arXiv subjects

D. Samudio

Publications and source records attributed to D. Samudio.

10 recordsLinked to original sources

arXiv2026

Search for proton decay into a single charged antilepton and a massless invisible particle using the full pure water data set of Super-Kamiokande

A search for proton decay via $p\rightarrow l^{+}+X$, where $l^{+}$ is a positively charged lepton and $X$ is an invisible, massless, neutral particle, was performed using a 401~kton$\cdot$years exposure representing the entire pure water phase of Super-Kamiokande. No significant indication of a proton decay was observed beyond the expected atmospheric neutrino background. Lower limits on the partial lifetime of the proton were set to at $1.72\times10^{33}$ years for $p\rightarrow e^{+}+X$ and $0.61\times10^{33}$ years for $p\rightarrow \mu^{+}+X$ at the $90\%$ confidence level. These results improve on previous limits by factors of 2 and 1.5, respectively.

hep-ex↗

arXiv2026

TeV-scale neutrino cross-section measurement using upward through-going muons in Super-Kamiokande

Neutrinos provide a unique probe of both particle physics and the high-energy universe, traversing astronomical distances with minimal interaction. Their charged-current scattering cross section encodes fundamental information about weak interactions and nucleon structure across a vast energy range, yet measurements at TeV energies remain sparse. Here we report the first determination of the flux-averaged muon neutrino and anti-neutrino charged-current total cross section using high-energy atmospheric neutrinos observed in Super-Kamiokande. Using 3989 upward through-going muon events collected over 4269 days, together with a Bayesian fit to atmospheric flux and detector simulations, we measure the flux-averaged charged-current cross section in the 500-5000 GeV range to be $\sigma/E_\nu=(0.51\pm 0.11)\times 10^{-38}$ cm$^2$GeV$^{-1}$, with the highest precision to date in the TeV regime. Our results are consistent with accelerator-based measurements at lower energies and collider-based measurements at higher energies, bridging a critical gap between accelerator experiments and neutrino telescopes. This work demonstrates the capability of large underground detectors to perform precision cross-section measurements with atmospheric neutrinos, opening a new window for probing Standard Model physics and potential new physics searches at multi-TeV energies.

hep-ex↗

arXiv2026

Search for proton decay via $p \to e^{+}\pi^{0}\pi^{0}$ and $p \to \mu^{+}\pi^{0}\pi^{0}$ in 0.401 megaton-years exposure of Super-Kamiokande I-V

We searched for proton decay via $p \to e^{+}\pi^{0}\pi^{0}$ and $p \to \mu^{+}\pi^{0}\pi^{0}$ in 0.401 megaton-years of data collected in all pure water detector phases of Super-Kamiokande (SK) I-V. A theoretical study predicts proton decay rates without assuming a particular grand unified theory and suggests that three-body proton decays involving two pions can have decay rates comparable to those of $p \to e^{+}\pi^{0}$ and $p \to \mu^{+}\pi^{0}$. This is the first search for proton decay into a charged anti-lepton and two neutral pions in SK. One data candidate event was found for each of the two decay modes, which is consistent with the expected atmospheric neutrino background. We set lower limits on the lifetime of $\tau/B(p \to e^{+}\pi^{0}\pi^{0}) > 7.2 \times 10^{33}$ years and $\tau/B(p \to \mu^{+}\pi^{0}\pi^{0}) > 4.5 \times 10^{33}$ years at 90 $\%$ confidence level. These limits are more than one order of magnitude higher than those of the previous experiment.

hep-ex↗

arXiv2026

Development of Faster and More Accurate Supernova Localization at Super-Kamiokande

The next nearby core-collapse supernova (SN) promises to yield a treasure of scientific information through multi-messenger astronomy. Early observations of the shock breakout (SBO) emissions are especially critical to understand the SN explosive mechanism as well as the properties of the progenitor star. Neutrino observatories are able to provide an early alert of a SN before the arrival of the SBO radiation. Super-Kamiokande (SK) has the unique capability to independently reconstruct an accurate SN pointing direction as part of its real-time monitoring system, ``SNWATCH.'' Recent upgrades to SK by adding gadolinium (Gd) to the detection volume have been accompanied by efforts to improve the speed and accuracy of SN direction reconstruction. A new, novel HEALPix-based approach (``HP-Fitter'') can calculate the SN direction from the reconstructed burst event directions in less than one second. As well, the previous maximum-likelihood direction fitter (``ML-Fitter'') was upgraded by incorporating event information from Gd neutron-capture as well as using the HP-Fitter for the initial fit parameters and from code refactoring and optimization. The improved ML-Fitter has better angular resolution but direction reconstruction time is $\mathcal{O}$(sec). Together with improvements in burst detection and event reconstruction times, SNWATCH is now able to generate an SN alert with pointing information in about 90 seconds. These upgrades have been implemented at SK and integrated into a new automated system to provide GCN notices.

astro-ph.HE↗

arXiv2025

Measurement of the solar neutrino interaction rate below 3.49 MeV in Super-Kamiokande-IV

Super-Kamiokande (SK) has observed $^{8}\text{B}$ solar neutrino elastic scattering at recoil electron kinetic energies ($E_{\text{kin}}$) as low as 3.49 MeV to study neutrino flavor conversion within the Sun. At SK-observable energies, these conversions are dominated by the Mikheyev-Smirnov-Wolfenstein (MSW) effect. An upturn in the electron neutrino survival probability in which vacuum neutrino oscillations become dominant is predicted to occur at lower energies, but radioactive background increases exponentially with decreasing energy. New machine learning approaches provide substantial background reduction below 3.49 MeV such that statistical extraction of solar neutrino interactions becomes feasible. This article presents an analysis of the solar neutrino interaction rate at $E_{\text{kin}}$ < 3.49 MeV with the full SK-IV period, using data from a wideband intelligent trigger when available and with a boosted decision tree for event selection. A solar neutrino signal is observed between 2.99 MeV < $E_{\text{kin}}$ < 3.49 MeV with $2.76\sigma$ significance and a data to unoscillated Monte Carlo ratio of $0.307^{+0.112}_{-0.111}$. These additional low-energy data have a negligible effect on the $1\sigma$ intervals of the fits to the solar neutrino energy spectrum but have a noticeable effect on the best fit when using the exponential parametrization.

hep-ex↗

arXiv2025

Search for Diffuse Supernova Neutrino Background with 956.2 days of Super-Kamiokande Gadolinium Dataset

We report the search result for the Diffuse Supernova Neutrino Background (DSNB) in neutrino energies beyond 9.3~MeV in the gadolinium-loaded Super-Kamiokande (SK) detector with $22,500\times956.2$$~\rm m^3\cdot day$ exposure. %$22.5{\rm k}\times956.2$$~\rm m^3\cdot day$ exposure. Starting in the summer of 2020, SK introduced 0.01\% gadolinium (Gd) by mass into its ultra-pure water to enhance the neutron capture signal, termed the SK-VI phase. This was followed by a 0.03\% Gd-loading in 2022, a phase referred to as SK-VII. We then conducted a DSNB search using 552.2~days of SK-VI data and 404.0~days of SK-VII data through September 2023. This analysis includes several new features, such as two new machine-learning neutron detection algorithms with Gd, an improved atmospheric background reduction technique, and two parallel statistical approaches. No significant excess over background predictions was found in a DSNB spectrum-independent analysis, and 90\% C.L. upper limits on the astrophysical electron anti-neutrino flux were set. Additionally, a spectral fitting result exhibited a $\sim1.2\sigma$ disagreement with a null DSNB hypothesis, comparable to a previous result from 5823~days of all SK pure water phases.

astro-ph.HE↗

arXiv2025

Search for nucleon decay via $p\rightarrow\nu\pi^{+}$ and $n\rightarrow\nu\pi^{0}$ in 0.484 Mton-year of Super-Kamiokande data

We present the results of searches for nucleon decays via $p\rightarrow\nu\pi^{+}$ and $n\rightarrow\nu\pi^{0}$ using a 0.484 Mt$\cdot$yr exposure of Super-Kamiokande I-V data covering the entire pure water phase of the experiment. Various improvements on the previous 2014 nucleon decay search, which used an exposure of 0.173 Mt$\cdot$yr, are incorporated. The physics models related to pion production and nuclear interaction are refined with external data, and a more comprehensive set of systematic uncertainties, now including those associated with the atmospheric neutrino flux and pion production channels is considered. Also, the fiducial volume has been expanded by 21\%. No significant indication of a nucleon decay signal is found beyond the expected background. Lower bounds on the nucleon partial lifetimes are determined to be $3.5\times10^{32}$~yr for $p\rightarrow\nu\pi^{+}$ and $1.4\times10^{33}$~yr for $n\rightarrow\nu\pi^{0}$ at 90\% confidence level.

hep-ex↗

arXiv2025

Measurement of the branching ratio of $\mathrm{^{16}N}$, $\mathrm{^{15}C}$, $\mathrm{^{12}B}$, and $\mathrm{^{13}B}$ isotopes through the nuclear muon capture reaction in the Super-Kamiokande detector

The Super-Kamiokande detector has measured solar neutrinos for more than $25$ years. The sensitivity for solar neutrino measurement is limited by the uncertainties of energy scale and background modeling. Decays of unstable isotopes with relatively long half-lives through nuclear muon capture, such as $\mathrm{^{16}N}$, $\mathrm{^{15}C}$, $\mathrm{^{12}B}$ and $\mathrm{^{13}B}$, are detected as background events for solar neutrino observations. In this study, we developed a method to form a pair of stopping muon and decay candidate events and evaluated the production rates of such unstable isotopes. We then measured their branching ratios considering both their production rates and the estimated number of nuclear muon capture processes as $Br(\mathrm{^{16}N})=(9.0 \pm 0.1)\%$, $Br(\mathrm{^{15}C})=(0.6\pm0.1)\%$, $Br(\mathrm{^{12}B})=(0.98 \pm 0.18)\%$, $Br(\mathrm{^{13}B})=(0.14 \pm 0.12)\%$, respectively. The result for $\mathrm{^{16}N}$ has world-leading precision at present and the results for $\mathrm{^{15}C}$, $\mathrm{^{12}B}$, and $\mathrm{^{13}B}$ are the first branching ratio measurements for those isotopes.

nucl-ex↗

arXiv2025

Search for neutron decay into an antineutrino and a neutral kaon in 0.401 megaton-years exposure of Super-Kamiokande

We searched for bound neutron decay via $n\to\bar{\nu}+K^0$ predicted by the Grand Unified Theories in 0.401 Mton$\cdot$years exposure of all pure water phases in the Super-Kamiokande detector. About 4.4 times more data than in the previous search have been analyzed by a new method including a spectrum fit to kaon invariant mass distributions. No significant data excess has been observed in the signal regions. As a result of this analysis, we set a lower limit of $7.8\times10^{32}$ years on the neutron lifetime at a 90% confidence level.

hep-ex↗

arXiv2025

Measurement of neutron production in atmospheric neutrino interactions at Super-Kamiokande

We present measurements of total neutron production from atmospheric neutrino interactions in water, analyzed as a function of electron-equivalent visible energy over a range of 30 MeV to 10 GeV. These results are based on 4,270 days of data collected by Super-Kamiokande, including 564 days with 0.011 wt\% gadolinium added to enhance neutron detection. Neutron signal selection is based on a neural network trained on simulation, with its performance validated using an Am/Be neutron point source. The measurements are compared to predictions from neutrino event generators combined with various hadron-nucleus interaction models, which include an intranuclear cascade model and a nuclear de-excitation model. We observe significant variations in the predictions depending on the choice of hadron-nucleus interaction model. We discuss key factors that contribute to describing our data, such as in-medium effects in the intranuclear cascade and the accuracy of statistical evaporation modeling.

hep-ex↗