Study On Energy Non-linearity Response Model Of Daya Bay Reactor Neutrino Experiment And Fit Of Sin² 2θ₁₃

Neutrinos are elementary particles which make the physical word, and one of the keys to the new physics. Neutrino oscillation is the only directly new physics phenomena beyond the Standard Model. Neutrino oscillation can be described by PMNS matrix with 6 free parameters. Before Daya Bay, there are still two and a half parameters: θ13, sign of Δm322, and δCP. θ13 is one of the parameter of PMNS matrix, and the value of it determine the future of neutrino physics because it determine whether the other two parameters can be measured with current technology. The Daya Bay reactor neutrino experiment is designed to precisely measure sin2213, with a sensitivity to 0.01 or better at 90% C.L.. Now,based on 1230 days’ data from November 2011 to July 2015, Daya Bay experiment give the most precise value of sin2213: sin2213= 0.0842 ± 0.0028(.) ± 0.0017(.)Precise measurements of reactor antineutrino spectrum require an accurate understanding of the detector energy response. With this, we can do the precise measurement of neutrino mixing angle θ13 and effective mass-squared difference |Δmee2|. For this purpose, we developed an energy response model of the antineutrino detector using various in-situ calibrations and external measurements. The calibration data include special calibration data taken in the summer of 2012 and physics data. We can fit γ and β spectrum to get the non-linear value of different energy and then get the non-linear curve of the whole energy range. At above 2MeV, the uncertainty of energy non-linearity is better than 1%; however, at below 2MeV, energy non-linearity curve should be more precise. For better understanding of electronics non-linearity, we install FADC system on AD1 of Daya Bay in December 2015. In February 2016, FADC system start taking data. Now we have finish the calibration of single p.e. spectrum(SPE). The primary result show that at below 2MeV, FADC data consist to the nominal electronics non-linearity model; however, at above 2MeV, FADC data become flat. The possible reason is the residual non-linearity of analysis method. Then, based on 217 days data of 6AD period, we select IBD data and deduct background, use MCMC method to fit sin2213, and get sin2213= 0.0893 ± 0.0094, consist to the official value sin2213= 0.0895 ± 0.0094.