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Daya Bay Reactor Neutrino Experiment

Daya Bay is an international neutrino-oscillation experiment designed to determine the last unknown neutrino mixing angle θ13 using anti-neutrinos produced by the Daya Bay and Ling Ao Nuclear Power Plant reactors. The experiment is being built by blasting three kilometers of tunnel through the granite rock under the mountains where the power plants are located. Data collection is now scheduled to start in in 2011. On the PDSF cluster at NERSC, Daya Bay performs simulations of the detectors, reactors, and surrounding mountains to help design and anticipate detector properties and behavior. Once real data are available, Daya Bay will be using NERSC to analyze data and NERSC HPSS will be the central U.S. repository for all raw and simulated data, information and backups. U.S. collaborators from 15 institutions will access data stored at NERSC via a scientific gateway.

Key Challenges: There are three key challenges: (1) The need to insure the integrity of a small and precious dataset as it passes from a distant experimental facility to the hands of Daya Bay users. (2) The need to absorb and rapidly process data: Daya Bay projects 150 TB per year of raw, simulated and processed data in steady state starting in calendar year 2011. (3) The need to make both processed and raw data available in a meaningful way to researchers throught the U.S.

Why it Matters: Neutrinos are uncharged elementary particles produced naturally from the sun and cosmic rays. The particles transform, or oscillate, among three types as they travel through space, people, buildings, and even Earth itself, interacting only rarely with other matter. Scientists have characterized two of these transformations in detail, and are now seeking to measure details of the third. A crucial quantity related to the third oscillation is known as the mixing angle θ13 (pronounced "theta-one-three"). Knowing the value of theta-one-three will help scientists resolve numerous mysteries of neutrinos and of the early universe. One of the most perplexing questions has to do with the matter we're made of. The Big Bang should have created equal amounts of matter and antimatter; yet today, the universe still contains plenty of matter while the antimatter has disappeared.

Accomplishments: Daya Bay has now started detector commissioning, demonstrating the ability to generate 1 TB of raw data in 3 days of sustained running for a single Antineutrino detector. Analysis packages are being developed for data processing, calibration, and physics analyses.

Update, March 2012: In a paper submitted to Physical Review Letters, the Daya Bay Collaboration reports measurement of a non-zero value for the neutrino mixing angle θ13
with a significance of 5.2 standard deviations.  This new and surprisingly large type of neutrino oscillation affords new understanding of fundamental physics; it may eventually help solve the riddle of matter-antimatter asymmetry in the universe.

NERSC Science Gateway: Datasets will be available for download at

Investigators: Kam-Biu Luk and Craig Tull (LBNL)

More Information: See the main project web site and the Berkeley Daya Bay web site.