Particle physicists provide a roadmap for the next decade

Friday, December 8: This story has been updated to include the vote that took place after it was first published.

Scientists A agreed a plan For the next two decades of particle physics in the United States on Friday. It aims to restore American supremacy in high-energy particle physics.

The new strategy calls on physicists to begin laying the foundation for a revolutionary particle collider that could be built on American soil. The machine will collide tiny point-like muons, which are similar to electrons but larger. Muons provide more buzz than the protons used at CERN’s Large Hadron Collider, and will push the search for new forces and particles further into the unknown than ever before.

Locating such a project, perhaps in Fermi National Accelerator Laboratory In Illinois, it would restore American particle physics to the position of supremacy ceded to Europe in 1993 when Congress abolished the giant superconducting supercollider. But it will take at least 10 years To prove that the muon collider could work and how much it would cost.

“This is our muon shot,” the committee, charged with outlining a vision for the next decade for American particle physics, said in a report titled “Exploring the Quantum Universe: Pathways for Innovation and Discovery in Particle Physics.” It was presented and discussed in A interview In Washington, D.C., on Thursday and Friday, and will be discussed further At Fermilab next week.

The report also highlighted the need to invest in next-generation experiments investigating the nature of subatomic particles called neutrinos; The cosmic microwave background, the radiation leftover from the Big Bang; and dark matter, the gravitational glue that holds galaxies together. The committee also recommended participation in a future facility in Europe or Japan dedicated to studying the Higgs boson, whose discovery in 2012 was key to understanding how other particles get their mass.

“The size of the universe we see now, which is 14 billion light-years across, was actually smaller than the size of the nucleus” early in cosmic time, said Hitoshi Murayama, a physicist at the University of California, Berkeley, who led the panel. “So our field is actually not just looking for fundamental components, but getting a bigger picture of how the universe works as a whole.”

The committee, formally known as the Particle Physics Project Priority Setting Committee, or P5, was tasked by the U.S. Department of Energy and the National Science Foundation with developing a roadmap for the future of the field. The three-year process began by soliciting input from the particle physics community at large, and the final report will serve as a recommendation for what national agencies should prioritize over the next decade.

Recent P5 report, “Building for Discovery: The Strategic Plan for US Particle Physics in a Global Contextwas published in 2014 in the wake of the discovery of the Higgs boson. It was a huge success for the Standard Model, a set of quantum equations that explains everything scientists know and test in the laboratory about forces and particles in nature, and which has won several Nobel Prizes for its creators. .

But the Standard Model has nothing to say about gravity, and therefore about black holes or “dark energy” pushing the universe apart. It also does not explain dark matter, the invisible matter that surrounds galaxies. It also does not explain the Higgs boson.

In the past decade, physicists have not made much progress on these fronts. They have failed to identify dark matter, and some of their most popular hypotheses, especially an idea called supersymmetry, could be on the verge of being ruled out, at least as an explanation for dark matter.

It included the process of building the report for the next decade Seattle Snowmass Summer Study In 2022, physicists presented hundreds of research papers proposing future initiatives in this field. A summary of the study has been compiled in A A book of 700 pages. “I describe this as democracy in action,” Dr. Murayama said, noting that it is a “bottom-up” process.

Sally Seidel, a physicist at the University of New Mexico and chair of the Department of Energy’s High Energy Physics Advisory Committee, described the process as a “brilliant display of curiosity” that brought together thousands of researchers. “I can’t remember a more exciting time to explore particle physics,” she wrote in an email.

The recommendations of the five-nation panel took into account two budget scenarios presented to them by the US Department of Energy. In one “baseline” case, the ministry’s budget is expected to rise by 3 percent annually, mainly to keep pace with inflation. In this scenario, the committee emphasized on pursuing major projects e.g System of telescopes in Chile and Antarctica To study the cosmic microwave background, and establish the marine Higgs Factory Extended version of IceCubeIt is an observatory frozen in the Antarctic ice that captures neutrinos from strange sources in the universe.

With this budget scenario, there would also be room to support the vision for a US-based particle collider.

Particle colliders, such as the CERN machine, derive their appeal from Einstein’s discovery that energy and mass are interchangeable. The more energy released in a collision, the greater the mass of particles that can be created. Because protons are messy bags of smaller particles known as quarks and gluons, smashing them together releases only a small fraction of the proton’s total energy. Muons, on the other hand, are elementary; With no internal components (as far as scientists know), their collisions produce more energetic results.

The muon collider is one of three options considered as a successor to CERN’s Large Hadron Collider, which is currently the world’s largest and is expected to dominate particle physics for the next decade. Both China and the European Organization for Nuclear Research (CERN) have explored building a new collider 60 miles or so in circumference, which would reach collision energies of 100 trillion electron volts compared with 14 trillion electron volts at the Large Hadron Collider, opening up new possibilities for… Of energy and time.

Another possibility, which in principle could be done on a tabletop rather than on miles of underground tunnels, is called wake-field acceleration, where the particle is propelled like a surfer on waves of highly ionized gas, the plasma.

Toyoko Orimoto, a physicist at Northeastern University, finds these recommendations ambitious and exciting. “The next 10 years will be a very exciting time for particle physics,” she said.

The report also considered a bleaker budget scenario of just a 2 percent annual increase in funds, which would amount to an effective reduction in support. In that case, the committee said, the United States would have to abandon its hopes of hosting a next-generation dark matter experiment at a new underground laboratory in South Dakota, and scrap planned upgrades to the laboratory. The already ongoing and expensive construction of a deep underground neutrino experimentor DUNE, further diminishing the nation’s leadership in those areas.

“The United States will have to give up its leadership in certain areas of particle physics,” said Carsten Heeger, a physicist at Yale University and vice president of P5. “This will be an impact that will be felt on and off the field.”

If all that fails, the report urges the federal government to continue with projects it has already committed to, including increasing the brightness, or impact rates, of the Large Hadron Collider for deeper studies of the Higgs particle and other rare phenomena; Continuing to build Vera C. Rubin Observatorya telescope in Chile designed to create time-lapse movies of the universe; And a limited edition of DUNE.

“They did what they had to do,” said Lisa Randall, a Harvard physicist who was not on the P5, producing a hopeful vision for the future as they prepared to work through what could be fraught budgets at the moment.

Michael Turner, a retired cosmologist from the University of Chicago, and Maria Spiropoulou of the California Institute of Technology, who are leading a related study for the National Academy of Sciences, called the plan a “bold plan” in a joint emailed statement.

Because these projects are decades old, the committee emphasized support for early-career scientists who will eventually take charge of the projects. “They are the future,” Dr. Murayama said.

Up-and-coming physicists are excited about this endorsement. “As someone who has the better part of her career ahead of her, this is the kind of field I want to be a part of,” said Tova Holmes, a physicist at the University of Tennessee who was working on the muon collider. Designs. “Someone who has big ambitions, tries new things, develops new technologies and believes in his own potential.”

The committee will focus on gaining support for the plan, both within and outside the physics community. In particular, Dr. Murayama expressed his hope that it would attract the attention of staff who communicate with members of Congress about how to vote on the ministry’s budget.

“Basic research is elusive,” Dr. Murayama said. “It’s not an immediate benefit to the community.” But he added that the payoff is worth it: Particle physics has led to revolutions in medical applications, materials science, and even the creation of the iPhone and the World Wide Web.

But according to Dr. Murayama, the benefits go beyond the field’s impact on society. “Particle physics is really the essence of what we are, who we are,” he said, adding that all of us, whether physicists or not, “would like to understand why we exist, where we came from, and where we are going.” “.