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This work examines atmospheric effects on cosmic ray counts observed by a Water‐Cherenkov detector at the Argentine Antarctic Marambio Station. We analyze the influence of ground‐level barometric pressure and geopotential height at various pressure levels on daily particle rates, finding the strongest association at 100 hPa, linked to effective muon production. This relationship persists across low and high frequencies relative to the annual wave. Using barometric pressure and 100 hPa geopotential height, we developed a multiple linear regression model to describe atmospheric variations in cosmic ray flux, adjusted by meteorological seasons. By inverting the model, we estimate 100 hPa geopotential height from surface observations and validate against ERA5 reanalysis. The model performs best in spring, with reduced precision in other seasons. Further improvements in the signal‐to‐noise ratio could enhance model performance. Even with these considerations, this approach offers a practical and cost‐effective method to track 100 hPa geopotential height variability in Antarctica through daily surface observations from Water‐Cherenkov detectors, providing an important resource for Antarctic atmospheric studies. Plain Language Summary In this study, we used a detector in Antarctica to measure cosmic rays and investigate how they relate to atmospheric changes. We observed a strong connection between cosmic ray levels and the atmospheric pressure around 15 km above the surface. Based on this, we developed a model to estimate this variable using ground‐level data. This approach potentially provides a practical and cost‐effective method for monitoring the lower stratosphere in Antarctica, a region of particular interest due to its unique and dynamic behavior, which plays a critical role in global atmospheric processes. Key Points Atmospheric effects on cosmic ray counting in Antarctica Water‐Cherenkov detector enables multidisciplinary research, studying cosmic rays in relation to space weather and atmospheric dynamics Monitoring geopotential height variability at 100 hPa using ground‐level cosmic ray data

The Neutrinos Angra Experiment, a water-based Cherenkov detector, is located at the Angra dos Reis nuclear power plant in Brazil. Designed to detect electron antineutrinos produced in the nuclear reactor, the primary objective of the experiment is to demonstrate the feasibility of monitoring reactor activity using an antineutrino detector. This effort aligns with the International Atomic Energy Agency (IAEA) program to identify potential and novel technologies applicable to nonproliferation safeguards. Operating on the surface presents challenges such as high noise rates, necessitating the development of very sensitive, yet small-scale detectors. These conditions make the Angra experiment an excellent platform for both developing the application and gaining expertise in new technologies and analysis methods. The detector employs a water-based target doped with gadolinium to enhance its sensitivity to antineutrinos. In this work, we describe the main features of the detector and the electronics chain, including front-end and data acquisition components. We detail the data acquisition strategies and the methodologies applied for signal processing and event selection. Preliminary physics results suggest that the detector can reliably monitor reactor operations by detecting the inverse beta decay induced by electron antineutrinos from the reactor.

The Latin American Giant Observatory (LAGO) is a ground-based extended cosmic rays observatory designed to study transient astrophysical events, the role of the atmosphere on the formation of secondary particles, and space-weather-related phenomena. With the use of a network of Water Cherenkov Detectors (WCDs), LAGO measures the secondary particle flux, a consequence of the interaction of astroparticles impinging on the atmosphere of Earth. This flux can be grouped into three distinct basic constituents: electromagnetic, muonic, and hadronic components. When a particle enters a WCD, it generates a measurable signal characterized by unique features correlating to the particle’s type and the detector’s specific response. The resulting charge histograms from these signals provide valuable insights into the flux of primary astroparticles and their key characteristics. However, these data are insufficient to effectively distinguish between the contributions of different secondary particles. In this work, we extend our previous research by using detailed simulations of the expected atmospheric response to the primary flux and the corresponding response of our WCDs to atmospheric radiation. This dataset, which was created through the combination of the outputs of the ARTI and Meiga simulation frameworks, simulated the expected WCD signals produced by the flux of secondary particles during one day at the LAGO site in Bariloche, Argentina, situated at 865 m above sea level. This was achieved by analyzing the real-time magnetospheric and local atmospheric conditions for February and March of 2012, where the resultant atmospheric secondary-particle flux was integrated into a specific Meiga application featuring a comprehensive Geant4 model of the WCD at this LAGO location. The final output was modified for effective integration into our machine-learning pipeline. With an implementation of Ordering Points to Identify the Clustering Structure (OPTICS), a density-based clustering algorithm used to identify patterns in data collected by a single WCD, we have further refined our approach to implement a method that categorizes particle groups using advanced unsupervised machine learning techniques. This allowed for the differentiation among particle types and utilized the detector’s nuanced response to each, thus pinpointing the principal contributors within each group. Our analysis has demonstrated that applying our enhanced methodology can accurately identify the originating particles with a high degree of confidence on a single-pulse basis, highlighting its precision and reliability. These promising results suggest the feasibility of future implementations of machine-leaning-based models throughout LAGO’s distributed detection network and other astroparticle observatories for semi-automated, onboard and real-time data analysis.

Cherenkov radiation is a widely used detection mechanism in high-energy and astroparticle physics experiments, particularly in water-based detectors operated by leading cosmic-ray observatories. Its popularity stems from its robustness, cost-effectiveness, and high detection efficiency across a broad range of environmental conditions. In this study, we present a detailed Monte Carlo characterization of a Water Cherenkov Detector (WCD) using the Geant4 simulation toolkit as a general, experiment-independent reference for understanding detector responses to secondary cosmic-ray particles. The detector is modeled to register secondary particles produced by the interaction of high-energy cosmic-ray primaries with the Earth’s atmosphere, which give rise to extensive air showers composed of hadronic, electromagnetic, and muonic components capable of reaching ground level. By simulating the differential energy spectra and angular distributions of these particles at the surface, we evaluate the WCD response in terms of energy deposition, Cherenkov photon production, photoelectron generation at the photomultiplier tube, and the resulting charge spectra. The results establish a systematic and transferable baseline for detector performance characterization and particle identification, providing a physically grounded reference that can support calibration, trigger optimization, and analysis efforts across different WCD-based experiments.

During the last 20 years, TeV astronomy has turned from a fledgling field, with only a handful of sources, into a fully-developed astronomy discipline, broadening our knowledge on a variety of types of TeV gamma-ray sources. This progress has been mainly achieved due to the currently operating instruments: imaging atmospheric Cherenkov telescopes, surface arrays and water Cherenkov detectors. Moreover, we are at the brink of a next generation of instruments, with a considerable leap in performance parameters. This review summarizes the current status of the TeV astronomy instrumentation, mainly focusing on the comparison of the different types of instruments and analysis challenges, as well as providing an outlook into the future installations. The capabilities and limitations of different techniques of observations of TeV gamma rays are discussed, as well as synergies to other bands and messengers.

The advent of gadolinium-loaded Super-Kamiokande (SK-Gd) and of the soon-to-start JUNO liquid scintillator detector marks a substantial improvement in global sensitivity for the Diffuse Supernova Neutrino Background (DSNB). The present article reviews the detector properties most relevant for the DSNB searches in both experiments and estimates the expected signal and background levels. Based on these inputs, we evaluate the sensitivity of both experiments individually and combined. Using a simplified statistical approach, we find that both SK-Gd and JUNO have the potential to reach >3σ evidence of the DSNB signal within 10 years of measurement. Combination of their results is likely to enable a 5σ discovery of the DSNB signal within the next decade.

Gamma-Ray bursts (GRBs) are extremely powerful transient events that occur at cosmological distances. Observations of energy spectra of GRBs can provide information about the intervening space between the burst and Earth as well as about the source itself. GRBs have been observed up to nearly 100 GeV by satellite instruments; however, ground-based detectors are needed to provide enough exposure and statistics to determine the behavior of GRBs at those energies. The High Altitude Water Cherenkov Observatory (HAWC) is a second-generation extensive air shower detector that primarily observes very high-energy (VHE) photons, where VHE is defined as hundreds of GeV to hundreds of TeV. HAWC is built near the peak of Sierra Negra in Mexico at an altitude of 4100 m. The high altitude allows the detector to observe air showers when more information is available for reconstruction. Due to its wide field of view (∼2 sr) and high duty cycle (>90%), the HAWC observatory is sensitive to gamma rays in the sub-TeV to TeV energy range and can constrain the shape and cutoff of high-energy GRB spectra, especially in conjunction with observations from other detectors such as the Fermi LAT satellite. We present a likelihood-based search for VHE emission from the Fermi LAT GRBs that occurred in the field of view of HAWC during the last two years of its construction. Of the five bursts analyzed, no significant detections were observed; upper limits have been placed for each of the bursts. With less than 1/3 of the array active, the HAWC observatory limits for GRB 130702A, which is at a close redshift of z = 0.145, reach comparable sensitivity to lower energy instruments and are not limited by the EBL. With the array complete in March 2015, the sensitivity of HAWC is now greatly enhanced compared to the data analyzed in this dissertation. The future for a VHE GRB detetion by the HAWC observatory is bright.

Purpose This study evaluates methods for removing Cherenkov radiation (CR) from plastic scintillation detectors (PSDs), focusing on constraints specific to a 0.35 T MR‐Linac system. Methods Five CR‐removal methods were examined: cross calibration, fiber alone, multiloop, collimator rotation, and couch rotation. The first three (cross calibration, fiber alone, and multiloop) were tested on a 0.35 T MR‐Linac (ViewRay Inc., USA) using the BluePhysics PSD (Blue Physics LLC, USA). These methods do not require collimator or couch rotation. The remaining two methods (collimator rotation and couch rotation) were tested on a Varian TrueBeam (Varian Medical Systems, USA) for comparison. Measurements were performed under various setup configurations, and Cherenkov radiation extraction (CRE) values were calculated to determine each method's effectiveness. Results The multiloop approach yielded a CRE of 0.7288, making it the most practical and robust for MR‐Linac constraints because it requires neither collimator nor couch rotation. The cross calibration and fiber alone methods produced CRE values of 0.7318 and 0.7569, respectively. Collimator rotation gave 0.7255, comparable to multiloop. In contrast, couch rotation resulted in 0.7489 but exhibited more variability, suggesting lower reliability. Conclusion The multiloop method emerged as the most practical and robust technique for CR removal in 0.35 T MR‐Linac systems. Its simplicity and compatibility with MR‐Linac design constraints make it a highly effective approach for CR removal in PSD‐based radiotherapy applications.

This paper presents our experimental work to assess the capability to estimate the transient-induced power distribution in the CABRI experimental reactor using Cherenkov radiation. The CABRI reactor is designed to produce a power transient up to 21 GW within a time less than 100 ms in order to irradiate a test fuel pin in condition representative of a Reactivity insertion Accident in pressurized water reactors. The large response range and short response time required to follow the flux evolution during a complete transient makes classical means of detection, such as ionization or fission chamber, inoperative. For that purpose, we suggest to measure Cherenkov light produced within optical fibers. Indeed, Cherenkov light emission is linked to the local electron production, which is proportional to the local gamma flux through the Compton or pair production cross-section, the intensity of Cherenkov radiation is related to the photon flux intensity. The knowledge of the fission photons emitted by the reactor gives direct insight on the fission rate, hence a spatial power density distribution could be reconstructed thanks to the measure of the Cherenkov light at different point in the reactor.

Neutrinos are elementary particles that carry no electric charge and have little mass. As they interact only weakly with other particles, they can penetrate enormous amounts of matter, and therefore have the potential to directly convey astrophysical information from the edge of the Universe and from deep inside the most cataclysmic high-energy regions 1 . The neutrino's great penetrating power, however, also makes this particle difficult to detect. Underground detectors have observed low-energy neutrinos from the Sun and a nearby supernova 2 , as well as neutrinos generated in the Earth's atmosphere. But the very low fluxes of high-energy neutrinos from cosmic sources can be observed only by much larger, expandable detectors in, for example, deep water 3 , 4 or ice 5 . Here we report the detection of upwardly propagating atmospheric neutrinos by the ice-based Antarctic muon and neutrino detector array (AMANDA). These results establish a technology with which to build a kilometre-scale neutrino observatory necessary for astrophysical observations 1 .