Search Results (769)

Axions and axion-like particles are compelling candidates for ultralight bosonic dark matter, forming coherent oscillating fields that can be probed by experiments known as haloscopes. A broad range of haloscope concepts has been developed, including resonant cavity haloscopes, lumped-element circuit detectors, and spin-based experiments, each sensitive to different axion couplings and mass ranges. Rather than attempting an exhaustive survey of all existing approaches, this comparative review provides a unified framework for the major haloscope classes, establishing a common language for the descriptions of signal generation, noise properties, analytical methodologies, and scanning strategies. Key properties of ultralight bosonic dark matter relevant for detection are summarized first, including coherence time, spectral linewidth, and stochasticity under the standard halo model. The discussion then compares cavity, Earth-scale, lumped-element, and spin haloscopes, focusing on expected signal shapes, dominant noise sources, and statistical frameworks for axion searches. Particular emphasis is placed on consistent definitions of signal-to-noise ratio and on how detector bandwidth, axion coherence, and noise characteristics determine optimal scan strategies. By systematically comparing operating principles and performance metrics across these detector families, this framework clarifies shared concepts as well as the essential differences that govern sensitivity in different mass and coupling regimes. The resulting perspective synthesizes current search methodologies and offers guidance for optimizing future haloscope experiments. Full article

The NA64 experiment at the CERN H4 beamline recently started a high-energy positron-beam program to search for light dark matter particles through a thick-target, missing-energy measurement. To fulfill the energy resolution requirement of the physics measurement ${\sigma }_E/E\simeq 2.5\%/\sqrt{E\left[\mathrm{GeV}\right]}\oplus 0.5\%$ and cope with the constraints and performance requests of the NA64 setup, a new high-resolution homogeneous electromagnetic calorimeter PKR-CAL has been designed. The detector is based on PbWO₄ crystals, each read by multiple SiPM sensors to maximize the light collection. The PKR-CAL design has been optimized to mitigate and control unavoidable SiPM saturation effects at high light levels, as well as to minimize the gain fluctuations induced by instantaneous variations of the H4 beam intensity. The R&D program culminated in the construction of a small-scale prototype, POKERINO. In this work, we present the results from the experimental characterization campaign of the POKERINO, aiming at demonstrating that the obtained performances are compatible with the application requirements. Full article

In fundamental physics, sensors operating below liquid helium temperatures are highly vulnerable to vibrations, which can affect the sensitivity, for example, of high-performance particle detectors. Pulse-tube refrigerators, while generating vibrations lower than those of conventional systems, may still introduce several disturbances. Hence, flexible thermal connections are a commonly used mechanical solution to mitigate these undesirable effects. Among the materials that can be used, ultra-high-purity aluminum (UHP-Al) has attracted the attention for low-amplitude-vibration cryogenic applications, including gravitational wave interferometry, quantum information systems, precision space instrumentation, and cryogenic resonators. Thus, the aim of the paper is the characterization of the mechanical and microstructure properties of three UHP-Als (i.e., 5N—99.999 wt%, 5N5—99.9995 wt% and 6N—99.9999 wt%) intended for the production of thermal flexible connections with low stiffness, specifically designed to reduce vibration transmission in cryogenic environments. Mechanical properties were evaluated through standard tensile tests from room (+25 °C) to low temperature (i.e., −150 °C), providing insights into yield strength, ultimate tensile strength, elongation and elastic modulus. In addition, the dynamic elastic modulus of material loads, at cryogenic conditions (i.e., about −180 °C), was determined by measuring the natural resonance frequency, thereby assessing the material’s response to vibrational. Moreover, an extensive microstructural analysis was conducted using electron backscatter diffraction and x-ray diffraction. The correlation between the observed microstructure and the elastic properties was systematically examined. The results underscore the pivotal role of microstructural characteristics in dictating the elastic behavior of UHP Als. Eventually, the analysis provides valuable guidelines for the materials employment inside cryogenic systems, where severe vibration control is critical to maintain high operational performance. Full article

The 2x2 Demonstrator, a prototype for the Deep Underground Neutrino Experiment (DUNE) liquid argon (LAr) Near Detector, was exposed to the Neutrinos from the Main Injector (NuMI) neutrino beam at Fermi National Accelerator Laboratory (Fermilab). This detector is a prototype of a new modular design for a liquid argon time-projection chamber (LArTPC), comprising a two-by-two array of four modules, each further segmented into two optically isolated LArTPCs. The 2x2 Demonstrator features a number of pioneering technologies, including a low-profile resistive field shell to establish drift fields, native 3D ionization pixelated imaging, and a high-coverage dielectric light readout system. The 2.4-tonne active mass detector is flanked upstream and downstream by supplemental solid-scintillator tracking planes, repurposed from the MINERvA experiment, which track ionizing particles exiting the argon volume. The antineutrino beam data collected by the detector over a 4.5 day period in 2024 include over 30,000 neutrino interactions in the LAr active volume—the first neutrino interactions reported by a DUNE detector prototype. During its physics-quality run, the 2x2 Demonstrator operated at a nominal drift field of 500 V/cm and maintained good LAr purity, with a stable electron lifetime of approximately 1.25 ms. This paper describes the detector and supporting systems, summarizes the installation and commissioning, and presents the initial validation of collected NuMI beam and off-beam self-triggers. In addition, it highlights observed interactions in the detector volume, including candidate muon antineutrino events. Full article

Accurate and stable measurement of carbon dioxide (CO₂) concentrations in industrial flue gases is critical for emissions monitoring and carbon management. The present study developed a wavelength-modulated tunable diode laser absorption spectroscopy (WMS-TDLAS) system for measuring high-concentration carbon dioxide (CO₂) in flue gases, covering a range of 3–20% (by volume). To mitigate optical intensity fluctuations caused by particle scattering and detector gain drift in harsh flue gas environments, a normalized second harmonic (2f/1f) detection scheme based on a single-harmonic peak was employed. A digital phase-locked amplification algorithm replaces the conventional hardware lock-in amplifier, enabling simultaneous demodulation of multiple harmonic components and enhancing system integration. A comparison of the digital locking method with a commercial lock-in amplifier reveals that the former demonstrates comparable or superior stability, with relative standard deviations of 0.04% for the 2f signal and 0.02% for the first-harmonic signal. In order to address the sensitivity degradation of WMS-TDLAS at elevated CO₂ concentrations, a pressure control strategy was introduced. Maintaining the measurement cell pressure at 70 ± 0.005 kPa resulted in a 2.74-fold enhancement in system sensitivity at 13.01% CO₂ and a more than one-order-of-magnitude increase at 20.01% CO₂ compared to operation at atmospheric pressure. Concentration measurement error under reduced pressure also decreased from 1.101% to 0.075%. The system exhibited 0.6% repeatability in high-concentration CO₂ measurements, signifying its aptitude for industrial flue gas monitoring applications. Full article

This review summarizes recent experimental progress in the structure and correlations of light neutron-rich nuclei. We first highlight achievements based on quasi-free scattering reactions in inverse kinematics at the Radioactive Isotope Beam Factory (RIBF), including investigations of the single-particle composition of halo systems—for example, revealing the minimal s-wave component in the “weak-halo” nucleus ¹⁷B—and the mapping of universal, surface-localized dineutron correlations in Borromean nuclei such as ¹¹Li, ¹⁴Be and ¹⁷B. We then discuss recent advances in the study of multineutron correlations and cluster states, addressing both experimental challenges and major breakthroughs. These include the observation of a candidate $4n$ resonance, the absence of a resonant state in the $3n$ system, the characterization of direct two-neutron decay in ¹⁶Be, and evidence for a condensate-like $\alpha +{}^{2}n+{}^{2}n$ cluster structure in the ${}^8\mathrm{He}\left(0_2^{+}\right)$ state. Finally, we discuss prospects for extending such investigations to heavier halo candidates and more complex multineutron systems, and outline the development of next-generation neutron detector arrays that will drive future progress in this field. Full article

In this paper, an innovative design of a silicon spiral drift detector (SDD) has been proposed. In this design, gaps under the SiO₂ layer between the cathode rings are kept constant, with a minimum value to reduce the surface leakage current. The cathode pitch profile $\mathrm{P}\left(\mathrm{r}\right)$ as a function of radius $\mathrm{r}$ is allowed to change in an arbitrary way to achieve the optimum field distribution. The concept, design considerations, modeling and electrical simulations have been carried out for this novel structure with a hexagonal spiral silicon drift detector. Using one-dimensional analyses, we obtain the exact solution of the spiral design $\mathrm{r}=\mathrm{r}\left(\mathrm{\theta }\right)$ with a near-arbitrary pitch profile $\mathrm{P}\left(\mathrm{r}\right)={\mathrm{P}}_1{\left({\displaystyle \frac{\mathrm{r}}{{\mathrm{r}}_1}}\right)}^{{\displaystyle \frac{1}{\mathrm{\eta }}}}$, with $\mathrm{\eta }$ as an arbitrary real number. We also obtained the electric potential and field profiles on both surfaces of the detector. Using a Technology Computer-Aided Design (TCAD) tool, we made 3D simulations of the detector’s electrical properties. The hexagonal spiral silicon drift detector has excellent electrical properties: a uniform electric field, smooth distribution of electric potential and electron concentration, and a clear electron drift channel. The distributions of the electric field, electric potential, and electron concentration are symmetrical and smooth, which is beneficial for applications in photon sciences (X-ray) and safeguards and homeland security (particle radiation). The theoretical work and simulation results serve as solid foundations for the detector design and the expansion of semiconductor technology. Full article

Serial flow cytometry was recently introduced as a method that can estimate measurement uncertainty (i.e., imprecision, the coefficient of variation of repeated measurements of individual particles) independent from population characteristics. Replication of light sources and detectors at multiple sites along a flow cytometer’s microchannel requires more equipment and can complicate detector synchronization. Here, we introduce amplitude modulation to encode each region of a serial cytometer with a unique carrier frequency, which enables demultiplexing of the combined signal incident on a single photodetector by fast Fourier transform (FFT) peak magnitude. To facilitate validation of detection, matching, and uncertainty quantification of fluorescence signals, we designed a microfluidic amplitude modulation (AM) serial flow cytometer that has ground truth detectors on individual regions (serial cytometry) in parallel with the combined channel detection for AM demultiplexing. With this report, we present metrics for event detection and dynamic range, prevalence and processing of overlapping detections, region-decoding accuracy, process yield, and uncertainty quantification on a brightness ladder of calibration microspheres. Despite being operated with reduced light intensities, the AM cytometer was capable of high-fidelity performance in comparison to conventional serial cytometry. For events above the detection limit, over 97% were analyzed. Both conventional and AM serial cytometers achieved median imprecisions in the range of 0.53% to 2.1% after outlier removal, which was well below the inherent intensity distribution of any of the microsphere subpopulations. Overall, AM cytometry supports uncertainty quantification and temporal analyses of serial cytometry data with a reduced number of photodetectors, which offers simplification of chip design with multiple measurement regions and wide-field detectors. Full article

High-speed solid particles ejected during battery thermal runaway pose severe safety threats, yet their velocity measurement is hindered by high density, microscopic size, and intense glare. This study proposes a non-intrusive velocimetry framework that integrates an enhanced single-stage object detector with a structural similarity matching algorithm. The detector incorporates specialized feature extraction modules and a high-resolution layer to identify microscopic targets in extreme environments, while the matching algorithm employs adaptive direction constraints to ensure precise trajectory tracking. Experimental validation demonstrates that the framework achieves a mean average precision of 92.7% and supports real-time processing. The method successfully quantifies a three-stage velocity evolution in battery failure events, identifying a peak particle speed exceeding 120 m/s. These findings provide critical kinematic data for optimizing battery safety structures and modeling fire propagation mechanisms. Full article

The Bell inequality constrains the outcomes of measurements on pairs of distant entangled particles. The Bell contradiction states that the Bell inequality is inconsistent with the calculated outcomes of these quantum experiments. This contradiction led many to question the underlying assumptions, viz. so-called realism and locality. The probability model underlying the Bell inequality is generally left implicit. We propose an explicit probability model for the CHSH version of the Bell experiment. This model has only two simultaneously observable detector settings per measurement, and therefore does not assume realism. The quantum expectation now becomes a conditional expectation, given the two detector settings. This probability model is in full agreement with both quantum mechanics and experiments. As a result, the model satisfies the Bell inequality; there are no so-called violations. We extend this model to include a hidden variable. This extended model is not Bell-separable. This non-separability implies that the model is non-deterministic or non-local (or both). Full article

The existence of dark matter is supported by multiple astrophysical observations, yet its particle nature remains unknown. The development of gravitational wave astronomy, especially with future space-based detectors such as LISA, provides new opportunities to study the interactions between dark matter and compact-object systems. This review summarizes the main dark matter candidates and their macroscopic distributions, and highlights three mechanisms through which dark matter can affect gravitational wave observations: (1) modifications to compact-object orbits and the dynamics of systems such as extreme mass-ratio inspirals, including dark matter spikes, dynamical friction, and potential perturbations; (2) gravitational lensing effects induced by the spatial distribution of dark matter, altering waveform amplitudes and phases; and (3) direct couplings between ultralight dark matter fields and detectors. As low-frequency gravitational wave detection techniques are proposed and continue to develop, these effects may offer a novel avenue for probing the properties of dark matter, and combining precise waveform modeling with multi-messenger observations could reveal insights into its microscopic structure. Full article

The effect of ionising irradiation up to 30 MGy on the mechanical and dielectric properties of different polymers for potential use in particle accelerators and detectors was compared in this study. The materials studied include the high-performance polymers PEEK, PPS and PEI; pure anhydride- and amine-based epoxy resin systems for coil impregnation and adhesive bonding; glass fibre epoxy composites; and FDM, SLA and SLS 3D-printed materials and polyurethanes. Gamma irradiation was applied in ambient air at an approximate dose rate of 2 kGy/h. Dose-dependent radiation damage was monitored by three-point bending tests, Shore A hardness, tensile stress–strain measurements and breakdown voltage tests in liquid nitrogen. Radiation hardness was rated according to two criteria: the dose at which the initial mechanical strength is halved and the dose at which the mechanical strength is reduced below a certain threshold value. The degradation of the breakdown voltage was preceded by the degradation of mechanical properties. Full article

The X1.59 solar flare on 3 July 2021, was the first X-class flare of Solar Cycle 25 and the first since the X-class flare on 10 September 2017. This event was notable for producing a rare geomagnetic crochet, a temporary and localized perturbation in Earth’s magnetic field during the flare’s peak. To the best of our knowledge, this study represents the first VLF-based analysis of this event, as well as the first comprehensive multi-instrument investigation of it. VLF observations from the NAA and DHO transmitters were used to investigate the ionospheric response via amplitude and phase variations. Key low ionosphere parameters, including the effective reflection height, sharpness factor, time delay and electron density profiles were derived. The results reveal rapid ionospheric responses closely correlated with X-ray flux peaks, including sudden phase and amplitude perturbations indicative of increased low ionosphere ionization and the geomagnetic crochet effect. Simultaneously, cosmic-ray measurements from ground detectors showed negligible modulation and no significant Forbush decrease, consistent with the flare’s weak and partially Earth-directed CME. Also, the spectrum of energetic protons measured in-situ in near-Earth space shows little disturbance. This integrated study demonstrates the sensitivity of the lower ionosphere to intense solar radiation and highlights the limited short-term impact on cosmic-ray and solar energetic proton flux, providing a comprehensive assessment of flare-driven space-weather effects during the early phase of Solar Cycle 25. Full article

Small detector arrays, which are designed to record relatively small EAS with energy in the ‘knee’ region, are often equipped with clocks that measure the time difference between fast signals from several detectors, as well as spectrometric channels that provide the amplitudes of these signals. When analyzing them to determine the angles of arrival and the size of the registered showers, it is important to take into account uncertainties, i.e., the dispersion of measured time differences and shower size relative to the ‘true’ values, which are unknown in the actual situation. Analyses of these spreads are essentially only possible on the basis of correctly performed simulation calculations that take into account all possible stochastic processes in the development of showers in the atmosphere. In this paper, we present a simulation-based analysis using the CORSIKA program of a small EAS array model consisting of four charged particle detectors. We demonstrate the potential offered by ideal timing and how we can infer the energy of the primary particle by analyzing signal amplitudes. The analysis shows that the costs, not only financial, of introducing timing and shower spectrometry are not worth the potential physical gains that we can achieve by using them to analyse small showers. Full article

The photovoltaic (PV) bands on the mid-wave and long-wave infrared (MWIR and LWIR) cold focal plane assemblies of Terra and Aqua MODIS have suffered from gradually increasing electronic crosstalk contamination as both instruments have continued to operate in their extended missions, respectively. This contamination has considerable impact, particularly for the PV LWIR bands, which includes image striping and radiometric bias in the Level-1B (L1B)-calibrated radiance products as well as higher level (and mostly atmospheric but also land and oceanic) products (e.g., cloud phase particle, cloud mask, land and sea surface temperatures). The crosstalk was characterized early in the mission, and test corrections were developed then. Ultimately, the groundwork for a robust electronic crosstalk correction algorithm was developed in 2016 and implemented in MODIS Collection 6.1 (C6.1) back in 2017 for the Terra MODIS PV LWIR bands. It was later introduced in Aqua MODIS C6.1 for the same group of bands in April 2022. Additional improvements were made in MODIS Collection 7 (C7) to better characterize the electronic crosstalk in the PV LWIR bands, and the electronic crosstalk correction algorithm was also extended to select detectors in the MODIS MWIR bands. This work will describe the electronic crosstalk correction algorithm and its application on the MODIS L1B product, the differences in application between C6.1 and C7, as well as additional improvements made to enhance the contamination correction and improve image quality for the Aqua MODIS PV LWIR bands. The electronic crosstalk correction coefficient time series for the MODIS PV bands will be discussed, and some cases will be presented to illustrate how image quality improves on the L1B and Level 2 products after the correction is applied. Lastly, experiences gained regarding the PV bands electronic crosstalk and the strategy used to correct it will be discussed to provide future data users and scientists with an insight as to how to improve on the legacy record that the Terra and Aqua MODIS sensors will leave behind after both spacecrafts are decommissioned. Full article