arXiv subjects

E. Chauveau

Publications and source records attributed to E. Chauveau.

54 records · Page 3Linked to original sources

arXiv2016

Status Report for the 21th J-PARC PAC : Searching for a Sterile Neutrino at J-PARC MLF (J-PARC E56, JSNS2)

The JSNS2 (J-PARC E56) experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Sciences Experimental Facility (MLF).After the submission of a proposal to the J-PARC PAC, stage-1 approval was granted to the JSNS2 experiment. The approval followed a series of background measurements which were performed in 2014. Subsequent for stage-1 approval, the JSNS2 collaboration has made continuous efforts to write a Technical Design Report (TDR).This TDR will include two major items as discussed in the previous status report for the 20th J-PARC PAC: (1) A realistic detector location (2) Well understood and realistic detector performance using simulation studies, primarily in consideration of fast neutron rejection. Since August we have been in discussions with MLF staff regarding an appropriate detector location. We are also in the process of setting up a Monte Carlo (MC) simulation framework in order to study detector's performance in realistic conditions. In addition, we have pursued hardware R&D work for the liquid scintillator (LS) and to improve the dynamic range of the 10" photomultiplier tubes (PMTs). The LS R&D works includes Cherenkov studies inside the LS, and a Pulse Shape Discrimination (PSD) study with a test-beam, performed at Tohoku University. We also estimate the PSD performance of a full-sized detector using a detailed MC simulation. In this status report, we describe progress on this work.

physics.ins-det↗

arXiv2015

Measurement of $θ_{13}$ 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 $θ_{13}$ using reactor $\overlineν_{e}$ 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 1050m 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 $\overlineν_{e}$ without gadolinium loading. Spectral distortions from the $\overlineν_{e}$ reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of $\sin^{2}2θ_{13} = 0.095^{+0.038}_{-0.039}$(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 $\sin^{2}2θ_{13} = 0.088\pm0.033$(stat+syst).

hep-ex↗

arXiv2015

Result of the search for neutrinoless double-$β$ decay in $^{100}$Mo with the NEMO-3 experiment

The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double $β$ ($0νββ$) decay. We report final results of a search for $0νββ$ decays with $6.914$ kg of $^{100}$Mo using the entire NEMO-3 data set with a detector live time of $4.96$ yr, which corresponds to an exposure of 34.3 kg$\cdot$yr. We perform a detailed study of the expected background in the $0νββ$ signal region and find no evidence of $0νββ$ decays in the data. The level of observed background in the $0νββ$ signal region $[2.8-3.2]$ MeV is $0.44 \pm 0.13$ counts/yr/kg, and no events are observed in the interval $[3.2-10]$ MeV. We therefore derive a lower limit on the half-life of $0νββ$ decays in $^{100}$Mo of $T_{1/2}(0νββ)> 1.1 \times 10^{24}$ yr at the $90\%$ Confidence Level, under the hypothesis of light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range $\langle m_ν \rangle < 0.33$--$0.62$ eV. We also report constraints on other lepton-number violating mechanisms for $0νββ$ decays.

hep-ex↗

arXiv2015

Status Report for the 20th J-PARC PAC : A Search for Sterile Neutrino at J-PARC MLF (J-PARC E56, JSNS2)

On April 2015, the J-PARC E56 (JSNS2: J-PARC Sterile Neutrino Search using neutrinos from J-PARC Spallation Neutron Source) experiment officially obtained stage-1 approval from J-PARC. We have since started to perform liquid scintillator R&D for improving energy resolution and fast neutron rejection. Also, we are studying Avalanche Photo-Diodes (SiPM) inside the liquid scintillator. In addition to the R&D work, a background measurement for the proton beam bunch timing using a small liquid scintillator volume was planned, and the safety discussions for the measurement have been done. This report describes the status of the R&D work and the background measurements, in addition to the milestones required before stage-2 approval.

physics.ins-det↗

arXiv2015

On-site Background Measurements for the J-PARC E56 Experiment: A Search for Sterile Neutrino at J-PARC MLF

The J-PARC E56 experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). In order to examine the feasibility of the experiment, we measured the background rates of different detector candidate sites, which are located at the third floor of the MLF, using a detector consisting of plastic scintillators with a fiducial mass of 500 kg. The result of the measurements is described in this article. The gammas and neutrons induced by the beam as well as the backgrounds from the cosmic rays were measured.

physics.ins-det↗

arXiv2015

Status Report (BKG measurement): A Search for Sterile Neutrino at J-PARC MLF

At the 17th J-PARC PAC, which was held on September 2013, we proposed the sterile neutrino search at J-PARC MLF. After reviewing the proposal, PAC recommended to have a background measurement at the detector's candidate site location in their report to investigate whether the background rates can be manageable for the real experiment or not. Therefore, we have performed the background measurements (MLF; 2013BU1301 test experiment) during the summer of 2014, also following the 18th J-PARC PAC recommendations, and the measurements results are described here.

physics.ins-det↗

arXiv2015

Improved measurements of the neutrino mixing angle $θ_{13}$ with the Double Chooz detector

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 $\barν_{e}$ signal has increased. The value of $θ_{13}$ is measured to be $\sin^{2}2θ_{13} = 0.090 ^{+0.032}_{-0.029}$ from a fit to the observed energy spectrum. Deviations from the reactor $\barν_{e}$ 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.

hep-ex↗

arXiv2014

Ortho-positronium observation in the Double Chooz Experiment

The Double Chooz experiment measures the neutrino mixing angle $θ_{13}$ by detecting reactor $\barν_e$ 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 ortho-positronium (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$\%$ $\pm$ 12$\%$ (sys.) $\pm$ 5$\%$ (stat.) and $3.68$ns $\pm$ 0.17ns (sys.) $\pm$ 0.15ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.

physics.ins-det↗

arXiv2014

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 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 ~40 mm in each transverse dimension. High quality muon reconstruction is an important tool for reducing the impact of the cosmogenic isotope background in Double Chooz.

physics.ins-det↗

arXiv2014

Search for Neutrinoless Double-Beta Decay of $^{100}$Mo with the NEMO-3 Detector

We report the results of a search for the neutrinoless double-$β$ decay (0$νββ$) of $^{100}$Mo, using the NEMO-3 detector to reconstruct the full topology of the final state events. With an exposure of 34.7 kg.y, no evidence for the 0$νββ$ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of $T_{1/2}(0νββ)>1.1 \times 10^{24}$ years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the Nuclear Matrix Elements this corresponds to an upper limit on the Majorana effective neutrino mass of $< m_ν > < 0.3-0.9$ eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0$νββ$ decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region [3.2-10] MeV is observed for an exposure of 47 kg.y.

hep-ex↗

arXiv2014

Background-independent measurement of $θ_{13}$ in Double Chooz

The oscillation results published by the Double Chooz collaboration in 2011 and 2012 rely on background models substantiated by reactor-on data. In this analysis, we present a background-model-independent measurement of the mixing angle $θ_{13}$ by including 7.53 days of reactor-off data. A global fit of the observed neutrino rates for different reactor power conditions is performed, yielding a measurement of both $θ_{13}$ and the total background rate. The results on the mixing angle are improved significantly by including the reactor-off data in the fit, as it provides a direct measurement of the total background rate. This reactor rate modulation analysis considers antineutrino candidates with neutron captures on both Gd and H, whose combination yields $\sin^2(2θ_{13})=$ 0.102 $\pm$ 0.028(stat.) $\pm$ 0.033(syst.). The results presented in this study are fully consistent with the ones already published by Double Chooz, achieving a competitive precision. They provide, for the first time, a determination of $θ_{13}$ that does not depend on a background model.

hep-ex↗

arXiv2013

Proposal: A Search for Sterile Neutrino at J-PARC Materials and Life Science Experimental Facility

We propose a definite search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). With the 3 GeV Rapid Cycling Synchrotron (RCS) and spallation neutron target, an intense neutrino beam from muon decay at rest (DAR) is available. Neutrinos come from μ+ decay, and the oscillation to be searched for is (anti νμ-> anti νe) which is detected by the inverse βdecay interaction (anti νe + p -> e+ + n), followed by a gamma from neutron capture. The unique features of the proposed experiment, compared with the LSND and experiments using horn focused beams, are; (1) The pulsed beam with about 600 ns spill width from J-PARC RCS and muon long lifetime allow us to select neutrinos from μDAR only. (2) Due to nuclear absorption of π- and μ-, neutrinos from μ- decay are suppressed to about the $10^{-3}$ level. (3) Neutrino cross sections are well known. The inverse βdecay cross section is known to be a few percent accuracy. (4) The neutrino energy can be calculated from positron energy by adding ~1.8 MeV. (5) The anti νμand νe fluxes have different and well defined spectra. This allows us to separate oscillated signals from those due to μ- decay contamination. We propose to proceed with the oscillation search in steps since the region of Δm^2 to be searched can be anywhere between sub-eV^2 to several tens of eV^2. We start to examine the large Δm^2 region, which can be done with short baseline at first. At close distance to the MLF target gives a high neutrino flux, and allows us to use relatively small detector. If no definitive positive signal is found, a future option exists to cover small Δm^2 region. This needs a relatively long baseline and requires a large detector to compensate for the reduced neutrino flux.

physics.ins-det↗

arXiv2011

Measurement of the Double Beta Decay Half-life of 130Te with the NEMO-3 Detector

This Letter reports results from the NEMO-3 experiment based on an exposure of 1275 days with 661g of 130Te in the form of enriched and natural tellurium foils. The double beta decay rate of 130Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T1/2 = (7.0 +/- 0.9(stat) +/- 1.1(syst)) x 10^{20} yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.

nucl-ex↗

arXiv2010

Probing New Physics Models of Neutrinoless Double Beta Decay with SuperNEMO

The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double beta decay experiment SuperNEMO is discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double beta decay by measuring the decay half-life and the electron angular and energy distributions.

hep-ex↗

arXiv2010

Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors

We have constructed a GEANT4-based detailed software model of photon transport in plastic scintillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutrinoless double beta decay. We compare our simulations to measurements using conversion electrons from a calibration source of $\rm ^{207}Bi$ and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account. In this article, we briefly describe our modeling approach and results of our studies.

physics.ins-det↗

arXiv2010

Measurement of the two neutrino double beta decay half-life of Zr-96 with the NEMO-3 detector

Using 9.4 g of Zr-96 and 1221 days of data from the NEMO-3 detector corresponding to 0.031 kg yr, the obtained 2vbb decay half-life measurement is [2.35 +/- 0.14(stat) +/- 0.16(syst)] x 10^19 yr. Different characteristics of the final state electrons have been studied, such as the energy sum, individual electron energy, and angular distribution. The 2v nuclear matrix element is extracted using the measured 2vbb half-life and is 0.049 +/- 0.002. Constraints on 0vbb decay have also been set.

nucl-ex↗

arXiv2010

Results of the BiPo-1 prototype for radiopurity measurements for the SuperNEMO double beta decay source foils

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in $^{208}$Tl and $^{214}$Bi for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 $m^2$ of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in $^{208}$Tl. After more than one year of background measurement, a surface activity of the scintillators of $\mathcal{A}$($^{208}$Tl) $=$ 1.5 $μ$Bq/m$^2$ is reported here. Given this level of background, a larger BiPo detector having 12 m$^2$ of active surface area, is able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of $\mathcal{A}$($^{208}$Tl) $<$ 2 $μ$Bq/kg (90% C.L.) with a six month measurement.

physics.ins-det↗

arXiv2009

Measurement of the background in the NEMO 3 double beta decay experiment

In the double beta decay experiment NEMO~3 a precise knowledge of the background in the signal region is of outstanding importance. This article presents the methods used in NEMO~3 to evaluate the backgrounds resulting from most if not all possible origins. It also illustrates the power of the combined tracking-calorimetry technique used in the experiment.

nucl-ex↗