominant production modes (gluon-gluon fusion, ggH; vector boson fusion, vbfH; and associated production alongside a vector boson or higgsstrahlung, VH) are analysed through the $H\rightarrow\tau\tau$ decay channel. The analysis utilizes a partial Run 3 dataset from the ATLAS Experiment at the LHC and is intended to act as an intermediate step between the successful measurements of the Higgs cross-sections in this decay channel using the full Run 2 dataset, and a full investigation of the data collected in the recently concluded Run 3. Various machine learning techniques, such as the implementation of a multiclass classifier neural network for improved discrimination between signal and background sources will be introduced. Preliminary results from Asimov and hybrid fits will be shown and discussed.

Speaker: Martin Divisek (Charles University (CZ))

10:03 tbH+ Analysis with Multileptons Using Run-2 ATLAS Data

A charged Higgs boson remains undiscovered to this day, despite the significant impact it would have for improving our understanding of particle physics. The detection of such a particle could revolutionize areas such as the study of electroweak symmetry breaking, extensions to the Standard Model and potentially open doors to entirely new physics. This study focuses on the detection of the proposed charged Higgs boson using machine learning techniques applied to simulated proton-proton collisions. The main objective is to develop a machine learning model to identify and distinguish the desired events of the charged Higgs boson from background events.

Speaker: Azad Afandizada (Czech Technical University in Prague (CZ))

10:21 Higgs boson production in association with a single top tH(Hbb) using the ATLAS detector

This study investigates the separation of the rare tH(bb) signal from background processes using machine-learning methods in the ATLAS Release 22 framework. The tH(bb) process is sensitive to the interaction between the Higgs boson and the top quark, but its small production rate makes it
difficult to distinguish from dominant background processes.

As a reference study, the previous Release 21 analysis was reproduced. The main part of the study focuses on the Release 22 analysis, where XGBoost, a graph neural network, a Graph Attention Transformer, and a multi-class Graph Attention Transformer were implemented and evaluated. The models were compared using the area under the ROC curve and the expected median limit obtained with TRExFitter.

The best result was achieved with the multi-class Graph Attention transformer, reaching an AUC of 0.91 and an expected median limit of μ = 6.05. Compared with the previous Release 22 study, which obtained an AUC of 0.82 and an expected median limit of μ = 22.4 using TabNet, this represents an improvement in expected sensitivity. We also approximated Run-3 sensitivity projection by scaling luminosity to 500 fb⁻¹, which decreased the expected median limit to 3.55.

Speaker: Filip Rucka

10:30 → 11:00 Coffee break

11:00 → 12:30 Block 2

11:00 ATLAS Run 3 measurement of inclusive and differential cross sections of boosted ttZ production in the trilepton channel

Measurements of the associated production of a top-quark pair and a $Z$ boson ($t\bar{t}Z$) probe the coupling between the top quark and the $Z$ boson, thereby serving as indirect searches for new physics. Besides, $t\bar{t}Z$ measurements improve background estimation in some of the direct Beyond the Standard Model searches.
The latest ATLAS $t\bar{t}Z$ cross section measurement at $\sqrt{s}=13$ TeV based on the full Run 2 dataset reached unprecedented precision of 6.5% and is consistent with theory prediction at NLO+NNLL.
New $t\bar{t}Z$ analysis from ATLAS uses partial Run 3 dataset at $\sqrt{s}=13.6$ TeV and targets events where top quarks decay into boosted jets. Such boosted topology grants access to the high-energy phase space and thus enhances sensitivity to the Standard Model Effective Field Theory (SMEFT). Besides, it improves background suppression by targeting final state with both leptons and $b$-tagged large-$R$ jets. This ongoing boosted $t\bar{t}Z$ analysis aims to measure inclusive as well as differential cross sections and to interpret the differential measurements in the context of SMEFT. The analysis is divided into two channels based on lepton multiplicity. This talk will focus on the trilepton channel, which targets events with semileptonic decays of the $t\bar{t}$ pair and leptonic decays of the $Z$ boson.

Speakers: Dominik Babal (Slovak Academy of Sciences (SK)), Lucia Keszeghova (Comenius University (SK))

11:25 Jet energy scale and resolution calibration from hadronically decaying W boson in ttbar events in ATLAS

Jet energy scale (JES) and jet energy resolution (JER) uncertainties are among the dominant systematic uncertainties in many ATLAS measurements. After the application of simulation-based calibrations, residual differences between data and simulation are corrected using data-driven in situ techniques. In this contribution, a new in situ calibration approach exploiting $t\bar{t}$ events in the single-lepton decay channel is presented. The method uses events in which one of the $W$ bosons from top-quark decay decays hadronically into two jets, allowing the reconstruction of the $W$-boson invariant mass from the measured jet four-momenta. A forward-folding procedure is employed to generate template distributions of the reconstructed $W$-boson mass under different assumptions of the JES or JER. The mean (width) of these templates is then compared to the mean (width) of the mass distribution observed in data to extract optimal JES (JER) correction. Results obtained with this technique using the full Run 2 dataset and Run 3 data collected in 2022 and 2023 are presented. The method will be combined with other in situ calibration techniques to further improve the JES and JER precision in ATLAS.

Speaker: Adriana Dohnalova (Comenius University (SK))

11:45 Reconstruction and unfolding in the analysis of charge asymmetry in top-quark pair production at the ATLAS Experiment

The charge asymmetry is a property of top-quark pair production predicted by the Standard Model which has already been measured at various center-of-mass energies. This analysis would like to follow up on the previous measurement, which observed non-zero charge asymmetry at 4.7 sigma significance level. This effort aims to overcome the previous successful measurement and claim the discovery of the charge asymmetry phenomenon. Larger data set comprised of full Run2 and partial Run3 data should help to diminish the statistical uncertainty hence contribute to larger significance of the result.
This talk will be focused on the reconstruction method and unfolding procedure used in the analysis. Preliminary results of some related studies will be presented.

Speakers: Barbora Eckerova (Comenius University Bratislava), Jiri Hejbal (Czech Academy of Sciences (CZ))

12:10 Simultaneous Measurement of the Top-Quark Mass and Decay Width with the ATLAS Experiment

The top quark is the heaviest known fundamental particle, making the precise determination of its properties a critical test of the Standard Model (SM) of particle physics. While the top-quark mass and decay width are closely linked within the SM framework, a simultaneous measurement of both parameters has never previously been performed by the ATLAS experiment. This talk presents the current status of an ongoing sensitivity study for the simultaneous extraction of the top-quark mass and decay width using the full LHC Run 2 proton–proton collision dataset collected by ATLAS (140fb$^{-1}$ at $\sqrt{s}=13$ TeV). The analysis targets the dilepton decay channel of the $WWbb$ final state, exploiting the sensitivity of the invariant mass distribution of charged leptons and b-jets.

Speaker: Andrej Durica (Comenius University (SK))

12:30 → 14:00 Lunch break

14:00 → 15:30 Block 3

14:00 DRD Collaborations, Prague Activities in DRD3

This overview introduces DRD3 as the international framework coordinating research and development of semiconductor detector technologies for future experiments beyond the HL-LHC, and presents two complementary activities carried out by Prague teams mainly within OPJAK-FORTE. The talk provides context for the work on the OCTOPUS project and SiC sensor development activities, further discussed in other contributions.

The OCTOPUS project develops fine-pitch monolithic pixel sensors in the TPSCo 65 nm process for future lepton-collider based vertex detectors, with the Prague contribution covering ASIC design and simulation, as well as preparation of testing setups and beam-test systems for prototype characterisation.

In parallel, the 4H-SiC programme investigates radiation sensors, including fast LGAD concepts, with emphasis on timing performance, radiation hardness, and operation in demanding environments. The work includes sensor design, fabrication, electrical and radiation characterisation, and preparation of dedicated setups for source, laser, and beam measurements.

Speaker: Peter Svihra (Czech Academy of Sciences (CZ), Czech Technical University in Prague (CZ))

14:30 Prague's Contribution to the ATLAS Inner Tracker Upgrade

The LHC will undergo a major upgrade during the upcoming Long
Shutdown 3. The goal of the upgrade is to increase the collider luminosity, i.e. the
number of collisions per second. This means higher strain on the already ageing
ATLAS detector, so it also has to be upgraded. Part of the upgrade is replacement
of the current tracker for new full-silicon tracker called Inner Tracker (ITk). This
poster describes the process of manufacturing and testing the ITk modules as it is
done here in Prague.

Speaker: Jakub Bucko (Charles University (CZ))

14:48 Effects of irradiation by protons, neutrons, and gamma rays on the electrical and detection properties of 4H-SiC diodes and LGAD sensors

This contribution presents an overview of the investigation of radiation effects in 4H-SiC PN diodes and LGADs fabricated by onsemi, including both single-channel and segmented (strip and pixel) devices. The sensors were irradiated with protons, reactor neutrons, and 60Co gamma rays. Radiation-induced changes were assessed using current-voltage (IV) and capacitance-voltage (CV) measurements, complemented by two-photon absorption transient current technique (TPA-TCT) measurements employing a tightly focused femtosecond laser at the ELI ERIC research infrastructure.

The results reveal markedly different responses to the various types of irradiation. Proton irradiation primarily modifies the electrical properties of the epitaxial layer, whereas neutron irradiation strongly alters the effective space-charge concentration, resulting in a substantial expansion of the depletion region beyond the nominal epitaxial layer and deep into the substrate. In contrast, gamma irradiation predominantly influences the depletion characteristics through ionization-induced effects while producing only minor changes in the leakage current. Combined with detailed results from in-depth charge injection measurements using laser pulses, the findings provide new insights into the radiation response of 4H-SiC detectors and contribute to the optimization of detector designs for operation in extreme radiation environments.

Speaker: Vojtech Kracmar (Czech Technical University in Prague (CZ))

15:06 Efficiency and noise measurements on irradiated samples of H2M Monolithic Active Pixel Sensors

Monolithic Active Pixel Sensors (MAPS) are key candidates for future HEP tracking detectors due to their high granularity, low material budget and low power consumption.
The H2M (Hybrid-to-Monolithic) chip is one of the prototypes designed within this framework.
Multiple samples of the H2M detector were irradiated with either Protons or high energy electrons at different fluences.
The preliminary laboratory characterization and calibration have been carried out on the Caribou DAQ system, created as a universal framework for future work with semiconductor detectors.
This work presents the impact of irradiation on the overall performance of the H2M detector. Specifically, the focus was placed on the evaluation of signal noise and the degradation of detection efficiency.
The gathered results serve to provide further insight into the application of MAPS in high-radiation environments, providing needed information for the development of new devices within the OCTOPUS project.

Speaker: Ivan Raksanyi (Czech Technical University in Prague (CZ))

15:16 OCTOPUS project circuit design overview

The presentation compares Towerjazz 180 nm technology, used in current sensors at CERN, with TPSCo 65 nm technology for future molythic pixel detectors. The new technology will then be presented in relation to the target parameters of the OCTOPUS project, using measurement results from the already constructed MOSAIX prototype. The presentation will then cover the current status of the OCTOPUS project and the proposed detector. The design of the analog circuit, specifically, the parameters of the pixel array and the bias and monitoring circuits, will be discussed in detail. The implementation of the digital circuit processesing data from the pixel array will be briefly introduced, and the presentation will conclude with an overview of the current and future design of the OCTOPUS project detector.

Speaker: Lukas Kvasnicka (Czech Technical University in Prague (CZ))

15:30 → 16:00 Coffee break

16:00 → 18:00 Block 4

16:00 IPPOG: Czech and Slovak activities

Introduction to Czech and Slovak activities within IPPOG

Speaker: Vojtech Pleskot (Charles University (CZ))

16:18 ALICE highlights

News from ALICE experiment

Speaker: Marek Bombara (Pavol Jozef Safarik University (SK))

16:48 Hadron–strangeness correlations as a function of multiplicity in the pp collisions with ALICE

Measurements in pp and p-Pb collisions have revealed that these small collision systems exhibit several features traditionally attributed to heavy-ion collisions, including the smooth increase of the strange hadron yields with the collision multiplicity (strangeness enhancement). However, the microscopic origin of this phenomenon in small systems remains an open question. In particular, the relative contributions of soft (bulk-like particle production) and hard processes (related to parton fragmentation and jet production) to strangeness enhancement in small collision systems are not yet fully constrained. Angular correlations between a charged hadron and an associated strange hadron provide a differential tool to probe different strangeness production mechanisms and to study the interplay between bulk and hard particle production.

In this contribution, we present the first measurement of two-particle angular correlations involving identified strange hadrons as a function of multiplicity in pp collisions at 5.36 TeV. The results are compared with state-of-the-art model predictions, providing new insights into the interplay between hard and soft QCD processes governing strangeness production in small collision systems.

Speaker: Lucia Anna Tarasovicova (Pavol Jozef Safarik University (SK))

17:06 Probing jet quenching in OO collisions with ALICE

The ALICE experiment investigates the properties of the quark-gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions. Two of the most prominent signatures of QGP formation are the collective hydrodynamic expansion of the produced medium and the energy loss of high-energy partons traversing the medium, known as jet quenching. Measurements in small collision systems, such as p-Pb, have revealed flow-like signatures, while no unambiguous evidence for jet quenching has been observed, raising important questions about the relation between system size and the onset of QGP effects.

The recent OO collision run at the LHC provides a unique opportunity to bridge the gap between p-Pb and Pb-Pb collisions and to investigate how signatures of the QGP evolve with system size. This contribution will present the first ALICE measurements of inclusive π0 production, inclusive jet production, and hadron-jet correlations in OO collisions. The inclusive observables exhibit a suppression consistent with partonic energy loss in the produced medium, while no significant modification is observed in hadron-jet correlations within the current experimental precision. The different sensitivity of these observables will be discussed.

Speaker: Filip Krizek (Czech Academy of Sciences (CZ))

17:24 Study of Z-tagged jet substructure in PbPb and pp collisions at 5.36 TeV with the ATLAS experiment

This contribution presents the status of an ongoing ATLAS analysis of jet substructure in Z+jet events in heavy-ion and proton-proton collisions at the energy of 5.36 TeV. The study utilizes Z bosons reconstructed through their dilepton decay channels and examines jet substructure observables to investigate modifications of the parton shower in the quark-gluon plasma – extremely hot and dense medium created in ultra-relativistic heavy-ion collisions. In particular, jets produced in association with a Z boson offer a clean experimental probe, as the electroweak boson does not interract with the medium via strong interaction and thus, it provides an estimate of the initial parton kinematics. In addition, Z-tagged jets are predominantly quark-initiated, which is extremely useful for testing QCD predictions for quark-jet substructure.

Speaker: Emil Lelak (Charles University (CZ))

17:42 Jet nuclear modification measurements with the ATLAS detector

Measurements of jet production in nuclear collisions provide important constraints on parton energy loss and the properties of the quark–gluon plasma. This contribution presents recent ATLAS studies of jet nuclear modification using LHC collision data. Jet yields are compared with suitable proton–proton reference measurement and studied as functions of jet transverse momentum, collision centrality, and rapidity. The measurement extend tests of jet quenching into previously less explored kinematic regions and collision systems, providing new information about the dependence of parton energy loss on the collision geometry and medium size.

Speaker: Petr Baron (Palacky University (CZ))

19:00 → 21:00 Conference Dinner

Friday 11 September

09:00 → 10:30 Block 5

09:00 Neutrino Oscillations: Experimental Status and Prospects

Neutrino oscillations provide compelling evidence for physics beyond the Standard Model, suggesting that neutrinos have mass. This talk will review the current experimental picture and highlight the prospects of next-generation projects in addressing the open questions of neutrino oscillation physics: CP violation, the neutrino mass ordering, and precise measurements of neutrino mixing parameters.

Speaker: Tomas Nosek (Charles University (CZ))

09:18 Neutrino experiment JUNO and its first results

Experiment JUNO is a neutrino oscillation experiment located in southern China. It is located 53 km away from 2 nuclear powerplants with overall power of about 36 GW (one powerplant is not yet completed) and the experiment uses its 20 kton liquid scintillator as a target. The experiment has many goals and ambitions e.g. determining the neutrino mass hierarchy, measurement of the oscillation parameters with unprecedent precision. The experiment started taking data in August 2025.

This work introduces the JUNO experiment, its first results and at the end touches subjects which the speaker contributed the most within the collaboration. That means liquid scintillator nonlinearity measurement, flasher system and its usage eg. in the water attenuation measurement.

Speaker: Tomas Tmej (Charles University (CZ))

09:36 Recent results from the NA62 experiment

Recent measurements of rare kaon decays from the NA62 experiment will be presented, highlighting the contributions of the Charles University group. The results include new measurements of $K^+ \to \pi^+ \nu \bar{\nu}$, $K^+ \to \pi^+ \pi^+ \pi^- \gamma$, $K^+ \to e^{+} \nu \gamma$, and $K^+ \to \mu^+ \nu \mu^+ \mu^-$. Ongoing analyses and future prospects will also be discussed.

Speaker: Michal Lelák

09:54 Recent results from NA62

The NA62 experiment at CERN collected the largest sample of charged kaon decays in the world during the years 2016 - 2026. The most recent results and prospects of future analyses of the collected dataset will be presented.

Speaker: Matej Karas (Comenius University (SK))

10:12 Simulation and Reconstruction of e+ and e- Trajectories in a Time Projection Chamber with Orthogonal Fields

In this work, we describe the development of track- and energy-reconstruction algorithms for atypical Time Projection Chambers (TPCs) that will be used at the Institute of Experimental and Applied Physics, Czech Technical University in Prague, to search for the anomalous internal pair creation reported by the ATOMKI group.
These chambers operate with an inhomogeneous toroidal magnetic field oriented orthogonally to the electric field; we therefore refer to them as Orthogonal-Field TPCs (OFTPCs). Although this configuration distorts the drift of ionization electrons and complicates the resulting electron and positron trajectories, it also offers several practical advantages. We present the most effective of several tested approaches, which employs a simulated ionization-electron drift map for track reconstruction and a Runge–Kutta-based fit for energy reconstruction. Using simulations, we demonstrate that—under idealized conditions, namely an ideal charge readout with no amplification and no noise and with known initial track positions and directions—it is possible to achieve a fitted Gaussian width ($\sigma$) better than 1% in relative energy for both electrons and positrons, after applying corrections for systematic effects that depend on the track parameters.

Speaker: Martin Vavrik (work on IEAP CTU, student of IPNP CUNI)

10:22 Simulation of photon propagation generated by a particle traversing a crystal of arbitrary shape

This project focuses on the development of a fast, flexible, and modular simulation of photon propagation produced by a charged particle traversing a crystal of arbitrary shape. The physical model includes photon production via scintillation and Cherenkov radiation.

The main goal of the developed software tool is to enable targeted optimization of the optical geometry and output signal characteristics, with an emphasis on precise reconstruction of deposited energy and timing information in the detector. The tool is intended, among other applications, for identifying optimal hardware configurations, such as compensating chromatic dispersion to achieve the simultaneous arrival of photons of different wavelengths at the photodetector.

The correctness and physical validity of the model are verified through comparison with existing simulations, and the results are analyzed and visualized using available graphical and analytical tools. The results of the project will be presented.

Speaker: Jakub Motyčka

10:30 → 11:00 Coffee break

11:00 → 12:30 Block 6

11:00 Transverse-momentum dependent effects in semi-inclusive DIS at COMPASS

COMPASS experiment at CERN had a wide physics programme. One of its cornerstones were studies of hadron production in deep inelastic scattering (DIS), which can be interpreted in the transverse-momentum-dependent (TMD) factorisation framework, allowing to access the distributions of polarisation and transverse momentum of quarks within the nucleon in the language of TMD PDFs, and the hadronisation in terms of TMD fragmentation functions. In the 20 years of data taking from 2002 to 2022, unique data sets have been collected with high-energy muon beam and unpolarised and transversely polarised proton and deuteron targets, allowing for measurements that had a high impact on the knowledge of the transversity (transverse counterpart of the helicity PDF) and the other TMD parton distributions. The talk will focus on the unique data collected with a liquid hydrogen target in 2016 and with a transversely polarised deuteron target in 2022, which significantly improve the knowledge of the d-quark transversity and are yet to yield a number of interesting results on the other TMD distributions.

Speaker: Vendula Benesova (Charles University (CZ))

11:18 Angular analysis of B0 → K*0 μ+ μ- decays with the ATLAS detector

Rare flavour-changing neutral-current decays are powerful probes of the Standard Model and of possible new physics, as they are suppressed in the Standard Model and can receive contributions from virtual heavy particles. The decay $B^0 \to K^{*0}\mu^+\mu^-$ provides a particularly rich channel through its multidimensional angular distribution, from which observables sensitive to the $b \to s\mu^+\mu^-$ transition can be extracted. Previous measurements of angular observables, including $P'_5$, have shown tensions with Standard Model predictions and contribute to the broader pattern of flavour anomalies.

An angular analysis of $B^0 \to K^{*0}\mu^+\mu^-$ decays is being developed using the ATLAS Run-2 proton-proton collision data set collected at $\sqrt{s}=13~\mathrm{TeV}$. Compared with the previous ATLAS Run-1 result, the larger Run-2 data sample is expected to improve the statistical precision of the measurement. The analysis includes the reconstruction and selection of $B^0$ candidates, the implementation of the angular fit model, and the treatment of detector and selection effects through a multidimensional angular acceptance derived from simulation. This contribution reports the current status of the analysis framework and validation studies, and outlines the path towards extracting the angular observables from Run-2 data.

Speaker: Gokul Duraikandan (Charles University (CZ))

11:36 Performance and Internal Stability of the ATLAS Timepix3 Detector Network during the 2025 van der Meer Scans

The Timepix3 detector network installed inside the ATLAS cavern [1] has demonstrated reliable performance for measuring particle fluxes and monitoring luminosity during LHC operations [2, 4]. Comprising fourteen operational detectors distributed throughout the ATLAS experiment, the network is exposed to diverse radiation fields and flux levels. Detectors closer to the interaction point provide high-statistics measurements, while those at greater distances enable systematic uncertainty assessment.

Operating independently, the network is fully synchronized with the LHC orbit clock, allowing bunch-sensitive, real-time luminosity measurements. Furthermore, individual Timepix3 detectors provide detailed cluster analysis, enabling their classification into minimum ionizing particles, highly ionizing particles, gamma rays, neutrons, and electrons, as well as the reconstruction of particle trajectories. These capabilities are used to characterize the radiation environment [3] and to separate the collision peak in each bunch crossing, mitigating background and significantly improving the signal-to-background ratio [4].

This contribution presents the internal stability and performance of the Timepix3 network throughout 2025, alongside detailed measurements and analysis taken during the van der Meer (vdM) scans. Since the vdM scans provide the primary reference for absolute luminosity calibration and cross-section calculation, these studies show the potential of the Timepix3 network to contribute directly to absolute luminosity determination. Initial fits to the scan profiles confirm the consistency and reliability of the data collection.

Overall, these results demonstrate that the Timepix3 detector network is a versatile tool for both online and offline beam monitoring, positioning it as a strong, independent, and complementary candidate for luminosity calibration and long-term monitoring in luminosity LHC operations.

[1] P. Burian et al. “Timepix3 detector network at ATLAS experiment” JINST 13 C11024 (2018) \url{https://iopscience.iop.org/article/10.1088/1748-0221/13/11/C11024/meta}

[2] B. Bergmann et al., “Relative luminosity measurement with Timepix3 in ATLAS” JINST 15 C01039 (2020). \url{https://iopscience.iop.org/article/10.1088/1748-0221/15/01/C01039/meta}

[3] B. Bergmann et al., “Characterization of the Radiation Field in the ATLAS Experiment with Timepix Detectors”, in IEEE Transactions on Nuclear Science 66, no. 7, pp. 1861-1869 (2019) \url{https://ieeexplore.ieee.org/abstract/document/8720202}

[4] B. Bergmann et al., “Evaluation of Timepix3 as a luminosity detector at LHC during 2018 pp collisions at \sqrt{s}=13 TeV” Eur. Phys. J. C 85, 904 (2025). \url{https://doi.org/10.1140/epjc/s10052-025-14631-x}

Speaker: Catalina Lesmes Ramirez (Czech Technical University in Prague (CZ))

11:54 FastFrames - multithreaded analysis framework used by ATLAS collaboration

The talk will give an overview of an multithreaded (multiple CPU cores), physics framework FastFrames, used by the ATLAS collaboration. The goal of FastFrames is to enable analysis teams to efficiently scale their analysis specific code to multiple CPU cores, thus significantly speeding up physics analysis timescale by reducing computational time.

The talk will describe key problems that FastFrames package was designed to solve and our solutions to these problem. It will also describe some technical challenges that we faced during the development/maintenance process and what lessons have been learnt from these.

The talk is not supposed to be a summary of a FastFrames documentation or a tutorial. It should serve as an overview of how it is built, what technologies are used and the challenges that we faced during its development and maintenance. It aims to provide a relevant information for people who might be interested in building similar frameworks (solving similar problems) in another collaborations and groups.

Speaker: Michal Dubovsky (Comenius University (SK))

12:12 Benchmarking Machine Learning Architectures for ttH Multilepton Signal Sensitivity

Machine-learning benchmarks for signal--background separation in high-energy physics are often confounded by inconsistent feature definitions, training procedures, and evaluation metrics. We present a controlled comparison of six architectures for ttH multilepton classification, from XGBoost to Lorentz-equivariant graph networks, under standardised hyperparameter optimisation across a controlled feature hierarchy. We report both ROC AUC and profile likelihood signal-strength uncertainty, investigate model performance as a function of feature set and training-set size, and compare single-channel against unified multi-channel training, demonstrating that the choice of architecture and feature representation has a meaningful impact on analysis sensitivity.

Speaker: Lukáš Viceník (Czech Technical University in Prague (CZ))

12:30 → 14:00 Lunch break

14:00 → 15:20 Block 7

14:00 Quantum information observables at ATLAS

This talk will cover the quantum-information observables that can be measured with the ATLAS experiment at the LHC. After a short introduction to the relevant concepts, I will discuss current measurements and present the most recent results. Finally, I will introduce a future measurement in which our institute is involved.

Speaker: Ondrej Penc (CERN)

14:18 Search for QCD instantons in proton–proton collisions at ATLAS using inner detector and ALFA data

QCD instantons are non-perturbative, semiclassical solutions of the Yang–Mills equations that connect topologically distinct vacua and encode tunneling between them. They underlie key phenomena such as axial U(1)U(1)U(1) symmetry breaking, anomalous chirality violation via the axial anomaly, and contribute to the structure of the QCD vacuum and chiral symmetry breaking. Their observation would provide direct evidence of topological fluctuations and a unique window into non-perturbative dynamics beyond perturbation theory.

Searches for instanton-induced processes in proton–proton collisions at ATLAS, based mainly on inner detector data, remain inconclusive (yet) due to overwhelming QCD backgrounds and limited control of rare event topologies. This motivates the development of data-driven strategies and the exploration of complementary signatures.

We present recent progress using minimum-bias and ALFA-tagged datasets. Forward proton tagging with ALFA enhances sensitivity to diffractive topologies that may favor instanton-induced processes, improving the discrimination between signal-like and background events in ongoing ATLAS analyses.

Speaker: Radek Vavricka (Charles University (CZ))

14:36 Signal Generator for Instanton-Induced Processes in Proton-Proton Collisions

QCD instantons are non-perturbative, topological gluon-field configurations that mediate chirality-violating processes whose experimental signature is an isotropic, flavour-democratic, high-multiplicity final state, absent from the perturbative expansion and so far unobserved. We present a new Monte Carlo generator for QCD instanton-induced processes in proton–proton collisions, filling a gap left by existing tools. QCDINS targets eletron-proton DIS, while SHERPA's instanton implementation covers only inclusive production, not diffractive topologies with large rapidity gaps. The generator implements the 't Hooft effective vertex with full numerical integration over the instanton size $\rho$ and supports four process topologies distinguished by single/double Pomeron exchange (using H1 Fit B diffractive PDFs) versus inclusive gluon-PDF production. The output is provided as LHE or HepMC3 events for downstream parton showering and hadronization. This enables realistic predictions for high-multiplicity final states (soft bombs) and jet-correlation observables, providing a tool for instanton searches at the LHC and future hadron colliders. We discuss benchmark soft-bomb observables such as multiplicity, transverse energy, sphericity, and rapidity-gap structure, emphasizing robust shapes and flavour ratios over absolute rates, which carry the well-known instanton-size uncertainty.

Speaker: Vojtěch Loubal

14:47 Search for Axion-Like-Particles using di-photon signature with the ATLAS Forward Proton Detector

The search for an Axion-like particle in light-by-light scattering in Run-3 LHC data using the central ATLAS detector for di-photon signature and ATLAS Forward Proton (AFP) detector for a scattered forward proton signature is presented together with the operational and data quality challenges for the AFP detector.

Speaker: Viktoriia Lysenko (Czech Technical University in Prague (CZ))

15:05 Search for heavy long-lived charged particles at the ATLAS experiment

Speaker: Tadeas Petru (Charles University (CZ))

15:20 → 15:50 Coffee break

15:50 → 17:00 Block 8

15:50 Reinterpretation of ATLAS and CMS monojet and mono-V searches for excited neutrinos

Searches for final states with large missing transverse momentum recoiling against a jet or a hadronically decaying vector boson provide strong constraints on a wide range of physics scenarios beyond the Standard Model. This contribution presents a reinterpretation of existing ATLAS and CMS monojet and mono-V searches at center-of-mass energy of 13 TeV in the context of excited-neutrino production. Published signal-region selections, post-fit background estimates, observed event yields, and simulated excited-neutrino signal samples are used to derive upper limits on the production cross section as a function of the excited-neutrino mass. The monojet searches probe excited-neutrino masses up to approximately 4 TeV for representative benchmark scenarios, while the mono-V searches provide complementary sensitivity in regions of parameter space with large couplings to the Standard Model electroweak gauge bosons and excited-neutrino masses below the compositeness scale. The reinterpretation demonstrates how existing LHC searches can be used to constrain excited-neutrino models beyond their original scope.

Speaker: Gabriela Karkošová Martinovicová (Charles University)

16:08 ALLEGRO detector concept for FCC-ee

The ALLEGRO detector is one of the detector concepts proposed for the Future Circular Collider electron–positron programme (FCC-ee). A key component of the detector is a high-granularity electromagnetic calorimeter based on noble-liquid technology developed within the DRD Calo collaboration. The calorimeter design combines excellent energy resolution with fine detector segmentation, which is important for precision measurements and advanced reconstruction methods. Current studies focus on the optimisation of PCB-based readout electrodes, detector geometry and mechanical structure. The calorimeter is also implemented in the Key4hep framework as part of the ALLEGRO detector model.

Speaker: Filomena Sopkova (Slovak Academy of Sciences (SK))

16:26 Beyond Standard Model Searches at Future Circular Collider FCC-ee

The Future Circular Collider in its electron–positron configuration (FCC-ee) offers an exceptional environment for probing physics beyond the Standard Model through high-precision measurements and unprecedented luminosity. One of the targets for BSM searches are axion-like particles (ALPs), which arise naturally in many extensions of the Standard Model and may provide insights into unresolved questions such as the matter of dark matter. This contribution reviews the plans for ALP searches at the FCC-ee and discusses the optimalization of the ALLEGRO detector design for ALP detection.

Speaker: Matej Haviernik (Charles University (CZ))

16:44 ePIC

Speaker: Jana Bielcikova (Czech Academy of Sciences (CZ))