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DOE gives big boost to Fermilab's plans for new muon experiment


From left: Amy Allen, Doug Glenzinski, and Craig Group work on the Mu2e experiment test stand at Fermilab. Mu2e just passed the first DOE approval stage. Photo Courtesy of Fermilab.

While all eyes have been on the startup of the Large Hadron Collider in Europe, the world's largest scientific experiment, a small team of researchers based in the US has been toiling away.

The group has focused its energies on planning an experiment that creates a plenitude of muons and could reveal new phenomena that could only result from unknown physics.

That narrow focus, say the members of the Muon-to-Electron-Conversion experiment, will allow the Mu2e collaboration to indirectly search for new particles and let them look for signs of new types of interactions at energies up to 10,000 trillion electronvolts, far beyond the LHC's grasp. It also would help scientists to better understand future LHC discoveries.

Mu2e got a big boost on November 24 with the US Department of Energy endorsement of the scientific need for the project, called Critical Decision-0. This marks the first stage of DOE's 4-stage approval process that projects must pass before construction can start.

"Every CD is an important milestone.  CD-0 is unique in that most of the work is done by the DOE.  The fact that they put in the work to push this through is a clear indication that they are serious about Mu2e,” says Ron Ray, project manager.  “The ball is now in our court and we have a lot of work to do."

The idea behind the Mu2e experiment isn’t new--the similar and well-reviewed Muon to Electron COnversion (MECO) experiment proposed at Brookhaven National Laboratory in Long Island was canceled in 2005 for lack of funding. But funding agencies and research experts say the time now is right for such an endeavor. The US Particle Physics Project Prioritization Panel, P5, recommended construction of Mu2e in any federal budget funding scenario and Fermilab’s Physics Advisory Panel, comprised of global experts in the field, endorsed it.

DOE approval makes Mu2e the only US-based charged-lepton flavor violation experiment. Similar experiments are proposed in Japan:  Coherent Muon to Electron Transition, COMET, a neutrino-less conversion of muons to electrons and its follow up experiment PRISM Muon to Electron Conversion experiment, PRIME, which uses a different design than Mu2e, and the complementary MEG experiment at the Paul Scherrer Institute in Switzerland that searches for muon decaying into electrons and photons.

Potential design of Mu2e. Courtesy Fermilab.

Potential design of Mu2e. Courtesy Fermilab.

“This is a technically challenging experiment and this is an opportunity to build hardware. The LHC experiments are built,” Ray says. “For people who want to get involved in building something from the ground up and see the fruits of their labor in their lifetime this is an exciting project.”

Mu2e will introduce groundbreaking technological advances for superconducting solenoids and particle trackers.

The 100-member collaboration now can take on more members. Researchers come from 12 US universities; Muons Inc., a private US firm; Brookhaven and Fermilab, US national laboratories; and national laboratories and universities in Italy and Russia.

“A lot of the collaborators from Italy are the same that contributed over time to CDF,” Ray says. “We expect they will have the same impact on Mu2e that they had on [the Tevatron’s] CDF experiment, and that was substantial.”

Italy has primary responsibility for designing, building, and commissioning the calorimeter.

Mu2e has significant advantages over similar experiments. It will use the existing Fermilab accelerator complex with minor modifications once the Tevatron collider shuts down. Mu2e won’t interfere with the lab’s new flagship neutrino experiment, NOvA, which is under construction. The Fermilab accelerator complex produces more proton beam than NOvA can use, and Mu2e will use the excess.

Mu2e would use an 8 billion electronvolt, or 8 GeV, proton beam and a fixed target to generate a large number of muons and track whether they change into electrons.

The estimated total cost of the project is about $200 million.  Understanding the cost in more detail is one of the main goals of the project over the next year.

Collaborators are currently working on tracker and magnet prototypes and detailed simulations that should be complete by the summer.  This should allow the project to proceed to CD-1 by the spring of 2011 and operation in 2017.