Snowmass promises bright future

24 January 2022

We expect to emerge in July with a grand vision for the future of US high-energy physics.


Every seven to 10 years, the US high-energy physics community comes together to re-evaluate and update its vision of the field. These wide-ranging exercises, organised by the American Physical Society (APS)’s Division of Particles and Fields (DPF) since 1982, are now known as the Snowmass Community Studies on account of the final drafting having historically taken place in Snowmass, Colorado. They include all related disciplines that contribute to elementary particle physics and welcome the participation of physicists from outside the US.

Snowmass exists to identify the physics issues that should be addressed and possible approaches to pursuing them, but we do not seek to specify which projects should be carried out. That task is accomplished by a Particle Physics Project Prioritization Panel (P5), a subpanel of the US High Energy Physics Advisory Panel (HEPAP), which uses the Snowmass output to develop programmatic priorities based on specific budget scenarios and provides recommendations to US funding agencies. Snowmass 2013 and the subsequent 2014 P5 roadmap recommended a suite of new projects, including: the HL-LHC upgrade; DUNE/LBNF; a short-baseline neutrino programme; the PIP-II proton source upgrade; the Mu2e experiment; the LSST camera and DESI; the LUX-ZEPLIN and CDMS dark matter searches; preparation for a new cosmic-microwave-background explorer; and strong investment in R&D for future accelerators. With many of these projects now under construction, it is vital to prepare the next round of compelling US particle-physics initiatives.

In April 2020 we kicked off a new Snowmass study. Initially scheduled to conclude with a workshop at the University of Washington in Seattle in July 2021, the process was paused due to COVID-19. On 24 September, at a virtual “Snowmass Day” meeting, we declared the Snowmass process officially resumed, with the Seattle workshop scheduled for 17 to 26 July.

White papers describing ideas, proposals and projects are due by 15 March for discussion

The Snowmass 2021 study is divided into 10 “frontiers”: energy; neutrino physics; rare processes and precision measurements; cosmic; theory; accelerator; instrumentation; computation; underground facilities; and community engagement. Each frontier is led by two or three conveners and is divided into between six and 11 topical groups – with community development, demographics, and diversity and inclusion addressed across all frontiers. A Snowmass early-career organisation has also been formed to assist young physicists in contributing to the process. The whole exercise is overseen by a steering group, which includes the DPF chair line, and international representation is provided by an advisory group chosen by national and regional physics societies.

Informing Snowmass 2021 are many recent results: Higgs-boson properties obtained by ATLAS and CMS; the measurement of the angle θ13 in the neutrino mixing matrix; evidence for anomalies in B-meson decays from LHCb; and the tension between Fermilab’s measurement of muon g-2 and the Standard Model prediction. These topics will continue to be explored in current experiments. Snowmass 2021 and the latest European strategy update focus on what comes next.

Collider matters

In the Snowmass process, we collect all ideas, whether they are large or small, expensive or less so, require international collaboration or not, and are hosted in the US or elsewhere. One topic of intense interest worldwide is the next generation of colliders, both to study the Higgs boson with sub-percent level precision and to directly search for new phenomena in the multi-TeV regime. The proposed Higgs factories require some final development that could be completed in a few years, which would enable a decision on which machine to build, and the start of negotiations to fund it, as an international project. Machines to explore the multi-TeV terrain require significantly more R&D to develop and industrialise the necessary new technologies. We expect this Snowmass/P5 process to set the direction for US participation in this R&D effort and future construction projects. We also look forward to new experiments and upgrades to existing experiments in neutrino physics, rare decays and astrophysics, along with new R&D initiatives in detectors, computing, accelerators and theory.

White papers describing ideas, proposals and projects are due by 15 March 2022 for discussion at the Seattle meeting, where a draft report will be produced and then submitted to HEPAP and the APS in the fall. With hard work and good will, we expect to emerge from the Snowmass/P5 process with a grand vision for a vibrant US high-energy physics programme over the 10 years starting from 2025 and with a roadmap for large new initiatives that will come to fruition in the 2030s. Please join us and contribute your ideas to shaping our future!

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