Committee lays out research priorities for future of U.S. particle physics

There are many outstanding questions about the universe: What is the nature of dark matter? Why is the universe expanding? How do neutrinos acquire their mass?

Because experiments to answer these kinds of questions can require significant planning and construction, such as building new accelerator facilities—which can take years or decades, contributions from thousands of scientists, and billions of dollars—physicists plan for these projects many years ahead.

This week a group of eminent physicists released the Particle Physics Project Prioritization Panel (P5) report, outlining their recommendations to U.S. funding agencies for research priorities and creating a roadmap for the field of particle physics in the United States for the next decade. Among their priorities are several projects which University of Chicago scientists are leading or contributing, including a project to map the early universe known as CMB-S4 and the Deep Underground Neutrino Experiment.

“These are huge questions, which we divide into three major areas: deciphering the quantum realm, illuminating the invisible universe and exploring new paradigms in physics,” said University of Chicago Prof. Abby Vieregg, a member of the P5 committee and the David N. Schramm director of the Kavli Institute for Cosmological Physics. “One interesting thing is that we are increasingly looking towards blending cosmology and particle physics in one unified vision to learn about how the universe works at the biggest and smallest scales.”

‘The next generation’

According to the committee, the P5 report amounts to a strategic plan for the U.S. community with a 10-year budgetary timeline and a 20-year context.

The P5 report listed CMB-S4, a network of ground-based telescopes designed to observe the cosmic microwave background, as its highest priority project. CMB-S4, which is co-led by the University of Chicago and Lawrence Berkeley National Laboratory, aims to build telescopes and infrastructure in both Antarctica and Chile to search for what are known as “primordial” gravitational waves—the vibrations from the Big Bang itself—as well as mapping the microwave light from the cosmos in incredible detail and investigate the mystery known as dark matter.

“CMB-S4 will allow us to investigate the origin of our universe and will provide insights into physics at extreme energies and into the quantum nature of gravity,” said John Carlstrom, the Subrahmanyan Chandrasekhar Distinguished Service Professor of Astronomy and Astrophysics and Physics, who serves as the project scientist for CMB-S4.

P5 also endorses continued support for the Deep Underground Neutrino Experiment (DUNE), based out of Fermi National Accelerator Laboratory (Fermilab), a Department of Energy national lab affiliated with the University of Chicago. DUNE is a massive experiment spanning multiple states that aims to better understand the neutrino—one of the most elusive and mysterious subatomic particles in the universe.

The report also recommends that the United States supports a significant in-kind contribution to a new international facility, the “Higgs factory,” to further our understanding of the Higgs boson. It also recommends that the United States study the possibility of hosting the next most advanced particle collider facility, to reinforce the country’s leading role in international high energy physics for decades to come.

But the report also recommends making space in the budget for a mix of experiments—not just those at the largest scale.

“It’s really exciting to me to see the committee recommend a balance of the very large projects to tackle these big challenges, but also smaller-scale projects that allow people to ask questions creatively and pursue their ideas on a shorter time scale,” said Vieregg.

Broad visions

The P5 report is based on a year of discussions and town halls with physicists around the country. It includes a range of budget-conscious recommendations for federal investments in research programs, the U.S. technical workforce, and the technology and infrastructure needed to realize the next generation of transformative discoveries related to fundamental physics and the origin of the universe.

“We welcome the recommendations put forth by this distinguished panel, and we feel fortunate to be a part of the broader High Energy Physics community that is investigating some of the biggest questions in science through these projects,” said Juan de Pablo, the executive vice president for science, innovation, national laboratories and global initiatives at UChicago. “The proposals endorsed by the P5 report reinforce the value of the ongoing, close-knit relationship between the University of Chicago and the Fermilab and Argonne national laboratories, which are drawing upon deep expertise and cutting-edge technology to expand our understanding of energy, particle physics, and cosmology.”

P5 is one of several major reports charged with laying out visions for the future of the field. The P5 committee took into account recommendations from Snowmass, a group of thousands of members of the international particle physics community whose findings were released in 2021. P5 is also complementary to the Elementary Particle Physics: Progress and Promise study, designed to lay out a broader vision for the coming decades, scheduled to be released in 2024.

“The 2023 P5 report provides a bold, inspiring and balanced vision and roadmap for U.S. high-energy physics,” said Lia Merminga, director of Fermilab. “By strongly endorsing completion of ongoing experiments and construction projects, recommending the early implementation of DUNE as the definitive long-baseline neutrino oscillation experiment and supporting the HEP community’s aspirations to host a muon collider at Fermilab, it will ensure continued U.S. leadership in particle physics for the next decade and beyond. Fermilab strongly supports the P5 report in its entirety.”

P5 is delivered by the High Energy Physics Advisory Panel to the High Energy Physics program of the Office of Science of the U.S. Department of Energy and the National Science Foundation’s Division of Physics. The full report can be found online.