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Report on future of particle physics outlines exciting scientific priorities

By Adam Harrington

December 7, 2023 / 8:38 PM CST / CBS Chicago

CHICAGO (CBS) -- A powerful new particle accelerator that could be set up at Fermilab, a telescope to observe the oldest light in the universe, and research to learn more about mysteries such as dark matter were all among the priorities identified in a new report on the future of particle physics issued Thursday.

The report by the 2023 Particle Physics Project Prioritization Panel – or P5 – lists recommendations for federal funding agencies for what should be constructed to advance particle physics research over the next 10 years. This is the first new P5 report since 2014, and the panel behind it is hoping its suggestions will help shed light on some of the most puzzling mysteries of science and the universe.

Abigail Vieregg – a professor at the Department of Physics, the Enrico Fermi Institute, the Kavli Institute for Cosmological Physics, and the College at the University of Chicago – was a member of the 2023 P5. She talked with CBS 2 Thursday afternoon about some of the most ambitious and exciting science that P5 has identified as its priorities in the report.

A powerful new collider at Fermilab

Among the priorities identified by P5 is a muon collider – which would be even more powerful than the Large Hadron Collider at CERN in Geneva, Switzerland. The goal, Vieregg explained, is to "get to even higher energies of particles… accelerate them even faster – and make even more powerful collisions so we can learn about smaller and smaller scales."

The P5 report said the muon collider the committee has in mind would be about exactly the size of the campus of the Fermi National Accelerator Laboratory – or Fermilab – just outside west suburban Batavia. From 1983 until 2011, Fermilab hosted the Tevatron – which was the premier particle accelerator in the world when it was built, but which was considered outdated technology by the time it closed.

Currently, the distinction of the most powerful particle accelerator in the world belongs to CERN's Large Hadron Collider, or LHC. The LHC accelerates protons – which CERN said reach an energy of 6.5 million million electronvolts, or 6.5 tera-electronvolts. In the proposed muon accelerator, the particles would reach an energy of 10 tera-electronvolts, according to the P5 report.

Rather than protons, the proposed new accelerator would accelerate muons – subatomic particles that have a negative charge similar to electrons, but that each have 200 times as much mass as an electron. They would be even better for powerful collisions needed to advance the understanding of particle physics.

The report noted some challenges – including the need to capture and cool the muons before they decay. Muons have a lifetime of only 2.2 millionths of a second.

While the P5 panel said in its report that it did not know if a muon collider was "ultimately feasible," it would be "an unparalleled global facility on U.S. soil" if successful.

"This is our Muon Shot," the P5 committee wrote.

A 'Higgs factory'

Another priority for P5 involves the Higgs boson – popularly known as the "God particle." As explained years ago by The Straight Dope , the Standard Model of quantum physics succeeded in explaining the relationships between electromagnetism, the strong nuclear force that holds atomic nuclei together, and the weak nuclear force that relates to radioactivity. But the model did not take into account the force of gravity, and fails to explain why subatomic particles such as electrons and quarks have mass.

Scientists long believed subatomic particles gained mass by interacting with the "Higgs field," a "sticky" quantum field that fills all of space. The hypothesis was that the interaction involves, in essence, Higgs bosons sticking to the subatomic particles and thus gaining mass.

The Higgs boson was first predicted in 1964 – but it took until 2012 for scientists finally to observe and go on to confirm its existence. Now, Vieregg said, particle physicists hope to delve deeper into research on the Higgs boson by constructing a "Higgs factory."

"So what that would be is a particle collider that would make lots and lots of Higgs particles so we can really study the role that the Higgs plays in particle physics – and learn more about the mysteries of the Higgs boson," Vieregg said. "Discovering a particle is one thing, but then, figuring out more precisely how it works and how it fits into the rest of fundamental physics is what we'd like to do with a Higgs factory."

The Higgs factory would be constructed either at CERN in Switzerland, or in Japan.

Researching the mysteries of dark matter

The study of abundant, yet mysterious dark matter is also a major priority of P5.

"So it turns out that when you look at the way that the universe has evolved over time, and the way that galaxies work, we think that there's about five times as much dark matter as there is regular matter in the universe – which is kind of an astounding statement, actually," said Vieregg. "So regular matter is the things that you and I are made up of; that make up atoms and molecules. But it turns out that there is a lot more matter than that in the universe. They call it dark matter because it doesn't interact with light the way that regular matter does."

This means that when looking at a telescope pointed in the sky, one will not see dark matter. But it's there – and there's lots of it.

"We can tell it's there because of its gravitational effect," said Vieregg. "It's pulling on regular matter in the universe and making it clump in different ways."

But what is dark matter? It's a mystery – scientists still don't know. One of the goals of particle physics outlined by P5 is to focus on research to change that.

"So one of the things we'd like to do is discover dark matter in the lab. So we'd like to be able to build experiments that can measure dark matter particles and tell us what they are. So that's one of the major recommendations from the report as well, is to build experiments that can measure dark matter particles," Vieregg said. "And there's many, many different ways to do this, because there's many ideas for what dark matter might be. So dark matter is such an important question in particle physics – simply because it's more abundant than regular matter in the universe, and we'd like to figure out what it is."

Unlocking the enigmas of neutrinos

Another priority for P5 involving Fermilab focuses on its experiments with neutrinos . Neutrinos are the most abundant particles with mass in the universe. Each neutrino, as described by the U.S. Department of Energy , is "tiny, neutral, and weighs so little that no one has been able to measure its mass."

But neutrinos do, in fact, have mass – and particle physicists want to find out why. And while neutrinos were first predicted in 1930 and observed in 1956, they have many other properties that also remain mysteries.

Some research to solve those mysteries is already going on at Fermilab, and Vieregg said one of the P5 committee's priorities is to continue with those efforts and the construction needed for them.

The flagship experiment going on right now at Fermilab is called the Deep Underground Neutrino Experiment, or DUNE.

"DUNE is a neutrino experiment where using the accelerators and Fermilab, they can make neutrinos – and then they shoot a neutrino beam to a mine in South Dakota, actually," Vieregg said. "And then they are planning to build a large detector in South Dakota to detect the neutrinos when they get to South Dakota."

Why are neutrinos being fired nearly 1,000 miles underground from Fermilab to the Sanford Underground Research Facility in Lead, South Dakota, on the former site of a gold mine? Vieregg explained that scientists are already discovering curious properties of neutrinos from the experiments.

"So neutrinos have this really weird property where they do something that we call oscillation – so they change from one type of neutrino to another as they travel through space – which is an odd property if you think about it – that you can start with one type of particle; one type of neutrino, and then it goes 1,000 miles, and then when you detect it on the other side, it's a different type of neutrino," Vieregg said. "And so we'd like to find out the details of why neutrinos oscillate. That's question is related to sort of, what are the fundamental properties of neutrinos? Why do they have mass? Sort of, what's the physics that governs neutrinos?"

Vieregg said particle physicists believe neutrinos "hold secrets to physics beyond the standard model of particle physics."

Telescopes to observe the universe's oldest light

Vieregg said her personal highlight among all the projects the P5 committee listed as priorities is the CMB-Stage 4 – a cosmic microwave background telescope. There would be telescopes set up at the South Pole and in Chile.

One might ask – what does the study of incredibly minute subatomic particles have to do with the study of the most massive structures of the universe? The answer is, quite a lot. It can help scientists "find out sort of how the universe evolved over time, and what is the physics that's driving the acceleration of the universe?" said Vieregg.

To research that subject requires building telescopes and making detailed observations of the sky.

"So one way you do that is by looking at the oldest light in the universe – called the cosmic microwave background – which is leftover radiation from the Big Bang. And people have been measuring the cosmic microwave background with more and more precision since it was first discovered in the 1960s," Vieregg said. "But now, this panel has recommended to take a pretty large step forward and build the next generation of cosmic microwave background telescopes – called CMB-Stage 4."

The goal of the CMB-4 is to learn more about the physics of "the very early universe – the first tiny fractions of a second after the Big Bang," Vieregg said.

"We can learn about what happened in the universe at that time by making those measurements," she said.

The report also identifies several other priorities, such as a commitment to sustainability and energy management, a commitment to ethical research, and efforts to recruit, train, and retain a talented workforce and to engage with the public.

To read the full P5 report, follow this link.

• University of Chicago

Adam Harrington is a web producer at CBS Chicago, where he first arrived in January 2006.

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Particle physicists put forward research priorities for coming decade

By Robert Sanders

Courtesy of American Physical Society

December 11, 2023

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.

Courtesy of the IceCube collaboration

“In the P5 exercise, it’s really important that we take this broad look at where the field of particle physics is headed, to deliver a report that amounts to a strategic plan for the U.S. community with a 10-year budgetary timeline and a 20-year context. The panel thought about where the next big discoveries might lie and how we could maximize impact within budget to support future discoveries and the next generation of researchers and technical workers who will be needed to achieve them,” said  Karsten Heeger , P5 panel deputy chair and Eugene Higgins Professor and chair of physics at Yale University.

The panel also urged DOE to establish a fund, like NSF, that would support small-scale projects.

“We need to really look at the balance between big things — of course, we’re all excited about them — but also small things, to really keep young people going,” Murayama said. “In some cases, small projects can involve thinking really outside the box and can be high-risk, high-return, in terms of scientific results. That kind of combination we feel very strongly about.”

The panel was also tasked with looking at diversity issues within the particle physics community.

“We came up with actionable recommendations for how we can improve the climate in the community, which is still very much dominated by white males. I hate to say this, but that’s true,” Murayama said. “One of the big discussions we had was about how to make the community more inclusive and mutually caring for each other. We have clear recommendations along those lines.”

The report built on the output of a Snowmass 2021 high energy physics community planning exercise in Seattle, Washington, organized by the American Physical Society, the only independent body in the U.S. that represents particle physics community as a whole. The new knowledge and new technologies discussed there set the stage for the P5 report.

“The Higgs boson had just been discovered before the previous P5 process, and now our continued study of the particle has greatly informed what we think may lie beyond the standard model of particle physics,” Murayama said. “Our thinking about what dark matter might be has also changed, forcing the community to look elsewhere — to the cosmos. And in 2015, the discovery of gravitational waves was reported. Accelerator technology is changing, too, which has shifted the discussion to the technology R&D needed to build the next-generation particle collider.”

He noted that the two triangles on the cover of the report are meant to emphasize that looking at smaller and smaller things — the realm of traditional particle physics — must be combined with a look at larger structures, such as the evolution of universe, to get a complete picture of what the report describes as the “smallest constituents of our vast and complex universe.”

“The P5 report will lay the foundation for a very bright future in the field,” said  R. Sekhar Chivukula , 2023 chair of the APS Division of Particles and Fields and a Distinguished Professor of Physics at the University of California, San Diego. “There are extraordinarily important scientific questions remaining in particle physics, which the U.S. particle physics community has both the capability and opportunity to help address, within our own facilities and as a member of the global high energy physics community.”

RELATED INFORMATION

• Exploring the Quantum Universe: Pathways to Innovation and Discovery in Particle Physics  (Report of the 2023 Particle Physics Project Prioritization Panel) (PDF)
• High Energy Physics Advisory Panel
• American Physical Society press release
• New York Times story

• Collections

• APS Journals

US Particle Physicists Make Their Wish List

On Friday, a panel of high-energy physicists unanimously voted to approve a plan for the next decade of particle physics in the United States. The plan prioritizes US funding for ongoing and already-under-construction experiments and outlines a roadmap for possible new initiatives, including a big bang observatory and a muon collider. Response from the community to the report is largely positive. But in discussions immediately prior to the vote, high-energy scientists raised questions about the ranking and selection of future projects.

Once a decade, the Particle Physics Project Prioritization Panel (P5) convenes to strategize on where to focus efforts—and money—over the next ten years. The resulting P5 report acts as a roadmap for scientists and for the two main US agencies that fund high-energy physics, the Department of Energy (DOE) and the National Science Foundation (NSF).

The priorities of this iteration of the P5 report were selected from suggestions and proposals presented by the broader research community at townhalls and conferences that took place over the past year (see, for example, Research News: A “Retro” Collider Design for a Higgs Factory ). “The report is the culmination of a very long process,” said Sally Seidel, a physicist at the University of New Mexico and the interim chairperson of the US federal government’s advisory panel for high-energy physics.

The P5 committee’s first funding recommendation is to support ongoing experiments and complete current construction projects, which include the first phase of the Deep Underground Neutrino Experiment (DUNE) in the US, the high-luminosity upgrade of the Large Hadron Collider (LHC) at CERN in Switzerland, and the Vera C. Rubin Observatory in Chile. Looking ahead to the next generation of experiments, the committee offers a list of five plans, ranked in priority. Topping that chart is a big bang observatory called the Cosmic Microwave Background-Stage IV (CMB-S4). This facility and its anticipated 12 radio telescopes would probe the earliest moments of the Universe by detecting possible signatures of primordial gravitational waves in the microwave sky. These measurements could offer evidence of an early acceleration phase called cosmic inflation.

The other four future priorities include experiments to study neutrinos, dark matter particles, and Higgs bosons. The report also presents a 20-year plan to build the world’s first muon collider, a 10-TeV collider that, it is envisioned, could unlock the secrets of dark matter. “We don’t know if a muon collider is possible, but working toward it comes with high rewards,” said Hitoshi Murayama a physicist at the University of California, Berkeley, and the chair of the recommendation committee. “We envision a new era of scientific leadership centered on decoding the quantum realm, unveiling the hidden Universe, and exploring novel paradigms.”

The panel’s recommendations act only as a guideline; the DOE and the NSF must approve any new projects before they can go ahead. For facilities located outside of the US, such as those at CERN, other governments and international agencies must also sign on.

When forming their plan, the P5 panel considered two budget scenarios, both of which were supplied by the DOE. The more favorable scenario assumes a small bump in funding levels over the next two years, which would come from the CHIPS and Science Act, followed by an annual increase of 3% to keep pace with inflation. The less favorable outcome has no initial bump and an annual increase of 2%, which in real terms would mean a drop in funding.

In this second scenario, focus would go on maintaining current experiments. Of the hoped-for new facilities, only two would proceed as planned: the CMB-S4 and IceCube-Gen2, which would have a volume ten times bigger than that of the current IceCube neutrino detector at the South Pole. The volume increase would make IceCube-Gen2 sensitive to some dark matter candidates. The other planned projects, including the Higgs facility, would have significantly reduced scopes.

Following the presentation of the P5 report at a meeting in Washington, DC, physicists who attended in person and online engaged in a detailed discussion of the report. Sekhar Chivukula, a physicist at the University of California, San Diego, and the 2023 chair of the APS Division of Particles and Fields, opened the discussion saying that “the report reflects an accurate reading of what the community asked for.” While many agreed with that sentiment, others felt that the panel had missed a key recommendation—funding the so-called Forward Physics Facility (FPF). This future facility would enable experiments at the LHC to image neutrinos and would complement other planned neutrino observatories.

Jonathan Feng, a theoretical particle physicist at the University of California, Irvine, questioned the panel on their decision to leave funding for FPF out of the plan. Construction of this facility was one of the immediate priorities from the Snowmass energy frontier group, a community group that made recommendations for how to explore particles at the TeV scale and beyond. “This priority was from the entire community, not just a handful of people,” says Milind Diwan, a physicist at Brookhaven National Laboratory in New York and a former P5 panel member from two decades ago. At a townhall yesterday at Fermi National Accelerator Laboratory in Illinois, Diwan requested that the current P5 panel change their decision on FPF from a “no” to at least a “maybe.”

Feng and Diwan both noted that discussions have already begun about making this facility at CERN, and they are concerned that the “no” from the P5 committee will end those talks. “Saying no in the way they have, gives a clear signal to other funding agencies that the project lacks our support and that puts other funding in jeopardy,” Diwan says. “That goes against the principles of being a good international partner.”

“We would have loved to support all the projects that were proposed,” Murayama said in response to these concerns. Murayama acknowledged that the project had strong backing, but said that the panel felt that the required commitment to building new infrastructure and to agreeing to all the facility’s scientific components meant that it could not endorse the proposal. Murayama noted that currently there is no information from CERN about what size such a facility might be and exactly what science might go on there. “We were not given a blue-sky budget,” he said.

Another hard choice was the decision not to fund a US-based Higgs factory—an electron–positron collider that would produce large numbers of Higgs bosons for study. Instead, the panel recommended that the US collaborate with international partners to determine the feasibility of an “offshore” Higgs factory in Asia or Europe. A future panel would then have to review the plans before committing further US participation. In a “less favorable” budget scenario, any participation would be delayed and any financial contributions reduced.

In the report discussion, Andrew White, a physicist at the University of Texas at Arlington, voiced concerns that reduced investment in a Higgs factory would reflect poorly on US science. “Obviously, that would impact US leadership in such a project,” he said. Murayama acknowledged that possibility but said with full funding the plans should ensure the opposite. “We need to be a strong partner in the project,” he said. “We should not be sitting around. We should be actively engaged in feasibility and design studies [of a Higgs factory].”

Throughout the presentation of the P5 report, members of the P5 panel noted that the community presented them with many other “inspiring and ambitious” projects. But if they had accepted all proposals, the budget would have been blown up. Over the next decade, the community will likely see less than $20 billion combined from the DOE and NSF.

While the panel realizes that proponents of nonselected projects may feel bereft, Karsten Heeger, a physicist at Yale University and the deputy chair of the P5 committee, said that “we wanted to make sure that what we recommended fit within a few percent of the budget scenarios.” Meeting that constraint involved some hard choices, including turning down close to two thirds of community proposals. “Everything was on the table, including ongoing projects,” Heeger said. In the end, the committee chose experiments that they saw as having the potential for transformational discovery. “We are not mortgaging the future,” Heeger said.

–Katherine Wright

Katherine Wright is the Deputy Editor of Physics Magazine .

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