Reactor Neutrino Experiments Research Articles

Study of a prototype detector for the Daya Bay neutrino experiment

The Daya Bay reactor neutrino experiment is designed to precisely measure the neutrino mixing angle θ 13. In order to study the details of the detector response and finalize the detector design, a prototype neutrino detector with a scale of 1/3 in diameter is constructed at the Institute of High Energy Physics (IHEP), Beijing. The detector is viewed by 45 8″ photomultipliers, which are calibrated by LED light pulse. The energy response of the detector, including the resolution, linearity, spatial uniformity, etc., is studied by radioactive sources 133Ba, 137Cs, 60Co, and 22Na at various locations of the detector. The measurement shows that the detector, particularly the specially designed optical reflectors, works as expected. A Monte Carlo simulation based on the Geant4 package shows a good agreement with the experimental data.

Improving application of Bayesian Neural Networks to discriminate neutrino events from backgrounds in reactor neutrino experiments

The application of Bayesian Neural Networks (BNN) to discriminateneutrino events from backgrounds in reactor neutrino experiments hasbeen described in ref. [1]. In the paper, BNN are also usedto identify neutrino events in reactor neutrino experiments, but thenumbers of photoelectrons received by PMTs are used as inputs to BNNin the paper, not the reconstructed energy and position of events.The samples of neutrino events and three major backgrounds from theMonte-Carlo simulation of a toy detector are generated in the signalregion. Compared to the BNN method in [1], more8He/9Li background and uncorrelated background in thesignal region can be rejected by the BNN method in the paper, butmore fast neutron background events in the signal region areunidentified using the BNN method in the paper. The uncorrelatedbackground to signal ratio and the 8He/9Li background tosignal ratio are significantly improved using the BNN method in thepaper in comparison with the BNN method in ref. [1]. But thefast neutron background to signal ratio in the signal region is abit larger than the one in ref. [1].

Applying Bayesian Neural Network to determine neutrino incoming directionin reactor neutrino experiments and supernova explosion location byscintillator detectors

In the paper, it is discussed by using Monte-Carlo simulation thatthe Bayesian Neural Network (BNN) is applied to determine neutrinoincoming direction in reactor neutrino experiments and supernovaexplosion location by scintillator detectors. As a result, comparedto the method in ref. [1], the uncertainty on themeasurement of the neutrino direction using BNN is significantlyimproved. The uncertainty on the measurement of the reactor neutrinodirection is about 1.0° at the 68.3% C.L., and the one inthe case of supernova neutrino is about 0.6° at the 68.3%C.L. . Compared to the method in ref. [1], the uncertaintyattainable by using BNN reduces by a factor of about 20. Andcompared to the Super-Kamiokande experiment (SK), it reduces by afactor of about 8.

Determination of the neutrino mass hierarchy at an intermediate baseline

It is generally believed that neutrino mass hierarchy can be determined at a long baseline experiment, often using accelerator neutrino beams. Reactor neutrino experiments at an intermediate baseline have the capability to distinguish normal or inverted hierarchy. Recently, it has been demonstrated that the mass hierarchy could possibly be identified using Fourier transform to the $L/E$ spectrum if the mixing angle ${sin}^{2}(2{\ensuremath{\theta}}_{13})>0.02$. In this study, a more sensitive Fourier analysis is introduced. We found that an ideal detector at an intermediate baseline ($\ensuremath{\sim}60\text{ }\text{ }\mathrm{km}$) could identify the mass hierarchy for a mixing angle ${sin}^{2}(2{\ensuremath{\theta}}_{13})>0.005$, without requirements on accurate information of reactor neutrino spectra and the value of $\ensuremath{\Delta}{m}_{32}^{2}$.

Non-standard interaction effects at reactor neutrino experiments

We study non-standard interactions (NSIs) at reactor neutrino experiments, and in particular, the mimicking effects on θ13. We present generic formulas for oscillation probabilities including NSIs from sources and detectors. Instructive mappings between the fundamental leptonic mixing parameters and the effective leptonic mixing parameters are established. In addition, NSI corrections to the mixing angles θ13 and θ12 are discussed in detailed. Finally, we show that, even for a vanishing θ13, an oscillation phenomenon may still be observed in future short baseline reactor neutrino experiments, such as Double Chooz and Daya Bay, due to the existences of NSIs.

Applying Bayesian neural networks to separate neutrino events from backgrounds in reactor neutrino experiments

A toy detector has been designed to simulate central detectors inreactor neutrino experiments in the paper. The samples of neutrinoevents and three major backgrounds from the Monte-Carlo simulationof the toy detector are generated in the signal region. The BayesianNeural Networks (BNN) are applied to separate neutrino events frombackgrounds in reactor neutrino experiments. As a result, the mostneutrino events and uncorrelated background events in the signalregion can be identified with BNN, and the part events each of thefast neutron and 8He/9Li backgrounds in the signal regioncan be identified with BNN. Then, the signal to noise ratio in thesignal region is enhanced with BNN. The neutrino discriminationincreases with the increase of the neutrino rate in the trainingsample. However, the background discriminations decrease with thedecrease of the background rate in the training sample.

Reactor neutrino oscillation experiments: recent results and future prospects

Reactor neutrino experiments have played a key role in the history of neutrino physics. From the first observation of the free antineutrino by Reines and Cowan to the observation of ν̄e disappearance at KamLAND, reactors have been an invaluable tool in the study of neutrinos and helped shape our understanding of neutrinos and neutrino oscillation. Recent data from KamLAND unambiguously reveal the signature of neutrino oscillation in the observed ν̄e spectrum and determine the ν̄e oscillation parameter Δm212 to 2.8%. A suite of next-generation reactor experiments are now under construction to determine the yet unknown neutrino mixing angle θ13 with a sensitivity of sin22θ13 < 0.01. Stringent control of detector systematics and minimizing backgrounds will be key to the continued success of reactor neutrino oscillation experiments.

The double chooz reactor neutrino experiment

The Double Chooz reactor neutrino experiment will be the next detector to search for a non vanishing θ13 mixing angle with unprecedented sensitivity, which might open the way to unveiling CP violation in the leptonic sector. The measurement of this angle will be based in a precise comparison of the antineutrino spectrum at two identical detectors located at different distances from the Chooz nuclear reactor cores in France. Double Chooz is particularly attractive because of its capability to measure sin2 (2θ13) to 3σ if sin2(2θ13) > 0.05 or to exclude sin2(2θ13) down to 0.03 at 90% C.L. for δm2 = 2.5 × 10-3 eV2 in three years of data taking with both detectors. The construction of the far detector starts in 2008 and the first neutrino results are expected in 2009. The current status of the experiment, its physics potential and design and expected performance of the detector are reviewed.

Applying Bayesian neural networks to event reconstruction in reactor neutrino experiments

A toy detector has been designed to simulate central detectors in reactor neutrino experiments in the paper. The electron samples from the Monte-Carlo simulation of the toy detector have been reconstructed by the method of Bayesian neural networks (BNNs) and the standard algorithm, a maximum likelihood method (MLD), respectively. The result of the event reconstruction using BNN has been compared with the one using MLD. Compared to MLD, the uncertainties of the electron vertex are not improved, but the energy resolutions are significantly improved using BNN. And the improvement is more obvious for the high energy electrons than the low energy ones.

Nonstandard neutrino interactions in reactor and superbeam experiments

The formalism of nonstandard four-fermion interactions provides a convenient, model-independent way of parametrizing a wide class of ``new physics'' scenarios. In this article, we study the performance of reactor and superbeam neutrino experiments in the presence of such nonstandard interactions (NSI). Because of interference between the standard and nonstandard amplitudes, sizeable effects are to be expected if the NSI parameters are close to their current upper limits. We derive approximate formulas for the relevant oscillation probabilities including NSI, and show how the leading effects can be understood intuitively even without any calculations. We will present a classification of all possible NSI according to their impact on reactor and superbeam experiments, and it will turn out that these experiments are highly complementary in terms of their sensitivity to the nonstandard parameters. The second part of the paper is devoted to detailed numerical simulations, which will demonstrate how a standard oscillation fit of the mixing angle ${\ensuremath{\theta}}_{13}$ may fail if experimental data is affected by NSI. We find that for some nonstandard terms, reactor and superbeam experiments would yield seemingly conflicting results, while in other cases, they may agree well with each other, but the resulting value for ${\ensuremath{\theta}}_{13}$ could be far from the true value. This offset may be so large that the true ${\ensuremath{\theta}}_{13}$ is even ruled out erroneously. In the last section of the paper, we demonstrate that reactor and superbeam data can actually establish the presence of nonstandard interactions. Throughout our discussion, we pay special attention to the impact of the complex phases, and of the near detectors.

Constraints on unparticles from low energy neutrino-electron scattering

We place limits on scalar and vector unparticle couplings to electrons and neutrinos using data from reactor neutrino experiments originally designed to search for neutrino magnetic moment. Upper bounds on standard model lepton-scalar unparticle and lepton-vector unparticle couplings ${\ensuremath{\lambda}}_{0}$, and ${\ensuremath{\lambda}}_{1}$ are given for various values of the unparticle mass dimension $d$, and the unparticle energy scale ${\ensuremath{\Lambda}}_{\mathcal{U}}$. Especially for smaller values of the mass dimension $d$ ($1&lt;d&lt;1.3$) these bounds are very significant and comparable to those obtained from production rates at high energy colliders. These bounds are also similar to those obtained by the analysis of the absence of the decay of the low-energy solar and reactor neutrinos.

Self-calibration of neutrino detectors using characteristic backgrounds

We introduce the possibility to use natural neutrino backgrounds, such as Geo-neutrinos ( ν ¯ e ) or solar neutrinos ( ν e ), with known characteristic spectral shape for the energy calibration of future neutrino detectors, e.g. Large Liquid Scintillator Detectors. This “CalEffect” could be used without the need to apply any modifications to the experiment in all situations where one has a suitable background with sufficient statistics. After deriving the effect analytically using χ 2 statistics, we show that it is only tiny for reactor neutrino experiments, but can be applicable in other situations. As an example, we present its impact on the identification of the wiggles in the power spectrum of supernova neutrinos caused by Earth matter effects. The Self-Calibration Effect could be used for cross checking other calibration methods and to resolve systematical effects in the primary neutrino interaction processes, in particular in the energy dependence of low-energy cross-sections.

Challenging Lorentz noninvariant neutrino oscillations without neutrino masses

We show that the combined data from solar, long-baseline and reactor neutrino experiments can exclude the generalized bicycle model of Lorentz noninvariant direction-dependent and/or direction-independent oscillations of massless neutrinos. This model has five parameters, which is more than is needed in standard oscillation phenomenology with neutrino masses. Solar data alone are sufficient to exclude the pure direction-dependent case. The combination of solar and long-baseline data rules out the pure direction-independent case. With the addition of KamLAND data, a mixture of direction-dependent and direction-independent terms in the effective Hamiltonian is also excluded.

Results from Solar and Reactor Neutrino Experiments

The evidence for neutrino flavour change and for the LMA solution for the neutrino mixing parameters is briefly summarized. Recent results and current research from SNO and SK are then described along with the potential for KamLAND, Borexino and planned new experiments to extend our knowledge by studying low energy solar neutrinos. The sensitivity of reactor experiments in determining θ 13 is discussed and the detection technique and principal backgrounds are explained. Finally the status of proposed and funded reactor θ 13 experiments is presented.

New limit on millicharged particles from reactor neutrino experiments and the PVLAS anomaly

It has been recently suggested that the vacuum magnetic dichroism observed by the PVLAS experiment could be explained by pair production of a new light, ${m}_{\ensuremath{\epsilon}}\ensuremath{\simeq}0.1\text{ }\text{ }\mathrm{eV}$, millicharged, ${q}_{\ensuremath{\epsilon}}\ensuremath{\simeq}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}e$, fermions ($\ensuremath{\epsilon}$). In addition, it has been pointed out that millicharged particles with ${q}_{\ensuremath{\epsilon}}\ensuremath{\gtrsim}{10}^{\ensuremath{-}9}e$ appear naturally in models based on the string theory. We show that low energy reactor neutrino experiments provide a sensitive probe of millicharged particles. Considering, as an example, recent results of the TEXONO experiment searching for the neutrino magnetic moment, a new upper bound ${q}_{\ensuremath{\epsilon}}\ensuremath{\lesssim}{10}^{\ensuremath{-}5}e$ for the mass region ${m}_{\ensuremath{\epsilon}}&lt;1\text{ }\text{ }\mathrm{keV}$ is derived. These results enhance motivations for a more sensitive search for such particles in near future experiments. Furthermore, a direct experimental limit on the electric charge of the electron antineutrino ${q}_{{\overline{\ensuremath{\nu}}}_{e}}&lt;3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}e$ is obtained.

Reactor neutrino experiments with a large liquid scintillator detector

We discuss several new ideas for reactor neutrino oscillation experiments with a Large Liquid Scintillator Detector. We consider two different scenarios for a measurement of the small mixing angle $\theta_{13}$ with a mobile $\bar{\nu}_e$ source: a nuclear-powered ship, such as a submarine or an icebreaker, and a land-based scenario with a mobile reactor. The former setup can achieve a sensitivity to $\sin^2 2\theta_{13} \lesssim 0.003$ at the 90% confidence level, while the latter performs only slightly better than Double Chooz. Furthermore, we study the precision that can be achieved for the solar parameters, $\sin^2 2\theta_{12}$ and $\Delta m_{21}^2$, with a mobile reactor and with a conventional power station. With the mobile reactor, a precision slightly better than from current global fit data is possible, while with a power reactor, the accuracy can be reduced to less than 1%. Such a precision is crucial for testing theoretical models, e.g. quark-lepton complementarity.

Scintillating Oils and Compatible Materials for Next Generation of Electron Anti-neutrino Detectors, After Double Chooz

The Double Chooz reactor neutrino experiment will be built in the forthcoming years. Eventhough not dedicated to geo-neutrino detection, it is based on similar experimental methods. By pushing current technology to the limits an unprecedented precision will be reached due to careful reduction and control of systematic errors below the percent level. The experience and technical innovation achieved by this project could be valuable for future geo-neutrino experiments. After discussing the Double Chooz detector design we focus on progress achieved on scintillating oils and compatible materials.

On-site underground background measurements for the KASKA reactor-neutrino experiment

On-site underground background measurements were performed for the planned reactor-neutrino oscillation experiment KASKA at Kashiwazaki-Kariwa nuclear power station in Niigata, Japan. A small-diameter boring hole was excavated down to 70 m underground level, and a detector unit for γ -ray and cosmic-muon measurements was placed at various depths to take data. The data were analyzed to obtain abundance of natural radioactive elements in the surrounding soil and rates of cosmic muons that penetrate the overburden. The results will be reflected in the design of the KASKA experiment.

Earth matter effects in detection of supernova neutrinos

We calculated the matter effect, including both the Earth and supernova, on the detection of neutrinos from type II supernovae at the proposed Daya Bay reactor neutrino experiment. It is found that apart from the dependence on the flip probability ${P}_{H}$ inside the supernova and the mass hierarchy of neutrinos, the amount of the Earth matter effect depends on the direction of the incoming supernova neutrinos, and reaches the biggest value when the incident angle of neutrinos is around 93\ifmmode^\circ\else\textdegree\fi{}. In the reaction channel ${\overline{\ensuremath{\nu}}}_{e}+p\ensuremath{\rightarrow}{e}^{+}+n$ the Earth matter effect can be as big as about 12%. For other detection processes the amount of the Earth matter effect is a few per cent.

Measuring cosmogenic 9Li background in a reactor neutrino experiment

Cosmogenic isotopes 9Li and 8He produced in the detector are the most problematic background in the reactor neutrino experiments designed to determine precisely the neutrino mixing angle θ 13 . The average time interval of cosmic-ray muons in the detector is often on the order of the lifetimes of the 9Li and 8He isotopes. We have developed a method for determining this kind of background from the distribution of time since last muon for muon rate up to about 20 Hz when the background-to-signal ratio is small, on the order of a few percents.