The Double Chooz Experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944 ± 0.016 (stat) ± 0.040 (syst) was obtained in 101 days of running at the Chooz Nuclear Power Plant in France, with two 4.25 GW th reactors. The results were obtained from a single 10 m 3 fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a non-zero value of the still unmeasured neutrino mixing parameter sin 2 2θ13. Analyzing both the rate of the prompt positrons and their energy spectrum we find sin 2 2θ13= 0.086 ± 0.041 (stat) ±0.030 (syst), or, at 90% CL, 0.017 < sin 2 2θ13 < 0.16. We report first results of a search for a non-zero neutrino oscillation [1] mixing angle, θ 13 , based on reactor antineutrino disappearance. This is the last of the three neutrino oscillation mixing angles [2,3] for which only upper limits [4,5] are available. The size of θ 13 sets the required sensitivity of long-baseline oscillation experiments attempting to measure CP violation in the neutrino sector or the mass hierarchy.In reactor experiments [6,7] addressing the disappearance ofν e , θ 13 determines the survival probability of electron antineutrinos at the "atmospheric" squaredmass difference, ∆m 2 atm . This probability is given by:where L is the distance from reactor to detector in meters and E the energy of the antineutrino in MeV. The full formula can be found in Ref.[1]. Eq. 1 provides a direct way to measure θ 13 since the only additional input is the well measured value of |∆m 2 atm | = (2.32Other running reactor experiments [9,10] are using the same technique.Electron antineutrinos of < 9 MeV are produced by reactors and detected through inverse beta decay (IBD): ν e + p → e + + n. Detectors based on hydrocarbon liquid scintillators provide the free proton targets. The IBD signature is a coincidence of a prompt positron signal followed by a delayed neutron capture. We present here our first results with a detector located ∼ 1050 m from the two 4.25 GW th thermal power reactors of the Chooz Nuclear Power Plant and under a 300 MWE rock overburden. The analysis is based on 101 days of data including 16 days with one reactor off and one day with both reactors off.The antineutrino flux of each reactor depends on its thermal power and, for the four main fissioning isotopes, 235 U, 239 Pu, 238 U, 241 Pu, their fraction of the total fuel content, their energy released per fission, and their fission and capture cross-sections. The fission rates and associated errors were evaluated using two predictive and complementary reactor simulation codes: MURE [17,18] and DRAGON [19]. This allowed a study of the sensitivity to the important reactor parameters (e.g.. thermal power, boron concentration, temperatures and densities). The quality of these simulations...

The Double Chooz experiment has observed 8,249 candidate electron antineutrino events in 227.93 live days with 33.71 GW-ton-years (reactor power × detector mass × livetime) exposure using a 10.3 m 3 fiducial volume detector located at 1050 m from the reactor cores of the Chooz nuclear power plant in France. The expectation in case of θ13= 0 is 8,937 events. The deficit is interpreted as evidence of electron antineutrino disappearance. From a rate plus spectral shape analysis we find sin 2 2θ13 = 0.109 ± 0.030(stat) ± 0.025(syst). The data exclude the no-oscillation hypothesis at 99.8% CL (2.9σ).

A number of anomalous results in short-baseline oscillation may hint at the existence of one or more light sterile neutrino states in the eV mass range and have triggered a wave of new experimental efforts to search for a definite signature of oscillations between active and sterile neutrino states. The present paper aims to provide a comprehensive review on the status of light sterile neutrino searches in mid-2019: we discuss not only the basic experimental approaches and sensitivities of reactor, source, atmospheric, and accelerator neutrino oscillation experiments but also the complementary bounds arising from direct neutrino mass experiments and cosmological observations. Moreover, we review current results from global oscillation analyses that include the constraints set by running reactor and atmospheric neutrino experiments. They permit to set tighter bounds on the active-sterile oscillation parameters but as yet are not able to provide a definite conclusion on the existence of eV-scale sterile neutrinos.

The STEREO experiment is a very short baseline reactor antineutrino experiment. It is designed to test the hypothesis of light sterile neutrinos being the cause of a deficit of the observed antineutrino interaction rate at short baselines with respect to the predicted rate, known as the reactor antineutrino anomaly. The STEREO experiment measures the antineutrino energy spectrum in six identical detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this article, results from 179 days of reactor turned on and 235 days of reactor turned off are reported at a high degree of detail. The current results include improvements in the modelling of detector optical properties and the γ-cascade after neutron captures by gadolinium, the treatment of backgrounds, and the statistical method of the oscillation analysis. Using a direct comparison between antineutrino spectra of all cells, largely independent of any flux prediction, we find the data compatible with the null oscillation hypothesis. The best-fit point of the reactor antineutrino anomaly is rejected at more than 99.9% C.L.

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Originally designed as a new nuclear reactor monitoring device, the Nucifer detector has successfully detected its first neutrinos. We provide the second shortest baseline measurement of the reactor neutrino flux. The detection of electron antineutrinos emitted in the decay chains of the fission products, combined with reactor core simulations, provides a new tool to assess both the thermal power and the fissile content of the whole nuclear core and could be used by the International Agency for Atomic Energy (IAEA) to enhance the Safeguards of civil nuclear reactors. Deployed at only 7.2 m away from the compact Osiris research reactor core (70 MW) operating at the Saclay research centre of the French Alternative Energies and Atomic Energy Commission (CEA), the experiment also exhibits a well-suited configuration to search for a new short baseline oscillation. We report the first results of the Nucifer experiment, describing the performances of the ∼ 0.85 m 3 detector remotely operating at a shallow depth equivalent to ∼ 12 m of water and under intense background radiation conditions. Based on 145 (106) days of data with reactor ON (OFF), leading to the detection of an estimated 40 760 νe, the mean number of detected antineutrinos is 281 ± 7(stat) ± 18(syst) νe/day, in agreement with the prediction 277 ± 23 νe/day. Due to the large background no conclusive results on the existence of light sterile neutrinos could be derived, however. As a first societal application we quantify how antineutrinos could be used for the Plutonium Management and Disposition Agreement. arXiv:1509.05610v4 [physics.ins-det]

CONUS is a novel experiment aiming at detecting elastic neutrino nucleus scattering in the almost fully coherent regime using high-purity germanium (Ge) detectors and a reactor as antineutrino source. The detector setup is installed at the commercial nuclear power plant in Brokdorf, Germany, at a close distance to the reactor core to guarantee a high antineutrino flux. A good understanding of neutron-induced backgrounds is required, as the neutron recoil signals can mimic the predicted neutrino interactions. Especially events correlated with the reactor thermal power are troublesome. On-site measurements revealed such a correlated, highly thermalized neutron field with a maximum fluence rate of (745±30) cm −2 d −1 . These neutrons, produced inside the reactor core, are reduced by a factor of ∼10 20 on their way to the CONUS shield. With a high-purity Ge detector without shield the γ-ray background was examined including thermal power correlated 16 N decay products and neutron capture γ-lines. Using the measured neutron spectrum as input, Monte Carlo simulations demonstrated that the thermal power correlated field is successfully mitigated by the CONUS shield. The reactor-induced background contribution in the region of interest is exceeded by the expected signal by at least one order of magnitude assuming a realistic ionization quenching factor.Keywords neutron spectrometry · Bonner sphere spectrometer · neutron attenuation · low background gamma-ray spectroscopy · low radioactive material selection · neutron capture · radiation shield · Monte Carlo simulation · coherent elastic neutrino nucleus scattering a

Over the course of several decades, organic liquid scintillators have formed the basis for successful neutrino detectors. Gadolinium-loaded liquid scintillators provide efficient background suppression for electron antineutrino detection at nuclear reactor plants. In the Double Chooz reactor antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded scintillator is utilized for the first time. Its large scale production and characterization are described. A new, light yield matched metal-free companion scintillator is presented. Both organic liquids comprise the target and "Gamma Catcher" of the Double Chooz detectors. In the Double Chooz (DC) experiment [3] two new types of Gd-LS have been studied and further tested. These are Gd-BDK TM (for Gd beta-diketonate) and Gd-CBX TM (for Gd carboxylate) [4,5]. These two systems meet the basic requirements for the DC scintillator: chemical stability of the Gd molecules and the other LS components, compatibility with detector materials, transparency, intrinsic light yield, radiopurity, Gd solubility and the stability of these properties over several years of data taking. Optimization of the optical properties includes the need to tune the light yield while maintaining a constant density and matching the light emission to the spectral response of the photomultiplier tubes (PMTs).The Gd-LS that is currently loaded in the DC Far Detector is based on beta-diketone chemistry, the first use in a large scale antineutrino detector. The chemistry of this new Gd-BDK scintillator [6] is based in part on knowledge obtained from studies of the similar Indium (In-BDK) system [7] developed at MPIK, Heidelberg and used in the LENS (Low Energy Neutrino Spectroscopy) Prototype at Gran Sasso [8]. The specific Gd organic scintillator candidate, that we initially considered, was based on the use of the simplest five carbon BDK anion -ACAC (acetylacetonate). We found this BDK compound difficult to sublime and thus it lacked a potential productive route to achieving the level of optical and radiochemical purity needed in the DC experiment. Consequently, in the final version, the BDK was selected to be THD (2,2,6,6-tetramethyl-heptane-3,5-dionate) based on extensive research experience in producing solid, liquid and gaseous Gd-THD for testing in the Ho-163 neutrino mass experiments [9]. The more effective shielding of the metal ions by the