"Observation of Electron-Antineutrino Disappearance at Daya Bay"

ABSTRACT: 

 

The theory of neutrino oscillation has been widely accepted in recent years. In a three-neutrino framework, the size of the third mixing angle $\theta_{13}$ remained to be unknown. A precision measurement of $\theta_{13}$ would reduce the unknown fundamental parameters in standard model to four. Furthermore, a sizable $\theta_{13}$ is also the key to measure the CP violation phase in leptonic sector and determine the neutrino mass hierarchy. 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 $\pm$ 0.012. A rate-only analysis finds sin$^22\theta_{13}$ = 0.092 $\pm$ 0.016 (stat) $\pm$ 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 sin$^22\theta_{13}$. 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 sin$^22\theta_{13}$.