ROOT is a software framework at the heart of HEP’s Software Ecosystem. It is an open source project, hosted on GitHub. Laboratories such as GSI, FNAL, CERN, as well as several universities contribute to it. Moreover, many talented and motivated individuals develop ROOT: during 2025, more than 90 distinct contributors made ROOT development a sound success!

This developers community is a pillar for ROOT: interacting with it is of prime importance for the project. The ROOT core developers reach out to the community in a variety of ways, for example Hackathons (e.g. 1, 2), formal meetings, discussions or the ROOT Forum. Those channels are very important, however, the communication would be incomplete without the ROOT Users Workshops!

Since 1999, 12 ROOT Users Workshops have taken place. At the beginning, the locations were alternating between CERN and Laboratories in the U.S.. Since 2018, we have enjoyed venues from all around the world. The 13th ROOT Users Workshop took place in the wonderful city of Valencia, Spain, at the Universitat Politècnica de València (UPV).

The Workshop had a high attendance: 90 scientists and students from institutes in 16 countries convened together to discuss ROOT and shape its future. The programme presented innovative elements: it did not only consist of 56 high-quality oral presentations and 19 posters, but also of a ROOT Training, attended by more than 50 participants, as well as a Virtual Reality Booth - yes, ROOT and Virtual Reality! Such a mix kept the audience engaged at all times, and productive discussions happened during the dedicated slots in the agenda, but also during breaks, meals and very enjoyable evenings in Valencia.

International experts in the area of scientific software, data analysis, computing as well as students and postdocs convened together. Such a diverse mix of profiles and expertise was key to achieve the formula the organisers were after: something to collect actionable feedback, suggestions, advice and spark productive discussions that could shape the future of ROOT.

The week was subdivided in four tracks: presentations by physics experiments and large scientific initiatives, data analysis, statistical inference and programming language interoperability. Of course, LHC experiments as well as WLCG were present. Great value was also brought to the event by other large communities such as Belle II, BES III, Gravitational Waves or Future Circular Collider - their presentations were all informative and insightful.

The event was not even only about particle physics: we enjoyed presentations about compiler technology, finance and medical physics, reflecting the interdisciplinary nature of ROOT.

The workshop was a very rewarding experience for the ROOT Project, and the core developers are thankful to all the participants for making it a success. It took weeks to process all the notes, impressions and input received: a precious asset that influenced ROOT’s program of work for 2026 and the years to come.

Stay tuned for the next ROOT Users Workshop 😉!