Particle Physics Planning Process Moves Into Final Phase

February 15, 2023

Two men walking through a tunnel at the Large Hadron Collider

The future of particle physics in the U.S. hinges on what Hitoshi Murayama, a theoretical particle physicist at the University of California, Berkeley, and 30 other members of the Particle Physics Projects Prioritization Panel (P5) decide later this summer.

Last year, particle physicists conducted the Snowmass 2021 process (it was delayed until 2022 by the pandemic) and submitted over 500 white papers, each a vision of the future. Toward the end of the process — which is organized by the APS Division of Particles and Fields — they gathered in Seattle for 10 days to hash out a consensus on which scientific questions should be pursued, and the experiments they’d like to pursue them with. As the curtain closed, Murayama was announced as the chair of P5, which, as its name suggests, is designed to prioritize projects — eventually.

“We are not ready to discuss prioritization yet, because we haven't understood the cost and schedule for each project,” Murayama says. Currently, P5 is gathering more information, largely in the form of four town halls held at national laboratories: Lawrence Berkeley National Lab, Fermilab, Brookhaven National Lab, and SLAC National Accelerator Lab. Additionally, Murayama has added a subpanel under P5 specifically for cost assessment.

After aggregating all this information, P5 will deliver its preliminary recommendations in August, and a final report before Halloween. Nominally, the report goes to the High-Energy Physics Advisory Panel, but its ultimate destination is the Department of Energy, the National Science Foundation, and the legislative staff in Congress who control budgets. If the process is lengthy and a little byzantine, this is by design — planning experiments that can span decades and cost billions of dollars is complex work, even without the science.

Bureaucracy aside, particle physicists are excited. Karsten Heeger, an experimental neutrino physicist at Yale University, and co-chair of P5, says the first town hall had over 400 registered participants. “I’m very pleased by just seeing the engagement of the community, especially the young people,” he says. P5 is planning additional virtual town halls to increase access for community members who can’t be in person. This kind of accessibility is critical for early-career researchers who often lack the funds to travel, says Julia Gonski, a postdoctoral researcher at Columbia University.

At these town halls, whether in person or virtual, P5 is hoping to gain information that differs slightly from what was presented at Snowmass. “The Snowmass reports are basically about the aspirations of the community,” Murayama says. “P5 is an exercise to put them together into a program that fits within a certain budget profile, so we need more information about the cost and schedule.”

The DOE and NSF have already informed P5 that there are two main funding scenarios. “One of them looks really grim,” Murayama says. In the first scenario, the budget for particle physics would increase by 2% every year — less than the rate of inflation. A brighter scenario includes initial funding from the CHIPS Act and a 3% increase year-over-year.

“It won’t be possible to say yes to everything. That’s just the reality,” Heeger says. “But even if we have to de-emphasize certain aspects, there’s still a ton of exciting science.” In addition to monetary costs, particle physicists are also thinking about energy costs in light of climate change and the rise in European electricity prices, which cut short experiments at the Large Hadron Collider last year.

The trouble will be in the prioritization. P5 is composed of a broad swath of the particle physics community, from theorists who specialize in machine learning to accelerator physicists who build specialized machines. Five members of the panel are internationally based. This diversity of experience and expertise will lead to differing opinions, but Murayama hopes to reach consensus, instead of deciding with a numerical vote.

Part of the job involves translating this decision into a strong argument. “It's our responsibility to make the case why the science is important, why the science is exciting, and what our value is to society,” Heeger says. While P5 is not organized to attempt to convince funding agencies in other countries, it has to remain cognizant of international factors because almost any sizable experiment requires multinational cooperation.

But perhaps the most important buy-in comes from within the community. “Any time you see a timeline taking you out to 2070, people realize that we can't do this with one generation of a scientist,” Gonski says.

Heeger agrees. “One of the challenges in high energy physics is the timescale and the scale of experiments, and so we need to make sure that it also serves our younger colleagues,” he says.

This Snowmass process was the first time that early career issues were treated as a “frontier” (like neutrino physics, or theory), with a report of their own. In addition to the increased involvement of early career researchers, Gonski also points to improved conversations about equity and inclusion. “Ten years ago, these were very novel concepts,” she says. “We didn't have the diversity that we have now, in identity, in career stage, in socioeconomic [status].” The 2013 Snowmass survey found 79% of participants were male, and it did not even ask about race or ethnicity. The 2021 survey, by comparison, recorded 70% of participants as male and 68% as white.

The multigenerational aspect of Snowmass also means Gonski says she wants to learn things from those who have gone through it before her. “I really feel like we need to learn project management,” she says. “Hitting those project milestones, from an organizational standpoint, is so important.” Meenakshi Narain, a particle physicist at Brown University and P5 member, who died Jan. 1, was well-known as an expert in project management. “It was a big loss to the community and to the panel,” Murayama says.

He and Heeger hope Narain’s advocacy for early-career researchers — now memorialized in a mentorship award — lives on in Snowmass. “Young people are very engaged, they speak up [and] their voices are actually being heard,” Heeger says. “Young people are also the ones that clearly have a stake in the future of some very exciting and challenging projects.”

Another article on this topic has been published by AIP.

APS News