Particle physicists have a list of projects they hope to complete in the next decade, but financial constraints dictate to set priorities.
On Friday, a panel of high-energy physicists voted unanimously to approve the U.S. plan for particle physics for the next decade. The plan prioritizes U.S. funding for ongoing and already under construction experiments, and outlines a roadmap for possible new initiatives, including the Grand Observatory and the Muon Collider. The community's response to the report has been largely positive. But in the pre-vote discussions, high-energy scientists questioned the ranking and selection of future projects.
The Particle Physics Project Priority Group (P5) meets every 10 years to develop a strategy for priorities and funding for the next decade. The resulting P5 report provides a roadmap for scientists and the two main U.S. agencies that fund high-energy physics, the Department of Energy (DOE) and the National Science Society (NSF).
The priorities for this iteration of the P5 report were selected from the suggestions and proposals made by the broader research community at town halls and conferences held over the past year (see, for example, Research News: 'Vintage' Collider Design at the Higgs Plant). "This report is the culmination of a very long process," said Sally Seidel, a physicist at the University of New Mexico and interim chair of the Federal High Energy Physics Advisory Group.
The P5 Commission's first funding recommendation is to support ongoing experiments and complete current construction projects, which include the first phase of the Deep Subsurface Neutrino Experiment (DUNE) in the United States, a high-light upgrade at the Large Hadron Collider (LHC) in CERN, Switzerland, and Vera C. in ChileRubin Observatory. Looking ahead to the next generation of experiments, the committee provided a list of five programs, sorted by priority. At the top of this chart is a large ** observatory called Cosmic Microwave Background Stage 4 (CMB-S4). The facility and its expected 12 radio telescopes will probe the earliest moments of the universe by detecting possible signatures of primordial gravitational waves in the microwave sky. These measurements can provide evidence of an early acceleration phase, known as cosmic expansion.
China Merchants Bank-S4 will be deployed in Chile for the design of one of the CMB-S4 telescopes.
The other four future priorities include experiments that study neutrinos, dark matter particles, and the Higgs boson. The report also proposes a 20-year plan to build the world's first Muson Collider, a 10-tev collider that could unlock the secrets of dark matter. "We don't know if the Muson Collider is possible, but working in that direction will pay off very high," said Hitoshi Murayama, a physicist at the University of California, Berkeley, and chairman of the recommendation committee. "We envision a new era of scientific leadership centered on decoding the quantum realm, uncovering hidden universes, and exploring new paradigms. ”
The Panel's recommendations are intended as guidance only;The U.S. Department of Energy and the National Academy of Science must approve any new projects before they can proceed. For facilities located outside the United States, such as those at CERN, other** and international agencies must also sign.
In developing the plan, the P5 considered two budget options, both of which were provided by the Department of Energy. On a more favorable note, funding levels will rise slightly over the next two years, which will come from the CHIPS and Science Act, followed by an annual increase of 3% to keep pace with inflation. The less favorable result did not have the initial increase, which increased by 2% per year, which actually meant a decline in funding.
In the second case, the focus will be on maintaining the current experiment. Of the new facilities that are hoped, only two will go as planned: CMB-S4 and ICECUBE-Gen2, which will be ten times larger than the current ICECUBE neutrino detector in Antarctica. The increase in volume will make icecube-gen2 sensitive to some dark matter candidates. Other planned projects, including the Higgs facility, will be significantly narrowed down.
m.Brice CERN CERN is testing a prototype detector for the DUNE experiment.
After the presentation of the P5 report at a conference in Washington, D.C., the report was discussed at length by physicists who attended in person and **. Sekhar Chivukula, a physicist at UC San Diego and chair of the 2023 APS Particle and Field Division, said at the beginning of the discussion, "The report reflects an accurate reading of the community's requirements. While many agree with this view, others believe the group missed a key recommendation – funding for so-called Forward Physics Facilities (FPFs). This future facility will enable LHC experiments to image neutrinos and will complement other planned neutrino observatories.
Jonathan Feng, a theoretical particle physicist at the University of California, Irvine, questioned the group's decision to exclude FPF funding from the program. The construction of the facility is one of the top priorities of the Maas Energy Frontiers Group, a community group that has made recommendations on how to explore TEV and higher-scale particles. "This priority comes from the entire community, not just a few," said Milind Diwan, a physicist at Brookhaven National Laboratory in New York and a former P5 panel member two decades ago. Yesterday, at the town hall of the Fermi National Accelerator Laboratory in Illinois, Diwan asked the current P5 panel to change their decision on the FPF from "no" to at least "probably."
Both Feng and Diwan noted that discussions have begun on the establishment of such a facility at CERN, and they fear that the P5 committee's "no" will end these negotiations. "Saying no in their way sends a clear signal to other funding agencies that the project lacks our support and puts other funding at risk," Diwan said. "This goes against the principle of being a good international partner.
We are happy to support all proposed projects," Murayama said in response to these concerns. Murayama acknowledged that there was strong support for the project, but said the group felt that the commitment required to build the new infrastructure and agree to all the scientific components of the facility meant it could not endorse the proposal. Murayama noted that at the moment CERN does not have information on how large such a facility could be and what scientific research could be carried out there. "We didn't get the blue sky budget," he said.
Another difficult choice was the decision not to fund a U.S.-based Higgs plant — an electron-positron collider that could produce large quantities of Higgs bosons for research. Instead, the panel recommended that the United States work with international partners to determine the feasibility of establishing an "offshore" Higgs plant in Asia or Europe. Future panels will then have to review these plans before committing to further U.S. involvement. In the "less favourable" budget scenario, any participation will be postponed and any financial contributions will be reduced.
Andrew White, a physicist at the University of Texas at Arlington, said in a discussion of the report that he was concerned that reducing investment in the Higgs plant would have a negative impact on American science. "Obviously, this will affect the leadership of the United States in such a project," he said. Murayama acknowledges this possibility, but says that the plans should ensure the opposite when funds are sufficient. "We need to be a strong partner in the project," he said. "We should not sit idly by. We should be actively involved in feasibility and design studies (of the Higgs plant).
Throughout the presentation of the P5 report, P5 panelists noted that the community had shown them many other "inspiring and ambitious" projects. However, if they accept all the proposals, the budget will blow up. Over the next decade, the U.S. Department of Energy and the National Science Foundation (NSF) combined are likely to be less than $20 billion.
While the group was aware of the potential for loss among proponents of unselected projects, Karsten Heeger, a Yale physicist and vice chair of the P5 committee, said, "We want to make sure that what we're proposing fits into the budget scenario." Meeting this limit requires some difficult choices, including rejecting nearly two-thirds of community proposals. "Everything is on the table, including ongoing projects," Heeger said. In the end, the committee selected experiments that they believed had the potential for transformative discovery. "We're not going to mortgage the future," Heeger said.