The Daya Bay Experiment consists of eight identically designed detectors located in three underground experimental halls named as EH1, EH2, EH3, with 250, 265 and 860 meters of water equivalent vertical overburden, respectively. Cosmic muon events have been recorded over a two-year period. The underground muon rate is observed to be positively correlated with the effective atmospheric temperature and to follow a seasonal modulation pattern. The correlation coefficient α, describing how a variation in the muon rate relates to a variation in the effective atmospheric temperature, is found to be α EH1 = 0.362 ± 0.031, α EH2 = 0.433 ± 0.038 and α EH3 = 0.641 ± 0.057 for each experimental hall.

A search for a time-varyingν e signal was performed with 621 days of data acquired by the Daya Bay Reactor Neutrino Experiment over 704 calendar days. The time spectrum of the measuredν e flux normalized to its prediction was analyzed with a Lomb-Scargle periodogram, which yielded no significant signal for periods ranging from 2 hours to nearly 2 years. The normalized time spectrum was also fit for a sidereal modulation under the Standard Model Extension (SME) framework to search for Lorentz and CPT violation (LV-CPTV). Limits were obtained for all six flavor pairsēμ;ēτ,μτ,ēē;μμ andττ by fitting them one at a time, constituting the first experimental constraints on the latter three. Daya Bay's high statistics and unique layout of multiple directions from three pairs of reactors to three experimental halls allowed the simultaneous constraint of individual SME LV-CPTV coefficients without assuming others contribute negligibly, a first for a neutrino experiment.

Preliminary study of light yield dependence on LAB liquidscintillator composition * YE Xing-Chen( ) 1,2;1) YU Bo-Xiang( ) 2,3;2) ZHOU Xiang() 2,3 YAN Jia-Qing( ) 2,3 ZHAO Hang( ) 2,3 HONG Dao-Jin( ) 2,3

We studied the temperature dependence of the light yield of the linear alkyl benzene (LAB)-based and mesitylene-based liquid scintillators. The light yield increases by 23% for both liquid scintillators when the temperature is lowered from 26• C to −40• C, correcting for the temperature response of the photomultiplier tube. The measurements help to understand the energy response of the liquid scintillator detectors. Especially, the next generation reactor neutrino experiments for neutrino mass hierarchy, such as the Jiangmen Underground Neutrino Observatory (JUNO), require very high energy resolution. As no apparent degradation on the liquid scintillator transparency was observed, lowering the operation temperature of the detector to ∼ 4• C will increase the photoelectron yield of the detector by 13%, combining the light yield increase of the liquid scintillator and the quantum efficiency increase of the photomultiplier tubes.