X. L. Luo

Assembly and Installation of the Daya Bay Antineutrino Detectors

The Daya Bay reactor antineutrino experiment is designed to make a precision measurement of the neutrino mixing angle θ_(13), and recently made the definitive discovery of its non-zero value. It utilizes a set of eight, functionally identical antineutrino detectors to measure the reactor flux and spectrum at baselines of ~ 300–2000 m from the Daya Bay and Ling Ao Nuclear Power Plants. The Daya Bay antineutrino detectors were built in an above-ground facility and deployed side-by-side at three underground experimental sites near and far from the nuclear reactors. This configuration allows the experiment to make a precision measurement of reactor antineutrino disappearance over km-long baselines and reduces relative systematic uncertainties between detectors and nuclear reactors. This paper describes the assembly and installation of the Daya Bay antineutrino detectors.

Measurements of the Mass and Width of the eta(c) Using the Decay psi (3686) -> gamma eta(c)

The mass and width of the lowest-lying S-wave spin singlet charmonium state, the η(c), are measured using a data sample of 1.06×10(8) ψ(3686) decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates full interference between the signal reaction, ψ(3686)→γη(c), and a nonresonant radiative background to describe the line shape of the η(c) successfully. We measure the η(c) mass to be 2984.3±0.6±0.6 MeV/c(2) and the total width to be 32.0±1.2±1.0 MeV, where the first errors are statistical and the second are systematic.

First measurement of the branching fraction of the decay ψ(2S)→τ+τ-

The branching fraction of the ψ(2S) decay into τ+τ− has been measured for the first time using the BES detector at the Beijing Electron-Positron Collider. The result is Bττ = (2.71± 0.43± 0.55)× 10−3 , where the first error is statistical and the second is systematic. This value, along with those for the branching fractions into e+e− and μ+μ− of this resonance, satisfy well the relation predicted by the sequential lepton hypothesis. Combining all these values with the leptonic width of the resonance, the total width of the ψ(2S) is determined to be (252±37) keV. PACS numbers: 13.20.Gd, 14.40.Gx, 14.60.-z, 14.60.Fg Typeset using REVTEX