Lawrence Livermore National Laboratory (LLNL) scientists are working to solve a 50-year-old question: Can neutrinos – a particle that is relatively massless, has no electric charge yet is fundamental to the make-up of the universe – transform from one type to another?
The scientists are using two giant detectors, one at the Fermi National Accelerator Laboratory near Chicago and another in a historic iron mine in northern Minnesota, to look for the answer.
As part of the international team working on the Main Injector Neutrino Oscillation Search (MINOS) project, LLNL researchers will use the detectors to explore the mysterious nature and properties of neutrinos. Specifically, they will seek to discover how neutrinos change “flavors.”
Neutrinos come in three “flavors”: electron, muon and tau. Each is related to a charged particle, which gives the corresponding neutrino its name. Neutrinos are extremely difficult to detect because they rarely interact with anything. They can easily pass through a human body, solid walls or even a planet, rarely leaving a trace of their existence.
“The probability of a neutrino interacting with anything is very small,” said LLNL’s Peter Barnes, who along with Livermore’s Doug Wright and Ed Hartouni is working on the MINOS experiment. “If you want to detect any neutrinos, you need something big.”
Barnes, Wright and Hartouni are hoping that "something big" is a 6,000-ton detector lying deep in the iron mine in Soudan, Minn. The neutrinos will be generated along an underground particle accelerator beamline at Fermilab, will pass through the near detector at the lab, and will travel through the Earth to the detector in Minnesota. Neutrinos are more easily detected when they are generated at a high energy, such as those at Fermilab.
The MINOS scientists chose the distance to the far detector to maximize the oscillation probability, which gives them the best opportunity to directly study the neutrino “flavor” change.
Nuclear fusion in the sun produces electron neutrinos, and scientists have predicted that if they can measure the electron neutrinos coming from the sun, they can measure the sun‘s core. Early experiments, however, showed that fewer than half of the expected neutrinos were observed on Earth. The idea that the missing electron neutrinos may have transformed into another type or flavor came alive.
This theory requires that neutrinos have some mass, small as it may be, in order for them to oscillate. So a portion of the electron neutrinos emitted from the sun could have changed flavors, to muon or tau neutrinos, before reaching Earth, thus solving the missing neutrino problem.
But it still doesn’t explain how or why this occurs, Barnes said. “Our goal is to understand the flavor oscillation properties of neutrinos,” he said.
Studying the elusive neutrino will help scientists better understand particle physics – specifically how particles acquire mass – as well as its role in the formation of the universe and its relationship to "dark matter" – the elusive "missing mass" in the universe that scientists have been unable to account for.
Livermore’s portion of the project is funded by the Laboratory Directed Research and Development and Physical Data Research programs. The MINOS effort as a whole is funded by the Department of Energy’s Office of Science, High Energy Physics division.
MINOS was formally dedicated in a ceremony today (March 4) at Fermilab. Click here for more photos.
Founded in 1952, Lawrence Livermore National Laboratory has a mission to ensure national security and to apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.