Daya Bay Experiment Research Articles

Verification of the calibration method for the boundary effect in JUNO

Jiangmen Underground Neutrino Observatory (JUNO) is constructed to probe multiple physics goals, including determining the neutrino mass ordering (MO), measuring solar neutrinos, detecting supernova neutrinos, etc. A large Liquid Scintillator (LS) detector with a high energy resolution is being built to determine the neutrino MO within 6-year of data taking. To accomplish this goal, a calibration complex has been designed. Concerning the energy leakage near the LS boundary, a Guide Tube Calibration System (GTCS) will be deployed on the outer surface of the JUNO central detector to help better understand the boundary effect. A fitting algorithm has been presented during the design of GTCS considering the overlap of full-energy peak and Compton tail. In this paper, we verify the fitting algorithm experimentally, using a radioactive source in the Daya Bay experiment. The maximum bias of full-energy peak for the experiment at Daya Bay is less than 1.0% even if a change of ±20.0% in acrylic density was assumed. Besides, the tuned acrylic density is applied in JUNO GTCS simulation. The maximum uncertainty estimation of GTCS energy response in total is 0.52%, satisfying the JUNO GTCS requirement which is 1.0%.

A step forward in understanding the universe: The latest results from the Daya Bay experiment

Why is the current universe dominated by matter when there should have been equal amounts of matter and anti-matter at the beginning? One of the keys to answering this question is to find out a currently undiscovered charge-parity (CP) violation in the lepton sector. The CP violation can be tested through studies of the phenomenon called neutrino oscillation. Neutrino oscillation occurs because the weak eigenstates, |νl>(l=e,μ,τ), and mass eigenstates, |νi>(i=1,2,3), are mixed, as follows:where UPMNS is the 3 × 3 Pontecorvo-Maki-Nakagawa-Sakata mixing matrix, which is defined with three mixing angles, θ12, θ23, and θ13, and one complex Dirac CP phase, δCP.

Generating CP Violation from a Modified Fridberg-Lee Model

The overall characteristics of the solar and atmospheric neutrino oscillations are approximately consistent with a tribimaximal form of the mixing matrix U of the lepton sector. Exact tribimaximal mixing leads to θ13=0. However, the results from the Daya Bay and RENO experiments have established, such that in comparison to the other neutrino mixing angles, θ13 is small. Moreover, the atmospheric and solar mass splitting differ by two orders of magnitude. These significant differences constitutes the great enthusiasm and main motivation for our research herein reported. Keeping the behavior of U as tribimaximal, we would make a response to the following questions: at some level, whether or not the small parameters such as the solar neutrino mass splitting and Ue3, which vanish in a new framework, can be interpreted as a modified FL neutrino mass model? Subsequently, a minimal single perturbation leads to nonzero values for both of them? Our minimal perturbation matrix is constructed solely from computing the third mass eigenstate, using the rules of perturbation theory. Let us point out that, unlike other investigations, this matrix is not adopted on an ad hoc basis, but is created following a series of steps that we will describe. Also in compared to the original FL neutrino mass model which generalize it by inserting phase factors, our work is more accurate. Subsequently, we produce the following results that add new contributions to the literature: (a) we obtain a realistic neutrino mixing matrix with δ≠0 and θ23=45∘; (b) the solar mass splitting term is dominated by an imaginary term, which could induce the existence of Majorana neutrinos, along with explaining a large CP violation in nature; (c) the ordering of the neutrino masses is normal; however, at the end of the allowed range, it becomes more degenerate (97%); (d) we also obtain the allowed range of the mass parameters, which not only are in accordance with the experimental data but also allow falsifiable predictions for the masses of the neutrinos and the CP violating phases which none of these results has been achieved in the original FL neutrino mass model. Finally, let us emphasize that the results obtained by our framework here are much more efficient compared to those obtained in previous works in terms of currently available experimental data (namely, the best fit column).

New test of neutrino oscillation coherence with Leggett\u2013Garg inequality

Leggett–Garg inequality (LGI) is a time analogue of Bell’s inequality that concerns measurements performed on a system at different times. Violation to LGI indicates quantum coherence. We present a Leggett–Garg-type inequality compatible with more general neutrino oscillation frameworks, allowing the effects of decoherence to be taken into consideration. The inequality is applied to test coherence for data from Daya Bay, MINOS, and KamLAND experiments, and their results are compared to theoretical predictions to investigate decoherence. Both Daya Bay and MINOS data exhibit clear violations of over 10sigma , and of over 90% of theoretical predictions, while the KamLAND data exhibit violation of 1.9sigma , being of 58% of the theoretical prediction. The present work is the first to have considered the energy uncertainties in neutrino coherence tests.

Reevaluating reactor antineutrino spectra with new measurements of the ratio between U235 and Pu239 β spectra

We report a reanalysis of the reactor antineutrino energy spectra based on the new relative measurements of the ratio $R=\!^{e}S_5/^{e}S_9$ between cumulative $\beta$ spectra from $^{235}$U and $^{239}$Pu, performed at a research reactor in National Research Centre Kurchatov Institute (KI). A discrepancy with the $\beta$ spectra measured at Institut Laue-Langevin (ILL) was observed, indicating a steady excess of the ILL ratio by the factor of $1.054\pm0.002$. We find a value of the ratio between inverse beta decay cross section per fission for $^{235}$U and $^{239}$Pu: $(^5\sigma_f/^9\sigma_f)_{KI} = 1.45 \pm 0.03$, and then we reevaluate the converted antineutrino spectra for $^{235}$U and $^{238}$U. We conclude that the new predictions are consistent with the results of Daya Bay and STEREO experiments.

From Daya Bay experiment to Jiangmen Underground Neutrino Observatory experiment

Currently, the neutrino oscillation phenomenon is of research interest in particle physics. The discovery of the neutrino oscillation phenomenon confirmed that neutrinos have a minute mass, which is an important way to explore new physics beyond the standard model. The Daya Bay reactor neutrino experiment is an underground experiment that studies short-baseline reactor neutrino oscillations. It uses the far and near-identical detectors to reduce the detector uncertainty and the reactor neutrino expected flux uncertainty to measure the anti-neutrino rate and energy spectrum. The Daya Bay experiment released the latest neutrino oscillation parameters $\sin^{2}2\theta_{13}$ and $|\Delta$$m^{2}_{32}|$ in 2018, which used 1958 days of data. The $\sin^{2}2\theta_{13}$ had the highest measurement precision to date, which reached 3.4$%$, and the precision of $|\Delta$$m^{2}_{32}|$ was 2.8$%$, which was comparable with that of the accelerator-based experiments, such as MINOS, No$\nu$A and T2K. The accurate measurement of $\theta_{13}$ will be helpful to the next-generation of neutrino experiments that will determine the neutrino mass ordering and measure the CP-violating phase. Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment that is under construction. The main scientific aim of JUNO is to determine the neutrino mass ordering by measuring the neutrino energy spectrum with a resolution of 3$%$ at 1 MeV and a $~\ge$ 1$%$ energy linearity. The neutrino mass ordering can be measured with a significance 3–4$\sigma$ based on six years of data that has been collected. In addition, JUNO will make a significant contribution to the precise measurement of neutrino oscillation parameters and the study of supernova neutrinos, solar neutrinos, atmospheric neutrinos, geoneutrinos, and nucleon decay.

Antineutrino energy spectrum unfolding based on the Daya Bay measurement and its applications * *Supported in part by the Ministry of Science and Technology of China, the U.S. Department of Energy, the Chinese Academy of Sciences, the CAS Center for Excellence in Particle Physics, the National Natural Science Foundation of China, the Guangdong provincial government, the Shenzhen municipal government, the

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.

Combined analysis of neutrino decoherence at reactor experiments

Reactor experiments are well suited to probe the possible loss of coherence of neutrino oscillations due to wave-packets separation. We combine data from the short-baseline experiments Daya Bay and the Reactor Experiment for Neutrino Oscillation (RENO) and from the long baseline reactor experiment KamLAND to obtain the best current limit on the reactor antineutrino wave-packet width, σ > 2.1 × 10−4 nm at 90% CL. We also find that the determination of standard oscillation parameters is robust, i.e., it is mostly insensitive to the presence of hypothetical decoherence effects once one combines the results of the different reactor neutrino experiments.

2020 global reassessment of the neutrino oscillation picture

We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework. In the present study we include up-to-date analyses from a number of experiments. Concerning the atmospheric and solar sectors, besides the data considered previously, we give updated analyses of IceCube DeepCore and Sudbury Neutrino Observatory data, respectively. We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NOνA measurements, as reported in the Neutrino 2020 conference. All in all, these new analyses result in more accurate measurements of θ13, θ12, Delta {m}_{21}^2 and left|Delta {m}_{31}^2right| . The best fit value for the atmospheric angle θ23 lies in the second octant, but first octant solutions remain allowed at ∼ 2.4σ. Regarding CP violation measurements, the preferred value of δ we obtain is 1.08π (1.58π) for normal (inverted) neutrino mass ordering. The global analysis still prefers normal neutrino mass ordering with 2.5σ statistical significance. This preference is milder than the one found in previous global analyses. These new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches. Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of 2.00σ. While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to 2.68σ within a conservative approach. A more aggressive data set combination of cosmological observations leads to a similar preference for normal with respect to inverted mass ordering, namely 2.70σ. This very same cosmological data set provides 2σ upper limits on the total neutrino mass corresponding to Σmν< 0.12 (0.15) eV in the normal (inverted) neutrino mass ordering scenario. The bounds on the neutrino mixing parameters and masses presented in this up-to-date global fit analysis include all currently available neutrino physics inputs.

Impact of the Most Recent Total Absorption Gamma-ray Spectroscopy Data for Fission Fragments on Reactor Antineutrino Spectra and Comparison with the Daya Bay Results

The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya Bay experiment has measured the evolution of the antineutrino flux with the fuel content of the reactor core. The observed deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of 235U while the part dominated by the fission of 239Pu was in good agreement with the conversion model. The TAGS collaboration has carried out two experimental campaigns during the last decade at the JYFLTRAP of Jyväskylä (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. These measurements allow the correction of the nuclear data for the Pandemonium effect, thus making an important contribution to calculating the antineutrino spectra. The impact of these ten years of measurement from our collaboration on the predicted antineutrino energy spectrum and flux are shown using our summation calculations. The results are compared with the Daya Bay measurements showing the best agreement in shape (in the antineutrino energy range 2 to 5 MeV) and in flux obtained so far with a model. The flux deficit observed by Daya Bay with respect to the summation method is now reduced to 1.9% leaving little room for the reactor anomaly. The shape anomaly between 5 and 7 MeV in antineutrino energy is still observed and remains unexplained.

Search for electron-antineutrinos associated with gravitational-wave events GW150914, GW151012, GW151226, GW170104, GW170608, GW170814, and GW170817 at Daya Bay * *Daya Bay is supported in part by the Ministry of Science and Technology of China, the U.S. Department of Energy, the Chinese Academy of Sciences, the CAS Center for Excellence in Particle Physics, the National Natural Science Foundation of China, the

The establishment of a possible connection between neutrino emission and gravitational-wave (GW) bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge. In the Daya Bay experiment, using the data collected from December 2011 to August 2017, a search was performed for electron-antineutrino signals that coincided with detected GW events, including GW150914, GW151012, GW151226, GW170104, GW170608, GW170814, and GW170817. We used three time windows of ±10, ±500, and ±1000 s relative to the occurrence of the GW events and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates. The detected electron-antineutrino candidates were consistent with the expected background rates for all the three time windows. Assuming monochromatic spectra, we found upper limits (90% confidence level) of the electron-antineutrino fluence of (1.13 − 2.44)×1011 cm−2 at 5 MeV to 8.0×107 cm−2 at 100 MeV for the three time windows. Under the assumption of a Fermi-Dirac spectrum, the upper limits were found to be (5.4 − 7.0)×109 cm−2 for the three time windows.

Probing neutrino quantum decoherence at reactor experiments

We explore how well reactor antineutrino experiments can constrain or measure the loss of quantum coherence in neutrino oscillations. We assume that decoherence effects are encoded in the size of the neutrino wave-packet, σ. We find that the current experiments Daya Bay and the Reactor Experiment for Neutrino Oscillation (RENO) already constrain σ > 1.0×10−4 nm and estimate that future data from the Jiangmen Underground Neutrino Observatory (JUNO) would be sensitive to σ < 2.1 × 10−3 nm. If the effects of loss of coherence are within the sensitivity of JUNO, we expect σ to be measured with good precision. The discovery of nontrivial decoherence effects in JUNO would indicate that our understanding of the coherence of neutrino sources is, at least, incomplete.

Phenomenological advantages of the normal neutrino mass ordering * * SFG is supported by JSPS KAKENHI (JP18K13536) and the Double First Class start-up fund (WF220442604) provided by Shanghai Jiao Tong University. JYZ is supported by the National Natural Science Foundation of China (11275101, 11835005)

The preference of the normal neutrino mass ordering from the recent cosmological constraint and the global fit of neutrino oscillation experiments does not seem like a wise choice at first glance since it obscures the neutrinoless double beta decay and hence the Majorana nature of neutrinos. Contrary to this naive expectation, we point out that the actual situation is the opposite. The normal neutrino mass ordering opens the possibility of excluding the higher solar octant and simultaneously measuring the two Majorana CP phases in future experiments. Especially, the funnel region will completely disappear if the solar mixing angle takes the higher octant. The combined precision measurement by the JUNO and Daya Bay experiments can significantly reduce the uncertainty in excluding the higher octant. With a typical sensitivity on the effective mass , the neutrinoless double beta decay experiment can tell if the funnel region really exists and hence exclude the higher solar octant. With the sensitivity further improved to sub-meV, the two Majorana CP phases can be simultaneously determined. Thus, the normal neutrino mass ordering clearly shows phenomenological advantages over the inverted one.

Double Chooz θ13 measurement via total neutron capture detection

The establishment of the neutrino oscillations phenomenon as a solution to both solar and atmospheric neutrino anomalies had two consequences: a new oscillation mode, labelled $\mathbf{\theta_{13}}$, and the possibility to observe CP violation, if $\mathbf{\theta_{13}}$ was sizeable. CP violation implies that neutrino oscillations behave differently for neutrinos and anti-neutrinos -- a rare fundamental phenomenon key for our understanding of the Universe. The experimental demonstration of $\mathbf{\theta_{13}}$ has aided the completion of a quest lasting half a century. The best $\mathbf{\theta_{13}}$ knowledge is today inferred from high-precision reactor neutrino disappearance. The Double Chooz (DC) experiment has played a pioneering role in this channel by providing the first positive evidence, in 2011, in combination with the T2K experiment appearance data. The establishment of $\mathbf{\theta_{13}}$ awaited the Daya Bay experiment's observation in 2012; confirmed soon after by the RENO experiment. Today's best knowledge on $\mathbf{\theta_{13}}$ from reactor experiments is a key input to many neutrino experiments. Here DC reports its first multi-detector $\mathbf{\theta_{13}}$ measurement exploiting several unprecedented techniques for a major precision improvement.

Neutrino Oscillation Analysis of 217 Live Days of Daya Bay and 500 Live Days of RENO

We present a neutrino oscillation analysis of two particular data sets from the Daya Bay and RENO reactor neutrino experiments aiming to study the increase in precision in the oscillation parameters sin22θ13 and the effective mass splitting Δmee2 gained by combining two relatively simple to reproduce analyses available in the literature. For Daya Bay, the data from 217 days between December 2011 and July 2012 were used. For RENO, we used the data from 500 live days between August 2011 and January 2012. We reproduce reasonably well the results of the individual analyses, both rate-only and spectral, defining a suitable χ2 statistic for each case. Finally, we performed a combined spectral analysis and extract tighter constraints on the parameters, with an improved precision between 30 and 40% with respect to the individual analyses considered.

Recent results from Daya Bay reactor neutrino Experiment

Neutrinos are elementary particles in the standard model of particle physics. There are 3 flavors of neutrinos that oscillate among themselves and their oscillation can be described by a 3×3 unitary matrix, containing three mixing angles θ12, θ23, θ13, and one CP phase. Both θ12 and θ23 are known from previous experiments. The Daya Bay experiment gave the first definitive non-zero value in 2012. Daya Bay use the 1230 days data to obtain the most precise measurement of sin22θ13 =0.08421±0.0027(stat.)±0.0019(syst.) and = (math) × 10−3eV2. Experiment has measured the flux and spectrum of the reactor antineutrino. Flux is consistent with previous short baseline experiments and spectrum different from prediction with significance 4.4σ in 4-6 MeV energy region. Experiment also measure the IBD yield per fission from individual isotopes (235U, 239Pu, 238U, 241Pu) and found that IBD yield of 235U is 7.8% lower than prediction. For light sterile neutrino serach, there are no hint of light sterile neutrino observed from Daya Bay data and give the most stringent limit for (math) <0.2eV2.

Editorial for the 4th International Conference on Particle Physics and Astrophysics (ICPPA-2018)

PrefaceThe 4th International Conference on Particle Physics and Astrophysics (ICPPA-2018) was held in Moscow, Russia, from October 22 to 26, 2018. The conference is organized by the National Research Nuclear University “MEPhI”. The aim of the Conference is to share scientific knowledge, to promote contacts between scientists and to develop new ideas in fundamental research. We bring together experts and young scientists working in experimental and theoretical areas of nuclear physics, particle physics (including astroparticle physics), and cosmology. Most recent results from the modern experiments in these areas and advanced detector technology development have been presented and discussed.One of the significant plenary talks referred to observational effects of gravitational waves and physics on the supermassive black holes horizons. Event Horizon Telescope (EHT) data seem to be able to put severe limitations on alternative theories of gravity. Gravitational subjects continued during sectional talks where problems of extra dimensions and wormholes stability have been discussed. Neutrino topic was presented by the report from NEUTRINO-4 experiment indicating positive results in search for sterile neutrinos, by status-reports of EXO, COHERENT and DayaBay experiments and also of RED-100 experiment which is now starting its operation in the National Research Nuclear University “MEPhI”. Large-scale accelerator experiments were presented by the talks given by ATLAS and CMS collaborations from the Large Hadron Collider concerning the search for “new physics” and the absence of deviations from the Standard Model of particle physics. Scientific programs of such projects as FAIR and XFEL - highly advanced accelerators that will be devoted, in addition, to the research of quark-gluon plasma - were also introduced. Flavour physics is currently the closest one in “feeling for” the effects of “new physics”. Deviations in lepton universality for rare decays are now reaching 4 sigmas, which is close to the discovery. Reports on lepton universality verifications were of great interest for the audience.List of Conference Photograph, Sponsor, International Program Committee and Organizing Committee are available in this pdf.

Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes.

A new summation method model of the reactor antineutrino energy spectrum is presented. It is updated with the most recent evaluated decay databases and with our total absorption gamma-ray spectroscopy measurements performed during the last decade. For the first time, the spectral measurements from the Daya Bay experiment are compared with the antineutrino energy spectrum computed with the updated summation method without any renormalization. The results exhibit a better agreement than is obtained with the Huber-Mueller model in the 2-5MeV range, the region that dominates the detected flux. A systematic trend is found in which the antineutrino flux computed with the summation model decreases with the inclusion of more pandemonium-free data. The calculated flux obtained now lies only 1.9% above that detected in the Daya Bay experiment, a value that may be reduced with forthcoming new pandemonium-free data, leaving less room for a reactor anomaly. Eventually, the new predictions of individual antineutrino spectra for the ^{235}U, ^{239}Pu, ^{241}Pu, and ^{238}U are used to compute the dependence of the reactor antineutrino spectral shape on the fission fractions.

Reactor neutrino oscillations as constraints on effective field theory

We study constraints on the Standard Model Effective Field Theory (SMEFT) from neutrino oscillations in short-baseline reactor experiments. We calculate the survival probability of reactor antineutrinos at the leading order in the SMEFT expansion, that is including linear effects of dimension-6 operators. It is shown that, at this order, reactor experiments alone cannot probe charged-current contact interactions between leptons and quarks that are of the (pseudo)vector (V±A) or pseudo-scalar type. We also note that flavor-diagonal (pseudo)vector coefficients do not have observable effects in oscillation experiments. In this we reach novel or different conclusions than prior analyses of non-standard neutrino interactions. On the other hand, reactor experiments offer a unique opportunity to probe tensor and scalar SMEFT operators that are off-diagonal in the lepton-flavor space. We derive constraints on the corresponding SMEFT parameters using the most recent data from the Daya Bay and RENO experiments.

Quantifying quantum coherence in experimentally observed neutrino oscillations

Neutrino oscillation represents an intriguing physical phenomenon where the quantumness can be maintained and detected over a long distance. Previously, the non-classical character of neutrino oscillation was tested with the Leggett-Garg inequality, where a clear violation of the classical bound was observed [J. A. Formaggio et al., Phys. Rev. Lett. 117, 050402 (2016)]. However, there are several limitations in testing neutrino oscillations with the Leggett-Garg inequality. In particular, the degree of violation of the Leggett-Garg inequality cannot be taken as a "measure of quantumness". Here we focus on quantifying the quantumness of experimentally-observed neutrino oscillation, using the tools of recently-developed quantum resource theory. We analyzed ensembles of reactor and accelerator neutrinos at distinct energies from a variety of neutrino sources, including Daya Bay (0.5 km and 1.6 km), Kamland (180 km), MINOS (735 km), and T2K (295 km). The quantumness of the three-flavoured neutrino oscillation is characterized within a 3{\sigma} range relative to the theoretical prediction. It is found that the maximal coherence was observed in the neutrino source from the Kamland reactor. However, even though the survival probability of the Daya Bay experiment did not vary significantly (dropped about 10 percent), the coherence recorded can reach up to 40 percent of the maximal value. These results represent the longest distance over which quantumness were experimentally determined for quantum particles other than photons.