Search

The Hyper-Kamiokande (Hyper-K) project is the world's leading international neutrino and nucleon decay experiment comprising a next-generation underground water Cherenkov detector and upgraded Japan Proton Accelerator Research Complex (J-PARC) neutrino beam. It will provide an enormous potential to discover the leptonic charge-parity violation, to investigate the Grand Unified Theory by proton decay exploration, and to determine the neutrino mass ordering. Further, Hyper-K will significantly enhance the capability to observe solar neutrinos and neutrinos from other astronomical sources in comparison with its predecessors. After the budget approval in January 2020, the Hyper-K project officially began, and the operation is expected to start in 2027. The excavations of a 2.0 km long access tunnel and the tunnels for the detector facility have been completed. In October 2022 it was started the excavation of one of the world's largest underground caverns to suite the HK detector. This article discusses the status and the prospects of the Hyper-K detector construction. [ABSTRACT FROM AUTHOR]

Copyright of Avances en Ciencias e Ingeniería is the property of Avances en Ciencias e Ingenieria and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The first loading of gadolinium (Gd) into Super-Kamiokande in 2020 was successful, and the neutron capture efficiency on Gd reached 50%. To further increase the Gd neutron capture efficiency to 75%, 26.1 tons of Gd 2 (SO 4) 3 ⋅ 8H 2 O was additionally loaded into Super-Kamiokande (SK) from May 31 to July 4, 2022. As the amount of loaded Gd 2 (SO 4) 3 ⋅ 8H 2 O was doubled compared to the first loading, the capacity of the powder dissolving system was doubled. We also developed new batches of gadolinium sulfate with even further reduced radioactive impurities. In addition, a more efficient screening method was devised and implemented to evaluate these new batches of Gd 2 (SO 4) 3 ⋅ 8H 2 O. Following the second loading, the Gd concentration in SK was measured to be 333. 5 ± 2. 5 ppm via an Atomic Absorption Spectrometer (AAS). From the mean neutron capture time constant of neutrons from an Am/Be calibration source, the Gd concentration was independently measured to be 332.7 ± 6.8(sys.) ± 1.1(stat.) ppm, consistent with the AAS result. Furthermore, during the loading the Gd concentration was monitored continually using the capture time constant of each spallation neutron produced by cosmic-ray muons, and the final neutron capture efficiency was shown to become 1.5 times higher than that of the first loaded phase, as expected. [Display omitted] • We conducted additional loading of 26.1 tons of Gd 2 (SO 4) 3 ⋅ 8H 2 O to Super-Kmaioknade in 2022. • Developed new batches of gadolinium sulfate with reduced radioactive impurities. • Gd concentration in SK measured to be 333. 5 ± 2. 5 ppm by an AAS. • Gd concentration derived from the neutron capture time is consistent with AAS. • Demonstrated a 1.5 times higher neutron capture efficiency as expected. [ABSTRACT FROM AUTHOR]

Water Cherenkov detectors like Super-Kamiokande, and the next generation Hyper-Kamiokande are adding gadolinium to their water to improve the detection of neutrons. By detecting neutrons in addition to the leptons in neutrino interactions, an improved separation between neutrino and anti-neutrinos, and reduced backgrounds for proton decay searches can be expected. The neutron signal itself is still small and can be confused with muon spallation and other background sources. In this paper, machine learning techniques are employed to optimize the neutron capture detection capability in the new intermediate water Cherenkov detector (IWCD) for Hyper-K. In particular, boosted decision tree (XGBoost), graph convolutional network (GCN), and dynamic graph convolutional neural network (DGCNN) models are developed and benchmarked against a statistical likelihood-based approach, achieving up to a 10% increase in classification accuracy. Characteristic features are also engineered from the datasets and analyzed using SHAP (SHapley Additive exPlanations) to provide insight into the pivotal factors influencing event type outcomes. The dataset used in this research consisted of roughly 1.6 million simulated particle gun events, divided nearly evenly between neutron capture and a background electron source. The current samples used for training are representative only, and more realistic samples will need to be made for the analyses of real data. The current class split is 50/50, but there is expected to be a difference between the classes in the real experiment, and one might consider using resampling techniques to address the issue of serious imbalances in the class distribution in real data if necessary.

For research on cosmic gamma rays with energies in the range of several tens of teraelectronvolts or more, we investigated a method to improve the angular resolution of an air shower. In an air shower, the density of secondary gamma rays is several times higher than that of electrons and those measurement is important for determining the shower direction. It was found that the angular resolution in the shower front-fit method decreases in inverse proportion to the square root of the number of measured particles. Even if the total number of measured particles is the same, secondary gamma rays contribute more to the improvement of angular resolution than electrons. If secondary gamma rays could be measured at an altitude of 4,740 m with a sensitivity of 100 %, an improvement of approximately 40 % was determined for a 500 TeV shower. A water Cherenkov detector with high gamma-ray sensitivity was investigated through Monte Carlo simulation. Detection efficiencies of approximately 0.38 and 0.76 were obtained for vertically incident gamma rays and electrons, respectively, using 19 8-inch diameter PMTs inside a detector installed in a water tank of radius 4.5 m and water depth 1.6 m. The detection time error for secondary gamma rays is approximately 2.18 ns at an incident angle of 0∘ and the standard error in the detection time for shower front particles was found to be approximately 10 times lower than that obtained by using a plastic scintillation detector with an area of 1 m2. [ABSTRACT FROM AUTHOR]

Muons are detected due to the Cherenkov radiation of electrons caused by muon decay. Different parameters can affect the efficiency of the muon Cherenkov detector. In this paper, a simple water Cherenkov detector was simulated using Geant4 Monte Carlo code. Then, the performance of Cherenkov detector was evaluated using considering of effect of some parameters such as the number of PMTs, the height of the detector, and the reflector effect. The information such as mean lifetime of muon, electron energy spectrum of muon decay, and detector efficiency was measured. The mean relative error indicates good agreement between the simulation data and the experimental and similar researches data. Also, produced optical photons and detector efficiency improved with increasing of the number of PMTs, detector height, and use of a reflector. [ABSTRACT FROM AUTHOR]

The GERDA experiment at LNGS of INFN is equipped with an active muon veto. The main part of the system is a water Cherenkov veto with 66 PMTs in the water tank surrounding the GERDA cryostat. The muon flux recorded by this veto shows a seasonal modulation. Two causes have been identified: (i) secondary muons from the CNGS neutrino beam (2.2%) and (ii) a temperature modulation of the atmosphere (1.4%). A mean cosmic muon rate of Iμ0=(3.477±0.002stat±0.067sys)×10−4/(s · m2) was found in good agreement with other experiments at LNGS. Combining the present result with those from previous experiments at LNGS the effective temperature coefficient αT,Lngs is determined to 0.93 ± 0.03. A fit of the temperature coefficients measured at various underground sites yields a kaon to pion ratio rK/π of 0.10 ± 0.03.

The GERDA experiment at LNGS of INFN is equipped with an active muon veto. The main part of the system is a water Cherenkov veto with 66 PMTs in the water tank surrounding the GERDA cryostat. The muon flux recorded by this veto shows a seasonal modulation. Two causes have been identified: (i) secondary muons from the CNGS neutrino beam (2.2%) and (ii) a temperature modulation of the atmosphere (1.4%). A mean cosmic muon rate of Iμ0=(3.477±0.002stat±0.067sys)×10−4/(s · m2) was found in good agreement with other experiments at LNGS. Combining the present result with those from previous experiments at LNGS the effective temperature coefficient αT,Lngs is determined to 0.93 ± 0.03. A fit of the temperature coefficients measured at various underground sites yields a kaon to pion ratio rK/π of 0.10 ± 0.03.

The measurement of shower muons on an event-by-event basis offers a potent tool for conducting ground-based experiments on gamma rays and cosmic rays due to its sensitivity to primary mass and interaction models. In recent years, underground water Cherenkov detectors as large-area muon counters provide the most powerful way of rejecting cosmic ray background when searching for TeV–PeV gamma rays and cosmic ray electrons, an unprecedented rejection power of 1 0 4 – 1 0 5 is achieved. Unburied water Cherenkov detectors are widely used in ground-based gamma astronomy experiments, e.g, Milagro, HAWC, LHAASO-WCDA, etc. However, due to the presence of electromagnetic components, their deployment as event-by-event muon counters has encountered considerable challenges. All the experiments mentioned above reconstruct lateral-distribution-function related parameters to tell a gamma from hadrons. In this work, we first developed a method to utilize the WCDA, to specify muon content in each shower with LHAASO KM2A-WCDA synergy and help LHAASO to gain approximately a 37,650-meter-square effective area as a muon counter. [ABSTRACT FROM AUTHOR]

In this work we show the capabilities of a water Cherenkov detector (WCD) to detect high energy neutrons. We present the simulation of the response of a doped WCD to 500 MeV monochromatic neutrons using Geant4. To do this, a detailed model of the WCD has been implemented. The active volume of the detector is composed of pure water and different concentrations of a 35 Cl based additive. The addition of this dopant shows an enhancement in the detection of high energetic neutrons. The sensitivity of this detector to neutrons achieved in our simulations is a relevant result for cosmic rays and space weather studies. [ABSTRACT FROM AUTHOR]

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton liquid scintillator detector with the primary physics goal of the neutrino mass ordering determination. The detector will be built in a laboratory 650-m underground. The pool is filled with 34 kton ultrapure water outside the central detector as a water Cherenkov detector for cosmic muon detection. 2400 MCP-PMTs detect the water Cherenkov light produced by cosmic muons. The inner surface of the water veto is covered with a Tyvek reflector to increase the light collection efficiency. A water system is used for water purification and circulation to maintain high water quality for optimal detector performance. A set of radon removal equipment will be integrated with the water system to reduce the radon-induced background in the central detector. Based on prototype studies, the radon concentration in water could be reduced to less than 10 mBq/m3. The cosmic muon detection efficiency of the water Cherenkov detector can reach 99.5%. With this veto system, the cosmic muon-induced fast neutron background can also be reduced to the level of about ∼ 0.1/day level. [ABSTRACT FROM AUTHOR]

Gamma-Ray Bursts (GRBs) are one of the brightest transient events detected, with energies in their prompt phase ranging from keV to GeV. Theoretical models predict emissions at higher energies in the early times of the afterglow emission, and recently GRB190114C was the first GRB detected at TeV energies by the MAGIC experiment. The Latin American Giant Observatory (LAGO) operates a network of water Cherenkov detectors (WCD) at different sites in Latin America. Spanning over different altitudes and geomagnetic rigidity cutoffs, the geographic distribution of the LAGO sites, combined with the new electronics for control, atmospheric sensing, and data acquisition, allows the realization of diverse astrophysics studies at a regional scale. LAGO WCDs located at high altitudes possess good sensitivity to electromagnetic secondary radiation, which is the main expected signature of this kind of high-energy event on the ground. Due to the characteristics of the WCD and the wide field of view, LAGO possesses a large aperture high-duty cycle. In this work, we present the results of the sensitivity of LAGO small arrays of WCDs for the detection of events like GRB190114C. Also, we extend the study to other TeV galactic emitters, such as pulsar wind nebulas, TeV-halos, and some additional sources with unidentified categorizations. These are interesting sources to study taking advantage of the long-term monitoring capabilities of LAGO. We use a dedicated simulation process: ARTI, a toolkit developed by LAGO for high-energy air showers, MEIGA, a framework to simulate the response of the detectors, and oneDataSim, the new high-performance computing and cloud-based implementation of our simulation framework. [ABSTRACT FROM AUTHOR]

Neutrino-nucleus reaction cross sections on 18O are evaluated by shell-model calculations and compared with those on 16O. Important contributions from Gamow-Teller transitions are noticed for 18O (ν e , e−) 18F in contrary to the case for 16O, where spin-dipole transitions are dominant contributions. Calculated cross sections for 18O (ν e , e−) 18F are shown to be larger than for 16O at low neutrino energies below 20 MeV in natural water with the 0.205% admixture of 18O due to the lower threshold energy (1.66 MeV) for 18O than that for 16O (15.42 MeV). The resulting electron spectra, that is, the cross sections as functions of emitted electron energy T e , are also shown to be quite different, reflecting the different threshold energies. The electron spectra from (ν e , e−) reactions on 18O and 16O in water Cherenkov detectors for supernova neutrino detection are investigated for both the cases with and without the neutrino oscillation and compared with those of the neutrino-electron scattering. It has been shown that the contribution from 18O (0.205% mixture) enhances the rates from 16O by 60% for the case without the oscillation and by 20-30% for the case with the oscillation below T e =20 MeV. For the case with the neutrino oscillation, the event rates for 18O and 16O become comparable to those of the neutrino-electron scattering. However, their rates at low energy (T e < 20 MeV) are much lower than those of the neutrino-electron scattering, which is important for the pointing accuracy to the supernova direction. [ABSTRACT FROM AUTHOR]

The Latin American Giant Observatory (LAGO) is a ground-based observatory studying solar or high-energy astrophysics transient events. LAGO takes advantage of its distributed network of Water Cherenkov Detectors (WCDs) in Latin America as a tool to measure the secondary particle flux reaching the ground. These secondary particles are produced during the interaction between the modulated cosmic rays flux and the atmosphere. The LAGO WCDs are sensitive to secondary charged particles, high energy photons through pair creation and Compton scattering, and even neutrons thanks to, e.g., the deuteration of protons in the water volume. The pulse shape generated by these particles depends on several factors, such as the detector geometry, the water purity, the sensor response, or the reflectivity and diffusivity of the inner coating. Due to the decentralized nature of LAGO, these properties are different for each node. Additionally, the pulse shape depends on the convolution between the response of the central photomultiplier (PMT) to individual photons and the time distribution of the Cherenkov photons reaching the PMT. Typically, a WCD gives pulses with a sharp rise time (∼ 10 ns) and a longer decay time (∼ 70 ns). In this work, the WCD data used is acquired using the original LAGO data-acquisition system that digitizes pulses at a sampling rate of 40 MHz and 10 bits resolution on time windows of 400 ns. Here, we apply unsupervised machine learning techniques to find patterns in the WCDs data and subsequently create groups, through clustering, that can be used to provide particle separation. We use data acquired from an individual WCD, showing that density-based clustering algorithms are suitable for automatic particle separation producing good candidate groups. Improved separation would help LAGO to reconstruct in situ the properties of primary cosmic rays flux. These results open the possibility to deploy machine learning-based models in our distributed detection network for onboard data analysis as an operative prototype, allowing detectors to be installed at very remote sites. [ABSTRACT FROM AUTHOR]

Hyper-Kamiokande is a next-generation neutrino experiment built in Japan and is scheduled to become operational in 2027. It will be the world's largest underground water Cherenkov detector instrumented with three kinds of photomultipliers (PMTs): 20- and 3- inch PMTs, supplemented with multi-PMTs. The physics program of the Hyper-Kamiokande experiment will address the most important, unsolved questions in physics, including CP violation in neutrino oscillations and nucleon decay. An overview of the experiment is presented, emphasizing photo-sensors and electronics. [ABSTRACT FROM AUTHOR]

Abstract In this paper, novel methods are presented to measure the optical properties of the cylindrical water Cherenkov detector with high-reflectivity and diffuse reflection dominated Tyvek material as the inner surface. The mean transmission distance of photons between each reflection in the cylindrical water Cherenkov detector (the mean step length), is constant when there is a sufficient number of photons with random directions in the tank. The time distribution of the photons collected by the photomultiplier tube (PMT) in the water Cherenkov detector is approximately exponential, and the decay factor of the time distribution is determined by the absorption length of photons in the water, the reflectivity of the inner Tyvek surface, the mean step length of photons reflected in the tank, and the ratio of reflective Tyvek area to the total inner surface area. By considering the principles of photon propagation in the water Cherenkov detector, we developed novel methods to measure the water absorption length, Tyvek reflectivity, and mean step length of photons in the tank. The water absorption length and Tyvek reflectivity can be measured simultaneously by changing the height of the water, while the step length and Tyvek reflectivity in air can be measured simultaneously by changing the area of Tyvek, and the mean step length of photons can also be measured even all other parameters unknown. The proposed novel methods are supported by the deduction of formulae and verified by GEANT4 simulations and the prototype experiment. [ABSTRACT FROM AUTHOR]

Current and future neutrino and direct detection dark matter experiments hope to take advantage of improving technologies in photon detection. Many of these detectors are large, monolithic optical detectors that use relatively low-cost, large-area, and efficient photomultiplier tubes (PMTs). A candidate PMT for future experiments is a newly developed prototype Hamamatsu PMT, the R5912-MOD. In this paper we describe measurements made of the single photoelectron time and charge response of the R5912-MOD, as well as detail some direct comparisons to similar PMTs. Most of these measurements were performed on three R5912-MOD PMTs operating at gains close to 1 × 1 0 7 . The transit time spread ( σ ) and the charge peak-to-valley were measured to be on average 680ps and 4.2 respectively. The results of this paper show the R5912-MOD is an excellent candidate for future experiments in several regards, particularly due to its narrow spread in timing. [ABSTRACT FROM AUTHOR]

The Large High Altitude Air Shower Observatory (LHAASO) will be constructed at 4400 m asl in Daocheng, Sichuan Province, with the aim of discovering sources of ultra-high energy cosmic rays and studying cosmic ray physics. The whole array includes 1171 muon detectors (MDs), constituting the largest muon detector array in the world. The special high altitude and wide-field environment requires simple and stable calibration as well as monitoring method of MDs. In this paper, the muon decay events will be selected for calibrating the charge and monitoring the water level of each MD. In the prototype muon detector, the simulation and experiment results reveal that the charge of the decay electron is approximately 0.147 times that of the vertical equivalent muon for a standard MD, and the Q V E M ∕ Q e shows a linear correlation with the water level. [ABSTRACT FROM AUTHOR]

The Latin American Giant Observatory (LAGO) is an international network of water-Cherenkov detectors (WCD) set in different sites across Latin America. On top of the Sierra Negra volcano in Mexico at an altitude of 4530 m, LAGO has completed its first out of three instrumented detector. It consists of a cylindrical water tank with a diameter of 7.3 m and a height of 1 m and a total detection area of 40 m 2 that is sectioned in four equal slices. In this work we present the full calibration procedure of this detector and the initial measurements of stability in rate. We also derive the effective area to gamma-ray bursts for the complete array using the LAGO simulation chain, based on CORSIKA and GEANT4. [ABSTRACT FROM AUTHOR]

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 σ significance in large Gd-doped water Cherenkov detectors with greater than 10-km standoff from a nuclear reactor. [ABSTRACT FROM AUTHOR]

Event reconstruction is a central step in many particle physics experiments, turning detector observables into parameter estimates; for example estimating the energy of an interaction given the sensor readout of a detector. A corresponding likelihood function is often intractable, and approximations need to be constructed. In our work, we first show how the full likelihood for a many-sensor detector can be broken apart into smaller terms, and secondly how we can train neural networks to approximate all terms solely based on forward simulation. Our technique results in a fast, flexible, and close-to-optimal surrogate model proportional to the likelihood and can be used in conjunction with standard inference techniques allowing for a consistent treatment of uncertainties. We illustrate our technique for parameter inference in neutrino telescopes based on maximum likelihood and Bayesian posterior sampling. Given its great flexibility, we also showcase our method for geometry optimization enabling to learn optimal detector designs. Lastly, we apply our method to realistic simulation of a ton-scale water-based liquid scintillator detector. [ABSTRACT FROM AUTHOR]

This paper describes measurements of photosensing units developed for the Outer Detector of Hyper-Kamiokande to increase the effective acceptance of Cherenkov radiation. The photosensing unit consists of a photomultiplier and a wavelength shifting plate optically coupled to it. Plates doped with different fluors and covered by different reflectors were tested using UV LED light sources in air and water. The effects of wavelength shifting fluors, side reflectors, water interface, and shaping of optical coupling are studied. Results of measurements of the light yield and its uniformity are presented. [ABSTRACT FROM AUTHOR]

The results of the study of the near-horizontal muon flux in the zenith angle range of 85-95 degrees are presented. In particular, the so-called albedo muons (atmospheric muons backscattered in the ground to the upper hemisphere are recorded in this range. The data of measurement series performed at the NEVOD-DECOR experimental complex are analyzed for 30 thousand of 'live' time hours. Multiple Coulomb scattering of muons in the ground is simulated by theMonte-Carlo method using various models. The measured muon flux intensity is compared with the simulation results. [ABSTRACT FROM AUTHOR]

We present the performance of a novel neutron detector based on a water Cherenkov detector (WCD) employing pure water and a single photomultiplier tube (PMT). The experiments presented in this work were performed using 241 AmBe and 252 Cf neutron sources in different neutron moderator and shielding configurations. We show that fast neutrons from the 241 AmBe and 241 Cf sources, as well as thermal neutrons from a neutron moderator, despite having different spectral characteristics, produce essentially the same pulse histogram shape. This characteristic pulse-height histogram shapes are recorded as a clear signature of neutrons with energies lower than ≃ 11 MeV . This is verified in different experimental conditions. Our estimation of the neutron detection efficiency is at the level of (15±5)%, for fast neutrons. Since water is the material employed as active volume, the results of this study are of interest for the construction of low cost and large active volume neutron detectors for various applications. Of special importance are those related with space weather phenomena monitoring as well as those for the detection of fissile special nuclear material, including uranium or plutonium. [ABSTRACT FROM AUTHOR]

In the Large High Altitude Air Shower Observatory project, 1221 muon detectors will be built to discriminate cosmic gamma rays from nuclei and between cosmic ray species with energies in 10 13 – 10 18 eV . The muon detector has been designed to meet the physical requirements, according to which two muon detector prototypes have been built at the Yangbajing Cosmic Ray Observatory at the end of 2012 and in October 2014, respectively. The first one has been stably operated for more than 2 years. The performances of the two detectors have been evaluated, especially for position dependence and punch-through effect. In this paper, the design and the performances of the prototype muon detectors are presented. [ABSTRACT FROM AUTHOR]

A search for Supernova Relic Neutrinos ...e's is first conducted via inverse-beta-decay by tagging neutron capture on hydrogen at Super-Kamiokande-IV. The neutron tagging efficiency is determined to be (17.74±0.04stat.±1.05sys.), while the corresponding accidental background probability is (1.06±0.01stat.±0.18sys.). Using 960 days of data, we obtain 13 inverse-beta-decay candidates in the range of ... between 13.3 MeV and 31.3 MeV. All of the observed candidates are attributed to background. Upper limits at 90% C.L. are calculated in the absence of a signal. [ABSTRACT FROM AUTHOR]

The method for reconstructing the cascade curve by the Cherenkov radiation in water of the NEVOD detector with a dense spatial array of optical modules is discussed. Cascades are generated by near-horizontal muons which are separated by the DECOR coordinate detector. The cascade curves and the cascade energy spectrum measured in an ∼8000-hour measurement series are presented. [ABSTRACT FROM AUTHOR]

Due to a very low production rate of electron anti-neutrinos ( ν ̄ e) via nuclear fusion in the Sun, a flux of solar ν ̄ e is unexpected. An appearance of ν ̄ e in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino ( ν e → ν ̄ e ) when neutrino has a finite magnetic moment. In this work, we have searched for solar ν ̄ e in the Super-Kamiokande experiment, using neutron tagging to identify their inverse beta decay signature. We identified 78 ν ̄ e candidates for neutrino energies of 9.3 to 17.3 MeV in 2970.1 live days with a fiducial volume of 22.5 kiloton water (183.0 kton ⋅ year exposure). The energy spectrum has been consistent with background predictions and we thus derived a 90% confidence level upper limit of 4. 7 × 1 0 − 4 on the ν e → ν ̄ e conversion probability in the Sun. We used this result to evaluate the sensitivity of future experiments, notably the Super-Kamiokande Gadolinium (SK-Gd) upgrade. [ABSTRACT FROM AUTHOR]

The results of the analysis of the first experimental data on the energy release of inclined muon groups of cosmic rays in the water Cherenkov detector, obtained at the NEVOD-DECOR complex, are presented. It was found that the average specific energy release in the Cherenkov calorimeter (normalized to the muon densitymeasured by the data of the coordinate detector)weakly depends on the muon density; however, the significant dependence on the zenith angle is observed, which indicates an increase in the average muon energy in groups with an increase in the zenith angle. [ABSTRACT FROM AUTHOR]

Abstract: Procedures and results on hardware-level detector calibration in Super-Kamiokande (SK) are presented in this paper. In particular, we report improvements made in our calibration methods for the experimental phase IV in which new readout electronics have been operating since 2008. The topics are separated into two parts. The first part describes the determination of constants needed to interpret the digitized output of our electronics so that we can obtain physical numbers such as photon counts and their arrival times for each photomultiplier tube (PMT). In this context, we developed an in situ procedure to determine high-voltage settings for PMTs in large detectors like SK, as well as a new method for measuring PMT quantum efficiency and gain in such a detector. The second part describes modeling of the detector in Monte Carlo simulations, including, in particular, the optical properties of the water target and their variability over time. Detailed studies on water quality are also presented. As a result of this work, we have achieved a precision sufficient for physics analyses over a wide energy range (from a few MeV to above 1TeV). For example, charge determination was at the level of 1%, and the timing resolution was 2.1ns at the one-photoelectron charge level and 0.5ns at the 100-photoelectron charge level. [Copyright &y& Elsevier]