Daya Bay experiment overview & Measurement of neutrino oscillation mixing angle θ13 via unified neutron capture followed by inverse β decay.

Po-An Chen^1*, Yee Bob Hsiung¹, Bei-Zhen Hu¹

¹物理學系暨研究所, 國立臺灣大學, 台北市, Taiwan

* Presenter:Po-An Chen, email:chenpoan@outlook.com

From December 24, 2011, to present, Daya Bay experiment collected almost 10 millions of reactor electron antineutrino induced inverse β decay (IBD) events. Using the far-near technic, Daya Bay experiment successfully made the first discovery of non-zero value of θ13 with 5.2 σ of significance. (RENO experiment also share the first discovery with Daya Bay with their 4.9 σ of confidence level for non-zero value of θ13.). Up to now, Daya Bay experiment leads the most precise measurement on θ13 with more than 7 millions of IBD events, and this experiment is going to be decommissioned in December 12 with all its achievements.
After the discovery, Daya Bay experiment continue the data taking so as to increase the sensitivity of mixing angle measurement. Besides, lots of topics are been studied, including mixing angle analysis of using different mode to selecting IBD event, the investigation the reactor neutrino anomaly, which is roughly 5% from the prediction of Huber and Mueller's model, and test of sterile neutrino hypothesis.
Nevertheless, as a member of Daya Bay collaboration, we (National Taiwan University) keep working on measurement of θ13 via unified neutron capture, which are all followed by the anti-neutrino and proton interaction, the final results of sin^{2}2θ13 = 0.077±0.0070(stat)±0.0047(syst) is consistent with the other analysis from Daya Bay experiment. We will present a concise summary of backgrounds and efficiencies which related to our selection criteria. Background including accidental pairs, cosmogenic 9Li & 8He, cosmogenic fast neutron and 241Am13C neutron calibration source induced event. And accidental pairs serve as the dominant background which was more than 90% of contribution. Last but not least, how to construct a statistical hypothesis test from comparing prediction with or without θ13 will be introduced.

Keywords: Daya Bay experiment, neutrino oscillation, reactor neutrino, reactor neutrino anomaly