ROOT is a modular software toolkit mainly developed in the SFT group and is made for processing, analysing and visualising scientific data. It also allows to read and write data: presently, LHC experiments alone produced about 1 Exabyte (one million Terabytes!) of data stored on disks and tapes in ROOT file format. 

Thousands of HEP physicists use ROOT daily to produce scientific results: for us, the ROOT team, this is a big responsibility especially considering the unprecedented challenges Run III and HL-LHC pose to the field of scientific computation. Luckily we can rely on a very lively community of users. Their contribution is so useful for us that, periodically, a ROOT Users’ Workshop is organised. This event has the objective of gathering together the ROOT community to collect criticism, praise, suggestions and complaints. It is a unique occasion to shape the future of the ROOT project, together, users and developers.

The 10th ROOT Users Workshop took place in Sarajevo, at the Academy of Science and Arts, from the 10th to 13th September. Easily reachable from Geneva, the city  of Sarajevo is a fantastic location: an exceptional setting made even better by the well known Balkan hospitality. The workshop was also an unprecedented opportunity to involve Bosnia and Herzegovina in the activities of CERN. More than one hundred people attended, also from the local university, making the event a real success: a 30% increment with respect to the previous workshop organised in 2015. The participants came from Europe and America, bringing about different levels of expertise: students, about a third of the audience, analysis physicists, framework developers, software experts and ROOT enthusiasts.

The workshop featured 69 high quality contributions as well as hours of engaging discussions, during the officially scheduled sessions but also during breaks, lunches, dinners, social events or walks around the city. Companies also participated to the event with three invited contributions. Peter Müßig (SAP) presented OpenUI5, the open source core of the SAP javascript framework used to build enterprise-grade web user interfaces that will be used for ROOT's GUI. Chandler Carruth (Google) discussed ways to make large-scale software projects written in C++, the main language for number crunching code in HEP, simpler, faster and safer. Sylvain Corlay (Quantstack) showed novel ways to tackle numerical analysis with multi-dimensional array expressions. These industry speakers enjoyed the workshop, too, and plan to come to CERN in the future to extend the collaboration.

ROOT Users’ Workshop 2018 attendees at the Academy of Science and Arts of Bosnia and Herzegovina.

Indeed ROOT’s renovation was the main theme of the workshop. ROOT started to be the cornerstone of virtually all HENP software stacks about two decades ago. Presently, the toolkit, in order to be at the bleeding edge of software technology, is undergoing an intense upgrade program of its key components: this huge effort represents really exciting times for physicists and software developers. ROOT’s users appreciated the effort to make ROOT easier to use, faster on modern computer architectures and ultimately more modern with the sole objective of reducing the time interval between data delivery and presentation of plots to illustrate results.

In particular the spotlight was on the modernisation of the I/O subsystem, crucial for the future Physics Programme of the LHC, the parallelisation of ROOT, a prerequisite to face the analysis of Run III and HL-LHC datasets, as well as the new graphics, statistical and multivariate tools and interface to the Python language: all elements of prime importance for the everyday work of physicists.

Participants' feedback on the workshop was enthusiastic. The setting was wonderful and the local logistics flawless. The atmosphere has always been positive, criticism was constructive and extremely useful for the ROOT team. The whole team would like to thank the participating physicists and computer scientists during the workshop: we sincerely appreciated your active engagement! We are eagerly looking forward to organising the next ROOT workshop!

We would like to thank Edmond Offermann and the EP department for making this event possible with their contributions.