Explore the vast range of titles available.

Neutrinos were assumed to be massless particles until the discovery of the neutrino oscillation process. This phenomenon indicates that the neutrinos have non-zero masses and the mass eigenstates ( ν 1 , ν 2 , ν 3 ) are mixtures of their flavour eigenstates ( ν e , ν μ , ν τ ). The oscillations between different flavour eigenstates are described by three mixing angles ( θ 12 , θ 23 , θ 13 ), two differences of the squared neutrino masses of the ν 2 / ν 1 and ν 3 / ν 1 pairs and a charge conjugation parity symmetry violating phase δ CP . The Double Chooz experiment, located near the Chooz Electricité de France reactors, measures the oscillation parameter θ 13 using reactor neutrinos. Here, the Double Chooz collaboration reports the measurement of the mixing angle θ 13 with the new total neutron capture detection technique from the full data set, yielding sin 2 (2 θ 13 ) = 0.105 ± 0.014. This measurement exploits the multidetector configuration, the isoflux baseline and data recorded when the reactors were switched off. In addition to the neutrino mixing angle measurement, Double Chooz provides a precise measurement of the reactor neutrino flux, given by the mean cross-section per fission 〈 σ f 〉 = (5.71 ± 0.06) × 10 −43  cm 2 per fission, and reports an empirical model of the distortion in the reactor neutrino spectrum. The Double Chooz collaboration reports the neutrino oscillation parameter θ 13 from a measurement of the disappearance of reactor anti-electron neutrinos with the total neutron capture technique.

We present a search for signatures of neutrino mixing of electron anti-neutrinos with additional hypothetical sterile neutrino flavors using the Double Chooz experiment. The search is based on data from 5 years of operation of Double Chooz, including 2 years in the two-detector configuration. The analysis is based on a profile likelihood, i.e. comparing the data to the model prediction of disappearance in a data-to-data comparison of the two respective detectors. The analysis is optimized for a model of three active and one sterile neutrino. It is sensitive in the typical mass range 5×10-3eV2≲Δm412≲3×10-1eV2 for mixing angles down to sin22θ14≳0.02. No significant disappearance additionally to the conventional disappearance related to θ13 is observed and correspondingly exclusion bounds on the sterile mixing parameter θ14 as a function of Δm412 are obtained.

A bstract A θ 13 oscillation analysis based on the observed antineutrino rates at the Double Chooz far and near detectors for different reactor power conditions is presented. This approach provides a so far unique simultaneous determination of θ 13 and the total background rates without relying on any assumptions on the specific background contributions. The analysis comprises 865 days of data collected in both detectors with at least one reactor in operation. The oscillation results are enhanced by the use of 24.06 days (12.74 days) of reactor-off data in the far (near) detector. The analysis considers the ν ¯ e interactions up to a visible energy of 8.5 MeV, using the events at higher energies to build a cosmogenic background model considering fast-neutrons interactions and 9 Li decays. The background-model-independent determination of the mixing angle yields sin 2 (2 θ 13 ) = 0 . 094 ± 0 . 017, being the best-fit total background rates fully consistent with the cosmogenic background model. A second oscillation analysis is also performed constraining the total background rates to the cosmogenic background estimates. While the central value is not significantly modified due to the consistency between the reactor-off data and the background estimates, the addition of the background model reduces the uncertainty on θ 13 to 0.015. Along with the oscillation results, the normalization of the anti-neutrino rate is measured with a precision of 0.86%, reducing the 1.43% uncertainty associated to the expectation.

A bstract The yields and production rates of the radioisotopes 9 Li and 8 He created by cosmic muon spallation on 12 C, have been measured by the two detectors of the Double Chooz experiment. The identical detectors are located at separate sites and depths, which means that they are subject to different muon spectra. The near (far) detector has an overburden of ∼120 m.w.e. (∼300 m.w.e.) corresponding to a mean muon energy of 32.1 ± 2.0 GeV (63.7 ± 5.5 GeV). Comparing the data to a detailed simulation of the 9 Li and 8 He decays, the contribution of the 8 He radioisotope at both detectors is found to be compatible with zero. The observed 9 Li yields in the near and far detectors are 5.51 ± 0.51 and 7.90 ± 0.51, respectively, in units of 10 −8 μ −1 g −1 cm 2 . The shallow overburdens of the near and far detectors give a unique insight when combined with measurements by KamLAND and Borexino to give the first multi-experiment, data driven relationship between the 9 Li yield and the mean muon energy according to the power law Y = Y 0 E μ / 1 GeV α ¯ , giving α ¯ = 0.72 ± 0.06 and Y 0 = (0.43 ± 0.11) × 10 −8 μ −1 g −1 cm 2 . This relationship gives future liquid scintillator based experiments the ability to predict their cosmogenic 9 Li background rates.

Primary challenges for current and future precision neutrino experiments using liquid argon time projection chambers (LArTPCs) include understanding detector effects and quantifying the associated systematic uncertainties. This paper presents a novel technique for assessing and propagating LArTPC detector-related systematic uncertainties. The technique makes modifications to simulation waveforms based on a parameterization of observed differences in ionization signals from the TPC between data and simulation, while remaining insensitive to the details of the detector model. The modifications are then used to quantify the systematic differences in low- and high-level reconstructed quantities. This approach could be applied to future LArTPC detectors, such as those used in SBN and DUNE.

A bstract The Double Chooz experiment presents improved measurements of the neutrino mixing angle θ 13 using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m 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 ν ¯ e signal has increased. The value of θ 13 is measured to be sin 2  2 θ 13  = 0.090 − 0.029 + 0.032 from a fit to the observed energy spectrum. Deviations from the reactor ν ¯ e prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of θ 13 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 θ 13 measurement despite the observed distortion.

A bstract The MicroBooNE liquid argon time projection chamber located at Fermilab is a neutrino experiment dedicated to the study of short-baseline oscillations, the measurements of neutrino cross sections in liquid argon, and to the research and development of this novel detector technology. Accurate and precise measurements of calorimetry are essential to the event reconstruction and are achieved by leveraging the TPC to measure deposited energy per unit length along the particle trajectory, with mm resolution. We describe the non-uniform calorimetric reconstruction performance in the detector, showing dependence on the angle of the particle trajectory. Such non-uniform reconstruction directly affects the performance of the particle identification algorithms which infer particle type from calorimetric measurements. This work presents a new particle identification method which accounts for and effectively addresses such non-uniformity. The newly developed method shows improved performance compared to previous algorithms, illustrated by a 93.7% proton selection efficiency and a 10% muon mis-identification rate, with a fairly loose selection of tracks performed on beam data. The performance is further demonstrated by identifying exclusive final states in ν μ CC interactions. While developed using MicroBooNE data and simulation, this method is easily applicable to future LArTPC experiments, such as SBND, ICARUS, and DUNE.

A significant challenge in measurements of neutrino oscillations is reconstructing the incoming neutrino energies. While modern fully-active tracking calorimeters such as liquid argon time projection chambers in principle allow the measurement of all final state particles above some detection threshold, undetected neutrons remain a considerable source of missing energy with little to no data constraining their production rates and kinematics. We present the first demonstration of tagging neutrino-induced neutrons in liquid argon time projection chambers using secondary protons emitted from neutron-argon interactions in the MicroBooNE detector. We describe the method developed to identify neutrino-induced neutrons and demonstrate its performance using neutrons produced in muon-neutrino charged current interactions. The method is validated using a small subset of MicroBooNE’s total dataset. The selection yields a sample with 60 % of selected tracks corresponding to neutron-induced secondary protons. At this purity, the integrated efficiency is 8.4% for neutrons that produce a detectable proton.

A bstract The Double Chooz collaboration presents a measurement of the neutrino mixing angle θ 13 using reactor ν e ¯ 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 ν e ¯ without gadolinium loading. Spectral distortions from the ν e ¯ reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of sin 2 2 θ 13  = 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 sin 2 2 θ 13 = 0 . 088 ± 0 . 033(stat+syst).

Cosmic ray (CR) interactions can be a challenging source of background for neutrino oscillation and cross-section measurements in surface detectors. We present methods for CR rejection in measurements of charged-current quasielastic-like (CCQE-like) neutrino interactions, with a muon and a proton in the final state, measured using liquid argon time projection chambers (LArTPCs). Using a sample of cosmic data collected with the MicroBooNE detector, mixed with simulated neutrino scattering events, a set of event selection criteria is developed that produces an event sample with minimal contribution from CR background. Depending on the selection criteria used a purity between 50 and 80% can be achieved with a signal selection efficiency between 50 and 25%, with higher purity coming at the expense of lower efficiency. While using a specific dataset and selection criteria values optimized for the MicroBooNE detector, the concepts presented here are generic and can be adapted for various studies of exclusive \\[\\nu _{\\mu }\\] CCQE interactions in LArTPCs.