Collisions among proton bunches occur inside the ATLAS experiment at CERN’s Large Hadron Collider up to 40 million times a second. Only a fraction of the collision events are valuable for research and the ATLAS detector must decide which events to store for analysis. This decision-making is done courtesy of the sophisticated Trigger and Data Acquisition System (TDAQ) software. A central component of the ATLAS operation, TDAQ is custom software that extracts data in real-time from the experiment, processes it and selects interesting events – all others are discarded. ATLAS has now released this software openly under the Apache 2.0 licence, allowing modification, reuse and citation.
“The full TDAQ software collection, a diverse set of software packages that cover the full scope of data acquisition, represents nearly two decades of work by some 170 ATLAS members,” says Wainer Vandelli from CERN and member of the TDAQ management team. “Altogether, the software has around 1.6 million lines of code: 72% C/C++, 12% Java, 10% Python and 6% others.”
The TDAQ software is closely related to Athena, which was ATLAS’s first major release of open-source software at the end of 2018. Athena is a collision-event-processing software used by the experiment for reconstructing a collision event from the fragments data in each sub-detector, for detector simulation and for other key tasks required for data analysis. “Athena contains some 5 million lines of code in C++ and Python, and was developed by hundreds of collaborators,” says Edward Moyse, ATLAS Software Coordinator from the University of Massachusetts. “Its release helps broaden our collaboration beyond groups involved in particle physics research – and also allows ATLAS students and postdocs to showcase their work to external employers, hopefully boosting their future careers.” Athena was also released under the Apache 2.0 licence, which is the licence recommended by the High-Energy Physics Software Foundation (HSF).”
One of the TDAQ packages has already garnered external interest. As part of the ATLAS Phase-I upgrades, physicists installed a new interface between the data-acquisition system and the experiment’s front-end and trigger electronics. This novel way of reading out detector signals – known as the Front-End Link eXchange (FELIX) – is also being considered by other experiments. “Fermilab’s Deep Underground Neutrino Experiment (DUNE) and CERN’s NA62 experiment have both invested in FELIX hardware and expressed an interest in the software we developed,” explains Reiner Hauser, DAQ/HLT (High-Level Trigger) Software Coordinator from Michigan State University. “The DUNE collaboration is also considering parts of our TDAQ software for their trigger system. These were all great motivations for us to release the software.”
The TDAQ software had before only been available through limited collaborations with high-energy-physics experiments or through outreach activities (Beamline for Schools, ISOTDAQ). Having it fully accessible and open source will allow for new types of interactions with the high-energy-physics community and beyond. “The TDAQ software itself may benefit from the suggestions from other experiments, as they are faced with new challenges,” confirms Vandelli.
With the open release of both the Athena and TDAQ software, the majority of ATLAS software is now in the public sphere. Not only are the current versions openly accessible, all future versions will be automatically public as well.