21st International Conference on Computing in High Energy and Nuclear Physics (CHEP2015)

The International Conference on Computing in High Energy and Nuclear Physics (CHEP) is a major series of international conferences intended to attract physicists and computing professionals to discuss on recent developments and trends in software and computing for their research communities. Experts from the high energy and nuclear physics, computer science, and information technology communities attend CHEP events. This conference series provides an international forum to exchange experiences and the needs of a wide community, and to present and discuss recent, ongoing, and future activities. At the beginning of the successful series of CHEP conferences in 1985, the latest developments in embedded systems, networking, vector and parallel processing were presented in Amsterdam. The software and computing ecosystem massively evolved since then, and along this path each CHEP event has marked a step further. A vibrant community of experts on a wide range of different high-energy and nuclear physics experiments, as well as technology explorer and industry contacts, attend and discuss the present and future challenges, and shape the future of an entire community. In such a rapidly evolving area, aiming to capture the state-of-the-art on software and computing through a collection of proceedings papers on a journal is a big challenge. Due to the large attendance, the final papers appear on the journal a few months after the conference is over. Additionally, the contributions often report about studies at very heterogeneous statuses, namely studies that are completed, or are just started, or yet to be done. It is not uncommon that by the time a specific paper appears on the journal some of the work is over a year old, or the investigation actually happened in different directions and with different methodologies than originally presented at the conference just a few months before. And by the time the proceedings appear in journal form, new ideas and explorations have quickly formed, have already started, and presumably have also followed previously unpredictable directions. In this scenario, it is normal and healthy for the entire community to question itself as of whether it is a set of proceedings the best way to document and communicate to peers (present and future) the work that has been done at a precise time and the vivid and live ideas of a precise moment in the evolution of the discipline. Pointing the attention to a specific CHEP event alone does not give the right answer: in fact, the heritage value lies in the quality and continuity of the documentation work, despite the changes of times, trends and actors. The CHEP proceedings, in their variety and thanks to the condensed form of knowledge they offer, are what most likely will be more easily preserved for future generations, thanks to the outstanding efforts over digital libraries for all kinds of cultural heritage. Since 1985, this long-standing tradition continued with the 21st CHEP edition in Okinawa. The successful model that brings together high-energy and nuclear physicist and computer scientists was repeated in the Okinawa prefecture, an outstanding location consisting of a few dozen small islands in the southern half of the Nansei Shoto, the island chain which stretches over about one thousand kilometres from Kyushu to Taiwan. The OIST (Okinawa Institute of Science and Technology) centre hosted the event, and offered an outstanding location and efficient facilities for the event. As for the CHEP history, contributions from 'general purpose' physics experiments mixed together with highly specialized work on the frontier of precision and intensity. The year 2015 is marked by the LHC restart in Run 2. Experimental groups at the LHC reviewed and presented their Run 1 experiences in detail, and reported the work done in acquiring the latest computing and software technologies, as well as in evolving their computing models in preparation for Run 2 (and beyond). On the side of the intensity frontier, 2015 is also the start of Super-KEKB commissioning. Fixed-target experiments at CERN, Fermilab and J-PARC are growing bigger in size. In the field of nuclear physics, FAIR is under construction and RHIC well engaged into its Phase-II research program facing increased datasets and new challenges with precision physics. For the future, developments are progressing towards the construction of ILC. In all these projects, computing and software will be even more important than before. Beyond those examples, non-accelerator experiments reported on their search for novel computing models as their apparatus and operation become larger and more distributed. The CHEP edition in Okinawa explored the synergy of HEP experimental physicists and computer scientists with data engineers and data scientists even further. Many area of research are covered, and the techniques developed and adopted are presented in a richness and diversity never seen before. In numbers, CHEP 2015 attracted a very high number of oral and poster contribution, 535 in total, and hosted 450 participants from 28 countries. For the first time in the conference history, a system of 'keywords' at the abstracts submission time was set up and exploited to produce conference tracks depending on the topics covered in the proposed contributions. Authors were asked to select some 'application keywords' and/or 'technology keywords' to specify the content of their contribution. A bottom-up approach that was tried at CHEP 2015 in Okinawa for the first time in the history of this conference series, this encountered vast satisfaction both in the International Advisory Committee and among the conference attendees. This process created 8 topical tracks, well balanced in content, manageable in terms of number of contributions, and able to create the adequate discussion space for trend topics (e.g. cloud computing and virtualization). CHEP 2015 hosted contributions on online computing; offline software; data store and access; middleware, software development and tools, experiment frameworks, tools for distributed computing; computing activities and computing models; facilities, infrastructure, network; clouds and virtualization; performance increase and optimization exploiting hardware features. Throughout the entire process, we were blessed with a forward-looking group of competent colleagues in our International Advisory Committee, whom we warmly thank. All the individuals in the Program Committee team, who put together the technical tracks of the conference and reviewed all papers to prepare the sections of this proceedings journal, have to be credited for their outstanding work. And of course the gratitude goes to all people who submitted a contribution, presented it, and spent time to prepare a careful paper to document the work. These people, in the first place, are the main authors of the big success that CHEP continues to be. After almost 30 years, and 21 CHEP editions, this conference cycle continues to stay strong and to evolve in rapidly changing times towards a challenging future, covering new grounds and intercepting new trends as our field of research evolves. The next stop in this journey will be at the 22nd CHEP Conference on October 12th-14th, in San Francisco, hosted by SLAC and LBNL.