ALICE Event Display -- from the legacy ROOT-based visualization to the web-based application
Julian Wojciech Myrcha
TL;DR
The paper documents ALICE's transition of event visualization from a legacy ROOT TEve-based system to a web-based application within the O2 Framework, preserving real-time online visualization while enabling browser-based access. It outlines the data-handling workflow (o2-eve-workflow), the legacy viewer, and the new web-oriented EVE format with a converter (o2-eve-converter) to facilitate format transitions. The web visualization leverages THREE.js and React.js with web sockets for updates, achieving interactive performance for up to 50,000 tracks and clusters and enabling remote access without local software installation. The study demonstrates a complete, scalable path from a C++ ROOT-based pipeline to a browser-friendly visualization, with improved maintenance, extensibility, and cross-machine accessibility.
Abstract
A Large Ion Collider Experiment (ALICE) is one of the four big CERN experiments at the LHC. The area of interest is the study of the Quark-Gluon Plasma which is produced in heavy-ion collisions. The trajectories of particles created in collisions are reconstructed online and are visualized together with the detector geometry to provide proper augmentation of the presented data. This interactive visualization tool allows 3D visualization of samples taken from the collected data. Starting with LHC Run 3 (from 2022), a newly developed solution has been adopted following the creation of the new ALICE O\textsuperscript{2} Framework. In the first step the data handling part was implemented. The visualization part was developed using technologies from LHC Run 2. This paper presents the process of transition of the visualization component to the modern web based solution. The architecture of the existing ALICE LHC Run 3 online real-time visualization solution is presented. The advantages of the new approach are discussed.