Precision muon reconstruction in Double Chooz

We describe a muon track reconstruction algorithm for the reactor anti-neutrino experiment Double Chooz. The Double Chooz detector consists of two optically isolated volumes of the liquid scintillator viewed by PMTs, and an Outer Veto above these made of crossed scintillator strips. Muons are reconstructed by their Outer Veto hit positions along with timing information from the other two detector volumes. All muons are fit under the hypothesis that they are through-going and ultrarelativistic. If the energy depositions suggest that the muon may have stopped, the reconstruction fits also for this hypothesis and chooses between the two via the relative goodness-of-fit. In the ideal case of a through-going muon intersecting the center of the detector, the resolution is ~40mm in each transverse dimension. High quality muon reconstruction is an important tool for reducing the impact of the cosmogenic isotope background in Double Chooz. © 2014 Elsevier B.V

Housing conditions as a social determinant of low birthweight and preterm low birthweight

OBJECTIVE: To assess the relationship between housing conditions and low birthweight and preterm low birthweight among low-income women. METHODS: A case-control study was conducted with post-partum women living in the city of Rio de Janeiro, Southeast Brazil, in 2003-2005. Two groups of cases, low birthweight (n=96) and preterm low birthweight infants (n=68), were compared against normal weight term controls (n=393). Housing conditions were categorized into three levels: adequate, inadequate, and highly inadequate. Covariates included sociodemographic and anthropometric characteristics, risk behaviors, violence, anxiety, satisfaction during pregnancy, obstetric history and prenatal care. RESULTS: Poor housing conditions was independently associated with low birthweight (inadequate - OR 2.3 [1.1;4.6]; highly inadequate - OR 7.6 [2.1;27.6]) and preterm low birthweight (inadequate - OR 2.2 [1.1;4.3]; highly inadequate - OR 7.6 [2.4;23.9]) and factors associated with outcomes were inadequate prenatal care and previous preterm birth. Low income and low maternal body mass index remained associated with low birthweight. CONCLUSIONS: Poor housing conditions were associated with low birthweight and preterm low birthweight

Ortho-positronium observation in the double chooz experiment

The Double Chooz experiment measures the neutrino mixing angle θ13 by detecting reactor ¯νe via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the orthopositronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44 % ± 12 % (sys.) ± 5 % (stat.) and 3.68 ns ± 0.17 ns (sys.) ± 0.15 ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup

Improved measurements of the neutrino mixing angle Ɵ<inf>13</inf> with the double chooz detector

The Double Chooz experiment presents improved measurements of the neutrino mixing angle Ɵ13 using the data collected in 467.90 live days from a detector positioned at an average distance of 1050m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the (Formula Presented.) signal has increased. The value of Ɵ13 is measured to be sin22Ɵ13 = 0.090-0.029+0.032 from a fit to the observed energy spectrum. Deviations from the reactor (Formula Presented.) prediction observed above a prompt signal energy of 4MeV and possible explanations are also reported. A consistent value of Ɵ13 is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the Ɵ13 measurement despite the observed distortion

Angra dos Reis reactor neutrino oscillation experiment

We present the status and plans of the Angra Project, a new reactor neutrino oscillation experiment, proposed to be built in Brazil at the Angra dos Reis nuclear complex. This experiment is aimed to measure theta13, the last unknown of the three neutrino mixing angles. We propose a high sensitivity multi-detector experiment, able to reach a sensitivity to antineutrino disappearance down to sin² 2theta13 = 0.006 in a three years running period, by combining a high luminosity design, very low background from cosmic rays and careful control of systematic errors. We also intend to explore the possibility to use the neutrino detector for purposes of safeguards and non-proliferation of nuclear weapons.1118112

Characterization of the spontaneous light emission of the PMTs used in the Double Chooz experiment

During the commissioning of the first of the two detectors of the Double Chooz experiment, an unexpected and dominant background caused by the emission of light inside the optical volume has been observed. A specific study of the ensemble of phenomena called Light Noise has been carried out in-situ, and in an external laboratory, in order to characterize the signals and to identify the possible processes underlying the effect. Some mechanisms of instrumental noise originating from the PMTs were identified and it has been found that the leading one arises from the light emission localized on the photomultiplier base and produced by the combined effect of heat and high voltage across the transparent epoxy resin covering the electric components. The correlation of the rate and the amplitude of the signal with the temperature has been observed. For the first detector in operation the induced background has been mitigated using online and offline analysis selections based on timing and light pattern of the signals, while a modification of the photomultiplier assembly has been implemented for the second detector in order to blacken the PMT bases

Improved measurements of the neutrino mixing angle Ɵ13 with the double chooz detector

The Double Chooz experiment presents improved measurements of the neutrino mixing angle Ɵ13 using the data collected in 467.90 live days from a detector positioned at an average distance of 1050m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the (Formula Presented.) signal has increased. The value of Ɵ13 is measured to be sin22Ɵ13 = 0.090-0.029+0.032 from a fit to the observed energy spectrum. Deviations from the reactor (Formula Presented.) prediction observed above a prompt signal energy of 4MeV and possible explanations are also reported. A consistent value of Ɵ13 is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the Ɵ13 measurement despite the observed distortion

Measurement of θ13 in Double Chooz using neutron captures on hydrogen with novel background rejection techniques

The Double Chooz collaboration presents a measurement of the neutrino mixing angle θ13 using reactor νe¯ (Formula presented.) observed via the inverse beta decay reaction in which the neutron is captured on hydrogen. This measurement is based on 462.72 live days data, approximately twice as much data as in the previous such analysis, collected with a detector positioned at an average distance of 1050 m from two reactor cores. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties. Accidental coincidences, the dominant background in this analysis, are suppressed by more than an order of magnitude with respect to our previous publication by a multi-variate analysis. These improvements demonstrate the capability of precise measurement of reactor νe¯ (Formula presented.) without gadolinium loading. Spectral distortions from the νe¯ (Formula presented.) reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of sin2 2θ13 =&nbsp;0.095− 0.039+ 0.038 (stat+syst) is obtained from a fit to the observed event rate as a function of the reactor power, a method insensitive to the energy spectrum shape. A simultaneous fit of the hydrogen capture events and of the gadolinium capture events yields a measurement of sin2 2θ13 = 0.088 ± 0.033(stat+syst)