Neutrino find may uncover matter secrets

Discussion in 'China' started by cir, Mar 9, 2012.

  1. cir

    cir Senior Member Senior Member

    Joined:
    Dec 28, 2010
    Messages:
    1,996
    Likes Received:
    269
    Updated: 2012-03-08 15:58(Xinhua)

    BEIJING/SHENZHEN - Chinese and American physicists have made a pivotal breakthrough in the study of neutrinos, which may explain the predominance of matter over antimatter in the universe.

    The research on the subatomic particles, which was conducted at a nuclear power plant in south China, is expected to define the future of particle physics.

    The findings come from the Daya Bay Reactor Neutrino Experiment, which was conducted close to the Daya Bay Nuclear Power Station in Guangdong Province.

    Based on data collected from two powerful nuclear reactors, multinational scientists have been able to confirm and measure a third type of neutrino oscillation, Wang Yifang, a co-spokesperson for the experiment and head of the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS), said at a press conference Thursday in Beijing.

    Neutrinos, the wispy particles that flooded the universe in the earliest moments after the Big Bang, are continually produced in the hearts of stars and and other nuclear reactions.

    Traveling at close to the speed of light, the three basic neutrino "flavors" -- electron, muon, and tau neutrinos, as well as their corresponding antineutrinos -- mix together and oscillate. This activity, however, is extremely difficult to detect.

    Two types of oscillation, solar and atmospheric neutrino oscillation, were confirmed in experiments conducted in the 1960s and 1990s, while the third type of oscillation had not been detected prior to the Daya Bay experiment.

    From last December, the scientists in the Daya Bay experiment observed tens of thousands of interactions of electron antineutrinos caught by six detectors installed in the mountains adjacent to the powerful nuclear reactors, Wang said.

    The data revealed for the first time the strong signal of the effect that the scientists were searching for -- a so-called "mixing angle" named theta one third, a new type for neutrino oscillation, he said.

    "It is surprisingly large," Wang said. "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."

    Scientists believe the intense heat of the Big Bang should have forged equal amounts of matter and its "mirror image" antimatter. But as we live in a universe composed overwhelmingly of matter today, physicists have been puzzled by the apparent "disappearance" of antimatter.

    The findings have been submitted to the Physical Review Letters for publication, Wang said.

    Chinese physicists proposed to look for the third type of neutrino oscillation by studying neutrinos produced by nuclear reactors and measure the amplitude of the oscillation due to the least-known mixing angle denoted by theta one-three, said Zhao Guangda, a CAS academician and director general of the China Society of High Energy Physics.

    Zhao said the value of theta one-three would "determine the future of particle physics."

    "The mystery of why antimatter disappears can be solved," Zhao said.

    Co-spokesperson Kam-Biu Luk, a lead physicist at the U.S. Department of Energy Lawrence Berkeley National Laboratory and the University of California at Berkeley, said the study results would also represent a major contribution to understanding the role of neutrinos in the evolution of basic kinds of matter in the earliest moments after the Big Bang.

    "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," Luk said.

    "The Daya Bay experiment is of crucial scientific significance, leading to a bright future for particle physics," said CAS academician Zhan Wenlong, who is also vice CAS president and president of the Chinese Physical Society.

    China and the United States launched the Daya Bay experiment in 2006. It involves collaboration of 250 researchers from 39 global institutes including the IHEP, Lawrence Berkeley National Laboratory, Brookhaven National Laboratory, California Institute of Technology, Tsinghua University and Charles University in Prague.

    Neutrino find may uncover matter secrets|Sci-Tech|chinadaily.com.cn
     
  2.  
  3. cir

    cir Senior Member Senior Member

    Joined:
    Dec 28, 2010
    Messages:
    1,996
    Likes Received:
    269
    Daya Bay unveils the last neutrino mixing angle

    Thursday, March 8, 2012

    [​IMG]
    Each antineutrino detector at Daya Bay is lined with photomultiplier tubes to catch the faint trace of antineutrino reactions in the scintillator fluids that fill the detectors. Image: Roy Kaltschmidt, Lawrence Berkeley National Laboratory

    The Daya Bay Reactor Neutrino Experiment, a multinational collaboration operating in the south of China, reported the first results of its search for the last, most elusive piece of a long-standing puzzle: How is it that neutrinos can appear to vanish as they travel? The surprising answer opens a gateway to a new understanding of fundamental physics and may eventually solve the riddle of why there is far more ordinary matter than antimatter in the universe today.

    Traveling at close to the speed of light, the three basic neutrino "flavors"—electron, muon, and tau neutrinos, as well as their corresponding antineutrinos—mix together and oscillate (transform), but this activity is extremely difficult to detect. From Dec. 24, 2011, until Feb. 17, 2012, scientists in the Daya Bay collaboration observed tens of thousands of interactions of electron antineutrinos, caught by six massive detectors buried in the mountains adjacent to the powerful nuclear reactors of the China Guangdong Nuclear Power Group. These reactors, at Daya Bay and nearby Ling Ao, produce millions of quadrillions of elusive electron antineutrinos every second.

    The copious data revealed for the first time the strong signal of the effect that the scientists were searching for, a so‑called mixing angle named theta one-three, which the researchers measured with unmatched precision. Theta one-three, the last mixing angle to be precisely measured, expresses how electron neutrinos and their antineutrino counterparts mix and change into the other flavors. The Daya Bay collaboration's first results indicate that sin2 2 θ13 is equal to 0.092 plus or minus 0.017.

    "This is a new type of neutrino oscillation, and it is surprisingly large," says Yifang Wang of China's Institute of High Energy Physics (IHEP), co-spokesperson and Chinese project manager of the Daya Bay experiment. "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."

    Neutrinos, the wispy particles that flooded the universe in the earliest moments after the Big Bang, are continually produced in the hearts of stars and other nuclear reactions. Untouched by electromagnetism, they respond only to the weak nuclear force and even weaker gravity, passing mostly unhindered through everything from planets to people. The challenge of capturing these elusive particles inspired the Daya Bay collaboration in the design and precise placement of its 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 United States Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley. Luk is co-spokesperson of the Daya Bay Experiment and heads U.S. participation. "What we didn't expect was the sizable disappearance, equal to about 6%. Although disappearance has been observed in another reactor experiment over large distances, this is a new kind of disappearance for the reactor electron antineutrino."

    The Daya Bay experiment counts the number of electron antineutrinos detected in the halls nearest the Daya Bay and Ling Ao reactors and calculates how many would reach the detectors in the Far Hall if there were no oscillation. The number that apparently vanish on the way—oscillating into other flavors, in fact—gives the value of theta one-three. Because of the near-hall/far-hall arrangement, it’s not even necessary to have a precise estimate of the antineutrino flux from the reactors.

    "Even with only the six detectors already operating, we have more target mass than any similar experiment, plus as much or more reactor power," says William Edwards of Berkeley Lab and UC Berkeley, the U.S. project and operations manager for the Daya Bay Experiment. Since Daya Bay will continue to have an interaction rate higher than any other experiment, Edwards explains, "it is the leading theta one-three experiment in the world."

    The first Daya Bay results show that theta one-three, once feared to be near zero, instead is "comparatively huge," Kam-Biu Luk remarks, adding that "Nature was good to us." In coming months and years the initial results will be honed by collecting far more data and reducing statistical and systematic errors.

    "The Daya Bay experiment plans to stop the current data-taking this summer to install a second detector in the Ling Ao Near Hall, and a fourth detector in the Far Hall, completing the experimental design," says Yifang Wang.

    Refined results will open the door to further investigations and influence the design of future neutrino experiments—including how to determine which neutrino flavors are the most massive, whether there is a difference between neutrino and antineutrino oscillations, and, eventually, why there is more matter than antimatter in the universe—because these were presumably created in equal amounts in the big bang and should have completely annihilated one another, the real question is why there is any matter in the universe at all.

    "It has been very gratifying to be able to work with such an outstanding international collaboration at the world’s most sensitive reactor neutrino experiment," says Steve Kettell of Brookhaven National Laboratory, the chief scientist for the U.S. effort. "This moment is exciting because we have finally observed all three mixing angles, and now the way is cleared to explore the remaining parameters of neutrino oscillation."

    "This is really remarkable," says Wenlong Zhan, vice president of the Chinese Academy of Sciences and president of the Chinese Physical Society. "We hoped for a positive result when we decided to fund the project, but we never imagined it could come so quickly."

    "Exemplary teamwork among the partners has led to this outstanding performance," says James Siegrist, DOE Associate Director of Science for High Energy Physics. "These notable first results are just the beginning for the world’s foremost reactor neutrino experiment."

    Daya Bay unveils the last neutrino mixing angle | R&D Mag
     
  4. cir

    cir Senior Member Senior Member

    Joined:
    Dec 28, 2010
    Messages:
    1,996
    Likes Received:
    269
    [​IMG]
    Assembly of the antineutrino detectors in the Daya Bay Reactor Neutrino Experiment at the China Guangdong Nuclear Power Group power plant in southern China. The image shows the light sensors recording the neutrino interactions and the acrylic target vessels. (Credit: Photo by Roy Kaltschmidt, Lawrence Berkeley National Laboratory)
     
    W.G.Ewald likes this.

Share This Page