What next: White Paper of CSN1 Proposal for a long term strategy for accelerator based experiments

The CSN1 (Commissione Scientifica Nazionale 1) is the INFN committee which manages experiments at high energy particle accelerators. This document describes our understanding of the current scientific scenarios and proposes a strategy for the next 10 years in the context of a 20-year global vision for this field of research. The idea for this document was born during 2013. Many excellent experimental results had been obtained, including the newly discovered low mass Higgs boson, but there was still no hint of new physics both in direct and indirect searches. The future was full of proposals for new experiments and research infrastructures, and major upgrades of the existing ones, but all motivations had to be evaluated in a global context. In general there was a clear need to re-analyze in depth our science drivers and then find a consensus within our community about the strategy for the future. This need was reinforced by the perception that funding in our field was becoming more difficult. Since potential new programs are expensive, choices were going to be needed and priorities would need to be set. During the November 2013 meeting of CSN1 there was a discussion on how to deal with this situation. In the end we decided to start a process leading to the proposal of a long term strategy to be published in a "White Paper" on the time scale of approximately a year. We decided that the whole community should be involved with the help of many well known theorists 1. This required some organization, so we formed four working groups covering the following scientific topics: "Direct searches of new physics", "Precise Standard Model measurements", "Flavour physics" and "Non-perturbative QCD". These topics cover completely all scientific activities present in CSN1. Each working group is coordinated by four conveners: two theorists and two experimental physicists. A similar process involving all INFN activities was started one month later by the INFN top management under the name of "What Next" and the CSN1 working groups morphed quite naturally into this extended organization, while retaining also their original scope. In addition to its use for CSN1, this document represents our main contribution to the more global "What Next" process. Two widely attended workshops have been organized to discuss the activities ongoing within the working groups. First a kick off meeting of the whole "What Next" in Rome on April 7-8, 2014; then a dedicated CSN1 workshop in Elba on May 22-24, 2014. Thereafter an editorial committee was setup to coordinate the writing of the document and a preliminary draft was discussed during the December 2014 meeting of CSN1. An updated version was released shortly afterwards for comments from the members of CSN1, the conveners and participants of the working groups. After inclusion of the suggestions received, an open meeting was held on January 15th to discuss the document and in particular its conclusions. The conclusions were approved during the CSN1 meeting of January 19-20, 2015 and the full document has been released for public distribution in May 2015.