America's Particle Physics Plan Spans the Globe — and the Cosmos

RALEIGH, N.C. — Particle physicist Hitoshi Murayama admits that he used to worry about being known as the “most hated man” in his field of science. However, he has now come to joke about it.

Last year, the Berkeley professor chaired the Particle Physics Project Prioritization Panel, or P5, which outlined a list of multimillion-dollar experiments in physics to be undertaken in the next decade. This list focused on phenomena ranging from subatomic interactions to cosmic inflation. The challenge lay in determining which projects could move forward amidst budget constraints, potentially relegating Murayama to the role of Dr. No in the world of physics.

Despite some regrets regarding postponed projects, Murayama felt satisfied with the outcome and expressed his hopes that the federal government would support the P5’s top priorities.

Highlighted Projects

“There are five actually exciting projects we think we can do within the budget program,” Murayama mentioned during a presentation at the ScienceWriters 2024 conference. Not all the projects receiving U.S. funding are new, and not all are based in the United States. Below is a breakdown of these projects:

• Looking for Dark Matter: Approximately 85% of the universe's total matter is theorized to exist in a form that has yet to be detected other than through its gravitational effects. An ongoing experiment in a repurposed gold mine in South Dakota is searching for hints of dark matter interactions with a massive reservoir of liquid xenon. While the search to date has yielded no results, the P5 report urges for an increase in the reservoir's size from seven to 70 tons.
• Following up on the Higgs Boson: The discovery of the Higgs boson in 2012 completed the framework of the Standard Model of particle physics, a pivotal scientific theory. Yet, a detailed comprehension of how the Higgs operates remains elusive. “To truly understand it, you'd want to mass-produce Higgs bosons to study their properties,” remarked Murayama. This undertaking will necessitate the construction of a larger particle collider capable of colliding electrons and positrons. However, the P5 panel concluded that such a machine could not be built on U.S. soil and recommended supporting “offshore Higgs factories” such as CERN’s FCC-ee facility or Japan’s proposed International Linear Collider.
• Studying Neutrinos: The Big Bang likely produced equal amounts of matter and antimatter, which should have annihilated one another. Instead, matter prevailed. “Neutrinos are one of the only particle candidates that could account for this phenomenon,” elucidated Murayama. The Deep Underground Neutrino Experiment is being constructed with plans for upgrades aimed at improving their capabilities.
• Capturing Neutrinos from the Cosmos: The P5 panel has also proposed a significant expansion of the IceCube Neutrino Observatory located in Antarctica. The observatory successfully detected neutrinos emanating from a supermassive black hole situated in a nearby galaxy. Murayama noted, “This can become a true mechanism for observing the universe distinct from traditional telescopes.”
• Investigating Cosmic Inflation: A prevalent theory postulates that the universe underwent rapid inflation immediately following the Big Bang, solidifying the initial perturbations seen in cosmic microwave background radiation. Following claims in 2014 of an experiment picking up evidence for this inflation at the South Pole, later investigations retracted such assertions. Nevertheless, studies are ongoing, with the P5 committee advocating for the CMB-S4 experiment to broaden the quest for evidence. This undertaking will necessitate the establishment of two sites: one in Chile and another at the South Pole.

Additionally, the panel endorsed a long-term strategy to develop an advanced particle accelerator capable of producing collisions between subatomic particles known as muons. Establishing such a facility would bolster opportunities for breakthrough discoveries in physics by the 2030s.

“We refer to this as the ‘muon shot’, akin to the moonshot, because while the goal may be uncertain, the endeavor will inevitably yield numerous fascinating findings along the way, advancing science and technology.” – Hitoshi Murayama

Future Prospects

Funding and Support

The fate of these priorities now lies in the hands of the U.S. Department of Energy and the National Science Foundation, which will review the recommendations put forth by the P5. The prospects for success remain uncertain, as evidenced by the NSF's recent decision to postpone the CMB-S4 experiment in favor of upgrading aging infrastructure at its Antarctic facilities.

Looking into the future, the implications for particle physics under a potential return of Donald Trump to the White House remain to be seen. The price tag for four of the projects under consideration totals over $2.5 billion over several years, with the cost of the offshore Higgs factory expected to run into the billions as well.

Murayama highlighted a timely issue that could impact projects such as IceCube, CMB-S4, and other Antarctic endeavors: “A fleet of cargo planes owned by the U.S. Air Force has served our operations well for decades, yet these aircraft, built in the 1970s, are now slated for retirement, with no current plans for replacement. Access would be lost if that occurs.”

Senate Majority Leader Chuck Schumer has successfully included a $229 million appropriation for new aircraft in the Senate’s defense budget proposal for the current fiscal year, though the House still must take action, creating a congressional cliffhanger in the weeks and months ahead.

“It’s challenging to gauge the urgency of these priorities,” offered Murayama. “However, given that this is supposedly part of the defense budget, which is significantly larger than the science budget, it constitutes a modest sum. Hopefully, this will proceed smoothly for funding.”

Discussion and Perspectives

For a critical analysis of the P5 recommendations and the future trajectory of particle physics, it's recommended to view physicist Sabine Hossenfelder's YouTube video.

Alan Boyle is a volunteer board member for the Council for the Advancement of Science Writing, which was one of the organizers of the ScienceWriters 2024 conference.

Conclusion

The developments in particle physics as outlined by the P5 report highlight the ambitious goals set by scientists both within the United States and globally. As they seek answers to questions about the fabric of our universe, funding and political support will play a tremendous role in realizing these vital experiments.

For More Information

P5 Report: https://www.usparticlephysics.org/2023-p5-report/

Deep Underground Neutrino Experiment: https://lbnf-dune.fnal.gov/

Cosmic Microwave Background S4: https://cmb-s4.org/

Understanding Dark Matter: https://www.universetoday.com/168399/largest-dark-matter-detector-is-narrowing-down-dark-matter-candidate/

Future of Particle Physics: https://www.science.org/content/article/their-budget-already-stretched-near-bursting-u-s-particle-physicists-dream-small

For any further inquiries, please feel free to suggest additional resources or ask any questions.