A panel of the nation‘s top particle physicists, chaired by University of California, Berkeley, theoretician Hitoshi Murayama, has issued its final report recommending how the U.S. government should commit its high-energy physics research funds for the next decade and beyond, focusing on neutrinos, dark matter and the cosmic microwave background.

The report by the Particle Physics Project Prioritization Panel (P5) was approved on Friday, Dec. 8, by the High Energy Physics Advisory Panel (HEPAP) and will be sent to the two main funding agencies for physics in the U.S. — the Department of Energy (DOE) and the National Science Foundation (NSF) — to aid them in their decisions about which research to fund. The HEPAP, a permanent advisory committee to DOE and NSF, constitutes a prioritization panel every 10 years.

The panel, consisting of 31 members and one ex-officio member from the U.S. and abroad, considered only large- and medium-sized physics research projects — the kind that can take years or decades to plan and build, enlist contributions from thousands of scientists and cost billions of dollars.

To fit within budget constraints — likely less than $5 billion from the two agencies over 10 years for new projects — the panel had to combine or reconfigure many proposed projects and turn down perhaps two-thirds of them.

"Fiscal responsibility has been a big thing on our mind to make sure that the recommendations are actionable by agencies and can be followed up," said Murayama, the MacAdams Professor of Physics at the UC Berkeley. "We had to be really realistic about our plan."

The five recommended projects with estimated budgets exceeding a quarter of a billion dollars each are:

The Cosmic Microwave Background Stage IV experiment (CMB-S4), which will use telescopes sited in Chile and Antarctica, supported by U.S. infrastructure at the South Pole, to study the oldest light from the beginning of the universe. The polarization of the CMB can tell cosmologists about the gravitational waves generated during inflation in the early universe and help them understand what was going on when the cosmos was still microscopic.
Enhancements, including an upgrade in power and experimental capabilities, to the Deep Underground Neutrino Experiment (DUNE) in South Dakota. The DUNE is the centerpiece of a decades-long program to reveal the mysteries of elusive neutrinos. The U.S.-hosted international project will exploit a unique underground laboratory, the Sanford Underground Research Laboratory, now nearing completion, and neutrino beams produced at Fermi National Accelerator Laboratory in Illinois.
A Higgs boson factory, located in either Europe or Japan, to advance studies of a still mysterious particle that was only discovered in 2012, yet which gives mass to all other forms of matter. An accelerator that produces lots of Higgs bosons would allow precise measurements of the boson‘s properties and help physicists understand how the particle fits into current models of the universe and whether it is connected with dark matter.
A Generation 3 (G3) Dark Matter experiment that would combine four different international experiments — including the LZ experiment led by Lawrence Berkeley National Laboratory — into one comprehensive program to probe the enigmatic nature of dark matter, which makes up a significant portion of the universe’s mass and energy and has been one of the most enduring mysteries in modern physics. The panel recommended that this experiment be built in the U.S.
Expansion at the South Pole of a neutrino observatory, which earlier this year mapped for the first time the sources of neutrinos from the Milky Way galaxy and outside our galaxy. Called IceCube-Gen2, it would be an international collaboration operated by the University of Wisconsin–Madison. The observatory now consists of detectors embedded in 1 cubic kilometer of ice; the expansion would increase the observatory‘s sensitivity by a factor of 10.
The panel also recommended investing in studies of a future muon collider. While most particle accelerators today rev up electrons or protons and smash them together, a muon collider would accelerate short-lived muons, which are fundamental particles like electrons (they‘re both leptons), but much heavier. A muon collider could explore new frontiers of physics with much less energy input than a proton collider. The panel proposed Fermilab as a good place to build a demonstration collider to test the unique technology.