28th Conference on Computing in High Energy and Nuclear Physics (CHEP 2026)

Session

Track 5 - Event generation and simulation

25 May 2026, 13:45

Chulalongkorn University

177. Generative Muon Punch-Through with Flow-Matching in ATLAS

Firdaus Soberi (The University of Edinburgh (GB))

25/05/2026, 13:45

Track 5 - Event generation and simulation

Oral Presentation

The ATLAS experiment at the Large Hadron Collider uses the Geant4 toolkit to simulate detailed Monte Carlo events spanning a broad range of physics processes. However, the full simulation is computationally expensive, with the main bottleneck originating from the modelling of particle showers in the calorimeter systems. To meet increasing demands, especially for the high-luminosity LHC era,...

522. Simulating the CMS High-Granularity Calorimeter with Generative AI

Oz Amram (Fermi National Accelerator Lab. (US))

25/05/2026, 14:03

Track 5 - Event generation and simulation

Oral Presentation

In the upcoming High Luminosity LHC era, detector simulation will face computing resource constraints; at the same time CMS will be upgraded with the new High Granularity Calorimeter (HGCal), which is more intensive to simulate. This computing challenge motivates the use of generative machine learning models as surrogates to replace full physics-based simulation of particle showers in the...

408. DiT-based fast simulation for the CEPC long-bar crystal electromagnetic calorimeter

ZHIHAO LI (Institute of High Energy Physics, Chinese Academy of Sciences)

25/05/2026, 14:21

Track 5 - Event generation and simulation

Oral Presentation

The CEPC is a proposed high luminosity e+e− collider designed for precision measurements of the Higgs, W, and Z bosons. Its reference detector incorporates a long bar crystal ECAL, which employs long, narrow crystal bars arranged in orthogonal layers to deliver fine 3D shower imaging and excellent compatibility with Particle Flow reconstruction. [1]

For CEPC physics analyses, large volumes...

486. Modern Generative Models for Fast Calorimeter Simulation in ATLAS

Florian Ernst (Heidelberg University (DE))

25/05/2026, 14:39

Track 5 - Event generation and simulation

Oral Presentation

Accurate modelling of electromagnetic and hadronic showers is one of the most expensive components of the ATLAS detector simulation. To reduce CPU usage for Run 3, the collaboration introduced AtlFast3, a fast simulation tool which combines classical histogram based parameterisations with GAN based calorimeter models.

Following Run 3, a new optimisation of the voxelisation scheme used for...

178. Adapting PARNASSUS: A Fast Simulation Tool for the ATLAS Experiment

Abdelrahman Asem Elabd (University of Washington (US))

25/05/2026, 14:57

Track 5 - Event generation and simulation

Oral Presentation

Detector simulation and reconstruction are significant computational bottlenecks in particle physics. A state-of-the-art GenAI-based paradigm, Particle-flow Neural Assisted Simulations (PARNASSUS), has shown great promise for fast simulation in the context of CMS Open Data. Unlike conventional fast simulation models that target only simulation, PARNASSUS is an end-to-end approach that goes...

412. Fast Hybrid Simulation for the LHCb Calorimeters

Matteo Rama (INFN Pisa (IT))

25/05/2026, 16:15

Track 5 - Event generation and simulation

Oral Presentation

About 90% of the distributed computing resources available to the LHCb experiment are used for physics event simulation, and half of the corresponding CPU time is spent on the Geant4-based simulation of the calorimetric system.
This talk presents a hybrid fast-simulation approach, implemented in the LHCb Gauss Simulation Framework, that combines the established hit-library technique with...

316. End-to-End Fast Simulation of the ALICE Zero Degree Calorimeter using Generative Models

Davide Fuligno (University of Pisa and INFN Trieste (IT))

25/05/2026, 16:33

Track 5 - Event generation and simulation

Oral Presentation

End-to-End Fast Simulation of the ALICE Zero Degree Calorimeter using Generative Models

Davide Fuligno
On behalf of the ALICE Collaboration
Università di Pisa and INFN, Trieste Italy

The ALICE experiment at the LHC faces unprecedented computing challenges in Run 3 and 4, necessitating innovative solutions to cope with the increased data-taking luminosity and the continuous...

309. Electro-magnetic calorimeter shower simulation using machine learning techniques at BESIII experiment

Tong Liu

25/05/2026, 16:51

Track 5 - Event generation and simulation

Oral Presentation

The detailed simulation of electromagnetic calorimeters (EMC) remains computationally intensive due to simulation of millions of secondary particles.
Machine learning offers a promising alternative by bypassing explicit shower simulation, though its accuracy must be rigorously validated.

In this work, we develop fast simulation models for the BESIII EMC using generative adversarial...

410. Improving simulation of extreme EM calorimeter showers with deep neural networks

Minh-Tuan Pham (University of Wisconsin Madison (US))

25/05/2026, 17:09

Track 5 - Event generation and simulation

Oral Presentation

Calorimeter simulation is among the most resource-hungry components of modern collider experiments such as ATLAS and CMS, currently accounting for half of the total CPU budgets at the LHC, and will only increase in the future High Luminosity phase. This exploding computing demand and the arrival of sizeable open datasets such as CaloChallenge have spurred the development of numerous...

259. Exploring Potential Pathways to Accelerate ePIC Detector Simulation

Sakib Rahman, Sakib Rahman

25/05/2026, 17:27

Track 5 - Event generation and simulation

Oral Presentation

The ePIC Physics and Detector Simulations leverage the Geant 4 and DD4hep software frameworks, which serves as a single source of truth for detector description, ensuring consistent configuration across full (Geant 4/DDG4) and accelerated simulation models. As simulation complexity scales, we employed a systematic profiling methodology using the DD4hep plugin mechanism to pinpoint...

160. Evaluation of VecGeom Solids in the Context of ALICE O2 Simulation

Ivana Hrivnacova (Université Paris-Saclay (FR))

25/05/2026, 17:45

Track 5 - Event generation and simulation

Oral Presentation

VecGeom is a modern C++ geometry modeling library specifically designed to accelerate particle detector simulation by leveraging Single Instruction Multiple Data (SIMD) vectorization. It offers optimized geometric primitives, developed in collaboration with the USolids project. Since Geant4 10.5, users can replace native Geant4 geometry primitives with VecGeom solids. This feature has already...

518. CC4SF - Calibrated classifiers for scale factors (FastSim)

Samuel Louis Bein (Northeastern University (US))

26/05/2026, 13:45

Track 5 - Event generation and simulation

Oral Presentation

As the LHC moves into its high-luminosity phase, the CMS experiment must handle increasingly complex data collected at much higher rates. To complement real data, simulated samples must also scale in volume and complexity while meeting the growing demands of the CMS physics program. Increased use of the CMS fast Monte Carlo production framework (FastSim) can help meet these demands,...

96. Accelerating ALICE background simulations: A WGAN Approach to slow-neutron induced TPC loopers

Marco Giacalone (CERN)

26/05/2026, 14:03

Track 5 - Event generation and simulation

Oral Presentation

The simulation of background processes in high-energy physics can be computationally expensive and time–consuming. To provide the most realistic data description at the ALICE experiment using Monte Carlo simulations, we investigated alternative solutions to generate the products of electromagnetic interactions initiated by slow neutrons in the Time Projection Chamber (TPC). Specifically,...

257. Quantum based Generative Models for Fast Calorimeter Simulation in ATLAS and Future Colliders

Prof. Matteo Franchini (University of Bologna and INFN), Matteo Franchini (University of Bologna and INFN (IT))

26/05/2026, 14:21

Track 5 - Event generation and simulation

Oral Presentation

The increasing demands on simulation statistics for HL-LHC analyses challenge the scalability of traditional calorimeter simulation across all LHC collaborations. While machine learning based fast simulation techniques have demonstrated strong performance, future collider experiments will require generative models that are not only accurate and fast, but also scalable and interpretable in...

274. Machine Learning for Faster Simulations at Belle II

David Giesegh (Belle II Experiment)

26/05/2026, 14:39

Track 5 - Event generation and simulation

Oral Presentation

One of the major goals of the Belle II Experiment is the search for rare decay processes, which manifest as tiny signals over large background contributions. Measuring such delicate signals with the highest possible precision requires not only large datasets from the actual experiment, but typically even larger simulated datasets for the development of such analyses.

Since running the...

513. step2point: Enhancing data preparation for point-cloud-based fast simulation

Anna Zaborowska (CERN)

26/05/2026, 14:57

Track 5 - Event generation and simulation

Oral Presentation

Fast calorimeter shower simulation is an active field of study, with numerous models having been explored. Recently, several models have explored a point cloud representation of energy deposits, as opposed to the more common image-like voxelisation of a shower. However, direct use of the output from the detailed Geant4 simulation as an input to these machine learning models is computationally...

477. Data Overlay for Underlying Event modeling in Heavy Ion collisions in ATLAS

Tadej Novak (Jozef Stefan Institute (SI))

26/05/2026, 16:15

Track 5 - Event generation and simulation

Oral Presentation

Accurate modeling of the underlying event (UE) in heavy-ion collisions poses a significant challenge, particularly for analyses involving hard probes. No existing Monte Carlo (MC) simulation can reproduce the complex underlying physics. To address this, the ATLAS Collaboration developed an innovative technique that overlays simulated signal events onto real minimum-bias data recorded by the...

103. CaloTrilogy: Toward a Breakthrough in One Step, End-to-End, Physics-Guided Shower Generation for Modern Calorimeters

Cheng Jiang (The University of Edinburgh (GB))

26/05/2026, 16:33

Track 5 - Event generation and simulation

Oral Presentation

High-precision calorimeter simulation at current and future colliders puts growing demands on computing resources, motivating ML-based alternatives to traditional Monte Carlo tools such as Geant4. In practice, generative models based on flow matching and diffusion have become de facto standards for high-dimensional fast calorimeter simulation, thanks to their excellent fidelity and strong...

228. The electronics simulation software in the JUNO experiment

Ze Chen

26/05/2026, 16:51

Track 5 - Event generation and simulation

Oral Presentation

The Jiangmen Underground Neutrino Observatory (JUNO) is a large-scale neutrino experiment using a 20-kt liquid scintillator Central Detector surrounded by a 35-kt water Cherenkov veto Detector, and an almost 1000-m2 plastic scintillator Top Tracker. Following the completion of detector commissioning, JUNO began physics data taking on August 26, 2025.

The electronics simulation (ElecSim) is...

461. Updates on ML-based fast and flash simulations at LHCb

Michał Mazurek (National Centre for Nuclear Research (PL))

26/05/2026, 17:09

Track 5 - Event generation and simulation

Oral Presentation

Experiments in high energy physics rely heavily on simulations to interpret data, optimise detector design, and test theoretical models. Traditionally, simulations involve Monte Carlo event generators and detailed particle interactions with detectors. For the LHCb experiment, 90 % of computing resources are used for simulations, with the calorimeter simulation being the most computationally...

76. CMS FlashSim: how an end-to-end ML approach speeds up simulation in CMS

Filippo Cattafesta (Scuola Normale Superiore & INFN Pisa (IT))

26/05/2026, 17:27

Track 5 - Event generation and simulation

Oral Presentation

Detailed event simulation at the LHC is taking a large fraction of computing budget. CMS developed an end-to-end ML based simulation framework, called FlashSim, that can speed up the time for production of analysis samples of several orders of magnitude with a limited loss of accuracy. We show how this approach achieves a high degree of accuracy, not just on basic kinematics but on the complex...

182. PARSIFAL: a parametrized simulation for µ-RWELL detectors

Riccardo Farinelli (INFN Bologna (IT))

26/05/2026, 17:45

Track 5 - Event generation and simulation

Oral Presentation

PARSIFAL (PARametrized SImulation) is a software tool designed to reproduce the complete response of Gaseous Detectors. It models the involved physical processes through simple parametrization, thus achieving a fast processing times. Existing software, such as GARFIELD++, while robust and reliable, is highly CPU time-consuming. The development of PARSIFAL is motivated by the need to...

320. Geant4 electromagnetic physics for future experiments at colliders

Prof. Vladimir Ivantchenko (CERN)

27/05/2026, 13:45

Track 5 - Event generation and simulation

Oral Presentation

In this presentation we review recent updates in Geant4 electromagnetic (EM) physics sub-libraries in view of Run4 and other collider experiments. The evolution of EM sub-libraries is performed in order to make code more robust, compact, and compatible with requirements of Run4 detectors at LHC and other future collider experiments. A significant role in this respect is taken by the G4HepEm...

370. Hardware Acceleration of NLO Event Generation with MadGraph4GPU and PEPPER

Daniele Massaro (CERN)

27/05/2026, 13:45

Track 5 - Event generation and simulation

Oral Presentation

The High-Luminosity LHC will reach unprecedented precision in the measurements of key observables in proton-proton collisions. To accurately predict the rates of such collision events, the simulation of the hard scattering event must include higher-order corrections, in particular Next-to-Leading Order (NLO) terms in the perturbative expansion of the cross section.
The computational...

524. Full-chain Simulation and Data-driven Refinement of the BESIII CGEM Detector Response

Xinnan Wang (IHEP)

27/05/2026, 14:03

Track 5 - Event generation and simulation

Oral Presentation

To meet the requirements of enhanced radiation tolerance and sustained tracking performance, the BESIII inner tracker has been upgraded to a Cylindrical Gas Electron Multiplier (CGEM). We have developed a comprehensive simulation framework for the CGEM response, featuring a realistic digitization model refined with experimental data. The framework simulates the full signal-formation chain...

130. New GPU developments in the Madgraph CUDACPP plugin: kernel splitting, helicity streams, cuBLAS color sums

Andrea Valassi (CERN)

27/05/2026, 14:03

Track 5 - Event generation and simulation

Oral Presentation

The first production release of the CUDACPP plugin for the Madgraph5_aMC@NLO generator, which speeds up matrix element (ME) calculations for leading-order (LO) processes using a data parallel approach on vector CPUs and GPUs, was delivered in October 2024. This was described at CHEP2024 and in other previous publications by the team behind that effort. In this CHEP2026 contribution, I present...

336. Event Generation Acceleration on AI Engine Cores: A Case Study

Pelayo Leguina (Universidad de Oviedo (ES))

27/05/2026, 14:21

Track 5 - Event generation and simulation

Oral Presentation

The generation of hard-scattering events in high-energy physics, is one of the computational bottlenecks in collider phenomenology. MadGraph provides a flexible framework to evaluate these matrix elements, but the sheer scale of Monte Carlo event production required at the LHC drives both execution time and power consumption to critical levels. In this work, we explore the use of Adaptive...

581. New developments in the experiment-independent Gaussino simulation software and its use in LHCb

Wojciech Krupa (CERN)

27/05/2026, 14:21

Track 5 - Event generation and simulation

Oral Presentation

Gaussino is an experiment-independent HEP simulation code built on top of the Gaudi software framework. It provides generic components and interfaces for event generation, detector simulation, geometry, monitoring and output. In this talk we give an overview of recent developments in Gaussino, and some examples of their adoption in the LHCb Simulation since our previous report at CHEP2024. In...

36. Generative AI for hadron physics

Marco Andrea Battaglieri (INFN e Universita Genova (IT))

27/05/2026, 14:39

Track 5 - Event generation and simulation

Oral Presentation

Modern accelerator facilities operating at the intensity frontier—such as CERN, Jefferson Lab, and the forthcoming EIC—produce petabyte-scale datasets that probe the structure of visible matter at the femtometer scale. Fully exploiting and preserving this information requires new AI-driven strategies for data analysis and modeling. We present a program to develop Machine-Learning-based Physics...

231. Muon simulation in JUNO

Jing Chen (Sun Yat-sen University)

27/05/2026, 14:39

Track 5 - Event generation and simulation

Oral Presentation

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kt liquid-
scintillator neutrino detector in China, ~53 km from two nuclear power plant complexes. It aims to determine the neutrino mass ordering and precisely measure neutrino oscillation parameters, while enabling studies on solar, atmospheric, geoneutrino, and supernova neutrino physics. The detector construction was completed,...

479. Integration and Performance of the ATLAS FastChain Workflow towards Run 4

Dominik Duda (The University of Edinburgh (GB))

27/05/2026, 14:57

Track 5 - Event generation and simulation

Oral Presentation

FastChain is a key component of ATLAS preparations for Run 4, providing a unified, configurable framework that integrates simulation, reconstruction, and downstream data reduction into a single end-to-end workflow. By eliminating intermediate data formats and enabling tight coupling between workflow stages, FastChain improves resource utilization efficiency and reduces disk I/O.

To improve...

556. Energy efficiency of GPU-based Monte-Carlo simulation using AdePT

Juan Gonzalez Caminero (CERN)

27/05/2026, 16:15

Track 5 - Event generation and simulation

Oral Presentation

The use of heterogeneous CPU–GPU architectures is becoming an increasingly important consideration for LHC experiments in view of the growing computing demands of the HL-LHC era. WLCG sites and LHC experiments must make decisions in the short to medium term on the deployment and integration of GPUs, in order for these resources to be available and effectively exploited for HL-LHC operations. A...

74. Full Simulation of the CMS experiment progress: from Run3 to Run4

CMS Collaboration

27/05/2026, 16:51

Track 5 - Event generation and simulation

Oral Presentation

During CERN LHC Run 3 data taking, the CMS Geant4-based full simulation was upgraded a few times. The Geant4 version was changed from 10.7.2 to 11.2.2. Other libraries used for the Monte Carlo simulation of CMS---CLHEP, DD4hep, VecGeom---were also updated. A new library G4HepEm was adopted for the CMS simulation, improving CPU performance both for Run 3 and Run 4. In this work, we discuss...

471. Geometry tracking in Celeritas for EM and optical physics

Seth Johnson (Oak Ridge National Laboratory (US))

27/05/2026, 17:09

Track 5 - Event generation and simulation

Oral Presentation

Computational geometry for high energy physics detector simulation is notoriously complex, and indeed it is the primary performance bottleneck in the GPU Monte Carlo codes Celeritas and AdePT.
Detector descriptions contain millions of distinct physical parts with length scales spanning over five orders of magnitude.
Electromagnetic physics simulations must contend with curved particle...

254. Impact of Siloed Geometry Data on LHC Experiments. The ATLAS Experiment Case Study.

Roger Jones (Lancaster University (GB))

27/05/2026, 17:45

Track 5 - Event generation and simulation

Oral Presentation

LHC experiments rely on highly complex detector geometries that support multiple phases of the experiment's lifecycle, including engineering design, manufacturing, installation, physics analyses, and outreach. Although the underlying detector components are the same across these tasks, the requirements differ significantly. For example, engineering integration typically needs only the external...

335. On numerical validation within MadGraph5 for performance and efficiency enhancement

František Stloukal (CERN)

28/05/2026, 13:45

Track 5 - Event generation and simulation

Oral Presentation

At the HL-LHC, computing demands, particularly for event generation, will reach an unprecedented volume for which simple scaling of current resources will be insufficient, requiring new algorithmic and architectural strategies to sustain performance within economic and energy constraints.

A particularly promising approach is to identify parts of the simulation workflow that can be safely...

21. Focused Angular N-Body Event Generator (FANG)

Itay Horin

28/05/2026, 14:03

Track 5 - Event generation and simulation

Oral Presentation

We introduce FANG (Focused Angular $N$-body event Generator), a new Monte Carlo tool for efficient event generation in restricted Lorentz-invariant phase space (LIPS). Unlike conventional approaches that uniformly sample the full $4\pi$ solid angle, FANG directly generates events in which selected final-state particles are constrained to fixed directions or finite angular regions in the...

425. New techniques for reducing negative-weight events in MC@NLO-type simulations

Andrea Valassi (CERN)

28/05/2026, 14:21

Track 5 - Event generation and simulation

Oral Presentation

Physics event generators are essential components of the simulation software chain of HEP experiments, providing theoretical predictions against which experimental data are compared. In the LHC experiments, the simulation of QCD physics processes at the Next-to-Leading-Order (NLO) or beyond is essential to reach the level of accuracy required. However, a distinctive feature of QCD NLO...

509. Cell Reweighting Algorithms for Pathological Weight Mitigation in LHC Simulations using Optimal Transport

Lauren Meryl Hay (SUNY Buffalo), Rishabh Jain (Brown University (US))

28/05/2026, 14:39

Track 5 - Event generation and simulation

Oral Presentation

As the accuracy of experimental results increase in high energy physics, so too must the precision of Monte Carlo simulations. Currently, event generation at next to leading order (NLO) accuracy in QCD and beyond results in the production of negatively-weighted events. The presence of these weights increases strain on computational resources by degrading the statistical power of MC samples,...

419. Revisiting the Fermi Break Up model for the Geant4 library

Aleksandr Svetlichnyi (INR RAS, MIPT(NRU))

28/05/2026, 14:57

Track 5 - Event generation and simulation

Oral Presentation

The Geant4 toolkit is widely used for modelling light-nuclei beam fragmentation in human tissue and other radiological studies (see, for example, [1]). Precise and fast modelling of secondary fragments resulting from beam fragmentation in tissue is vital for studying the radiobiological effects of heavy ion therapy [1]. Short $^{16}$O–$^{16}$O and $^{20}$Ne–$^{20}$Ne runs have been conducted...

324. AI-Assisted Detector Design and optimization Environment for large-scale nuclear and particle physics experiments

Cristiano Fanelli (William & Mary)

28/05/2026, 16:15

Track 5 - Event generation and simulation

Oral Presentation

Artificial Intelligence (AI) is poised to play a central role in the design and optimization of complex, large-scale detectors, such as the future ePIC experiment at the Electron-Ion Collider (EIC), an international next-generation QCD facility in the United States.
The ePIC experiment consists in an integrated detector comprising a central apparatus complemented by forward and backward...

68. Reweight Me No More: Transformer-Based Mitigation of Multi-Dimensional Mismodelling in HEP Simulations

Matthias Schott (CERN / University of Mainz)

28/05/2026, 16:51

Track 5 - Event generation and simulation

Oral Presentation

Accurate Monte Carlo (MC) modelling of high-energy physics (HEP) data remains a central challenge, especially when simulated distributions fail to reproduce observations. Traditional remedies rely on reweighting individual observables to data, an approach that is effective when only one or two dimensions exhibit discrepancies. However, for N correlated observables with N > 2, conventional...

310. Simulation-based Inference for Precision Neutrino Physics through Neural Monte Carlo Tuning

Dr Arsenii Gavrikov

28/05/2026, 17:09

Track 5 - Event generation and simulation

Oral Presentation

The Jiangmen Underground Neutrino Observatory (JUNO) is a next-generation neutrino experiment located in China. To achieve its main objectives, the experiment demands highly accurate Monte Carlo (MC) simulations. These simulations must describe the complex response of the 20-kton liquid scintillator target within a 35.4 m diameter acrylic sphere, which is monitored by thousands of...

288. Differentiable particle simulation for detector optimization

Jeffrey Krupa (SLAC)

28/05/2026, 17:27

Track 5 - Event generation and simulation

Oral Presentation

Applying automatic differentiation (AD) to particle simulations such as Geant4 opens the possibility of gradient-based optimization for detector design and parameter tuning in high-energy physics. In this talk, we extend our previous work on differentiable Geant4 simulations by incorporating multiple Coulomb scattering into the physics model, moving closer to realistic detector modeling. The...

615. Machine Learning for Retrieving Published Experimental Data to Validate the Physics Content of Monte Carlo Transport Codes

Elisabetta Ronchieri

28/05/2026, 17:45

Track 5 - Event generation and simulation

Oral Presentation

Validation testing of the physics content of Monte Carlo particle transport systems—used extensively in high-energy, astroparticle, and nuclear physics—requires extensive retrieval of pertinent experimental measurements from the scientific literature. This process often entails examining thousands of papers published over several decades. The rapidly growing volume of literature poses a...

229. Opticks: GPU Accelerated Optical Photon Simulation for JUNO and Other Experiments

Dr Simon Blyth (IHEP, CAS)

Track 5 - Event generation and simulation

Oral Presentation

Opticks is an open source framework that accelerates Geant4 toolkit based
detector simulations by offloading the optical photon simulation to the GPU
using NVIDIA OptiX ray tracing and NVIDIA CUDA computation. Geant4 detector
geometries are auto-translated into mostly analytic Constructive Solid Geometry
forms, with only computationally demanding shapes like tori converted...

553. Towards the future SHiP simulation framework and geometry

Oliver Lantwin (Universitaet Siegen (DE))

Track 5 - Event generation and simulation

Oral Presentation

The SHiP experiment will search for new physics at the intensity frontier, particularly for feebly interacting particles. Full simulation of the signal and background is crucial to reach the planned sensitivity and to refine the subsystem designs for their TDRs. Besides standard event generators and Geant4, custom approaches are used for the efficient simulation of the thick target and...