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Balloon flight will shed new light on mysterious neutrinos

A New Mexico State University researcher will send a scientific balloon aloft on a mission next spring that could help unravel some of the mystery of neutrinos -- wispy subatomic particles that are passing through your body by the billions as you read this.

tochaj, director of NMSU's Particle Astrophysics Laboratory, has been awarded a National Science Foundation grant of about $535,000 for the project, which will provide scientists with new data in their quest to understand neutrinos and their role in the cosmos.

"Of all the subatomic particles, neutrinos are among the most interesting," Stochaj said. "They don't behave the way you would expect."

Scientists know that neutrinos are produced in a specific kind of particle interaction called "weak interaction." The decay of a variety of subatomic particles -- muons, pions kaons, etc. -- produce neutrinos. But the numbers of neutrinos detected by instruments on the Earth's surface fall far short of the numbers predicted by current theories of physics, Stochaj said.

A key to solving the discrepancy could be a better understanding of what happens to particles from space as they strike and pass through the Earth's atmosphere. Stochaj and a team of collaborators from Italy, Germany and Sweden will send a helium-filled balloon with a payload of sensitive particle detectors to the outer reaches of the atmosphere and take measurements at various altitudes as they bring the balloon down in stages.

They won't be measuring neutrinos directly, however.

"You have to have huge detectors to detect neutrinos, much bigger than we could lift with a balloon," he said. "But you can detect muons, one step back in the decay chain, and if you know the number of muons you can determine the number of neutrinos that will come from them."

The goal of the project is to provide statistics on atmospheric muons that are 10 times better than currently available data, Stochaj said. "Hopefully this will shed some light on the problem. This will give the people who do the models something to compare to."

Ultimately, understanding neutrinos better will mean understanding the makeup of the universe better, he said.

The existence of neutrinos was postulated in the 1930s, and for years the tiny particles were presumed to have no mass, Stochaj said. Recent experiments suggest they do have some mass, and because they are so numerous, even with the slightest amount of mass they could amount to a big part of the total mass of the universe.

Scientists now believe there are several types of neutrinos, and there is evidence that they can "oscillate" or change from one type to another, he said. Oscillation would be another sign that neutrinos have mass, he said, and it also could be one reason the numbers of neutrinos detected on the ground don't meet scientists' expectations of the numbers that should come from the sun and cosmic rays. Some of the neutrinos could be changing, as they pass through the atmosphere, into a type of neutrino the detectors aren't sensitive to, he said.

Stochaj and his international collaborators have sent their instruments aloft numerous times in the past 12 years, but this mission is different. Previous flights, funded by NASA and the collaborators' scientific agencies, have been used primarily to look for antimatter in cosmic rays at the edge of Earth's atmosphere.

The muon flight, which will be launched from Fort Sumner in eastern New Mexico next spring, will carry instruments initially to nearly the same altitude as the earlier flights -- about 120,000 feet -- but it will then descend and stop at seven different altitudes to measure atmospheric muons down to 60,000 feet.

"It's the first time we've done a flight this complicated," Stochaj said. "Balloon flights are tricky anyway, and this one will be even harder because winds can vary so much at different altitudes."

The Particle Astrophysics Laboratory is a unit of the NMSU College of Engineering's Klipsch School of Electrical and Computer Engineering.