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The detection and characterization of antineutrino emissions from nuclear reactors is a topic of great interest to the fundamental physics and nuclear nonproliferation communities. Reactor antineutrino spectra contain fuel-composition information, and can be used to infer fundamental physical parameters. The detection of reactor antineutrinos using the inverse beta decay (IBD) reaction has been proposed as a means of long-standoff reactor monitoring using kiloton-scale water-Cherenkov detectors. Detector fill materials capable of improved energy resolution and vertex reconstruction in comparison to water are an area of vigorous research, as they may lower detection thresholds and reduce backgrounds. One such candidate material is water-based liquid scintillator (WbLS), a hybrid detector medium which promises water-like attenuation and scattering behavior, while offering tuneable scintillation light yield. This dissertation focuses on the development of an optical property measurement device for IBD detector media including WbLS. The horizontal, adjustable path-length “long-arm” attenuation system developed for this application provides complete isolation from the atmosphere, a high degree of vibration insensitivity, and a simple and reliable method of calibration. Scattering measurements are available at multiple angles and with adjustable beam polarization, enabling both reliable quantitative scatter measurements and scattering phase-function reconstruction. The scattering and attenuation measurement performance of the device was benchmarked using deionized water. Subsequently, the system was used to quantify the attenuation, scattering and depolarization of diverse candidate fill materials throughout the visible spectrum. This work focused in large part on accurately characterizing WbLS produced by Brookhaven National Laboratory, which is a leading candidate fill material for nonproliferation-focused antineutrino detectors. This work represents the first high-sensitivity measurements of WbLS optical properties, and provides insight into the viability of Cherenkov-scintillation separation at scale. Additional work has been performed to characterize leaching of stainless steel components by Gd-loaded and non-Gd WbLS which may impact optical properties.

The DANSS detector, i.e., a scintillation detector with a sensitive volume of 1 m3, is installed at the Kalinin Nuclear Power Plant under the reactor on a moving stage. The distance from the detector center to the reactor core center can be varied from 10.9 to 12.9 m. The detector records about 5000 events of inverse beta decay per day with a background level from cosmic muons of the order of two percent. An analysis on the search for the sterile neutrino, based on only the ratio of spectra shapes at various distances is compared with an analysis which, along with the shape, accounts for changes in relative count rates. The effect of systematic errors contributing to the analysis using relative count rates is discussed. The analysis considering three detector positions is described.

DANSS is a highly segmented scintillator detector with a sensitive volume of 1 m3. The detector is located at the Kalinin Nuclear Power Plant under the reactor core on a moving platform. The distance from the detector center to the reactor center is varied from 10.7 to 12.7 m. The inverse beta decay reaction is used to detect antineutrino. DANSS detects about 5000 events per day with the background level of about two percent. Sterile neutrinos are searched for within the model of three active and one sterile neutrinos. The exclusion area in the space of parameters $$\Delta m_{{14}}^{2},{{\sin}^{2}}2{{\theta }_{{14}}}$$ is based only on the ratio of positron energy spectra recorded at different distances from the detector to the reactor core. Therefore, the results are independent of the absolute detector efficiency and predicted antineutrino fluxes. The experiment sensitivity is determined using the Gaussian CLs method taking into account the systematic errors. The experimentally obtained exclusion area covers a wide range of values and is in reasonable agreement with the sensitivity. The sensitivity for the upgraded detector is estimated.

This paper describes in detail the uncertainties due to several factors that may affect the direction vector of a reactor neutrino in a liquid scintillation detector. The reactor neutrino direction vector was reconstructed through a charge weighting method. The paper simulates the response of gadolinium-loaded, liquid scintillator detector to reactor electron anti-neutrinos. The reaction is based on neutrino capture on hydro-genic protons of inverse beta decay process in the scintillator. A Cherenkov radiation detector can reconstruct the directional information of incident neutrinos relatively well, compared to the liquid scintillation detector. Statistics, spatial resolution, neutrino energy, and multi-reactor and multi-detectors are examined by using Monte Carlo simulation based on the cylindrical liquid scintillating detector model. Furthermore, this simulated model is detailed down to the optical processes, and the source of reactor fuel composition. Finally, one of the main goals is to provide the potential of the detector to measure the origin direction of the incident neutrino. Furthermore, our intention is to help understanding of various uncertainties of the neutrino directionality study for the future massive liquid scintillating neutrino detectors.

There are several experimental indications of sterile neutrinos with a mass in the 1 eV ballpark and many experiments are trying to clarify the situation. During 6 years the DANSS experiment collected more than 6 million Inverse Beta Decay (IBD) events and measured the background level during 4 reactor-off periods. Data were collected at 3 distances (10.9 m, 11.9 m, and 12.9 m) from the center of the core of a 3.1 GW$_{th}$ reactor with event rate up to 5 thousand per day. The detector position was changed frequently usually 2-3 times a week. Therefore many systematic uncertainties were canceled out in the analysis. After collection of additional 0.7 million IBD events the significance of the best-fit point in the 4$\nu$ case increased from 1.3$\sigma$ to 2.35$\sigma$. This is still not statistically significant and we present the exclusion area that covers a very interesting range of the sterile neutrino parameters up to $\sin^22\theta_{ee} < 0.004$ in the most sensitive point. In particular DANSS excludes a large fraction of sterile neutrino parameters preferred by the recent BEST results including the BEST best-fit point. The IBD rate dependence on the fuel composition was measured. It agrees with predictions of the Huber-Mueller model. During almost 6 years the reactor power was measured with $\approx1.8\%$ accuracy in 2 days using the anti-neutrino event rate normalized to the reactor power at the initial period.

The JSNS^2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for oscillations involving a sterile neutrino in the eV^2 mass-splitting range. The experiment will search for the appearance of electron antineutrinos oscillated from muon antineutrinos. The electron antineutrinos are detected via the inverse beta decay process using a liquid scintillator detector. A 1MW beam of 3 GeV protons incident on a spallation neutron target produces an intense and pulsed neutrino source from pion, muon, and kaon decay at rest. The JSNS^2 detector is located 24 m away from the neutrino source and began operation from June 2020. The detector contains 17 tonnes of gadolinium (Gd) loaded liquid scintillator (LS) in an acrylic vessel, as a neutrino target. It is surrounded by 31 tonnes of unloaded LS in a stainless steel tank. Optical photons produced in LS are viewed by 120 R7081 Hamamatsu 10-inch Photomultiplier Tubes (PMTs). In this paper, we describe the JSNS^2 detector design, construction, and operation., 41 pages, 29 figures

We discuss a possibility that the so-called reactor antineutrino anomaly (RAA), which is a deficit of the ν¯e rates in the reactor experiments in comparison to the theoretical expectations, can at least in part be explained by applying a quantum field-theoretical approach to neutrino oscillations, which in particular predicts a small deviation from the classical inverse-square law at short (but still macroscopic) distances between the neutrino source and detector. An extensive statistical analysis of the current reactor data on the integrated ν¯e event rates vs. baseline is performed to examine this speculation. The obtained results are applied to study another long-standing puzzle—gallium neutrino anomaly (GNA), which is a missing νe flux from 37Ar and 51Cr electron-capture decays as measured by the gallium–germanium solar neutrino detectors GALLEX and SAGE.

The Jiangmen Underground Neutrino Observatory (JUNO) is designed to primarily measure the neutrino Mass Ordering(MO) by detecting reactor anti-neutrinos via inverse beta decay. JUNO also has other rich physical potentials.Its Central Detector (CD) ,which is an acrylic sphere with a diameter of 35.4 m, about 20 kton liquid scintillator (LS)，equipped with ~ 43 k photomultipliers (PMTs) in total to measure the energy of neutrinos with an unprecedented energy resolution of 3% /sqrt(E) and an energy nonlinearity better than 1%. Accordingly, a calibration complex, including ACU, CLS, GTCS and ROV, is designed to deliver multiple sources for the energy coverage of reactor neutrinos to the positions covering the full CD volume. In this proceeding, the new design details and up-to-date progress about JUNO calibration system are presented.

The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era. The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment, in combination with the fission rates of fissile isotopes in the reactor, is used to extract the positron energy spectra resulting from the fission of specific isotopes. This information can be used to produce a precise, data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay. The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method. Consistent results are obtained with other unfolding methods. A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated. Given the reactor fission fractions, the technique can predict the energy spectrum to a 2% precision. In addition, we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method., 22 pages, 10 figures, 6 supplemental materials

We report a novel correlated background in the antineutrino detection using the inverse beta decay reaction. Spontaneous fissions and $(\alpha,n)$ reactions in peripheral materials of the antineutrino detector, such as borosilicate glass of photomultipliers, produce fast neutrons and prompt gamma rays. If the shielding from the material to the detector target were not thick enough, neutrons and gammas could enter the target volume and mimic antineutrino signals. This paper revisits the yields and energy spectra of neutrons produced in B$(\alpha,n)$N and F$(\alpha,n)$Na reactions. A Geant4 based simulation has been carried out using a simplified detector geometry for the present generation reactor neutrino experiments. The background rates in these experiments are estimated. If this background was not taken into account, the value of the neutrino mixing angle $\sin^22\theta_{13}$ would be underestimated. We recommend that Daya Bay, RENO, Double Chooz, and JUNO, carefully examine the masses and radiopurity levels of detector materials that are close to the target and rich in boron and fluorine., Comment: 11 pages, 9 figures, 5 tables

The DANSS experiment collected 5.5 million Inverse Beta Decay (IBD) events during 5 years of operation. Data were collected at 3 distances (10.9~m, 11.9~m, and 12.9~m) from the center of the core of the industrial $3.1~GW$ reactor. The IBD event rate exceeds 5000/day at the smallest distance. The detector position was changed usually 3 times a week. Therefore in the analysis that uses information only about relative IBD counting rates and changes in positron energy spectra shapes many systematic uncertainties were canceled out. No statistically significant evidence for sterile neutrinos is found. The significance of the best-fit point in the 4$\nu$ case is only 1.3$\sigma$. The excluded area covers a very interesting range of the sterile neutrino parameters up to $sin^22\theta_{ee} < 0.008$ in the most sensitive region. The IBD rate dependence on the fission fraction of $^{239}$Pu was measured. It agrees with the predictions of the Huber-Mueller model. The reactor power was measured during more than 4 years with $\approx2\%$ accuracy in 2 days using the rate of neutrino events normalized to the thermal power at the initial period., Comment: The European Physical Society Conference on High Energy Physics (EPS-HEP2021)

Potential applications of neutrino detection to nuclear security have been discussed since the 1970s. Recent years have seen great progress in detector technologies based on inverse beta decay, with the demonstration of ton-scale surface-level detectors capable of high quality neutrino spectrum measurements. At the same time coherent elastic neutrino nucleus scattering has been experimentally confirmed in 2017 with neutrinos from stopped pion decay and there is a number of experiments aimed at seeing this reaction with reactor neutrinos. The large cross section and threshold-less nature of this reaction make it plausible to consider it for applications to nuclear security and here, we present a first direct comparison of the two reaction modes., 5 pages, 3 figures

We present a new method by which to retrieve energy spectrum for all flavor of neutrinos from core-collapse supernova (CCSN). In the retrieval process, we do not assume any analytic formulae to express the energy spectrum of neutrinos but rather take a direct way of spectrum reconstruction from the observed data; the Singular Value Decomposition algorithm with a newly developed adaptive energy-gridding technique is adopted. We employ three independent reaction channels having different flavor sensitivity to neutrinos. Two reaction channels, inverse beta decay on proton and elastic scattering on electrons, from a water Cherenkov detector such as Super-Kamiokande (SK) and Hyper-Kamiokande (HK), and a charged current reaction channel with Argon from the Deep Underground Neutrino Experiment (DUNE) are adopted. Given neutrino oscillation models, we iteratively search the neutrino energy spectra at the CCSN source until they provide the consistent event counts in the three reaction channels. We test the capability of our method by demonstrating the spectrum retrieval to a theoretical neutrino data computed by our recent three-dimensional CCSN simulation. Although the energy spectrum with either electron-type or electron-type anti-neutrinos at the CCSN source has relatively large error compared to that of other species, the joint analysis with HK + DUNE or SK + DUNE will provide precise energy spectrum of all flavors of neutrinos at the source. Finally, we discuss perspectives for improvements of our method by using neutrino data of other detectors., Accepted to MNRAS

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ν ¯ e is important when making theoretical predictions. One source of ν ¯ e that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ν ¯ e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ν ¯ e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ν ¯ e source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ν ¯ e contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8-2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ν ¯ e contribution.

We deployed a small, 80kg, antineutrino detector based on solid plastic scintillator, called MiniCHANDLER for nearly three months at a distance of 25m from a 2.9GW thermal power reactor core at the North Anna Nuclear Generating Station. We report the detection of an antineutrino signal resulting from inverse beta decay at 5.5 sigma significance with no overburden and minimal shielding. This result also demonstrates that 3D segmentation can be used to significantly improve the signal to noise ratio, in this case by a factor of 4. In addition, this measurement represents an observation of the positron spectrum in a small, surface-deployed detector; this observation of reactor antineutrinos was achieved with a mobile neutrino detector mounted in an ordinary, small trailer., Comment: 12 pages, 7 figures, version accepted for publication in Phys. Rev. Appl

Liquid scintillator(LS) calorimeter is a classical technology in the particle physics, especially for the reactor neutrino experiments, which is widely used for detecting electron anti-neutrinos though the inverse beta decay interaction channel. Because of the quenching effect, the scintillator detector has nonlinear energy response. It is critical to accurately measure the scintillator energy response for both the precision measurement of reactor antineutrino energy spectrum in Daya Bay Experiment and the neutrino mass hierarchy measurement determination in JUNO experiments. There are several bench measurements of the liquid scintillator energy nonlinearity response through the gamma-ray and the electron Compton scattering process. However, it is difficult to estimate the systematic uncertainties of those measurements are difficult to assess. In this paper, we used the Geant4 simulation package to study several systematic uncertainties, including the gamma-ray multiple scattering in the detector, the physical size of the detector and the edging effect. Our simulations shows that all these effects have marginal impact (

The compact material irradiation facility (CMIF) is a current project in China that will provide a compact deuteron-beryllium neutron source. The target of this facility will be an intense and compact Isotope Decay-At-Rest (IsoDAR) neutrino source. In this paper, we propose to test the sterile neutrino hypothesis using CMIF as the neutrino source. At CMIF platform, the electron antineutrino production rate can be up to $2.0\times 10^{19}$ per day. When paired with an 80 t liquid scintillator detector to study short baseline electron antineutrino disappearance, the inverse beta decay (IBD) event rate is large enough to investigate the parameter ranges of interest for neutrino anomalies. Our sensitivity analysis shows that a short baseline experiment at this platform will provide a very competitive sterile neutrino search, especially in the high-$\Delta m^2$ region ($\Delta m^2 >10\,\text{eV}^2$)., Comment: 9 pages, 9 figures

The Indian Scintillator Matrix for Reactor Anti-Neutrino detection - ISMRAN experiment aims to detect electron anti-neutrinos ($\bar\nu_e$) emitted from a reactor via inverse beta decay reaction (IBD). The setup, consisting of 1 ton segmented Gadolinium foil wrapped plastic scintillator array, is planned for remote reactor monitoring and sterile neutrino search. The detection of prompt positron and delayed neutron from IBD will provide the signature of $\bar\nu_e$ event in ISMRAN. The number of segments with energy deposit ($\mathrm{N_{bars}}$) and sum total of these deposited energies are used as discriminants for identifying prompt positron event and delayed neutron capture event. However, a simple cut based selection of above variables leads to a low $\bar\nu_e$ signal detection efficiency due to overlapping region of $\mathrm{N_{bars}}$ and sum energy for the prompt and delayed events. Multivariate analysis (MVA) tools, employing variables suitably tuned for discrimination, can be useful in such scenarios. In this work we report the results from an application of artificial neural network -- the multilayer perceptron (MLP), particularly the Bayesian extension -- MLPBNN, to the simulated signal and background events in ISMRAN. The results from application of MLP to classify prompt positron events from delayed neutron capture events on Hydrogen, Gadolinium nuclei and also from the typical reactor $\gamma$-ray and fast neutron backgrounds is reported. An enhanced efficiency of $\sim$91$\%$ with a background rejection of $\sim$73$\%$ for prompt selection and an efficiency of $\sim$89$\%$ with a background rejection of $\sim$71$\%$ for the delayed capture event, is achieved using the MLPBNN classifier for the ISMRAN experiment., Comment: 17 pages, 10 figures

Short distance reactor antineutrino experiments measure an antineutrino spectrum a few percent lower than expected from theoretical predictions. In this work we study the potential of low energy threshold reactor experiments in the context of a light sterile neutrino signal. We discuss the perspectives of the recently detected coherent elastic neutrino-nucleus scattering in future reactor antineutrino experiments. We find that the expectations to improve the current constraints on the mixing with sterile neutrinos are promising. We also analyse the measurements of antineutrino scattering off electrons from short distance reactor experiments. In this case, the statistics is not competitive with inverse beta decay experiments, although future experiments might play a role when compare it with the Gallium anomaly., 9 pages, 6 figures, 1 table, matches published version

Determination of the direction to a source of (anti)neutrinos is important for the physics of supernovae and of the Earth. Inverse beta decay reaction allows to reconstruct the direction to a source of antineutrinos. We present modern mathematical formalism and recent experimental data on antineutrino directionality.

We present a characterization of a small (9-liter) and mobile 0.1% 6 Li-doped pulse-shape-sensitive plastic scintillator antineutrino detector called SANDD (Segmented AntiNeutrino Directional Detector), constructed for the purpose of near-field reactor monitoring with sensitivity to antineutrino direction. SANDD comprises three different types of module. A detailed Monte Carlo simulation code was developed to match and validate the performance of each of the three modules. The combined model was then used to produce a prediction of the performance of the entire detector. Analysis cuts were established to isolate antineutrino inverse beta decay events while rejecting large fraction of backgrounds. The neutron and positron detection efficiencies are estimated to be 34.8% and 80.2%, respectively, while the coincidence detection efficiency is estimated to be 71.7%, resulting in inverse beta decay detection efficiency of 20.0% ± 0.2%(stat.) ± 2.1%(syst.). The predicted directional sensitivity of SANDD produces an uncertainty of 20 ∘ in the azimuthal direction per 100 detected antineutrino events.

Detection of low-energy electron antineutrinos is of importance for several purposes, such as ex-vessel reactor monitoring, neutrino oscillation studies, etc. The inverse beta decay (IBD) is the interaction that is responsible for detection mechanism in (organic) plastic scintillation detectors. Here, a detailed study will be presented dealing with the radiation and optical transport simulation of a typical segmented antineutrino detector withMonte Carlo method using MCNPX and FLUKA codes. This study shows different aspects of the detector, benefiting from inherent capabilities of the Monte Carlo simulation codes.

The evolution of the reactor-antineutrino spectrum and the evolution of the spectrum of positrons from the inverse-beta-decay reaction in the course of reactor operation and after reactor shutdown are considered. The present-day status in determining the initial reactor-antineutrino spectrum on the basis of spectra of beta particles from mixtures of products originating from uranium and plutonium fission is described. A local rise of the experimental spectrum of reactor antineutrinos with respect to the expected spectrum is studied.

The SoLid experiment intends to search for active-to-sterile anti-neutrino oscillations at a very short baseline from the SCK center dot CEN BR2 research reactor (Mol, Belgium). A novel detector approach to measure reactor anti-neutrinos was developed based on an innovative sandwich of composite polyvinyl-toluene and (LiF)-Li-6:ZnS(Ag) scintillators. The system is highly segmented and read out by a network of wavelength shifting fibers and SiPM. High experimental sensitivity can be achieved compared to other standard technologies thanks to the combination of high granularity, good neutron gamma discrimination using (LiF)-Li-6:ZnS(Ag) scintillator and precise localisation of the Inverse Beta Decay products. This technology can be considered as a new generation of an anti-neutrino detector. This compact system regbires limited passive shielding and relies on spatial topology to determine the different classes of backgrounds. We will describe the principle of detection and the detector design. Particular focus on the neutron discrimination will be made, as well as on the capability to use cosmic moons for channel equalisation and energy calibration. The performance of the first 288 kg SoLid module (SM1), based on the data taken at BR2 from February to September 2015, will be presented. We will conclude with the next phase, which will start in 2016, and the future plans of the experiment. (C) 2016 Elsevier B.V. All rights reserved.

The potential of elastic antineutrino-electron scattering in a Gd-doped water Cherenkov detector to determine the direction of a nuclear reactor antineutrino flux was investigated using the recently proposed WATCHMAN antineutrino experiment as a baseline model. The expected scattering rate was determined assuming a 13-km standoff from a 3.758-GWt light water nuclear reactor and the detector response was modeled using a Geant4-based simulation package. Background was estimated via independent simulations and by scaling published measurements from similar detectors. Background contributions were estimated for solar neutrinos, misidentified reactor-based inverse beta decay interactions, cosmogenic radionuclides, water-borne radon, and gamma rays from the photomultiplier tubes (PMTs), detector walls, and surrounding rock. We show that with the use of low background PMTs and sufficient fiducialization, water-borne radon and cosmogenic radionuclides pose the largest threats to sensitivity. Directional sensitivity was then analyzed as a function of radon contamination, detector depth, and detector size. The results provide a list of experimental conditions that, if satisfied in practice, would enable antineutrino directional reconstruction at 3$\sigma$ significance in large Gd-doped water Cherenkov detectors with greater than 10-km standoff from a nuclear reactor., Comment: 11 pages, 9 figures

We consider two possible schemes for generation and detection of a monoenergetic directed beam of neutrinos which may have application to neutrino communication. First, we consider generation of a directed neutrino beam using electron capture beta decay in hydrogen-like ions. Next, we suggest detection of a directed neutrino beam using resonant absorption of a neutrino by a bare nucleus with the generation of a bound electron. This reaction is inverse to electron capture beta decay, and we call it “Bound State Inverse Beta Decay (BSIBD)”. We show that the recoil effect can be eliminated by an appropriate choice of velocities for the ions and bare nuclei. Finally, we consider a combination of a solid state source of a directed mono-energetic neutrino beam and its detection using BSIBD.

The SoLid experiment aims to measure neutrino oscillation at a baseline of 6.4 m from the BR2 nuclear reactor in Belgium. Anti-neutrinos interact via inverse beta decay (IBD), resulting in a positron and neutron signal that are correlated in time and space. The detector operates in a surface building, with modest shielding, and relies on extremely efficient online rejection of backgrounds in order to identify these interactions. A novel detector design has been developed using 12800 5 cm cubes for high segmentation. Each cube is formed of a sandwich of two scintillators, PVT and 6LiF:ZnS(Ag), allowing the detection and identification of positrons and neutrons respectively. The active volume of the detector is an array of cubes measuring 80× 80× 250 cm (corresponding to a fiducial mass of 1.6 T), which is read out in layers using two dimensional arrays of wavelength shifting fibres and silicon photomultipliers, for a total of 3200 readout channels. Signals are recorded with 14 bit resolution, and at 40 MHz sampling frequency, for a total raw data rate of over 2 Tbit/s. In this paper, we describe a novel readout and trigger system built for the experiment, that satisfies requirements on: compactness, low power, high performance, and very low cost per channel. The system uses a combination of high price-performance FPGAs with a gigabit Ethernet based readout system, and its total power consumption is under 1 kW. The use of zero suppression techniques, combined with pulse shape discrimination trigger algorithms to detect neutrons, results in an online data reduction factor of around 10000. The neutron trigger is combined with a large per-channel history time buffer, allowing for unbiased positron detection. The system was commissioned in late 2017, with successful physics data taking established in early 2018. The SoLid experiment aims to measure neutrino oscillation at a baseline of 6.4 m from the BR2 nuclear reactor in Belgium. Anti-neutrinos interact via inverse beta decay (IBD), resulting in a positron and neutron signal that are correlated in time and space. The detector operates in a surface building, with modest shielding, and relies on extremely efficient online rejection of backgrounds in order to identify these interactions. A novel detector design has been developed using 12800 5 cm cubes for high segmentation. Each cube is formed of a sandwich of two scintillators, PVT and 6LiF:ZnS(Ag), allowing the detection and identification of positrons and neutrons respectively. The active volume of the detector is an array of cubes measuring 80x80x250 cm (corresponding to a fiducial mass of 1.6 T), which is read out in layers using two dimensional arrays of wavelength shifting fibres and silicon photomultipliers, for a total of 3200 readout channels. Signals are recorded with 14 bit resolution, and at 40 MHz sampling frequency, for a total raw data rate of over 2 Tbit/s. In this paper, we describe a novel readout and trigger system built for the experiment, that satisfies requirements on: compactness, low power, high performance, and very low cost per channel. The system uses a combination of high price-performance FPGAs with a gigabit Ethernet based readout system, and its total power consumption is under 1 kW. The use of zero suppression techniques, combined with pulse shape discrimination trigger algorithms to detect neutrons, results in an online data reduction factor of around 10000. The neutron trigger is combined with a large per-channel history time buffer, allowing for unbiased positron detection. The system was commissioned in late 2017, with successful physics data taking established in early 2018.

This Letter reports the first extraction of individual antineutrino spectra from ^{235}U and ^{239}Pu fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses 3.5×10^{6} inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, ^{235}U and ^{239}Pu, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4-6 MeV, a 7% (9%) excess of events is observed for the ^{235}U (^{239}Pu) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is 4.0σ for ^{235}U spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at 5.3σ. In the energy range of 4-6 MeV, a maximal local discrepancy of 6.3σ is observed.

Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ability of the detector to identify neutrons. A core-collapse supernova will be preceded by an increasing flux of neutrinos and anti-neutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent core-collapse supernova, hours earlier than the detection of the neutrinos from core collapse. Electron anti-neutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximising detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hours before core collapse for a 15-25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, $\mathrm{\alpha}$Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hours before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading., Comment: 20 pages, 12 figures. Accepted by The Astrophysical Journal

Several anomalies in the neutrino sector are pointing towards the existence of a new (sterile) neutrino state with a mass around 1 eV. The SoLid experiment is located at the SCK$\bullet$CEN BR2 research reactor in Belgium and will investigate this possibility. Using the large flux of anti-neutrinos generated in the reactor, it will collect a high statistics sample of Inverse Beta Decay (IBD) events. These will be used to study the energy and distance dependence of the neutrino flux, which in turn will be used to unambiguously support or reject the evidence of sterile neutrinos being the cause of these anomalies. The measurement is challenging as one has to operate a detector very close to the high radiation environment of a nuclear reactor and on the surface with little overburden to shield against cosmic rays. SoLid is employing a new technology using highly segmented scintillators with excellent particle ID to face these challenges. The 1.6-tons detector was installed towards the end of 2017 and is taking data since early 2018. We will describe the detector design, the experimental setup at BR2 and the detection principle. This will be followed by a first look at the data.

The Daya Bay Reactor Neutrino Experiment consists of eight functionally identical detectors placed underground at different baselines from six 2.9 $\mathrm{GW}_{th}$ reactor cores. Since Dec. 2011, the experiment has collected more than 2.2 million inverse beta decay (IBD) candidates, enabling a precision measurement of the absolute reactor antineutrino flux and spectrum, and their fuel-dependent evolution. The comparison between measured spectrum and predictions from Huber-Mueller model revealed a 2.9 $\sigma$ deviation for the whole energy region and mostly pronounced in the region around 4-6 MeV. The measurement of the evolution of the reactor antineutrino flux and spectrum showed a 2.8 $\sigma$ discrepancy in the antineutrino flux variation with respect to the reactor fuel composition. The discrepancy suggests an overestimation of the predicted contribution from the $\mathrm{^{235}U}$ fission isotope and indicates that this isotope could be primary contributor to the reactor antineutrino anomaly.

The isotopes of $^{9}$Li and $^{8}$He produced by cosmic-rays are one of main source for backgrounds in reactor neutrino experiments. The isotope decays to a neutron and an electron and mimics an inverse beta decay of an electron antineutrino from reactors. The $^{9}$Li/$^{8}$He background spectrum and rate are measured using the data taken by the RENO, and compared with Monte-Carlo prediction. In this presentation, we report the measured cosmogenic background spectrum and rate at RENO.

The RENO experiment has been taking electron antineutrino data from the reactors at Hanbit nuclear power plant(Younggwang, Korea), using two identical detectors since 2011. The RENO experiment has measured using inverse beta decay events where neutrons are captured on Gadolinium(Gd). The result of RENO experimenth as published the results only the Gd-captured analysis 2012 and 2016. However, the neutrons also can be captured by hydrogen. Neutron captured on hydrogen analysis can give independent result from neutron capture on Gd analysis. Hydrogen analysis(nH) has longer time interval of delayed signal than Gd-captured and it contains more accidental background. We have measured number of the inverse beta decay events and the backgrounds even accidental and fast neutrons, Li/He. In RENO experiment, Hydrogen analysis can use the about 2000 days data and we have been preparing the result using 1500 days data.

The Precision Reactor Oscillation and Spectrum (PROSPECT) Experiment is a reactor neutrino experiment designed to search for sterile neutrinos with a mass on the order of 1 eV/c$^2$ and to measure the spectrum of electron antineutrinos from a highly-enriched $^{235}$U nuclear reactor. The PROSPECT detector consists of an 11 by 14 array of optical segments in $^{6}$Li-loaded liquid scintillator at the High Flux Isotope Reactor in Oak Ridge National Laboratory. Antineutrino events are identified via inverse beta decay and read out by photomultiplier tubes located at the ends of each segment. The detector response is characterized using a radioactive source calibration system. This paper describes the design, operation, and performance of the PROSPECT source calibration system.

We report a fuel-dependent reactor electron antineutrino ($\overline{\nu}_e$) yield using six 2.8 GW$_{\text{th}}$ reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses $850\,666$ $\overline{\nu}_e$ candidate events with a background fraction of 2.0 % acquired through inverse beta decay (IBD) interactions in the near detector for 1807.9 live days from August 2011 to February 2018. Based on multiple fuel cycles, we observe a fuel $^{235}$U dependent variation of measured IBD yields with a slope of $(1.51 \pm 0.23) \times 10^{-43} $cm$^2$/fission and measure a total average IBD yield of $(5.84 \pm 0.13) \times 10^{-43} $cm$^2$/fission. The hypothesis of no fuel-dependent IBD yield is ruled out at 6.6 $\sigma$. The observed IBD yield variation over $^{235}$U isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at 1.3 $\sigma$. The measured fuel-dependent variation determines IBD yields of $(6.15 \pm 0.19) \times 10^{-43} $cm$^2$/fission and $(4.18\pm 0.26) \times 10^{-43} $cm$^2$/fission for two dominant fuel isotopes $^{235}$U and $^{239}$Pu, respectively. The measured IBD yield per $^{235}$U fission shows the largest deficit relative to the HM prediction. Reevaluation of the $^{235}$U IBD yield per fission may mostly solve the Reactor Antineutrino Anomaly (RAA) while $^{239}$Pu is not completely ruled out as a possible contributor of the anomaly. We also report a 2.9 $\sigma$ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of $^{235}$U., Comment: 6 pages and 5 figures, v4 note: (1) data files for figure 1, figure 2, figure 5 are included for arXiv users (2) minor modifications in abstract and main text for clarification

We have examined the impact of new Daya Bay, Double Chooz, and RENO measurements on global fits of reactor antineutrino flux data to a variety of hypotheses regarding the origin of the reactor antineutrino anomaly. In comparing RENO and Daya Bay measurements of inverse beta decay (IBD) yield versus $^{239}$Pu fission fraction, we find differing levels of precision in measurements of time-integrated yield and yield slope, but similar central values, leading to modestly enhanced isotopic IBD yield measurements in a joint fit of the two datasets. In the absence of sterile neutrino oscillations, global fits to all measurements now provide 3{\sigma} preference for incorrect modeling of specific fission isotopes over common mis-modeling of all beta-converted isotopes. If sterile neutrino oscillations are considered, global IBD yield fits provide no substantial preference between oscillation-including and oscillation-excluding hypotheses: hybrid models containing both sterile neutrino oscillations and incorrect $^{235}$U or $^{239}$Pu flux predictions are favored at only 1-2{\sigma} with respect to models where $^{235}$U, $^{238}$U, and $^{239}$Pu are assumed to be incorrectly predicted., Comment: 7 pages, 4 figures, 3 tables

International audience; The detection of a neutrino burst from the next Galactic Core-Collapse SuperNova (CCSN) will yield major breakthroughs in different fields of fundamental physics. The KM3NeT ORCA and ARCA neutrino telescopes in the Mediterranean Sea are expected to observe a significant number of neutrino interactions through the detection of Cherenkov light mostly induced by inverse beta decay processes in sea water. The detection of photons in coincidence between the 31 photomultipliers of KM3NeT digital optical modules (DOMs) allows to discriminate the CCSN signal against radioactive decays, bioluminescence and atmospheric muon backgrounds.The detection sensitivity and the potential to resolve the time profile of the neutrinos have been studied by means of accurate Monte Carlo simulations coupled to in-depth studies of the KM3NeT background features. Online triggering criteria have been determined to send real-time alerts for low-energy CCSN neutrino bursts, and also to meet the requirements for the integration in the SNEWS global alert network. In view of future developments, a preliminary study has been conducted on the determination of the neutrino arrival time and the fast triangulation of the source by different detectors to constrain the CCSN localisation in the sky.

The STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes, $^{155}$Gd and $^{157}$Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8 MeV. The complex level schemes of $^{156}$Gd and $^{158}$Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd(n,${\gamma}$) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user., Comment: 5 pages, 3 figures