AtlFast3: the next generation of fast simulation in ATLAS

TL;DR

AtlFast3 is an advanced fast simulation tool for the ATLAS experiment that combines machine learning and parameterization to produce accurate and efficient Monte Carlo event simulations, especially for jet substructure.

Contribution

Introduces AtlFast3, a novel high-accuracy fast simulation method integrating machine learning with parameterized models for ATLAS detector simulation.

Findings

Achieves highly accurate jet substructure modeling.

Significantly reduces CPU resources needed for simulation.

Enables large-scale event generation for diverse physics analyses.

Abstract

The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with \textsc{Geant4} is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation -- the calorimeter shower simulation -- with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.