Options given for the future of US particle astrophysics

The Particle Astrophysics Science Assessment Group (PASAG) which was formed in April by the US Department of Energy (DOE) and National Science Foundation (NSF) to assess priorities in high-energy physics research under four different funding scenarios over the coming decade has released its conclusions .

The group looked at projects in dark matter , dark energy , high-energy cosmic particles (cosmic rays , gamma rays , and neutrinos ), and projects seeking high energy physics resources to study the cosmic microwave background (CMB).

Budget numbers

The four scenarios are:A. Constant effort at the FY 2008 funding level (i.e., funding in FY 2010 at the level provided by the FY 2008 Omnibus Bill, inflated by 3.5% per year and continuing at this rate for the foreseeable future).

B. Constant effort at the FY 2009 President’s Request level (i.e., funding in FY 2010 at the level provided by the FY 2009 Request,inflated by 3.5%).

C. Doubling of funding over a ten year period starting in FY2009 (i.e., funding in FY 2010 at the level provided by the FY 2009 President’s Request, inflated by 6.5%).

D. Additional funding above funding scenario C, in priority order, associated with specific activities needed to mount a leadership program that addresses opportunities identified in the National Academies of Sciences EPP2010 report or the HEPAP Particle Physics Project Prioritization Panel (P5) report.

“These budget scenarios provided very tight constraints that forced difficult choices in the planning,” says the report. But “by constructing the optimal science program possible in each budget scenario, there emerged a consensus view of the priorities.”

On the list

Even under the tightest constraints DOE and NSF should fund two next generation dark-matter experiments: upgrading VERITAS , a ground-based VHE gamma-ray detector, and the proposed $15 million High Altitude Water Cherenkov (HAWC) gamma-ray observatory .

“Even in this very lean scenario, the diversity offered by [the VERITAS and HAWC] projects is a priority, and their impacts are large for a relatively small investment,” they argue.

The SuperCDMS-SNOLAB. , an underground dark matter experiment based in Canada, should also be funded says the report.

Moreover, “Given the central importance of the CMB to our understanding of energy, matter, space, and time, and the unique contributions high energy physics can provide,” CMB experiments would continue as they are relatively cheap.

Nearly all the projects have an international component: HAWC for example, would be based at a high-altitude site in central Mexico, and consist of 300 large, closely spaced water tanks, each outfitted with three 20-cm photomultiplier tubes to detect the Cherenkov light of charged particles from gamma-ray and cosmic-ray showers as they hit the tanks.

But funds from international collaborations would not help keep major US participation in other proposed projects—in areas such as dark energy—under scenario A, as there would not be enough funds to pay for major hardware.

No third generation dark matter experiments can be started in this decade under scenario A, says the report, “risking loss of US world leadership” in the field.

The best guess

The most likely budget for the field may be scenario C, as the NSF budget for 2009 is 7.8% above 2008, and the proposed 2010 budget is 8.5% above 2009.

Moreover Congress approved a doubling of science budgets over 10 years when it passed the 2007 America Competes Act .

In this scenario the US could have “a world-leading program [in dark energy]... with coordinated activities in space and on the ground,” says the report.

PASAG recommended two additional third generation experiments for dark matter, and a global ground and space based program in dark energy.

“A significant DOE contribution to Joint Dark Energy Mission —a NASA-DOE space-based visible/NIR observatory—is possible, along with full support of BigBOSS —a new 4000-fiber visible/near infrared spectrograph for the existing Mayall 4-meter telescope in Arizona—and support for the Large Synoptic Survey Telescope (LSST)—a new ground-based 8-meter-diameter telescope to discover and measure the shapes and photometric redshifts of more than 3 billion galaxies,” says PASAG.

Moreover, under this scenario C, the group recommends funding the Auger North observatory—a US$127-million array of 4,400 cosmic-ray detectors to be based in southeastern Colorado—as a northern counterpart to the Pierre Auger Observatory in Argentina. This project would be 60% funded by international partners.

“PASAG finds the science reach of Auger North to be important, and it recognizes the strong international support with the corresponding expectation that the US would be the host site,” says the report. “Technically, construction could start in 2011.”

PASAG suggests that the proposed US-led $299 million Advanced Gamma Imaging System (AGIS)—an array of 36 telescopes, each having a primary mirror diameter of 11m and making use of a novel two-reflector design—should be merged with the similar European-led Cherenkov Telescope Array (CTA). “It is generally understood on both sides of the Atlantic that a merger of the two projects should occur to develop a global effort,” they say. Under this proposal the US would have a reduced, but still significant, role in the project.

A conservative position

Although the majority of direct research funding is from programs at DOE and NSF, there are indirect funds from facilities such as the proposed Deep Underground Science and Engineering Lab (DUSEL) could have been included in creating the recommendations.

Instead, PASAG decided to take a conservative approach and not include the potential of any additional DUSEL research funding due to the “uncertainty in [DUSEL] funding...even though the US dark matter program would be greatly strengthened by it.”

Although PASAG lists the recommendations for each budget scenario, they did not state which scenario DOE and NSF should fund. A decision over which planning model to follow will be made by the agencies sometime around April next year.

Paul Guinnessy