Wen-Wen Wang

Mass Hierarchy Resolution in Reactor Anti-neutrino Experiments: Parameter Degeneracies and Detector Energy Response

Determination of the neutrino mass hierarchy using a reactor neutrino experiment at ∼60u2009u2009km is analyzed. Such a measurement is challenging due to the finite detector resolution, the absolute energy scale calibration, and the degeneracies caused by current experimental uncertainty of |Δm_(32)^2|. The standard χ^2 method is compared with a proposed Fourier transformation method. In addition, we show that for such a measurement to succeed, one must understand the nonlinearity of the detector energy scale at the level of a few tenths of percent.

Statistical Evaluation of Experimental Determinations of Neutrino Mass Hierarchy

Statistical methods of presenting experimental results in constraining the neutrino mass hierarchy n(MH) are discussed. Two problems are considered and are related to each other: how to report the nfindings for observed experimental data, and how to evaluate the ability of a future experiment to ndetermine the neutrino mass hierarchy, namely, sensitivity of the experiment. For the first problem nwhere experimental data have already been observed, the classical statistical analysis involves constructing confidence intervals for the parameter Δm^2_(32). These intervals are deduced from the parent ndistribution of the estimation of Δm^2_(32) nbased on experimental data. Due to existing experimental nconstraints on |Δm^2_(32)|, the estimation of Δm^2_(32) is better approximated by a Bernoulli distribution n(a Binomial distribution with 1 trial) rather than a Gaussian distribution. Therefore, the Feldman- nCousins approach needs to be used instead of the Gaussian approximation in constructing confidence nintervals. Furthermore, as a result of the definition of confidence intervals, even if it is correctly nconstructed, its confidence level does not directly reflect how much one hypothesis of the MH is nsupported by the data rather than the other hypothesis. We thus describe a Bayesian approach nthat quantifies the evidence provided by the observed experimental data through the (posterior) nprobability that either one hypothesis of MH is true. This Bayesian presentation of observed experimental results is then used to develop several metrics to assess the sensitivity of future experiments. nIllustrations are made using a simple example with a confined parameter space, which approximates nthe MH determination problem with experimental constraints on the |Δm^2_(32)|.

Some new progress on the light absorption properties of linear alkyl benzene solvent

Linear alkyl benzene(LAB) will be used as the solvent in a liquid scintillator mixture for the JUNO antineutrino experiment. Its light absorption properties should therefore be understood prior to its effective use in the experiment. Attenuation length measurements at a light wavelength of 430 nm have been performed on samples of LAB prepared for the JUNO experiment. Inorganic impurities in LAB have also been studied for their possibilities of light absorption in our wavelength of interest. In view of a tentative plan by the JUNO collaboration to utilize neutron capture with hydrogen in the detector, we also present in this work a preliminary study on the carbon–hydrogen ratio and the attenuation length of the samples.Linear alkyl benzene(LAB) will be used as the solvent in a liquid scintillator mixture for the JUNO antineutrino experiment. Its light absorption properties should therefore be understood prior to its effective use in the experiment. Attenuation length measurements at a light wavelength of 430 nm have been performed on samples of LAB prepared for the JUNO experiment. Inorganic impurities in LAB have also been studied for their possibilities of light absorption in our wavelength of interest. In view of a tentative plan by the JUNO collaboration to utilize neutron capture with hydrogen in the detector, we also present in this work a preliminary study on the carbon–hydrogen ratio and the attenuation length of the samples.

Evaluation of new large area PMT with high quantum efficiency

The neutrino detector of the Jiangmen Underground Neutrino Observatory (JUNO) is designed to use 20 kilotons of liquid scintillator and approximately 16 000 20 inch photomultipliers (PMTs). One of the options is to use the 20 inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics. The performance of the newly developed PMT preproduction samples is evaluated. The results show that its quantum efficiency is 30% at 400 nm. Its Peak/Valley (P/V) ratio for the single photoelectron is 4.75 and the dark count rate is 27 kHz at the threshold of 3 mV while the gain is at 1 × 107. The transit time spread of a single photoelectron is 2.86 ns. Generally the performances of this new 20 inch PMT are improved over the old one of R3600.