Proposed plan for the future of particle physics in the United States

Particle physics will become even more of an international enterprise in the coming decades, according to a panel tasked with developing a strategic plan for the future of particle physics in the United States, whose long-awaited recommendations were released today. today.

According to the panel, top priorities for particle physics in the United States include continuing to play a major role at the Large Hadron Collider in Europe; building a state-of-the-art neutrino program hosted in the United States; and participate in the development of a proposed future linear collider, if built in Japan.

“The United States and key players in other regions can together address the full breadth of the field’s most pressing scientific questions if each hosts a unique, world-class facility at home and partners in high-priority facilities hosted elsewhere. “, wrote the members of the panel in their executive summary.

The 25-member Particle Physics Project Prioritization Group (P5) was tasked in September 2013 to develop a draft strategic plan for particle physics in the United States for the next decade and beyond. . The P5 reports to the Federal High Energy Physics Advisory Panel (HEPAP), a 24-member body that formally advises both the U.S. Department of Energy’s Office of Science and the National Science Foundation on support for the particle physics.

HEPAP is expected to review and vote on the panel’s recommendations at a two-day public meeting to be held in Bethesda, Maryland, today and Friday.

The P5 report culminates a more than year-long process that began with meetings of members of the US particle physics community in late July and early August last year and ended with P5 working by consensus to create a unified strategy.

“The community was deeply engaged, and we’re very grateful for that,” said physicist Steven Ritz of the University of California, Santa Cruz, who led the P5 panel.

The plan recommends a U.S. particle physics program that will continue research related to the Higgs boson, neutrinos, dark matter, dark energy, and inflation, as well as particles, interactions, and still more physical principles. unknown.

To keep the United States at the forefront of particle physics, the plan calls for investing more of the DOE’s high-energy physics budget in building new experimental facilities, raising the level of 16 to 20 to 25%.

“This is a discovery-driven field,” says Ritz. “To discover, you have to build.”

The P5 panel recommends moving forward with a variety of projects, including a number of large add-on facilities, which the panel says must be commissioned in time to accommodate budget constraints. The sequence of recommended major projects is as follows: the Mu2e experience; upgrades to the Large Hadron Collider and its experiments; and a long-baseline neutrino experiment to be based at the Fermi National Accelerator Laboratory. P5 also recommends US participation in the development of an international linear collider in Japan, if a decision is made in Japan to go ahead with the installation.

The P5 Group envisions the United States as host of an international neutrino research program that will attract the global neutrino community, harnessing the world’s most powerful neutrino beam and, with international partners, building a major long-based neutrinos supplemented by several smaller, short-based neutrino experiments.

Launching this program will, however, involve a change of direction, as the panel recommends reformulating the current long-baseline neutrino experiment into an internationally designed, coordinated and funded program called the Long-Based Neutrino Facility. base, or LBNF. The facility would use a neutrino beam at Fermilab, upgraded under the proposed project called Proton Improvement Plan II; a huge liquid argon neutrino detector placed underground, probably at the Sanford Underground Research Facility in South Dakota; and a smaller detector placed closer to the source of the beam.

The P5 panel recommends directing resources to a variety of other projects requiring medium or low levels of funding.

The plan outlines the need for the United States to immediately begin several planned second-generation dark matter experiments, with a vision to build at least one large third-generation experiment in the United States sometime around the start of the next decade.

It also recommends increasing funding for the particle physics components of cosmic studies. The expert group recommends completing the Large Synoptic Sky Survey (LSST) and, if funding is available, building the Dark Energy Spectroscopic Instrument (DESI). He recommends working with other agencies to fund additional joint projects such as CMB-S3, CMB-S4 and the Cherenkov Telescope Array.

The recommendations call for a shift in focus in the area of ​​accelerator and instrumentation R&D to better align it with P5 priorities. The report states that, as recent physics results have reduced the near-term need for muon colliders, the expert group recommends consulting international partners on the early termination of the MICE muon cooling project currently underway.

The panel’s report offers a roadmap for particle physics in the United States under three budget scenarios: one in which funding is constant for three years and then increases by 3% per year; one in which funding is constant for three years and then increases by 2% per year; and a third in which funding is not limited. The two constrained scenarios differ by about $500 million added over a decade.

“Although seemingly small, these differences would have very significant short- and long-term impacts,” the report said. “So the relatively small increase in funding in the highest scenario generates a very large return on investment.”

In the lowest budget scenario, DESI would be reduced; R&D on accelerators and detectors would be significantly reduced; staff would be reduced; LBNF would be delayed; capabilities to build a third-generation dark matter experiment would be reduced or delayed; and the Mu2e funding profile would be changed.

“The panel made some tough choices in the face of the reality of particle physics budgets that have shrunk since the previous P5 plan,” says physicist Andrew Lankford of the University of California, Irvine, who served on the previous P5 panel. in 2008 and currently serves as President of HEPAP.

Within an unlimited budget, the P5 group recommends working on a significantly expanded accelerator R&D program with an emphasis on developing transformative technologies for discovery machines beyond the capabilities of the LHC and ILC ; play a leading role in the ILC detection program and provide critical components for the ILC accelerator; and to house a second large groundwater Cherenkov neutrino detector to complement the proposed LBNF detector.

Update: HEPAP voted to accept the P5 report on May 22.

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