Towards a Proposal for an Advanced Linear Collider Report on the Advanced and Novel Accelerators for High Energy Physics Roadmap Workshop, CERN, Geneva, April 2017

The Advanced and Novel Accelerators for High Energy Physics Roadmap (ANAR) Workshop was organized on the initiative of the Advanced and Novel Accelerator (ANA) panel of the International Committee for Future Accelerators 1 (ICFA-ANA panel, members of this panel are listed below). It was chaired by B. Cros and co-chaired by P. Muggli. The workshop focused on the application of ANAs to high energy physics (HEP), keeping in mind the ultimate goal of an electron/positron (e−/e+) collider or an electron/proton (e−/p+) collider, both at the energy frontier. The development of ANAs is conducted at universities and national laboratories worldwide. The community is thematically broad and diverse, in particular since lasers suitable for ANA research (multi-terawatt peak power, a few tens of femtosecond-long pulses) and acceleration of electrons to tens to hundreds of mega electron volts became commercially available. The community spans over several continents (Europe, America, Asia), including more than 62 laboratories in more than 20 countries. It is among the missions of the ICFA-ANA panel to feature the amazing progress made with ANAs, to provide international coordination and to foster international collaborations towards a future HEP collider. The ANAR workshop was organized as a first step towards the development of an international ANA scientific roadmap for such an advanced linear collider, with the delivery of a technical design report by 2035. The first step towards this goal includes taking stock of the scientific landscape, outlining global priorities for scientific progress, identifying facilities necessary for this progress, identifying existing and local roadmaps, and imagining strategies to encourage the development of a genuinely international roadmap.