But their measurements of the mass hierarchy so far remain inconclusive. The current leading long-baseline experiments-the NOvA experiment in the United States and the T2K experiment in Japan-have helped refine scientists’ understanding of oscillation. “This extra impact affects how much oscillation will happen.” “When a neutrino is traveling, the electron neutrino part of it wants to interact with the electrons in the Earth, and the muon and tau neutrino parts are unaffected,” says Zoya Vallari, a postdoc at Caltech. To distinguish between the “normal mass hierarchy” (the order 1, 2, 3) and the “inverted mass hierarchy” (3, 1, 2), researchers fire beams of neutrinos through hundreds of kilometers of solid rock in what are called “long-baseline” neutrino experiments. Measurements of the oscillations of atmospheric and accelerator-made muon neutrinos indicate a large difference in mass between the third mass state and the other two.īut so far scientists have been unable to determine whether mass state 3 is much heavier or much lighter than states 1 and 2. Careful measurements of solar neutrinos show that the second mass state is only slightly heavier than the first. Knowing the rates at which neutrinos oscillate from one type to another allows scientists to make some inferences about the relationships between the three mass states. Instead, there are three “neutrino mass states” numbered 1, 2 and 3, each with different likelihoods of interacting with matter as an electron neutrino, a muon neutrino or a tau neutrino. When high-energy particles strike Earth’s atmosphere, muon neutrinos are created they may oscillate to electron or tau neutrinos before being detected.īut the three types of neutrinos do not correspond directly to the three masses. The nuclear processes in the sun’s core generate a deluge of electron neutrinos, many of which turn into muon and tau neutrinos by the time they reach Earth. And neutrinos can oscillate, meaning they shift between those three identities. Neutrinos interact with matter as electron neutrinos, muon neutrinos or tau neutrinos, named after the partner particles they like to hang around with.
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