Search for astrophysical electron antineutrinos in Super-Kamiokande with 0.01wt% gadolinium-loaded water

We report the first search result for the flux of astrophysical electron antineutrinos for energies O(10) MeV in the gadolinium-loaded Super-Kamiokande (SK) detector. In June 2020, gadolinium was introduced to the ultra-pure water of the SK detector in order to detect neutrons more efficiently. In this new experimental phase, SK-Gd, we can search for electron antineutrinos via inverse beta decay with efficient background rejection and higher signal efficiency thanks to the high efficiency of the neutron tagging technique. In this paper, we report the result for the initial stage of SK-Gd with a $22.5\times552$ $\rm kton\cdot day$ exposure at 0.01% Gd mass concentration. No significant excess over the expected background in the observed events is found for the neutrino energies below 31.3 MeV. Thus, the flux upper limits are placed at the 90% confidence level. The limits and sensitivities are already comparable with the previous SK result with pure-water ($22.5 \times 2970 \rm kton\cdot day$) owing to the enhanced neutron tagging

Construction status and prospects of the Hyper-Kamiokande project

The Hyper-Kamiokande project is a 258-kton Water Cherenkov together with a 1.3-MW high-intensity neutrino beam from the Japan Proton Accelerator Research Complex (J-PARC). The inner detector with 186-kton fiducial volume is viewed by 20-inch photomultiplier tubes (PMTs) and multi-PMT modules, and thereby provides state-of-the-art of Cherenkov ring reconstruction with thresholds in the range of few MeVs. The project is expected to lead to precision neutrino oscillation studies, especially neutrino CP violation, nucleon decay searches, and low energy neutrino astronomy. In 2020, the project was officially approved and construction of the far detector was started at Kamioka. In 2021, the excavation of the access tunnel and initial mass production of the newly developed 20-inch PMTs was also started. In this paper, we present a basic overview of the project and the latest updates on the construction status of the project, which is expected to commence operation in 2027

Prospects for neutrino astrophysics with Hyper-Kamiokande

Hyper-Kamiokande is a multi-purpose next generation neutrino experiment. The detector is a two-layered cylindrical shape ultra-pure water tank, with its height of 64 m and diameter of 71 m. The inner detector will be surrounded by tens of thousands of twenty-inch photosensors and multi-PMT modules to detect water Cherenkov radiation due to the charged particles and provide our fiducial volume of 188 kt. This detection technique is established by Kamiokande and Super-Kamiokande. As the successor of these experiments, Hyper-K will be located deep underground, 600 m below Mt. Tochibora at Kamioka in Japan to reduce cosmic-ray backgrounds. Besides our physics program with accelerator neutrino, atmospheric neutrino and proton decay, neutrino astrophysics is an important research topic for Hyper-K. With its fruitful physics research programs, Hyper-K will play a critical role in the next neutrino physics frontier. It will also provide important information via astrophysical neutrino measurements, i.e., solar neutrino, supernova burst neutrinos and supernova relic neutrino. Here, we will discuss the physics potential of Hyper-K neutrino astrophysics

Performance of SK-Gd's upgraded real-time supernova monitoring system

Among multi-messenger observations of the next galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. On 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd's real-time supernova monitoring system (Abe te al. 2016b) has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on December 13, 2021, and is available through GCN Notices (Barthelmy et al. 2000). When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd's response to a simulated galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd's pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3-7∘ depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view

Measurements of the charge ratio and polarization of cosmic-ray muons with the Super-Kamiokande detector

We present the results of the charge ratio (R) and polarization (Pμ0) measurements using the decay electron events collected from 2008 September to 2022 June by the Super-Kamiokande detector. Because of its underground location and long operation, we performed high precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be R=1.32±0.02 (stat.+syst.) at EμcosθZenith=0.7+0.3−0.2 TeV, where Eμ is the muon energy and θZenith is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while this suggests a tension with the πK model of 1.9σ. We also measured the muon polarization at the production location to be Pμ0=0.52±0.02 (stat.+syst.) at the muon momentum of 0.9+0.6−0.1 TeV/c at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5σ. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near 1 TeV/c. These measurement results are useful to improve the atmospheric neutrino simulations

Composição corporal e exigências energéticas e protéicas de bovinos F1 Limousin x Nelore, não-castrados, alimentados com rações contendo diferentes níveis de concentrado Body composition and energy and protein requirements of F1 Limousin x Nellore bulls fed diets with different concentrate levels

Foram utilizados 50 novilhos F1 Limousin x Nelore inteiros, alocados em dez tratamentos, com cinco níveis de concentrado (25; 37,5; 50; 62,5; e 75%) e duas formas de balanceamento protéico da dieta (uma isoprotéica com 12% de proteína bruta [PB] e outra variando proteína com energia). Avaliaram-se os consumos de matéria seca (MS), matéria orgânica (MO), PB, fibra em detergente neutro (FDN) e nutrientes digestíveis totais (NDT). Após o abate, todas as partes do corpo do animal foram pesadas, amostradas e analisadas para MS, teores de compostos nitrogenados totais e extrato etéreo. Os conteúdos de proteína, gordura e energia retidos no corpo foram estimados por meio de equações de regressão do logaritmo do conteúdo corporal de proteína, gordura ou energia, em função do logaritmo do peso de corpo vazio (PCVZ). As exigências líquidas de proteína e energia, para ganho de 1 kg de PCVZ foram obtidas a partir da equação Y = b. 10ª. Xb-1, sendo a e b o intercepto e o coeficiente de regressão, respectivamente, das equações de predição dos conteúdos corporais de proteína ou energia. A exigência líquida de energia para mantença (ELm) foi estimada como o anti-log do intercepto da equação obtida pela regressão linear entre o logaritmo da produção de calor e o consumo de energia metabolizável. A forma de balanceamento da dieta não influenciou os consumos dos nutrientes. O consumo de MS, em kg/dia, não foi influenciado pelo nível de concentrado (NC), apresentando média de 7,39 kg/dia. O NC das dietas não influenciou o consumo de MO (7,08 kg/dia). Com o aumento do NC, o consumo de FDN reduziu e o de NDT aumentou linearmente. Nas dietas com níveis de proteína variados, o consumo de PB aumentou linearmente. Já as dietas isoprotéicas não foram influenciadas pelo NC, apresentando média de consumo de PB de 0,89 kg/dia. As exigências de energia líquida para ganho de peso de bovinos F1 Limousin x Nelore não-castrados, em Mcal/kg, podem ser obtidas pela equação: ELg = 0,038 x PCVZ0,75 x GDPCVZ0,9896. A ELm para estes animais foi de 76,36 kcal/PCVZ0,75. Foi obtida a seguinte equação para estimativa da proteína retida (PR), em g/dia, em função do ganho de PV em jejum (GPVJ), em kg/dia: PR = 174,14524 x GPVJ.<br>Fifty F1 Limousin x Nellore bulls were allotted to ten treatments, with five concentrate levels (25, 37.5, 50, 62.5, and 75%) and two diet protein balance methods (one isoprotein and the other changing protein as diet energy changed). The intake of dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF) and total digestible nutrients (TDN) were determined. After the slaughter, all animal body parts were weighed, sampled and DM, total nitrogen and ether extract concentrations were determined. Protein, fat and energy contents retained in the body were estimated by regression equations of logarithm of protein, fat or energy body content, as a function of logarithm of empty body weight (EBW). By deriving the prediction equations of body content of protein, fat, or energy, as a function of the logarithm of EBW, the net requirements of protein and energy, for gain of 1 kg EBW, were determined. The deriving equation was Y = b. 10ª. Xb-1, where a and b were the intercept and regression coefficient, respectively, of the prediction equations of protein or energy body contents. Net energy requirement for maintenance (NEm) was estimated as the intercept anti-log of the equation obtained by the linear regression of the logarithm of heat production and the metabolizable energy intake. The diet balance methods did not influence the nutrients intakes. The DM intake (DMI) was not affected by the concentrate level (CL), with means of 7.39 kg/day. Dietary CL did not affect OM intake (7.08 kg/day). Increasing CL and NDF intake showed a linear decrease and TDN intake showed a linear increase. In diets with variable protein levels, CP intake increased linearly. Isoprotein diets were not affected by the CL (0.89 kg/day). Net energy requirement for weight gain of F1 Limousin x Nellore bulls, in Mcal/kg, can be obtained by the equation: NEg = 0.038 x EBW0.75 x EBW gain0.9896. The NEm for these animals was 76.36 kcal/EBW0.75. The following equation was obtained to estimate the retained protein (RP), in g/day, as a function of EBW gain, in kg/day: RP = 174.14524 x EBW gain