KamLAND Research Articles

RFSoC-based front-end electronics for pulse detection

Radiation measurement relies on pulse detection, which can be performed using various configurations of high-speed analog-to-digital converters (ADCs) and field-programmable gate arrays (FPGAs). For optimal power consumption, design simplicity, system flexibility, and the availability of DSP slices, we consider the Radio Frequency System-on-Chip (RFSoC) to be a more suitable option than traditional setups. To this end, we have developed custom RFSoC-based electronics and verified its feasibility. The ADCs on RFSoC exhibit a flat frequency response of 1–125 MHz. The root-mean-square (RMS) noise level is 2.1 ADC without any digital signal processing. The digital signal processing improves the RMS noise level to 0.8 ADC (input equivalent 40 μVrms). Baseline correction via digital signal processing can effectively prevent photomultiplier overshoot after a large pulse. Crosstalk between all channels is less than -55 dB. The measured data transfer speed can support up to 32 kHz trigger rates (corresponding to 750 Mbps). Overall, our RFSoC-based electronics are highly suitable for pulse detection, and after some modifications, they will be employed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND).

Prediction of supernova neutrino signals by detectors and its future challenges

Supernova neutrinos produced during a core collapse of a massive star, carries 99% of the energy produced during the violent phenomenon. These neutrinos are weakly interacting massive particles and can provide useful information for both particle physics (neutrino oscillations parameters) and astrophysics (explosion mechanism). This information can be used to explore physics beyond the standard model. Neutrinos escape from the supernova core hours before the light, so a neutrino signal providing information about supernova direction can enable early observation. The current generation of detectors, like, Super-Kamiokande (Super-K), Large Volume Detector (LVD), Borexino, Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), and IceCube, as well as HALO, Daya Bay(reactor neutrino experiment) and NuMI Off-Axis νe Appearance experiment (NOvA), have the ability to detect only a few orders of magnitude of events and the next generation experiment like, Hyper-Kamiokande (Hyper-K), Deep Underground Neutrino Experiment (DUNE), and Jiangmen Underground Neutrino Observatory (JUNO) will have yet another order of magnitude in reach, as well as richer flavor sensitivity. This work will present a Monte Carlo based study using the SNOwGLoBES [1] package, which is used to estimate the event rate using folded fluxes, cross-sections, and detector smearing to determine mean expected neutrino interaction signals in multiple current and future detectors. A study is carried out for the calculation of core-collapse neutrino event rates in realistic detectors for different flux models, effects of different parameters on flux and its variation with time.

Parametric resonance in neutrino oscillations induced by ultra-light dark matter and implications for KamLAND and JUNO

If Ultra-light dark matter (ULDM) exists and couples to neutrinos, the neutrino oscillation probability might be significantly altered by a parametric resonance. This resonance can occur if the typical frequency of neutrino flavor-oscillations ∆m2/(2E), where ∆m2 is the mass-squared difference of the neutrinos and E is the neutrino energy, matches the oscillation frequency of the ULDM field, determined by its mass, mϕ. The resonance could lead to observable effects even if the ULDM coupling is very small, and even if its typical oscillation period, given by τϕ = 2π/mϕ, is much shorter than the experimental temporal resolution. Defining a small parameter ϵϕ to be the ratio between the contribution of the ULDM field to the neutrino mass and the vacuum value of the neutrino mass, the impact of the resonance is particularly significant if ϵϕmϕL ≳ 4, where L is the distance between the neutrino source and the detector. An outlier in the data collected by the KamLAND experiment which, until now, has been assumed to constitute a statistical fluctuation, or associated with the binning, can actually be explained by such narrow parametric resonance, without affecting the measurements of other current neutrino oscillation experiments. This scenario will be tested by the JUNO experiment.

Scalability of Gadolinium-Doped-Water Cherenkov Detectors for Nuclear Nonproliferation

Antineutrinos are an inextricable element of the fission process. The kiloton-scale KamLAND experiment has demonstrated a capability to detect reactor antineutrinos at a range of a few hundred kilometers. But to detect or rule out the existence of a single small reactor over many kilometers requires a large detector, so large in fact that the optical opacity of the detection medium itself becomes an important factor. If the detector is so large that photons cannot traverse the detector medium to an optical detector, then it becomes impractical. For this reason, gadolinium-doped-water Cherenkov detectors have been proposed for large volumes, due to their appealing light-attenuation properties. Even though Cherenkov emission does not produce many photons and the energy resolution is poor, there may be a place for Gd-doped-water detectors in far-field nuclear-reactor monitoring. In this paper, we focus on the reactor-discovery potential of large-volume Gd-doped-water Cherenkov detectors for nuclear-nonproliferation applications. Realistic background models for the worldwide reactor flux, geoneutrinos, cosmogenic fast neutrons, and detector-associated backgrounds are included. We calculate the detector run time required to detect a small 50-MWt reactor at a variety of stand-off distances as a function of detector size. We highlight that, at present, the photomultiplier-tube dark rate and event reconstruction algorithms are the limiting factors to extending such detectors beyond a fiducial mass of approximately 50 kt.

Abundances of Uranium and Thorium Elements in Earth Estimated by Geoneutrino Spectroscopy

AbstractThe decay of the primordial isotopes 238U, 235U, 232Th, and 40K has contributed to the terrestrial heat budget throughout the Earth's history. Hence, the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth models. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid‐Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18‐year observation time, and improvement in detector background levels mainly with an 8‐year nearly reactor‐free period, which now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. The KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High‐Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2σ assuming a homogeneous heat producing element distribution in the mantle.

Quantifying Earth's radiogenic heat budget

Earth's internal heat drives its dynamic engine, causing mantle convection, plate tectonics, and the geodynamo. These renewing and protective processes, which make Earth habitable, are fueled by primordial and radiogenic heat. For the past two decades, particle physicists have measured the flux of geoneutrinos, electron antineutrinos emitted during β− decay. These ghost-like particles provide a direct measure of the amount of heat producing elements (HPE: Th & U) in the Earth and in turn define the planet's absolute concentration of the refractory elements. The geoneutrino flux has contributions from the lithosphere and mantle. Detector sensitivity follows a 1/r2 (source detector separation distance) dependence. Accordingly, an accurate geologic model of the Near-Field Lithosphere (NFL, closest 500 km) surrounding each experiment is required to define the mantle's contribution. Because of its proximity to the detector and enrichment in HPEs, the local lithosphere contributes ∼50% of the signal and has the greatest effect on interpreting the mantle's signal.We re-analyzed the upper crustal compositional model used by Agostini et al. (2020) for the Borexino experiment. We documented the geology of the western Near-Field region as rich in potassic volcanism, including some centers within 50 km of the detector. In contrast, the Agostini study did not include these lithologies and used only a HPE-poor, carbonate-rich, model for upper crustal rocks in the surrounding ∼150 km of the Borexino experiment. Consequently, we report 3× higher U content for the local upper crust, which produces a 200% decrease in Earth's radiogenic heat budget, when compared to their study. Results from the KamLAND and Borexino geoneutrino experiments are at odds with one another and predict mantle compositional heterogeneity that is untenable. Combined analyses of the KamLAND and Borexino experiments using our revised local models strongly favor an Earth with ∼20 TW present-day total radiogenic power. The next generation of geoneutrino detectors (SNO+, counting; and JUNO, under construction) will better constrain the HPE budget of the Earth.

Can NSI affect non-local correlations in neutrino oscillations?

Non-local correlations in entangled systems are usually captured by measures such as Bell’s inequality violation. It was recently shown that in neutrino systems, a measure of non-local advantage of quantum coherence (NAQC) can be considered as a stronger measure of non-local correlations as compared to the Bell’s inequality violation. In this work, we analyze the effects of non standard interaction (NSI) on these measures in the context of two flavour neutrino oscillations for DUNE, MINOS, T2K, KamLAND, JUNO and Daya Bay experimental set-ups. We find that even in the presence of NSI, Bell’s inequality violation occurs in the entire energy range whereas the NAQC violation is observed only in some specific energy range justifying the more elementary feature of NAQC. Further, we find that NSI can enhance the violation of NAQC and Bell’s inequality parameter in the higher energy range of a given experimental set-up; these enhancements being maximal for the KamLAND experiment. However, the possible enhancement in the violation of the Bell’s inequality parameter over the standard model prediction can be up to 11% whereas for NAQC it is 7%. Thus although NAQC is a comparatively stronger witness of nonclassicality, it shows lesser sensitivity to NSI effects in comparison to the Bell’s inequality parameter.

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.

Feasibility and physics potential of detecting 8B solar neutrinos at JUNO * *This work was supported by the Chinese Academy of Sciences, the National Key R&D Program of China, the CAS Center for Excellence in Particle Physics, the Joint Large-Scale Scientific Facility Funds of the NSFC and CAS, Wuyi University, and the Tsung-Dao Lee Institute of Shanghai Jiao Tong University

The Jiangmen Underground Neutrino Observatory (JUNO) features a 20 kt multi-purpose underground liquid scintillator sphere as its main detector. Some of JUNO's features make it an excellent location for B solar neutrino measurements, such as its low-energy threshold, high energy resolution compared with water Cherenkov detectors, and much larger target mass compared with previous liquid scintillator detectors. In this paper, we present a comprehensive assessment of JUNO's potential for detecting B solar neutrinos via the neutrino-electron elastic scattering process. A reduced 2 MeV threshold for the recoil electron energy is found to be achievable, assuming that the intrinsic radioactive background U and Th in the liquid scintillator can be controlled to 10 g/g. With ten years of data acquisition, approximately 60,000 signal and 30,000 background events are expected. This large sample will enable an examination of the distortion of the recoil electron spectrum that is dominated by the neutrino flavor transformation in the dense solar matter, which will shed new light on the inconsistency between the measured electron spectra and the predictions of the standard three-flavor neutrino oscillation framework. If eV , JUNO can provide evidence of neutrino oscillation in the Earth at approximately the 3 (2 ) level by measuring the non-zero signal rate variation with respect to the solar zenith angle. Moreover, JUNO can simultaneously measure using B solar neutrinos to a precision of 20% or better, depending on the central value, and to sub-percent precision using reactor antineutrinos. A comparison of these two measurements from the same detector will help understand the current mild inconsistency between the value of reported by solar neutrino experiments and the KamLAND experiment.

Reactor antineutrino oscillations at Super-Kamiokande

SuperKamiokande (SK) doped with gadolinium has the capability to efficiently identify electron-antineutrinos through inverse beta-decay. Given the size of SK and the number of nuclear reactors in its vicinity, we argue that SK can observe the oscillations of reactor antineutrinos driven by the so-called solar mass-squared difference Δm212. After only one year of data taking, we estimate that SK can measure Δm212 with enough precision to help inform the current small tension between existing results from KamLAND and solar neutrino experiments.

The fate of hints: updated global analysis of three-flavor neutrino oscillations

Our herein described combined analysis of the latest neutrino oscillation data presented at the Neutrino2020 conference shows that previous hints for the neutrino mass ordering have significantly decreased, and normal ordering (NO) is favored only at the 1.6σ level. Combined with the χ2 map provided by Super-Kamiokande for their atmospheric neutrino data analysis the hint for NO is at 2.7σ. The CP conserving value δCP = 180° is within 0.6σ of the global best fit point. Only if we restrict to inverted mass ordering, CP violation is favored at the ∼ 3σ level. We discuss the origin of these results — which are driven by the new data from the T2K and NOvA long-baseline experiments —, and the relevance of the LBL-reactor oscillation frequency complementarity. The previous 2.2σ tension in ∆m221 preferred by KamLAND and solar experiments is also reduced to the 1.1σ level after the inclusion of the latest Super-Kamiokande solar neutrino results. Finally we present updated allowed ranges for the oscillation parameters and for the leptonic Jarlskog determinant from the global analysis.

Neutrino oscillations at low energy long baseline experiments in the presence of nonstandard interactions and parameter degeneracy

Abstract We discuss the analytical expression of the oscillation probabilities at low energy long baseline experiments, such as Tokai to HyperKamiokande (T2HK) and Tokai to HyperKamioka and Korea (T2HKK), in the presence of nonstandard interactions (NSIs). We show that these experiments are advantageous in the exploration of the NSI parameters ($\epsilon_D$, $\epsilon_N$), which were suggested to be nonvanishing to account for the discrepancy between the solar neutrino and Kamioka Liquid scintillator Anti-Neutrino Detector data. We also show that, when the NSI parameters are small, parameter degeneracy in the CP phase $\delta$, $\epsilon_D$ and $\epsilon_N$ can be resolved by combining data of the T2HK and T2HKK experiments.

Testing NSI suggested by solar neutrino tension in T2HKK and DUNE

It was shown that the tension between the mass-squared differences obtained from solar neutrinos and those acquired through KamLAND experiments may be solved by the introduction of a non-standard flavor-dependent interaction (NSI) in neutrino propagation. In this study, we discuss the possibility of testing such a hypothesis using the future long-baseline neutrino experiments T2HKK and DUNE. Assuming that the NSI does not exist, we provide the excluded region within the ([Formula: see text], [Formula: see text]) plane, where [Formula: see text] and [Formula: see text] are the parameters appearing in the solar neutrino analysis conducted with the NSI. We find that the best fit value from the solar neutrino and KamLAND data (global analysis of a particular coupling to quarks) can be tested at more than [Formula: see text] by these two experiments for most of the parameter space.

First results of KamLAND-Zen 800

KamLAND-Zen is a neutrinoless double beta decay (0vββ) search experiment using xenon 136 and ultra-low background environment of KamLAND (Kamioka Liquid scintillator Anti-Neutrino Detector). KamLAND-Zen collaboration has prepared the KamLAND-Zen 800 project with almost 750 kg of xenon and cleaner container for xenon loaded liquid scintillator. The container production was started in May 2017 and KamLAND-Zen 800 data acquisition was started in January 2019. In this paper, we will describe the KamLAND-Zen 800 project and report on the detector condition, data quality, the first analysis results, and the prospects.

Scintillation balloon for neutrinoless double-beta decay search with liquid scintillator detectors

Abstract Environmental radioactivity is a dominant background for rare decay search experiments, and it is difficult to completely remove such an impurity from detector vessels. We propose a scintillation balloon as the active vessel of a liquid scintillator in order to identify this undesirable radioactivity. According to our feasibility studies, the scintillation balloon enables the bismuth–polonium sequential decay to be tagged with a 99.7% efficiency, assuming a KamLAND-type (KamLAND = Kamioka Liquid scintillator AntiNeutrino Detector) liquid scintillator detector. This tagging of sequential decay using alpha rays from the polonium improves the sensitivity to neutrinoless double-beta decay while rejecting beta ray background from the bismuth.

Application of the RNN in the fundamental physics with KamLAND experiment

Application of the RNN in the fundamental physics with KamLAND experiment

Comments on the determination of the neutrino mass ordering in reactor neutrino experiments

We consider the problem of determination of the neutrino mass ordering via precise study of the vacuum neutrino oscillations in the JUNO and other future medium baseline reactor neutrino experiments. We are proposing to resolve neutrino mass ordering by determination of the neutrino oscillation parameters from analysis of the data of the reactor experiments and comparison them with the oscillation parameters obtained from analysis of the solar and KamLAND experiments.

The possibility to observe the non-standard interaction by the Hyperkamiokande atmospheric neutrino experiment

It was suggested that a tension between the mass-squared differences obtained from the solar neutrino and KamLAND experiments can be solved by introducing the non-standard flavor-dependent interaction in neutrino propagation. In this paper we discuss the possibility to test such a hypothesis by atmospheric neutrino observations at the future Hyper-Kamiokande experiment. Assuming that the mass hierarchy is known, we find that the best-fit value from the solar neutrino and KamLAND data can be tested at more than 8σ, while the one from the global analysis can be examined at 5.0σ (1.4σ) for the normal (inverted) mass hierarchy.

Limits onCPTviolation from solar neutrinos

Violations of $CPT$ invariance can induce neutrino-to-antineutrino transitions. We study this effect for solar neutrinos and use the upper bound on the solar neutrino-to-antineutrino transition probability from the KamLAND experiment to constrain $CPT$-symmetry-violating coefficients of the general Standard-Model Extension. The long propagation distance from the Sun to the Earth allows us to improve existing limits by factors ranging from about a thousand to ${10}^{11}$.

KamLAND's precision neutrino oscillation measurements

The KamLAND experiment started operation in the Spring of 2002 and is operational to this day. The experiment observes signals from electron antineutrinos from distant nuclear reactors. The program, spanning more than a decade, allowed the determination of LMA-MSW as the solution to the solar neutrino transformation results (under the assumption of CPT invariance) and the measurement of various neutrino oscillation parameters. In particular, the solar mass-splitting Δm212 was determined to high precision. Besides the study of neutrino oscillation, KamLAND started the investigation of geologically produced antineutrinos (geo-ν‾e). The collaboration also reported on a variety of other topics related to particle and astroparticle physics.