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| Fermilab's MiniBooNE detector features hundreds of photodetectors designed to detect the light particles produced by interactions between neutrino interacts and atomic nuclei. Photo by Reidar Hahn |
By Brooks Hays, UP
For the first time, scientists have precisely measured the interactions between neutrinos hitting the atomic nuclei in the heart of the Department of Energy's Fermilab particle detector.
The findings -- detailed in the journal Physical Review Letters -- remove much of the uncertainty undermining theoretical models of neutrino oscillations and interactions.
"The issue of neutrino energy is so important," Fermilab researcher Joshua Spitz, a professor or particle physics at the University of Michigan, said in a news release. "It is extraordinarily rare to know the energy of a neutrino and how much energy it transfers to the target atom. For neutrino-based studies of nuclei, this is the first time it has been achieved."
Neutrinos possess an extremely weak nuclear force and are without a charge, making them much more sensitive to interactions with an atom's nucleus. As such, they can help scientists analyze the inner workings of atomic nuclei. The only problem is they're very hard to create, isolate and measure.
To study the atomic nuclei, researchers use the particle accelerator to propel particles at nuclei at high speeds. A direct hit can break apart the nucleus and illuminate its inner workings.
But to properly interpret the collision and breakup, scientists need to understand the energy properties of the accelerated particle, the muon neutrino.
The accelerator launches millions of tiny particles at the MiniBooNE detector, not all with the same energy signature. Because scientists don't have a way to filter the muon neutrinos, they can't be sure which are responsible for the measured collisions.
However, Spitz and his colleagues have developed a workaround.
Neutrinos are produced from the decay of particles called kaons. Decaying kaons yield muon neutrinos with a range of energies. But using conservation of energy and momentum principles, scientists determined that muon neutrinos produced by kaon-at-rest decay would have the precise energy of 236 million electronvolts.
"It is not often in neutrino physics that you know the energy of the incoming neutrino," said Richard Van De Water, a physicist at Los Alamos National Laboratory. "With the first observation by MiniBooNE of monoenergetic muon neutrinos from kaon decay, we can study the charged current interactions with a known probe that enable theorists to improve their cross section models. This is important work for the future short- and long-baseline neutrino programs at Fermilab."
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