arXiv subjects

K. Abe

Publications and source records attributed to K. Abe.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting EBL Constraints from Gamma-Ray Observations: A Critical Assessment and Methodological Improvements

The extragalactic background light (EBL), ranging from the infrared to the ultraviolet bands, is the second most intense photon field in the universe, surpassed only by the cosmic microwave background (CMB). It is primarily generated by starlight in galaxies, either directly or through absorption by dust and re-emission at longer wavelengths. Very high energy (VHE, $E$ > $100\,$GeV) photons can be absorbed via $\gamma \gamma$ interactions with the EBL during their propagation across cosmological distances, providing an indirect method to probe the EBL by studying its impact on the energy spectra of distant VHE sources. This paper examines the robustness of EBL constraints derived from gamma-ray data, critically assessing the assumptions made in previous studies about the intrinsic source spectra, the uncertainties of the observations and the validity of the analysis tools. We find that earlier studies likely underestimated the uncertainties in the EBL intensity constraints, underscoring the need to account for systematic uncertainties comprehensively. By employing a Monte Carlo (MC) simulation and a plausible model for unknown systematic errors, we compute more realistic uncertainties. Additionally, we discuss possible alternatives to set EBL constraints, relaxing the assumptions on the intrinsic spectra of gamma-ray sources, with the goal of achieving more robust constraints.

astro-ph.HE↗

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

First Measurement of Solar Neutrinos through Elastic Neutrino-Electron Scattering at the keV Scale

We report on the first measurement of low-energy solar neutrinos through elastic neutrino-electron scattering in a dark matter experiment, establishing the lowest energy threshold for any neutrino detection to date. The measurement utilizes data from the first two science runs of XENONnT, corresponding to an exposure of 2.46 t $\cdot$ y, and covers electron recoil energies between 1 keV and 140 keV, providing sensitivity to solar neutrinos with energies down to 17 keV. We reject the background-only hypothesis with a statistical significance of $5.0\sigma$ and measure a solar $pp$ neutrino flux of $(10.2 \pm 2.0) \times 10^{10}$ cm$^{-2}$ s$^{-1}$. The result is larger, but statistically consistent with the previous measurement by Borexino at $1.9\sigma$. Together with recent observations of coherent elastic neutrino-nucleus scattering of $^8$B solar neutrinos in XENONnT and other liquid-xenon time projection chambers, these results demonstrate the growing potential of liquid xenon detectors for neutrino physics down to the keV-scale and represent an important milestone towards a next-generation multipurpose observatory.

hep-ex↗

arXiv2026

Search for Magnetic and Spin-Independent Inelastic Dark Matter with XENONnT

We present a search for Magnetic and Spin-Independent inelastic Dark Matter using 2.1 tonne-years of data from the XENONnT experiment. We consider both single- and double-site event topologies, targeting the unique signature of an initial nuclear recoil followed by a delayed de-excitation photon. To suppress backgrounds, we introduce novel directional and kinematic selections based on the inferred speed and direction of the excited dark matter particle between the scatter and decay sites. We find that the collected data are consistent with background expectations, and report 90% C.L. upper limits for both models across the GeV/c2-TeV/c2 mass range.

hep-ex↗

arXiv2026

Constraints on the VHE counterpart of two binary black hole mergers observed by the MAGIC and CTAO LST-1 telescopes

We present very-high-energy gamma-ray observations of two binary black hole merger candidates, GW240615_113620 and GW241125_010116, performed with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the first Large-Sized Telescope of the Cherenkov Telescope Array Observatory's (CTAO LST-1). GW240615_113620 was the best localized event of the fourth observing run of the LIGO-Virgo-KAGRA gravitational waves interferometers. GW241125_010116 was temporally and spatially coincident with a sub-threshold short-duration burst detected with the Swift-Burst Alert Telescope (BAT), the Swift-X-Ray Telescope (XRT) and the Einstein Probe Follow-up X-ray Telescope (FXT). We observed the two events in stereoscopic mode, taking advantage of the improved sensitivity of joint MAGIC+LST-1 observations. No detection was achieved in the GeV-TeV gamma-ray band for any of the two sources. The unfavourable observing conditions of both events posed a challenge for a standard analysis and therefore a non standard analysis was necessary for both objects. Owing to the small localization area and the association with a GRB-like burst respectively, these events represented an unprecedented opportunity to study in details the electromagnetic emission from binary black holes merger events and, in particular, we discussed two theoretical models that predict a detectable gamma-ray emission and the possible future applications.

astro-ph.HE↗

arXiv2026

First double-differential measurement of pionless charged-current muon neutrino interactions using kinematic imbalance observables on carbon and oxygen with the T2K experiment

We report the first measurement of muon-neutrino charged-current cross section as a function of kinematic imbalance (KI) observables on oxygen with no pions and at least one proton in the final state, using the T2K ND280 detector. The cross section is extracted simultaneously for carbon and oxygen targets and double-differentially as a function of several KI observables, providing new insight into the modeling of nuclear effects. This joint measurement offers direct sensitivity to the correlations between two targets, a key ingredient for reducing systematic uncertainties in neutrino oscillation experiments that employ multiple target nuclei, such as T2K and Hyper-Kamiokande. Comparisons with predictions from widely used neutrino event generators show that none of the models fully describe the data across all regions of measured phase space. These results highlight possible directions where improvements in neutrino-nucleus interaction modeling are needed for current and future neutrino oscillation experiments.

hep-ex↗

arXiv2026

Signal selection and model-independent extraction of pionless charged-current muon neutrino cross section using double-differential kinematic imbalance observables on carbon and oxygen with the T2K experiment

We present the first joint measurement of muon neutrino CC$0\pi Np$ interactions on carbon and oxygen targets, in two double-differential kinematic imbalance (KI) observable spaces, $\delta p_{T}$-$\delta \alpha_{T}$ and $p_{N}$-$\cos\theta_{\mu}$. The measurement employs the ND280 detector of the T2K experiment and includes a detailed description of the event selection used to define signal and control regions, the evaluation of systematic uncertainties, and the signal extraction procedure, together with validation studies supporting a robust cross-section measurement. The results of this analysis indicate that current neutrino-nucleus interaction models do not adequately describe the data, and demonstrate the strong discriminating power of KI observables. This measurement highlights the need for improved theoretical nuclear modeling within neutrino interaction generators to achieve increased precision in neutrino oscillation measurements.

hep-ex↗

arXiv2026

A New High-Intensity Source for Ultracold Neutrons

The TRIUMF UltraCold Advanced Neutron (TUCAN) collaboration has completed a new superthermal source for ultracold neutrons (UCNs) at TRIUMF. It uses neutrons from a spallation target driven by TRIUMF's %520-MeV main cyclotron. Heavy water and liquid deuterium serve as neutron moderators, and inelastic scattering inside superfluid $^4$He at around \qty{1.1}{\kelvin} slows the neutrons down to become ultracold. During commissioning runs with the completed source, including the deuterium moderator, up to $1.47(2)\times 10^7$ UCNs were detected in the experimental area after irradiating the target and accumulating UCNs in the source for \qty{60}{\second}. Up to \qty{6.75(3)e5} UCN/s were detected during continuous operation, more than at any other source in the world.

physics.ins-det↗

arXiv2026

Direct Measurement of the $^{212}\mathrm{Pb}$ and $^{214}\mathrm{Pb}$ $\beta$ Decay Branching Ratios with the XENONnT Experiment

We present precision measurements of $^{212}\mathrm{Pb}$ and $^{214}\mathrm{Pb}$ $\beta$ decay branching ratios using $^{220}\mathrm{Rn}$ and $^{222}\mathrm{Rn}$ calibration data from the XENONnT detector, a dual-phase liquid xenon time projection chamber. Characterizing these isotopes is critical, as they lead to significant low-energy backgrounds in rare-event searches. We report ground-state branching ratios of $(14.75 \pm 0.20(\mathrm{stat}) ^{+0.14}_{-0.40}(\mathrm{sys}))\%$ for $^{212}\mathrm{Pb}$ and $(9.8 \pm 0.3(\mathrm{stat}) ^{+0.8}_{-0.2}(\mathrm{sys}))\%$ for $^{214}\mathrm{Pb}$, providing the most precise direct measurements of these transitions to date. These results contribute to enhancing background modeling for dark matter and neutrino experiments, improving sensitivity to solar neutrinos and physics beyond the Standard Model.

nucl-ex↗

arXiv2026

Constraining Neutrino Interaction Uncertainties for Neutrino Oscillation Measurements at the T2K Experiment

In the context of neutrino oscillation measurements from the T2K experiment, the off-axis near detector ND280 plays a crucial role in constraining the incoming neutrino flux and neutrino-nucleus interaction cross sections. The result is a robust control over systematic uncertainties in the fit of neutrino oscillation parameters to the data at the T2K far detector, Super-Kamiokande. This paper details the methodology and results of these constraints in the context of the latest neutrino oscillation analysis from T2K. It describes how a new neutrino cross-section model and refined flux prediction are parameterized and fit to data in new ND280 event selections. Additionally, this work reports the results of extensive robustness studies, including fits with alternative interaction models, consistency checks against publicly available cross-section measurements, and \textit{p}-value evaluations, to demonstrate the reliability and robustness of our methodology. Finally, we present a sensitivity study demonstrating that the upgraded ND280, with improved acceptance and a lower hadron threshold, may enhance future constraints and further reduce systematic uncertainties in oscillation measurements.

hep-ex↗

arXiv2026

Detection of the distant quasar OP 313 with the first Large-Sized Telescope of CTAO

In December 2023, the Large-Sized Telescope prototype (LST-1) detected for the first time VHE $\gamma$-ray emission from the FSRQ OP~313 becoming the furthest blazar ever observed at VHE with z=0.997. We aim to characterize the $\gamma$-ray emission of OP 313 during this flare, comparing it with its average emission state in order to understand the processes leading to this detection. Its remarkable distance also enables studies on the Extragalactic Background Light (EBL), with the goal of evaluating the attenuation of VHE $\gamma$-ray photons. We characterize the $\gamma$-ray emission during the flare in December 2023 and the low emission state observed in January 2024 thanks to the LST-1 and MAGIC data and quasi-simultaneous \textit{Fermi}-LAT observations. This dataset also enables us to evaluate the EBL attenuation by systematically exploring the EBL intensity over the $\gamma$-ray spectrum. Finally, we study the multi-wavelength emission and interpret the broadband spectral energy distribution (SED) within blazar radiative models including the thermal contributions from the accretion disc, dusty torus and broad line region. We also characterize the flare brightness in the high-energy (HE, $E>100$~MeV) $\gamma$-ray band, that was found to be a factor 50 above the average emission seen by \textit{Fermi}-LAT. The HE and VHE observations allow us to set constrains to the EBL density. Finally, thanks to the extensive multi-wavelength campaign organized, we are able to construct and model the broadband SED of OP~313 within the framework of a two-zone leptonic model where the $\gamma$-ray emission is produced via inverse-Compton scattering of the broad line region, accretion disk and dusty torus photon fields. However the dominant external photon field remains unknown, as several combinations are able to successfully explain the $\gamma$-ray emission observed.

astro-ph.HE↗

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

Long-term study of the gamma-ray emission of Cygnus X-3 with MAGIC and Fermi-LAT

Cygnus X-3 is a microquasar composed of a compact object of unknown nature closely orbiting around a Wolf-Rayet star. The particularities of this source make it a unique case among microquasars. This fact, together with its recent establishment as a PeV particle accelerator, makes Cygnus X-3 a very interesting target for the investigation of the physical processes leading to gamma-ray production. In this work, the TeV and GeV gamma-ray emission of Cygnus X-3 is studied in order to determine its origin and constrain the properties of the system. For that purpose, a point-like analysis of 130 h of data taken with the MAGIC telescopes between 2013 and 2024 was performed, which represents the largest available sample for Cygnus X-3 at $\sim$TeV energies. Additionally, contemporary data from Fermi-LAT were also analysed to better contextualize the MAGIC observations. For a more detailed investigation of the source physics, the data were divided into three subsets according to the flaring state of the source and orbital phase. No significant detection of Cygnus X-3 is found between 0.1 and 7 TeV for any of the datasets, and differential and integral flux upper limits are reported over the long-term monitoring of the source. The Fermi-LAT fluxes can be considered compatible with previous results, taking into account the different data samples used across studies. The MAGIC upper limits presented in this work represent the most constraining ones up to date at $\sim$TeV energies. An eventual detection of Cygnus X-3 at these energies would significantly constrain the source properties, and is not unreasonable to expect given that the source has already been detected in both the GeV and PeV regimes during flaring states. Further observations of Cygnus X-3 at energies above tens of GeV would be valuable for this purpose.

astro-ph.HE↗

arXiv2026

The January 2010 flare of Mrk421: Insights from a stochastic acceleration model

Mrk421 displayed its highest flux state ever observed in February of 2010 with very high TeV fluxes and interesting cross-band correlations and a spectral energy distribution (SED) evolution not entirely consistent with the standard single zone leptonic synchrotron self-Compton model. The source was already in a high state in January 2010 and displayed strong variability in the days preceding the highest state. We study the temporal evolution of the spectra in January to extract information about the particle dynamics and the physical properties of the emission region. We build up on the temporal variability and correlations studied in the previous work (MAGIC collaboration - Abe et al. 2025) and attempt to improve the SED model fits with a physics oriented approach. The multi-wavelength data was processed and the SEDs were fit using JetSeT. The SED evolution and cross band correlations were modelled using leptonic log-parabola with a low energy power-law branch (LPPL) and pile-up distributions that are predicted in a stochastic acceleration scenario. A simplified temporal evolution model was developed and fit to the SEDs and the resulting trends and phenomenology were characterised in context of theoretical literature. An expanding emission region model was also tested. We find the spectral variability to be well in agreement with stochastic acceleration. Our analysis suggests that the standard LPPL distribution develops a Maxwellian pile-up component at the transition from acceleration to cooling dominated phase on 3 nights in the dataset, as also hinted by the very-high energy and X-ray light curves. The resulting phenomenology of our sequential snapshot evolution SED model agrees well with theoretical and numerical simulation studies on temporal evolution using the diffusion equation approach.

astro-ph.HE↗

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↗

arXiv2026

Probing the Solar $^8$B Neutrino Fog with XENONnT

We report a 3.3 $\sigma$ measurement of coherent elastic neutrino-nucleus scattering from solar $^8$B neutrinos using a 6.77 t$\times$yr exposure from the XENONnT experiment, inferring a solar $^8$B neutrino flux of $(5_{-2}^{+3})\times 10^6\,\mathrm{cm}^{-2}\mathrm{s}^{-1}$, consistent with previous measurements. In the presence of the $^8$B "neutrino fog", we find no evidence for light dark matter, and observe diminishing returns in sensitivity with increasing exposure. A 93% increase in exposure from the previous search improves the median sensitivity to the nucleon scattering cross section for a 5 GeV/$c^2$ spin-independent weakly interacting massive particle by 10%. The dataset was also used to measure the weak mixing angle at $\sim$ 0.02 GeV/$c$ momentum transfer and constrain physics beyond the Standard Model.

hep-ex↗

arXiv2026

Extreme Blazars Observed with MAGIC: Second Catalog Release

Extremely high-peaked BL Lac objects - also named extreme blazars - are among the most energetic and persistent extragalactic accelerators in the Universe, defined by a synchrotron emission peaking above $10^{17}$ Hz in X-rays. Such emission is then reprocessed and produces radiation extending deeply into very-high-energy (VHE, energy E>100 GeV) gamma rays. Observations in this energy band - optimally investigated by the Imaging Air-Shower Cherenkov telescopes - are crucial for probing the physical processes that drive their extreme behavior. This study extends our investigation of extreme blazars in the VHE gamma-ray range, providing a second new mini-catalog of sources observed by the MAGIC telescopes. We report on the monitoring of seven targets between 2017 and 2025, including four newly observed sources and three that have been part of long-term observation campaigns, for a total of approximately 338 hours of observations. The analysis of MAGIC data reveals two new VHE detections of extreme blazars, along with three additional sources showing hints of VHE emission. Joint observations of MAGIC and the first Large-Sized Telescope (LST-1) also confirmed a new VHE extreme blazar. Our results are complemented by simultaneous multiwavelength observations in other energy bands, including optical-UV, X-rays, and high-energy gamma rays (100 MeV<E<100 GeV). We confirm typical behavior of extreme blazars, such as a modest variability and a ``harder-when-brighter'' trend in X-rays across the sample. This new set increases the population of extreme blazars and their broadband analysis confirms the physical properties of these extreme sources.

astro-ph.HE↗