Incoming Muons Research Articles

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 (P0μ) measurements using decay electron events collected between September 2008 and June 2022 with the Super-Kamiokande detector. Because of its underground location and long operation, we are able to perform 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=0.7−0.2+0.3 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 indicating a tension with the πK model of 1.9σ. We also measured the muon polarization at the production location to be P0μ=0.52±0.02 (stat+syst) at the muon momentum of 0.9−0.1+0.6 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 atmospheric neutrino simulations. Published by the American Physical Society 2024

Investigating μ±μ−→μ±μ− collisions under the effect of scalar and vector unparticles in Randall–Sundrum model

A theoretical attempt is made to present the unparticles contribution to the muon processes [Formula: see text], in Standard Model (SM), Randall–Sundrum (RS) model and RS model with unparticles (RS([Formula: see text])) including scalar and vector unparticles. We evaluated the cross-sections versus the scattering angle [Formula: see text], the kinetic energy [Formula: see text] of the outgoing muon beams, the collision energy [Formula: see text], the scaling dimension [Formula: see text] and the energy scale [Formula: see text]. The numerical results show that the cross-sections of two processes in RS([Formula: see text]) are much larger than in SM. The [Formula: see text] and [Formula: see text] beams can be accelerated and collided, producing the outgoing [Formula: see text] and [Formula: see text] beams as final states with large kinetic energy to probe new physics effects. The total cross-sections depend strongly on the polarization conditions of incoming muon and anti-muon beams, the scaling dimension [Formula: see text] and the energy scale [Formula: see text]. The final states of the muon collisions also depend on [Formula: see text] of colliders and unparticles parameter: ([Formula: see text], [Formula: see text]) if unparticle physics included. The results subsequently lead to the unparticle contribution as propagator significantly larger than SM and Higgs–radion propagator. Hence, it would be worthwhile probing at the future colliders when the muons become the accelerating candidates in the collisions we restricted.

Lepton pair production in muon-nucleus scattering

The MUonE experiment aims at providing a novel determination of the leading hadronic contribution to the muon anomalous magnetic moment through the study of elastic muon-electron scattering. Since the initial-state electrons are bound in a low-Z atomic target, the interaction between the incoming muons and the nuclei is expected to be the main source of experimental background. In this article, we study the production of a real lepton pair from the muon-nucleus scattering, discussing its numerical impact in the MUonE kinematic configuration. The process is described as a scattering of a muon in an external Coulomb field with the addition of a form factor to describe the nuclear charge distribution. The calculation is implemented in the fully differential Monte Carlo event generator Mesmer, without introducing any approximation on the angular variables.

Research and development of a muon entrance trigger for the muEDM experiment at PSI

The muEDM experiment at the Paul Scherrer Institute (PSI) in Switzerland aims to probe the muon electric dipole moment (EDM) using the frozen-spin technique in a compact storage ring, with a sensitivity of 6×10−23 e⋅cm. A fast entrance detector is expected to work in concert with a magnetic pulse generator to direct muons into the desired orbit. Simultaneously, the entrance detector is designed to veto muons that exceed the apparatus's admittance without introducing significant multiple scatterings. We developed a prototype entrance trigger detector consisting of a thin scintillator for detecting incoming muons and four wall scintillators as veto detectors. The prototype was tested at 27.5 MeV/c at the πE1 beamline at PSI. A total of 7×105 events were collected, which were read out by SiPMs coupled to the plastic scintillators under two different beam tunes. These events were analyzed to characterize the detector's performance, which was also cross-checked with Monte Carlo simulations that took into account the beam phase space and scintillation processes.

Nuclear material accountancy using momentum-informed muon scattering tomography

Screening cargo and vehicles to prevent proliferation of unauthorized nuclear and radioactive materials is essential to prevent threats to domestic and international security. Cosmic ray muons attracted attention as a potential next-generation radiographic technique to discover illicit transportation of nuclear and radioactive materials at borders or secure facilities. Unique features of cosmic muons—a high energy and deep penetration depth—enable them to be utilized for radiation probes, especially for large and dense materials. In muon scattering tomography, physical characteristics of target materials are estimated by measuring both incoming and outgoing muon trajectories using muon detectors. To reconstruct 3D tomographic images of target objects, a Point of Closest Approach (PoCA) algorithm is typically used to locate a scattering position, and the scattering angle values are used to map material density. However, high-resolution material mapping is often limited due to the absence of muon momentum information because the expected muon scattering angle depends on two variables: material atomic number and muon momentum. Despite the importance of measuring muon momentum, it is still challenging without deploying large and expensive muon spectrometers. Therefore, a mean muon momentum, 3 to 4 GeV/c, is often used to represent the entire cosmic ray muon spectrum. In this paper, we present a new momentum-informed muon scattering tomography (MST) approach for nuclear material accountancy based on a recently devised fieldable muon spectrometer. This approach uses a new imaging algorithm that improves the current PoCA algorithm by encoding momentum into the scattering angle. In our new algorithm, all muon measurements have a categorized momentum level with a scattering angle. We demonstrate the functionality and performance of momentum-informed MST using computational simulations. The results show that the image resolution is significantly improved, and this approach allows for visually differentiating nuclear materials from non-nuclear materials.

Muometric positioning system (muPS) utilizing direction vectors of cosmic-ray muons for wireless indoor navigation at a centimeter-level accuracy

Since the development of many future technologies are becoming more and more dependent on indoor navigation, various alternative navigation techniques have been proposed with radio waves, acoustic, and laser beam signals. In 2020, muometric positioning system (muPS) was proposed as a new indoor navigation technique; in 2022, the first prototype of wireless muPS was demonstrated in underground environments. However, in this first physical demonstration, its navigation accuracy was limited to 2–14 m which is far from the level required for the practical indoor navigation applications. This positioning error was an intrinsic problem associated with the clock that was used for determining the time of flight (ToF) of the muons, and it was practically impossible to attain cm-level accuracy with this initial approach. This paper introduces the completely new positioning concept for muPS, Vector muPS, which works by determining direction vectors of incoming muons instead of utilizing ToF. It is relatively easier to attain a 10-mrad level angular resolution with muon trackers that have been used for muographic imagery. Therefore, Vector muPS retains the unique capacity to operate wirelessly in indoor environments and also has the capacity to achieve a cm-level accuracy. By utilizing an essentially different concept from what is used in other navigation techniques, (measuring the distance between the reference and the receiver), Vector muPS enables more flexible, and longer-term stable positioning. Anticipated applications and the future outlook of Vector muPS is also discussed.

Investigation of deflection angle for muon energy classification in muon scattering tomography via GEANT4 simulations

In muon scattering tomography, the investigated materials are discriminated according to the scattering angle that mainly depends on the atomic number, the density, and the thickness of the medium at a given energy value. The scattering angles at different initial energies also provide the opportunity to classify the incoming muons into a number of energy groups. In this study, by employing the GEANT4 code, we show that the deflection angle exponentially decays as a function of energy, and the numerical values for the current configuration are below the detector accuracy except the initial energy bins owing to the low-Z, low density, and low thickness of the current plastic scintillators. This implies the necessity of additional components that provoke the muon scattering. Therefore, we introduce stainless steel surfaces into the top and bottom sections in order to amplify the deflection angle as well as to reduce the uncertainty, thereby improving the detector performance.

Large area LaBr3:Ce crystals read by SiPM arrays with improved timing and temperature gain drift control

Compact X-rays detectors made of 1/2” or 1” :LaBr3:Ce crystals of cubic shape with SiPM array readout have been developed for the FAMU experiment at RIKEN-RAL. The aim is a precise measurement of the proton Zemach radius with incoming muons. Additional applications may be found in medical physics, such as PET, homeland security and gamma-ray astronomy. Due to the high photon yield of LaBr3:Ce it was possible to use a simple readout scheme based on CAEN V1730 digitizers. Detectors, using Hamamatsu S13361 or S14161 arrays, have good FWHM energy resolutions up to 3% (8%) at the Cs137 (Co57) peak, comparing well with the best results obtained with a photomultiplier’s readout. Detailed studies were performed to correct online the drift with temperature of SiPM gain and to reduce the risetime/falltime of detectors’ signals, that increased going from 1/2” to 1” detectors, due to the larger capacity of the used SiPM arrays.

Advances in Cosmic Ray Muon Computed Tomography and Fieldable Spectroscopy

A recent example of successful technology transition from high energy physics to practical engineering applications is cosmic ray muon tomography. Cosmic ray muon tomography, is a promising non-destructive technique that has been recently utilized to monitor or image the contents of dense or well shielded objects, typically not feasible with conventional radiography techniques, e.g., x-ray or neutron. Cosmic ray muon tomography has been used with various levels of success in spent nuclear fuel monitoring, volcano imaging, and cargo container imaging. Further, knowledge of cosmic ray muon momentum spectrum has the potential to significantly improve and expand the use of a variety of recently developed muon-based radiographic techniques. However, existing muon tomography systems rely only on muon tracking and have no momentum measurement capabilities which reduces the image resolution and requires longer measurement times. A fieldable cosmic ray muon spectrometer with momentum measurement capabilities for use in muon tomography is currently missing. In this paper, we will discuss and explore recent advances in cosmic ray muon computed tomography and spectroscopy and their applications to engineering including a new concept for measuring muon momentum using multiple gaseous Cherenkov radiators. By varying the pressure of multiple gas Cherenkov radiators, a set of muon momentum threshold levels can be selected that are triggered only when the incoming muon momentum exceeds that level. As a result, depending on the incoming muon momentum, none to all Cherenkov radiators can be triggered. By analyzing the signals from each radiator, we can estimate the actual muon momentum.

Simulation study on position resolution of plastic scintillator strips for cosmic muon imaging

In applications of transmission muography for large objects, plastic scintillator strips with triangular or rectangular cross-sections are frequently selected to construct imaging detectors. Triangular scintillator strips have a better position resolution over those of rectangular ones by a factor of ∼ 3.5 with the same width. The big difference has been carefully studied using Geant4. Simulations show a good agreement with those of existing muography instruments. The position resolution is influenced by the geometry (the size and base angle of triangular strips) and the energy resolution of scintillators, and angles of incoming muons. Two empirical formulas have been proposed to quantitatively estimate the position resolution with respect to the abovementioned influential factors. Perpendicularly and randomly (real angular distribution) incoming muons are considered separately in them. A more widely spread angular distribution of muons can make the position resolution worse. For commonly used triangular scintillator strips with a base angle of 45∘, the ratio of the triangle base length to the position resolution is almost fixed to ∼ 12 varying the base length or energy resolution if an uncorrected Centre of Gravity (CoG) method is used. Such a ratio has a potential to be increased by a factor of ∼ 2 if the CoG method is corrected with the muon incoming angle. The influence of the energy resolution on the position resolution can be ignored.

Requirements on common solutions to the LSND and MiniBooNE excesses: a post-MicroBooNE study

The strong statistical significance of an observed electron-like event excess in the MiniBooNE (MB) experiment, along with an earlier similar excess seen in the Liquid Scintillator Neutrino Detector (LSND), when interpreted in conjunction with recent MicroBooNE results may have brought us to the cusp of new physics discoveries. This has led to many attempts to understand these observations, both for each experiment individually and in conjunction, via physics beyond the Standard Model (SM). We provide an overview of the current situation, and discuss three major categories under which the many proposals for new physics fall. The possibility that the same new, non-oscillation physics explains both anomalies leads to new restrictions and requirements. An important class of such common solutions, which we focus on in this work, consists of a heavy \U0001d4aa(MeV−sub-GeV) sterile neutral fermion produced in the detectors, (via up-scattering of the incoming muon neutrinos), and subsequently decaying to photons or e+e− pairs which mimic the observed signals. Such solutions are subject to strong demands from a) cross section requirements which would yield a sufficient number of total events in both LSND and MB, b) requirements imposed by the measured energy and angular distributions in both experiments and finally, c) consistency and compatibility of the new physics model and its particle content with other bounds from a diverse swathe of particle physics experiments. We find that these criteria often pull proposed solutions in different directions, and stringently limit the viable set of proposals which could resolve both anomalies. Our conclusions are relevant for both the general search for new physics and for the ongoing observations and analyses of the MicroBooNE experiment.

Development of detector and method for density structure measurement of fault zones using cosmic ray muons

We have developed a slim cylindrical muon detector using a plastic scintillator that can be installed in a borehole and a new muography technique that scans inside the borehole using secondary cosmic ray muon without measuring its zenith angle. The zenith angle distribution of incoming muons can be statistically limited by optimizing the detector acceptance. This new detector and technique can be used for the measurement of subsurface structures, as muography requires that the detector be installed below the measurement target. We performed a feasibility study in a borehole through the Atotsugawa fault zone in Hida City, Gifu Prefecture, Japan. We report the detector design, detector performance, analysis method, and the results of the feasibility study.

Design and characterization of a Muon tomography system for spent nuclear fuel monitoring

In recent years, monitoring of spent nuclear fuel inside dry cask storage has become an important area of national security. Muon tomography is a useful method for monitoring spent nuclear fuel because it uses high energy muons that penetrate deep into the target material and provides a 3-D structure of the inner materials.We designed a muon tomography system consisting of four 2-D position sensitive detector and characterized and optimized the system parameters. Each detector, measuring 200 × 200 cm2, consists of a plastic scintillator, wavelength shifting (WLS) fibers and, SiPMs. The reconstructed image is obtained by extracting the intersection of the incoming and outgoing muon tracks using a Point-of-Closest-Approach (PoCA) algorithm.The Geant4 simulation was used to evaluate the performance of the muon tomography system and to optimize the design parameters including the pixel size of the muon detector, the field of view (FOV), and the distance between detectors. Based on the optimized design parameters, the spent fuel assemblies were modeled and the line profile was analyzed to conduct a feasibility study. Line profile analysis confirmed that muon tomography system can monitor nuclear spent fuel in dry storage container.

Muon radiography to visualise individual fuel rods in sealed casks

Cosmic-ray muons can be used for the non-destructive imaging of spent nuclear fuel in sealed dry storage casks. The scattering data of the muons after traversing provides information on the thereby penetrated materials. Based on these properties, we investigate and discuss the theoretical feasibility of detecting single missing fuel rods in a sealed cask for the first time. We perform simulations of a vertically standing generic cask model loaded with fuel assemblies from a pressurized water reactor and muon detectors placed above and below the cask. By analysing the scattering angles and applying a significance ratio based on the Kolmogorov-Smirnov test statistic we conclude that missing rods can be reliably identified in a reasonable measuring time period depending on their position in the assembly and cask, and on the angular acceptance criterion of the primary, incoming muons.

Multiparametric approach to the assessment of muon tomographic results for the inspection of a full-scale container

Experimental results from a dataset collected with a full-scale muon tomograph for the inspection of cargo containers were studied in a single scattering scenario with a multiparametric analysis based on the method of the Point Of Closest Approach (Poca). To search for high-Z materials, a 4 hbox {dm}^3 Pb block was positioned inside the volume to be inspected, in order to quantitatively investigate the appearance of the Poca signal. Signal-to-noise ratio and significance of the Poca signal were investigated by means of mono-dimensional spectra of the Poca components, for different values of the scattering angle between the incoming and outgoing muon tracks and with different angle-dependent weights. A systematic scan of two-dimensional maps was also carried out, as a strategy to search for possible enhancements to the Poca signal. A comparison was also done between the results obtained from the two half-volumes, one containing the Pb block and one left empty, to take into account the response of the detector and some aspects of the Poca strategy.

Muon radiography employing the DIRC principle for density change measurements under volcanoes and fluid reservoirs

Mapping the density distribution and monitoring density changes under volcanoes and geological reservoirs is a major challenge in geology and volcanology. Muon radiography has a high potential to advance this field, but often there are no inexpensive high-end detectors available that are suitable for field installations. A DIRC-type Cherenkov detector as a muon camera has a small dimension and is suited for such field applications (MagmaDIRC idea). In measuring directions and energies of the incoming muons one can turn the mass density integrals along the lines of flight into a radiography image, and by discarting low-energy muons with their blurred angular information one obtains sharper images. In particular one may detect the time variation of the mass density distributions situated above the horizon line in a volcanic edifice that occurs when magma is filling its plumbing system or when the level of a lava lake changes. Using numerical simulations, we discuss design aspects and the requirements of such a DIRC system. Two sites are identified for proof-of-principle field measurements. The required measurement times are estimated for the given site conditions and morphology based on the specifications of an operational DIRC system. The merits of DIRC sensors are contrasted to other muon radiography techniques.

Proof-of-Principle of a Cherenkov-Tag Detector Prototype.

In a recent paper, the authors discussed the feasibility study of an innovative technique based on the directionality of Cherenkov light produced in a transparent material to improve the signal to noise ratio in muon imaging applications. In particular, the method was proposed to help in the correct identification of incoming muons direction. After the first study by means of Monte Carlo simulations with Geant4, the first reduced scale prototype of such a detector was built and tested at the Department of Physics and Astronomy "E. Majorana" of the University of Catania (Italy). The characterization technique is based on muon tracking by means of the prototype in coincidence with two scintillating tiles. The results of this preliminary test confirm the validity of the technique and stressed the importance to enhance the Cherenkov photons production to get a signal well distinguishable with respect to sensors and electronic noise.

Borexino and general neutrino interactions

We derive constraints on all possible general neutrino-electron interactions (scalar, vector, pseudoscalar, axialvector and tensor) using the recent real time Borexino event rate measurements of $pp$, $pep$ and $^{7}Be$ solar neutrinos. The limits improve several previous ones from TEXONO and CHARM-II for incoming electron and muon neutrinos, and are the first ones for the tau flavor. Future improvements by next-generation solar neutrino experiments are also studied. The limits extend the physics reach of solar neutrino measurements to TeV-scale physics. Finally, the different properties of the new interactions for Dirac and Majorana neutrinos are discussed.

Comment on “Role of the transition state in muon implantation” and “Thermal spike in muon implantation”

Vil\~ao et al. (Phys. Rev. B 96, 195205 (2017) and Phys. Rev. B 99, 195206 (2019)) have reported positive muon spin rotation/relaxation (${\ensuremath{\mu}}^{+}\mathrm{SR}$) experiments on various insulating metal oxides, solar cell materials, and alloyed Ge. They note the presence of a separate early component in the ${\ensuremath{\mu}}^{+}$ polarization time dependence which relaxes more rapidly than the longer lived signal and also exhibits (in ${\mathrm{ZrO}}_{2}$:Mg) a slightly increased frequency at low temperature in transverse field. They interpret this early component as a weakly bound ``transition state'' of the neutral muonium ($\mathrm{Mu}={\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}$) atom formed epithermally by the incoming 4-MeV muon, in which the hyperfine interaction between the muon and the electron is ``motionally narrowed'' by rapid spin exchange, resulting in a ``diamagneticlike'' Larmor precession signal. This ``diamagneticlike transition state'' supposedly takes microseconds to relax into its final ground state due to the reluctance of the surrounding lattice to deform around the Mu atom. However, numerous earlier experiments (including those in electric fields) on various liquids and solids ranging from wide-gap insulators to narrow-gap semiconductors have convincingly shown that Mu formation proceeds through capture of radiolysis electrons by thermalized muons---a process crucially dependent on the electron mobility rather than epithermal dynamics. Therefore, we question the validity of the interpretation by Vil\~ao et al. and raise some important issues that need clarification.

The HiSPARC experiment

The High School Project on Astrophysics Research with Cosmics (HiSPARC) is a large extensive air shower (EAS) array with detection stations throughout the Netherlands, United Kingdom, Denmark and Namibia. HiSPARC is a collaboration of universities, scientific institutes and high schools. The majority of detection stations is hosted by high schools. A HiSPARC station consists of two or four scintillators placed inside roof boxes on top of a building. The measured response of a detector to single incoming muons agrees well with GEANT4 simulations. The response of a station to EASs agrees with simulations as well. A four-scintillator station was integrated in the KASCADE experiment and was used to determine the accuracy of the shower direction reconstruction. Using simulations, the trigger efficiency of a station to detect a shower as function of both distance to the shower core and zenith angle was determined. The HiSPARC experiment is taking data since 2003. The number of stations (∼140 in 2019) still increases. The project demonstrates that its approach is viable for educational purposes and that scientific data can be obtained in a collaboration with high school students and teachers.