Physics (Internal)

Observation of Electron Antineutrino Disappearance at Daya Bay

This event is part of the HET Seminar Series.

The theory of neutrino oscillation has been widely accepted in recent years. In a three-neutrino framework, there are three mixing angles in the theory. However, an accurate measurement on one of the three mixing angles, 13, stayed elusive. Knowing all three mixing angles is necessary to explore the remaining parameters in neutrino oscillation. To measure this least known mixing angle, a few dedicated experiments have been constructed and collecting data. Located on a nuclear power plant campus in Southern China which hosts a complex of six 2.9 GW reactors, the Daya Bay reactor neutrino experiment is designed to be the most sensitive one. In the three underground experimental halls, Daya Bay currently has six 20t Gd-doped liquid scintillator antineutrino detectors deployed, detecting the copious electron-antineutrinos released by the six reactors. With eight weeks of data collected since Dec 24, 2011, 10,416 (80,376) electron antineutrino candidates were detected at the far hall (near halls). Using the near hall data to constrain the antineutrino flux, we find the ratio of the observed to expected number of antineutrinos at the far hall is 0.940+-0.012. A rate-only analysis finds sin2 2theta13 = 0.092 +- 016(stat)  +- 0.005(syst) in a three-neutrino framework. The significance level of the Daya Bay measurment is at 5.2 standard deviation level. This is the first over 5-sigma measurement of sin2 2theta13. In this talk, we will report how the Daya Bay experiment was designed, installed, commissioned and how we perform the data analysis to extract the value of sin2 2theta13.