The result obtained from the Daya Bay Reactor Neutrino experiment illustrates an important quality of neutrinos and antineutrinos that may elucidate the mechanism behind matter-antimatter imbalance in the universe.
In this experiment, neutrinos produced by potent reactors were utilized to accurately determine the possibility of an electron antineutrino transition to other types of neutrinos. The Daya Bay experiment was conducted under a mountain close to the China Guangdong Nuclear Power Group power plant.
The results showed that electron neutrinos change to other types of neutrinos at a high rate over a small distance. Professor Karsten Heeger from the University of Wisconsin–Madison physics and the U.S. manager for the Daya Bay antineutrino detectors, explained that 6% of the electron antineutrinos produced from the reactor change to another type of neutrino over 2 km. These results were described by Heeger at the Symposium on Electroweak Nuclear Physics, which was held at Duke University. Presentations were also delivered by other key investigators in the Daya Bay collaboration.
Neutrinos move to and fro among tau, electron, and muon as they pass through space. Among these oscillations, two have been determined in the past. However, the electron neutrinos transition to other types of neutrinos over this distance, also known as theta one-three, remained a mystery prior to the Daya Bay experiment.
In the new experiment, detectors were placed in two experimental halls close to the Ling Ao and Daya Bay reactors and the number of electron antineutrinos recorded by these detectors was counted. Then the number of these electron antineutrinos, which would reach the detectors in a far-off hall in the absence of oscillation, was calculated. The number that disappeared on the way because of oscillating into other types provided the theta one-three value.
The researchers, after studying the signals of numerous electron antineutrinos, identified that electron antineutrinos vanished at a rate of 6 % over 2 km between the far and near halls. According to Yifang Wang, Chinese project manager and co-spokesperson of the Daya Bay experiment, the accurate measurement will aid in understanding the neutrino oscillation and shed light on the asymmetry of matter-antimatter in the universe.
Moreover, accurate measurement was possible because the value was surprisingly large. These findings answer the longstanding question on neutrino oscillation and will guide in forthcoming neutrino experiments.
Kam-Biu Luk, another co-spokesperson of the Daya Bay Experiment, informed that although the team was short of two detectors, it was successful in tracing the number of electron antineutrinos, which vanished while moving from the reactors to the detectors.
The researchers are currently arranging the remaining two detectors, which will be deployed in summer 2001 to boost data collection and enhance accuracy. Since 2006, the Department of Physics and UW–Madison PSL have been developing the detectors.
The results will be presented by Heeger in a seminar on 13 March 2012 on the UW–Madison campus.
The Daya Bay collaboration is headed by the U.S. and China. Taiwan, Hong Kong, the Czech Republic, and Russia are other participants in the collaboration.
Source: http://www.wisc.edu/