Daya Bay Reactor Neutrino Experiment begins taking data

August 18 – Urbana, Ill. – UPDATE

Professor Jen-Chieh Peng will give a talk on "The Mysterious Neutrinos" on Saturday, October 15, at 10:15 a.m. in 141 Loomis Laboratory, as part of this year's Saturday Physics for Everyone public lecture series.

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The Daya Bay Reactor Neutrino Experiment Collaboration, which is led by China and the United States, announced today that the experiment's first completed set of twin detectors is now recording interactions of antineutrinos as they travel away from the powerful reactors of the China Guangdong Nuclear Power Group in southern China.

The University of Illinois at Urbana-Champaign has been a member of the collaboration since the inception of the project in 2004. Led by Professor of Physics Jen-Chieh Peng, the UI group includes Dr. Daweil Liu and graduate students Ry Ely and Wah-Kai Ngai. The UI group has been heavily involved in the R&D, testing, and commissioning of the photo multiplier tubes (PMTs) that line the walls of the experiment.

Each cylindrical antineutrino detector is nested like a Russian doll, where one transparent acrylic vessel is enclosed in a second one, which in turn sits inside a third vessel made of stainless steel. The detectors are filled with a clear scintillator fluid, which reveals antineutrino interactions by the very faint flashes of light they emit as they pass through the liquid. The sensitive PMTs line the detector walls, amplifying and recording the telltale flashes.

"The Daya Bay experiment is aiming at answering one of the fundamental questions in particle physics," said Peng, spokesman for the UI group. "It is the first major collaborative effort between the United States and China on a particle physics experiment. It shows how scientists from very different backgrounds can collaborate effectively towards a common scientific goal." 

Neutrinos are uncharged particles produced in nuclear reactions, such as in the sun, by cosmic rays, and in nuclear power plants. They come in three types or “flavors” — electron, muon, and tau neutrinos — that morph, or oscillate, from one form to another, interacting hardly at all as they travel through space and matter, including people, buildings, and planets like Earth.

The start-up of the Daya Bay experiment marks the first step in the international effort of the Daya Bay Collaboration to measure a crucial quantity related to the third type of oscillation, in which the electron-flavored neutrinos morph into the other two flavored neutrinos. This transformation is caused by the least-known neutrino “mixing angle,” denoted by θ₁₃ (theta one-three), and could reveal clues leading to an understanding of why matter predominates over antimatter in the universe.

The Daya Bay Experiment is well positioned for a precise measurement of the poorly known value of θ₁₃ because it is close to some of the world’s most powerful nuclear reactors — the Daya Bay and Ling Ao nuclear power reactors, located some 55 kilometers from Hong Kong — and it will take data from a total of eight large, virtually identical detectors in three experimental halls deep under the adjacent mountains.

The Daya Bay experiment is a “disappearance” experiment, powered by the enormous quantities of electron antineutrinos produced in the nearby reactors. The detectors in the two closest halls will measure the raw flux of electron antineutrinos from the reactors. The detectors at the far hall will look for a depletion in the expected antineutrino flux.

The collaborating institutions of the Daya Bay Reactor Neutrino Experiment are Beijing Normal University, Brookhaven National Laboratory, California Institute of Technology, Charles University in Prague, Chengdu University of Technology, China Guangdong Nuclear Power Group, China Institute of Atomic Energy, Chinese University of Hong Kong, Dongguan University of Technology, Joint Institute for Nuclear Research, University of Hong Kong, Institute of High Energy Physics, Illinois Institute of Technology, Iowa State University, Kurchatov Institute, Lawrence Berkeley National Laboratory, Nanjing University, Nankai University, National Chiao-Tung University, National Taiwan University, National United University, North China Electric Power University, Princeton University, Rensselaer Polytechnic Institute, Shandong University, Shanghai Jiao Tong University, Shenzhen University, Siena College, Tsinghua University, University of California at Berkeley, University of California at Los Angeles, University of Cincinnati, University of Houston, University of Illinois at Urbana-Champaign, University of Science and Technology of China, Virginia Polytechnic Institute and State University Blacksburg, University of Wisconsin - Madison, College of William and Mary, and Sun Yat-Sen (Zhongshan) University.