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By Michael Lucibella
When Fermilab’s Tevatron shut down for good on September 30, it was in part acquiescence to the fact that the United States had for the foreseeable future ceded to Europe its place at the cutting edge in high energy particle colliders. When brought to its full potential, the Large Hadron Collider at CERN will be able to create particle collisions seven times more energetic than the Tevatron could ever hope to achieve. The Tevatron had been the centerpiece of Fermilab for 28 years, but with its shutdown the lab has begun a process of reinventing itself to probe questions about the nature of neutrinos, matter-antimatter asymmetry and other new physics at the intensity frontier.
Long the leader at the energy frontier with the Tevatron, Fermilab is now looking to explore the intensity frontier, in hopes of detecting very unusual interactions that hold clues to new physics. The transition from one focus to the other is a gradual one, as there is still much to take care of after the Tevatron shut down.
“The energy frontier is still going to have Fermilab participation. Many of our staff are engaged in the CMS experiment at the LHC, so we’re continuing in that sense on the energy frontier as collaborators,” said Bob Tschirhart, a researcher at Fermilab. “For the next few years we’re going to aggressively analyze our own data and collaborate with CERN.”
There are mountains of information left over from the final run of the Tevatron. It could be as many as two years before the last of its collisions have been analyzed. In addition, the lab will help analyze data coming out of the LHC and even has a remote operating room to keep the LHC beams running when it’s night in Geneva.
Over the next couple of years, neutrinos will take their place at the forefront of the lab’s research. They’ve been one focus already, but as time progresses their share of the experimental activity will increase.
“Neutrinos will be one of the flagships,” said Sam Zeller, co-coordinator of the MiniBooNE experiment.
The neutrino projects that Zeller and other researchers are working on are part of a long-term plan to build bigger and more sensitive detectors that can probe questions like the hierarchy of neutrino masses and neutrino mixing angles.
MiniBooNE uses an 8 GeV neutrino beam that is directed through 800 tons of mineral oil. Inside, 1280 photomultiplier tubes lining the spherical detector look for the signature flashes of light produced when neutrinos strike atoms in the mineral oil. The experiment studies neutrino oscillations over short distances from their source. The booster neutrino source referred to in the “BooNE” is actually the main injector that used to feed into the Tevatron, dubbed the NuMI.
“Just the main ring [of the Tevatron] has been decommissioned, but the whole front end is still running,” Zeller said.
MiniBooNE has been collecting data since 2002, and construction on the next generation of detector has already begun. Dubbed MicroBooNE, it will be made up of 100 tons of liquid argon to look for neutrino signals along the same beam line. Researchers have been eyeing liquid argon detectors as the next iteration of neutrino detectors, and MicroBooNE will be the largest liquid argon detector ever built.
Around the same time that MicroBooNE starts up next year, the two-part NOvA experiment should fully come online as well. Its smaller 222-ton “near detector,” located at Fermilab, has been running since the end of December, while the much larger 15-kiloton far detector, located in northern Minnesota, should start taking data in 2013. Researchers will compare the neutrino composition of the beam over the 513 mile distance to detect muon neutrinos turning into electron neutrinos. NOvA will use the existing NuMI beam, which already shoots neutrinos into the MINERvA detector in Fermilab and the MINOS detector in the Soudan Mine in Minnesota.
Right now researchers working on MINOS are looking into the recent announcement by the OPERA experiment in Italy, claiming evidence of neutrinos traveling faster than the speed of light. Tschirhart said that he expected an announcement supporting or refuting the OPERA findings sometime in the next one to three years.
The lab will keep its focus on neutrino research well into the next decade. The facility is preparing a second, higher intensity beam of neutrinos dubbed the Long Baseline Neutrino Experiment aimed at the Homestake Mine in Lead, South Dakota. Starting out, the experiment will use the main injector accelerator, which used to feed into the Tevatron, to produce an intense beam of muons that will decay into muon neutrinos. At the same time, Fermilab will be working to upgrade its proton beam by building a powerful next-generation linear proton accelerator. Colorfully dubbed Project X, the linear accelerator will shoot a continuous 3 GeV proton beam that can be modulated and split up for proton-, muon- and kaon-based experiments as well as the production of intense neutrino beams.
“It’s a real game-changer,” said Brendan Casey, currently part of the Tevatron’s DZero collaboration. “With Project X it’s a continuous [beam] so we can do anything we want downstream.”
In the very long term, the lab has its sights set on a Neutrino Factory, a muon accelerator fed by Project X that could produce neutrinos for detectors located thousands of miles away. Development and planning for the factory has only just begun, and construction likely won’t begin until at least late in the 2020s.
Two muon experiments are in development as well. The first that is scheduled to come on line is the G-2 experiment which brings in Brookhaven’s old muon storage ring and combines it with the former antiproton source for the Tevatron. It will look for violations of lepton-flavor symmetries. Mu2e, which is scheduled to come online by the end of the decade, will look for muons converting to electrons.
In addition the laboratory is working on research at the cosmic frontier, looking for clues coming from deep space about the makeup of the universe. Researchers from Fermilab will participate in the upcoming Dark Energy Survey and the Joint Dark Energy Mission. The lab will also continue to be a partner in the Pierre Auger cosmic ray observatory as well as the CDMS, COUPP and DarkSide dark matter searches, while continuing to develop more sensitive detectors.
“It’s absolutely the best time to be a particle physicist,” Tschirhart said. “There’s lots of great opportunities at CERN, and there’s lots of great opportunities here in the US at the intensity frontier.”
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