The result from the Daya Bay Reactor Neutrino Experiment [link: http://dayawane.ihep.ac.cn/] describes a critical and previously unmeasured quality of neutrinos – and their antiparticles, antineutrinos – that may underlie basic properties of matter and explain why matter predominates over antimatter in the universe.
Embedded under a mountain near the China Guangdong Nuclear Power Group power plant about 55 kilometers from Hong Kong, the Daya Bay experiment used neutrinos emitted by powerful reactors to precisely measure the probability of an electron antineutrino transforming into one of the other neutrino types.
The results, detailed in a paper submitted to the journal Physical Review Letters, reveal that electron neutrinos transform into other neutrino types over a short distance and at a surprisingly high rate.
"Six percent of the electron antineutrinos emitted from the reactor transform over about two kilometers into another flavor of neutrino. Essentially they change identity," explains University of Wisconsin–Madison physics professor Karsten Heeger. [link: http://neutrino.physics.wisc.edu/heeger.php] Heeger is the U.S. manager for the Daya Bay antineutrino detectors.
Coincident with presentations by other principal investigators in the Daya Bay collaboration, Heeger is describing the results today in a talk at the Symposium on Electroweak Nuclear Physics, held at Duke University.
Neutrinos oscillate among three types or "flavors" – electron, muon, and tau – as they travel through space. Two of those oscillations were measured previously, but the transformation of electron neutrinos into other types over this distance (a so called "mixing angle" named theta one-three, written ?13) was unknown before the Daya Bay experiment.
"We expected that there would be such an oscillation, but we did not know what its probability would be," says Heeger.
The Daya Bay experiment counted the number of electron antineutrinos recorded by detectors in two experimental halls near the Daya Bay and Ling Ao reactors and calculated how many would reach the detectors in a more distant hall if there were no oscillation. The number that apparently vanished on the way – due to oscillating into other flavors – gave the value of theta one-three.
After analyzing signals of tens of thousands of electron antineutrinos emitted by the nuclear reactors, the researchers discovered that electron antineutrinos disappeared at a rate of six percent over the two kilometers between the near and far halls, a very short distance for a neutrino.
"Our precise measurement will complete the understanding of the neutrino oscillation and pave the way for the future understanding of matter-antimatter asymmetry in the universe," says Yifang Wang of China's Institute of High Energy Physics, co-spokesperson and Chinese project manager of the Daya Bay experiment.
The value is unexpectedly large and helps explain why the experiment was able to make a precise measurement so quickly, with less than two months' worth of data from just six of the planned eight detectors.
"Although we're still two detectors shy of the complete experimental design, we've had extraordinary success in detecting the number of electron antineutrinos that disappear as they travel from the reactors to the detectors two kilometers away," says Kam-Biu Luk of the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California at Berkeley. Luk is co-spokesperson of the Daya Bay Experiment and heads U.S. participation.
The researchers confirmed the finding with very high confidence, Heeger says – in statistical terms, greater than five sigma, which translates to a less than a 1 in 3.5 million chance that the result arose by random chance.
The findings fill in a major gap in understanding neutrino oscillation and will provide important guidance for future neutrino experiments, including looking for nonstandard effects outside of current theories.
Under the guidance of U.S. chief project engineer Jeff Cherwinka, an engineer at the UW–Madison Physical Sciences Laboratory (PSL), the collaboration is now assembling the last two detectors and will install them this summer to increase data collection and improve precision. The UW–Madison PSL [link: http://www.psl.wisc.edu/projects/large/dayabay] and Department of Physics have been involved in designing and building the detectors since 2006.
"What made this possible is that the detectors worked really well. We have a very strong technical engineering team with PSL, which led the onsite assembly and installation of the detectors. This allowed us to come online ahead of schedule and make these measurements so quickly," Heeger says.
Heeger will also present the findings locally in a seminar at 3:00 p.m. on Mar. 13 in 4272 Chamberlin Hall on the UW–Madison campus.
The Daya Bay collaboration is jointly led by China and the United States, with additional participants from Russia, the Czech Republic, Hong Kong, and Taiwan.
More information, including the submitted paper and photos of the experiment, are available at http://neutrino.physics.wisc.edu/dayabatheta13.
Karsten Heeger | EurekAlert!
DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)
New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
24.04.2017 | Physics and Astronomy
24.04.2017 | Materials Sciences
24.04.2017 | Life Sciences