A collaborative effort led by Fermilab, with contributions from Tufts University researchers, has initiated new findings. Analyzing data from the NOvA experiment and Japan's T2K project, scientists are investigating whether the oscillatory behavior of neutrinos could explain this imbalance.
Neutrinos are extremely light, neutral subatomic particles produced during processes such as radioactive decay in Earth's core or hydrogen fusion in the Sun. They occur in three "flavors" - electron, muon, and tau - each representing a mix of three mass states. As neutrinos traverse space, the mass states oscillate, akin to three strings in a musical chord vibrating at varied frequencies, causing a quantum beat that shifts the particle's flavor.
Experiments at Fermilab and T2K accelerated neutrinos and antineutrinos, sending them hundreds of miles through the Earth to distant detectors. The main NOvA detector in Ash River, Minnesota, weighs 14,000 tons and consists of over 340,000 PVC modules filled with liquid that glows when struck by charged particles. The team compared measurements from near and far detectors to map flavor transitions.
Jeremy Wolcott of Tufts University said, "In the experiments, which stretched over 10 years, we made neutrinos and antineutrinos of one flavor (tau) in a particle accelerator and let them propagate hundreds of miles through the Earth."
He continued, "The detectors - a near one and a far one - pick up neutrinos of a different flavor due to the oscillations. Our goal was to determine whether the oscillations were different between matter-based neutrinos and antimatter neutrinos. If neutrinos and antineutrinos oscillate differently, ending with slightly different mass, then their creation at the beginning of the universe could have led to an excess of matter over antimatter."
The NOvA and T2K experiments detected differences in neutrino and antineutrino oscillations, suggesting this effect could account for a matter-to-antimatter ratio increase of one part per billion. However, more data are needed for definitive conclusions. Wolcott added, "One of the challenges with measuring neutrino oscillation is that there are a lot of degrees of freedom, including uncertainty in the ordering of the mass states - we still don't know which mass function is the heaviest or lightest, so we need a lot of data to help sort that out."
Detection remains a major challenge. As Wolcott stated, "Detection is a challenge. We have to sort out oscillated neutrinos from the accelerator from unoscillated accelerator neutrinos, cosmic-ray particles, and other background particles that come in contact with the detector." Natural particle sources trigger the detector thousands of times per second, but only about one neutrino from the accelerator is captured each day. Most neutrinos pass through the Earth and detectors without interaction, earning the nickname "ghost particles."
Research Report:Joint neutrino oscillation analysis from the T2K and NOvA experiments
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