On 17 July 2022, hundreds of US high-energy physicists, along with colleagues from all over the world, gathered at the University of Washington in Seattle for a ten-day meeting to take one of the final steps in the latest US high-energy physics (HEP) community planning exercise. These exercises, hosted by the Division of Particles and Fields of the American Physical Society (APS), take place every seven to ten years. Their goal is to identify the most important questions in HEP for the next two decades and the tools and infrastructure required to address them. The process and the final meeting go by the name "Snowmass", harking back to the early editions, starting in 1982, which concluded with a community summer study in Snowmass, Colorado. The Seattle meeting, originally scheduled to take place in July 2021, was delayed by one year because of the COVID-19 pandemic.
Snowmass is a "science study" in which all scientifically credible ideas and proposals are welcome. It does not concern itself with costs or budget constraints. However, the projects and proposals that it develops provide input to a follow-up Particle Physics Project Prioritization Panel, known as P5, which makes recommendations to the US Department of Energy and National Science Foundation on which HEP projects to undertake, based on various funding scenarios.
The Snowmass study was organised into ten working groups, or "frontiers": accelerator, cosmic, community engagement, computing, energy, instrumentation, neutrino, rare processes and precision measurements, theory, and underground facilities and infrastructure. An organisation of early-career physicists helped bring the issues of young people into the community study. More than 2000 physicists from all over the world contributed to over 500 white papers that are now being distilled into frontier reports. The reports, together with an overall summary and all the white papers, will then be provided to P5.
The Seattle meeting, which ended on 26 July, was a hybrid event, with approximately 700 people attending all or part of the meeting in person and another 650 people participating remotely. It provided a final opportunity for the frontiers to discuss their visions internally, to ensure that they were aligned with those of the other frontiers and to resolve any issues before writing their final reports. The daily programme typically started at 8.00 a.m. and ran until 7.00 p.m. Days 2-8 were packed with parallel sessions in the mornings and three 90-minute plenary sessions in the afternoons. Days 1, 9 and 10 consisted entirely of plenary sessions that included special presentations of plans and planning processes by many leaders of US and international institutes and laboratories, including Fabiola Gianotti (CERN), Masanori Yamauchi (KEK, Japan), Yifang Wang (IHEP, China), and Lia Merminga (Fermilab, US).
Many scientists from the CERN community contributed their ideas to the Snowmass process and several attended the Seattle meeting. Both Director-General Gianotti and Fermilab Director Merminga acknowledged the importance of US-CERN collaboration on the LHC and the HL-LHC, the LHC Accelerator Upgrade Project and DUNE at LBNF, and expressed an openness to discuss collaboration on future projects, including future colliders.
On the final day, Priscilla Cushman of the University of Minnesota put it all in perspective with her inspiring "Community Summer Study and Workshop Synthesis". As the audience held its breath, JoAnne Hewett of SLAC National Accelerator Laboratory and chair of the US High Energy Physics Advisory Panel (HEPAP) announced that the new P5 chair would be Berkeley professor Hitoshi Murayama.
We wish to acknowledge the work of the University of Washington local organising committee, led by Professors Gordon Watts and Shih-Chieh Hsu, for running an outstanding workshop under difficult circumstances. We thank the four units of APS whose work is closely related to HEP, namely astrophysics, nuclear physics, physics of gravity, and especially the physics of particle beams, for their many contributions to this Snowmass process. Finally, we express our thanks and admiration to the Snowmass community, who produced great physics studies despite the many challenges facing them in this period.
Joel Butler, US Division of Particles and Fields, Chairperson, 2022, Fermilab, Batavia, IL, US.
Sekhar Chivukula, University of California, San Diego, San Diego, CA, US. (DPF Chairperson-elect)
Andre de Gouvea, Northwestern University, Evanston, IL, US. (DPF Vice-Chairperson)
Tao Han, University of Pittsburgh, Pittsburgh, PA, US. (DPF Chairperson, 2021)
Young- Kee Kim, University of Chicago, Chicago, IL, US. (DPF chairperson, 2020)
Priscilla Cushman, University of Minnesota, Minneapolis, MN, US. (DPF recent chairperson, 2019)
