Snowmass: Creating a vision for the future of particle physics

Daniel Inafuku for ICASU

Illinois Physics faculty members are helping to guide the next decade’s research agenda for the field of particle physics through the Snowmass study, a large-scale, multi-stage collaborative planning exercise. Snowmass is organized by the Division of Particles and Fields (DPF) of the American Physical Society (APS) and solicits participation from all members of this scientific community—a massive undertaking! The final report will reflect the community’s collective evaluation of the most promising research directions that hold the potential for fundamental scientific discoveries.

Particle physics is known for its large collaborations—membership in experiments can number in the thousands. Born out of the particle physics community’s wish to hear from its members, Snowmass can be traced to a 1982 summer study held in the town of Snowmass, Colorado. The study brought together community representatives to identify common interests and has since served as a model for subsequent community exercises. The DPF now organizes a new study each decade under the Snowmass name.

Faculty members of Illinois Physics and of the Illinois Center for Advanced Studies of the Universe (ICASU) are well-represented at all levels of the current Snowmass organization. Illinois Physics Professor and ICASU Director Nicolás Yunes is a Steering Committee member. Illinois Physics Professor Aida El-Khadra is one of three Theory Frontier conveners, while Illinois Physics Professors Jessie Shelton and Patrick Draper each serve as Topical Group co-conveners within the Theory Frontier. Moreover, Illinois Physics faculty members at all career stages are active in the Snowmass process, including early-career scientists Professors Jacquelyn Noronha-Hostler and Yonatan Kahn.

A community-driven approach to long-term planning helps inform research funding agencies

The National Science Foundation (NSF) and the U.S. Department of Energy (DOE) are jointly advised in their research funding decisions by the High Energy Physics Advisory Panel (HEPAP), which in turn appoints an expert committee called the Particle Physics Project Prioritization Panel (P5). The final Snowmass report serves as input to the deliberations of HEPAP and P5.

Illinois Physics Professor Aida X El-Khadra
Illinois Physics Professor Aida X El-Khadra

El-Khadra explains, “The Snowmass process is the particle physics community's long-term scientific 

planning exercise. The emphasis is on community—everybody is welcome to participate—and on exploring the scientific opportunities for the coming decade.”  

Community feedback is solicited through workshops, conferences, town halls, and focused meetings. All Snowmass participants are invited to propose ideas for future studies by contributing white papers, which may draw from work within and across different specializations.

The Snowmass process is the particle physics community's long-term scientific planning exercise. The emphasis is on community—everybody is welcome to participate—and on exploring the scientific opportunities for the coming decade."

Illinois Physics Professor Aida X El-Khadra

El-Khadra continues, “The contributed papers form the basis of reports from the various topical groups and frontiers, which are made available at various stages of completion so that community feedback can be incorporated before the reports are finalized.” 

Snowmass is organized into 10 frontiers: the Accelerator Frontier, the Computational Frontier, the Cosmic Frontier, the Energy Frontier, the Instrumentation Frontier, the Neutrino Physics Frontier, the Rare Processes & Precision Measurements Frontier, the Theory Frontier, and the Underground Facility Frontier. Additionally, a frontier is dedicated to community engagement and advocacy. 

Illinois Physics Professor Patrick Draper
Illinois Physics Professor Patrick Draper

Draper is a co-convener of the Effective Field Theories Topical Group within the Theory Frontier. He notes, “Snowmass is a process of community interaction and self-reflection. We focus on how each of our research programs contributes to the larger goals of particle physics. Snowmass is also a chance to communicate progress and to develop what our larger goals should be for the next decade.”  

Illinois Physics Professor Jessie Shelton, an Astro-Particle Physics & Cosmology Topical Group co-convener within the Theory Frontier, says Snowmass further provides a unique platform to broaden one’s reach within the particle physics community, beyond those traditionally afforded. 

Illinois Physics Professor Jessie Shelton
Illinois Physics Professor Jessie Shelton

“Snowmass is a chance to set the directions for the field,” Shelton adds. “It’s a fantastic forum for theorists and experimentalists to discuss goals and the possibilities that can be tested or discovered. These conversations don’t always happen in the narrow confines of research papers.” 



It’s fundamental science—in future tense

Where is particle physics headed? Kahn predicts two particular research objectives will command special attention in the coming years, namely, follow-ups to Fermi National Accelerator Laboratory’s (Fermilab) recent g-2 experiment, as well as renewed efforts in dark matter searches.


Fermilab Muon g-2 experiment. Credit: Reidar Hahn/Fermilab
Fermilab Muon g-2 experiment. Credit: Reidar Hahn/Fermilab

Kahn says, “I think the next year in particle physics will be dominated by the news of Fermilab’s g-2 experiment, which recently confirmed Brookhaven’s long-standing measurement of the muon anomalous magnetic moment.

Illinois Physics Professor Yonatan Kahn
Illinois Physics Professor Yonatan Kahn

“That calculation will be checked in multiple ways, and we should have a very good sense of whether an anomaly still persists. This result would be the best evidence we have of new physics beyond the standard model.

“In the next five to ten years, I believe new dark matter searches will attract much more attention. So much unexplored parameter space will be covered by new dark matter experiments coming online. Our understanding of the allowed parameters is sure to change with new data.” 

Draper is looking forward to specific theoretical developments that will emerge from Snowmass, related to hierarchy problems or to low-energy field theories.

Draper points out, “Hierarchy problems concern the enormous ranges of physical scales we see in nature. For example, the electrostatic force between two electrons is some 34 orders of magnitude stronger than the gravitational force. Why? Some hierarchies appear to require fine-tuned cancellations in our theories, and it would be much more satisfying to find dynamical explanations. 

“Another complementary effort is to uncover what low-energy field theories can arise from consistent theories of quantum gravity. A dizzying array of theoretical observations have been made in this area since the last Snowmass process, and I’m excited to see if Snowmass can help physicists identify these observations’ underlying structures and connect them to experiment.” 

For his part, Kahn has personally seen the effectiveness of the Snowmass process. In prior Snowmass iterations, Kahn contributed several white papers that drew attention for dark matter experiments. One report underlined the low-cost, high-impact nature of small-scale dark matter initiatives and bolstered interest in such experiments within the DOE. Subsequently, Kahn was invited to co-author a report for a DOE-led workshop, which resulted in a funding call for dark matter experiments. 

This is the optimal outcome of a Snowmass process: a basic research idea achieves a critical mass of community support and is identified as a funding priority, giving people the chance to work on these exciting new directions.

Illinois Physics Professor Yonatan Kahn

Kahn notes, “This is the optimal outcome of a Snowmass process: a basic research idea achieves a critical mass of community support and is identified as a funding priority, giving people the chance to work on these exciting new directions.” 

Another unique feature of Snowmass is its emphasis on interdisciplinary connections to fields beyond conventional particle physics. This aspect is especially important for Noronha-Hostler, a nuclear physics theorist interested in the connection between heavy-ion collisions and the quark-gluon plasma. 

Illinois Physics Professor Jacquelyn Noronha-Hostler
Illinois Physics Professor Jacquelyn Noronha-Hostler

Noronha-Hostler says, “In keeping with the rich history of nuclear theory at Illinois, my colleagues and I are working on building up the nuclear theory program and plan to play a big role in both large collider experiments and nuclear astrophysics. The hope is to continue to build the program and expand in other areas such as the Electron-Ion Collider under construction at Brookhaven National Lab.

“One of the benefits of organizing through Snowmass and coming up with long-range plans for the field is that one can point to a single document to demonstrate to funding agencies that a certain research question has broad support.”

Snowmass is doubling down on theory

The new Theory Frontier not only emphasizes the importance of theoretical research among the community, but also ensures that this is unmissable by funding agencies.

Illinois Physics Professor Jessie Shelton

Contributions by theorists have always been integral to each Snowmass frontier—and they still are. To highlight the role of theory in particle physics in general as well as among the various frontiers, this Snowmass study includes for the first time a separate Theory Frontier. Illinois Physics is playing particularly important roles within the Theory Frontier, with El-Khadra, Shelton, and Draper all in leadership positions.

El-Khadra comments, “The new Theory Frontier highlights the importance of theory in relation to projects as well as in its own right. My job as a Theory Frontier convener is to explore the recent advances and future opportunities across the broad spectrum of high energy theory.”

Shelton adds, “The new Theory Frontier not only emphasizes the importance of theoretical research among the community, but also ensures that this is unmissable by funding agencies. It’s not just about funding facilities and experiments; it’s also about funding the people who do the research enabled by those experiments, as well as the theory needed to guide and interpret these experiments. Congress allocates money to specific projects—for instance, for building a neutrino experiment at Fermilab. We’re underscoring that funding research means more than just building a facility. We need to fund researchers as well, including theorists.”

The pandemic delayed, but didn’t stop Snowmass

Like many other organizations worldwide, Snowmass has had to meet the challenges of the COVID-19 pandemic. The pandemic has largely affected project timelines, with many on hiatus in view of both short- and long-term uncertainties. Moreover, because in-person community discussions lie at the heart of the Snowmass process, with travel made impossible, the Snowmass study was paused for nine months and the Community Summer Study postponed to the summer of 2022.

Shelton explains, “One important factor is that much of our work has been remote and travel is still challenging. While there are some advantages to remote work—it’s a lot easier for people who have trouble traveling to be involved—many of us have had unexpected additional responsibilities.” 

In spite of these ongoing challenges, much progress has been made. Remote meetings laid the foundation for developing new directions and planning new white papers.

Shelton continues, “We have done a lot of work setting up the organization. We have been successful in getting many people involved in the Snowmass process, generating ideas, and writing white papers.”

After a hiatus, activity resumed with an official kick-off in September 2021. In February 2022, El-Khadra co-organized an in-person Theory Frontier conference at the Kavli Institute for Theoretical Physics (KITP). This year’s Snowmass activities will culminate in a Community Summer Study to be held in Seattle in July 2022.

El-Khadra adds, “With over 100 in-person and 400 online attendees, the KITP conference was the first large, in-person meeting since the start of the pandemic, bringing together theorists across the entire spectrum of high energy physics. Lively discussions examined connections, revealed common threads, and laid the groundwork towards a decadal vision for high energy theory, kicking off the next stage of the Snowmass study. Participants will have a lot to discuss at the Community Summer Study in July.”

To date, participants have submitted over 450 white papers to Snowmass, more than 120 of which are submissions to the Theory Frontier. The topical groups and frontiers are currently synthesizing white papers into larger reports, and first drafts are expected to be shared with community members in the coming weeks.