Muon Momentum 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

Magnetic skin effect in Pb(Fe _{1/2}$ Nb _{1/2}$ )O3

Relaxor-ferroelectrics display exceptional dielectric properties resulting from the underlying random dipolar fields induced by strong chemical inhomogeneity. An unusual structural aspect of relaxors is a skin-effect where the near-surface region in single crystals exhibit structures and critical phenomena that differ from the bulk. Relaxors are unique in that this skin effect extends over a macroscopic lengthscale of ∼100 μm whereas usual surface layers only extend over a few unit cells (or ∼nm). We present a muon spectroscopy study of Pb(Fe _{1/2} Nb _{1/2} )O3 (PFN) which displays ferroelectric order, including many relaxor-like dielectric properties such as a frequency broadened dielectric response, and antiferromagnetism with spatially short-range polar correlations and hence can be termed a multiferroic. In terms of the magnetic behavior determined by the Fe3+ ( S=5/2 , L ≈ 0) ions, PFN has been characterized as a unique example of a ‘cluster spin-glass’. We use variable momentum muon spectroscopy to study the depth dependence of the slow magnetic relaxations in a large 1 cm3 crystal of PFN. Zero-field positive muon spin relaxation is parameterized using a stretched exponential, indicative of a distribution of relaxation rates of the Fe3+ spins. This bandwidth of frequencies changes as a function of muon momentum, indicative of a change in the Fe3+ relaxation rates as a function of muon implantation depth in our single crystal. Using negative muon elemental analysis, we find small-to-no measurable change in the Fe3+/Nb5+ concentration with depth implying that chemical concentration alone cannot account for the change in the relaxational dynamics. PFN displays an analogous magnetic skin effect reported to exist in the structural properties of relaxor-ferroelectrics.

Enhanced material identification via momentum-integrated muon scattering tomography

Background Cosmic ray muons, originating from interactions in the upper atmosphere, possess high energy and unique penetrative capabilities suitable for non-traditional radiographic inspection. This study explores their application in various fields such as nuclear fuel cask monitoring, nuclear reactor imaging, and archaeology, leveraging the principle of multiple Coulomb scattering for imaging dense materials. While muon scattering tomography has shown promise, accurately measuring muon momentum remains challenging. Methods This research introduces the Momentum Integrated Point-of-Closest Approach (mPoCA) algorithm, integrating muon momentum data into the traditional Point-of-Closest Approach (PoCA) framework. Utilizing the Cherenkov muon spectrometer, renowned for precise muon momentum estimation, the mPoCA algorithm offers a novel imaging approach. Results Simulations conducted with GEANT4 evaluate the mPoCA algorithm’s performance against the standard PoCA method, demonstrating superior image resolution and enhanced material identification capabilities, particularly in distinguishing materials like uranium and lead. Conclusions These findings underscore the potential of the mPoCA algorithm for advancing muon scattering tomography applications.

Momentum informed muon scattering tomography for monitoring spent nuclear fuels in dry storage cask

Development of an effective monitoring method for spent nuclear fuel (SNF) in a dry storage cask (DSC) is important to meet the increasing demand for dry storage investigations. The DSC investigation should provide information about the quantity of stored SNF, and quality assurance of materials should be possible without opening the cask. However, traditional nondestructive examination (NDE) methods such as x-rays are difficult to deploy for DSC investigation because a typical DSC is intentionally designed to shield against radiation. To address this challenge, cosmic ray muons (CRMs) are used as an alternative NDE radiation probe because they can easily penetrate an entire DSC system; however, a wide application of muons is often hindered due to the naturally low CRM flux (~104 muons/m2/min). This paper introduces a newly proposed imaging algorithm, momentum-informed muon scattering tomography (MMST), and presents how a limitation of the current muon scattering tomography technique has been addressed by measuring muon momentum. To demonstrate its functionality, a commercial DSC with 24 pressurized light water reactor fuel assemblies (FAs) and the MMST system were designed in GEANT4. Three noticeable improvements were observed for MMST system as a DSC investigation tool: (1) a signal stabilization, (2) an enhanced capability to differentiate various materials, and (3) statistically increased precision to identify and locate missing FAs. The results show that MMST improves the investigation accuracy from 79 to 98% when one FA is missing and 51% to 88% when one-half FA is missing. The advancement of the NDE technique using CRM for DSC verification is expected to resolve long-standing problems in increasing demand for DSC inspections and nuclear security.

Magnetic field simulations and measurements on the mini-ICAL detector

The ICAL (Iron Calorimeter) is a 51 kton magnetized detector proposed by the INO collaboration. It is designed to detect muons with energies in the 1–20 GeV range. A magnetic field of ∼ 1.5 T in the ICAL detector will be generated by passing a DC current through suitable copper coils. This will enable it to distinguish between μ- and μ+ that will be generated from the interaction of atmospheric νμ and νμ with iron. This will help in resolving the open question of mass ordering in the neutrino sector. Apart from charge identification, the magnetic field will be used to reconstruct the muon momentum (direction and magnitude). Therefore it is important to know the magnetic field in the detector as accurately as possible. We present here an (indirect) measurement of the magnetic field in the 85 ton prototype mini-ICAL detector working in Madurai, Tamil Nadu, for different coil currents. A detailed 3-D finite element simulation was done for the mini-ICAL geometry using Infolytica MagNet software and the magnetic field was computed for different coil currents. This paper presents, for the first time, a comparison of the magnetic field measured in the air gaps with the simulated magnetic field, to validate the simulation using real time data. Using the simulations the magnetic field inside the iron is estimated.

Image reconstruction algorithm for momentum dependent muon scattering tomography

Nondestructive radiography using cosmic ray muons has been used for decades to monitor nuclear reactor and spent nuclear fuel storage. Because nuclear fuel assemblies are highly dense and large, typical radiation probes such as x-rays cannot penetrate these target imaging objects. Although cosmic ray muons are highly penetrative for nuclear fuels as a result of their relatively high energy, the wide application of muon tomography is limited because of naturally low cosmic ray muon flux. This work presents a new image reconstruction algorithm to maximize the utility of cosmic ray muon in tomography applications. Muon momentum information is used to improve imaging resolution, as well as muon scattering angle. In this work, a new convolution was introduced known as M-value, which is a mathematical integration of two measured quantities: scattering angle and momentum. It captures the objects’ quantity and density in a way that is easy to use with image reconstruction algorithms. The results demonstrate how to reconstruct images when muon momentum measurements are included in a typical muon scattering tomography algorithm. Using M-value improves muon tomography image resolution by replacing the scattering angle value without increasing computation costs. This new algorithm is projected to be a standard nondestructive radiography technique for spent nuclear fuel and nuclear material management.

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.

Search for Majorana neutrinos in same-sign WW scattering events from pp collisions at sqrt{s}=13 TeV

A search for Majorana neutrinos in same-sign WW scattering events is presented. The analysis uses sqrt{s}= 13 TeV proton–proton collision data with an integrated luminosity of 140 fb^{-1} recorded during 2015–2018 by the ATLAS detector at the Large Hadron Collider. The analysis targets final states including exactly two same-sign muons and at least two hadronic jets well separated in rapidity. The modelling of the main backgrounds, from Standard Model same-sign WW scattering and WZ production, is constrained with data in dedicated signal-depleted control regions. The distribution of the transverse momentum of the second-hardest muon is used to search for signals originating from a heavy Majorana neutrino with a mass between 50 GeV and 20 TeV. No significant excess is observed over the background expectation. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. In addition, the sensitivity to the Weinberg operator is investigated. Upper limits at the 95% confidence level are placed on the squared muon-neutrino–heavy-neutrino mass-mixing matrix element vert V_{mu N} vert ^{2} as a function of the heavy Majorana neutrino’s mass m_N, and on the effective mu mu Majorana neutrino mass |m_{mu mu }|.

Systematic effects in the search for a muon electric dipole moment using the frozen-spin technique

At the Paul Scherrer Institute we are developing a high precision instrument to measure the electric dipole moment (EDM) of the muon. The salient feature of the experiment is the use of the frozen-spin technique to suppress the anomalous precession of the muon spin, allowing for a sensitivity that cannot be achieved with conventional g-2 muon storage rings. With this technique, the expected statistical sensitivity for the EDM after one year of data taking is 6 × 10-23 e · cm with a p = 125 MeV/c muon beam available at PSI.Reaching this goal necessitates a comprehensive analysis on spurious effects that mimic the EDM signal. This work discusses a quantitative approach to study systematic effects for the frozen-spin technique when searching for the muon EDM with a focus on the kinematics of decay positrons in the context of this experiment, which operates at muon momenta well below the ultrarelativistic limit.

Studies of the muon momentum calibration and performance of the ATLAS detector with pp collisions at sqrt{s}=13 TeV

This paper presents the muon momentum calibration and performance studies for the ATLAS detector based on the pp collisions data sample produced at sqrt{s} = 13 TeV at the LHC during Run 2 and corresponding to an integrated luminosity of 139 {textrm{fb}}^{-1}. An innovative approach is used to correct for potential charge-dependent momentum biases related to the knowledge of the detector geometry, using the Zrightarrow mu ^{+}mu ^{-} resonance. The muon momentum scale and resolution are measured using samples of J/psi rightarrow mu ^{+}mu ^{-} and Zrightarrow mu ^{+}mu ^{-} events. A calibration procedure is defined and applied to simulated data to match the performance measured in real data. The calibration is validated using an independent sample of Upsilon rightarrow mu ^{+}mu ^{-} events. At the Z(J/psi ) peak, the momentum scale is measured with an uncertainty at the 0.05% (0.1%) level, and the resolution is measured with an uncertainty at the 1.5% (2%) level. The charge-dependent bias is removed with a dedicated in situ correction for momenta up to 450 GeV with a precision better than 0.03 {textrm{TeV}}^{-1}.

Towards a muon scattering tomography system for both low-Z and high-Z materials

Muon scattering tomography (MST) is a non-destructive technique to image various materials by utilizing cosmic ray muons as probes. A typical MST system with a two-fold track detectors is particularly effective in detecting high-Z materials (e.g. nuclear materials), but difficult to recognize low-Z materials (e.g. explosive materials). In this work, we present a concept of MST system to discriminate both low-Z and high-Z materials by extra measuring momentum of low-energy muons with a Cherenkov detector. A toy Monte Carlo simulation to describe detector responses and multiple scatterings of a muon tracking through materials is developed for statistical tests. Based on momentum-dependent track reconstruction and image reconstruction algorithm, we evaluate separation powers of different materials in the system. The results show that momentum measurement of low-energy muons and accurate track reconstruction can improve separation power of low-Z materials significantly. This may enable the MST system to detect both low-Z and high-Z materials with cosmic ray muons in the whole energy range.

Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector

This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at sqrt{s_{_text {NN}}}=5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 text {pb}^{-1} of pp collisions collected in 2017 and 1.4 text {nb}^{-1} of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-k_{t} algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R= 0.2 and R= 0.4, and only R= 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R= 0.2 jets are also measured using 1.7 text {nb}^{-1} of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, R_text {AA}, is calculated for both b-jets and inclusive jets with R= 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet R_text {AA} to inclusive jet R_text {AA} is also presented and suggests that the R_text {AA} for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.

Simultaneous Measurement of ν_{μ} Quasielasticlike Cross Sections on CH, C, H_{2}O, Fe, and Pb as a Function of Muon Kinematics at MINERvA.

This Letter presents the first simultaneous measurement of the quasielasticlike neutrino-nucleus cross sections on C, water, Fe, Pb, and scintillator (hydrocarbon or CH) as a function of longitudinal and transverse muon momentum. The ratio of cross sections per nucleon between Pb and CH is always above unity and has a characteristic shape as a function of transverse muon momentum that evolves slowly as a function of longitudinal muon momentum. The ratio is constant versus longitudinal momentum within uncertainties above a longitudinal momentum of 4.5 GeV/c. The cross section ratios to CH for C, water, and Fe remain roughly constant with increasing longitudinal momentum, and the ratios between water or C to CH do not have any significant deviation from unity. Both the overall cross section level and the shape for Pb and Fe as a function of transverse muon momentum are not reproduced by current neutrino event generators. These measurements provide a direct test of nuclear effects in quasielasticlike interactions, which are major contributors to long-baseline neutrino oscillation data samples.

Universality of the muon component of extensive air showers

In extensive air shower experiments, the number of muons crossing a detector at a given position, as well as their arrival time, arrival direction, and energy, are determined by a more fundamental 3-dimensional distribution linked to the hadronic core of the shower. Muons are produced high up in the atmosphere after the decay of mesons in the hadronic cascade. The distributions of production depth, energy, and transverse momentum of muons are enough to fully predict the muon component of air showers in any particular observational condition. By using air-shower simulations with the state-of-the-art hadronic interaction models, the mentioned distributions at production are analyzed as a function of zenith angle, primary mass, and hadronic interaction model, and their level of universality is studied and assessed in an exhaustive manner for the first time.

Preparations for a search of the muon EDM at PSI

Electric dipole moments (EDMs) of fundamental particles violate time invariance and the combined symmetry of charge and parity (CP). The existence of a large muon EDM (muEDM) is made plausible by tensions with Standard Model predictions for semileptonic decays of heavy meson measured at LHCb, BaBar, and Belle, as well as the muon’s anomalous magnetic moment (AMM). A discovery of the muEDM would manifest CP and lepton flavor universality (LFU) violation, revealing physics beyond the SM (BSM). The most sensitive muEDM search to date provides an upper limit of 1.8 × 10−19 e cm (CL 95%), extracted from high-precision data collected to measure the muon AMM. At the Paul Scherrer Institute, we are setting up a dedicated search for the muEDM using, for the first time, the frozen-spin technique to target an ultimate sensitivity better than 6 × 10−23 e cm. This novel technique increases the sensitivity to EDM-induced spin precession by cancelling the AMM-induced precession with the application of a precisely tuned electric field perpendicular to the muon momentum and the magnetic field. In this configuration, the dominant source of precession is the EDM coupling to the large relativistic electric field in the muon rest frame, generated by its motion in a strong 3 T uniform magnetic field. In a precursor experiment, we will apply the frozen-spin technique in a compact solenoid demonstrating a sensitivity of better than 3 × 10−21 e cm, probing uncharted and otherwise inaccessible territory in BSM theories.

Improvement of Material Discrimination Using Muon Momenta in MST

MST or Muon Scattering Tomography is a major non-destructive technique to discriminate materials by finding deviation in muon tracks which depends on Z and density (ρ) of the medium the muon passes through. The scattering angle also depends on the incoming momentum of muon which is a key to distinguish multiple small deviations through large path-lengths of low-Z material from significant deviations through smaller path lengths of a high-Z target. An analytical function, derived by fitting the muon momentum distribution in a selected range has been used to predict the momentum of individual events. The scattering angles have been normalized by the predicted momenta to improve the material discrimination.

The ATLAS ‘New Small Wheel’ Muon detector stations recently commissioned for LHC Run3

After nearly a decade of intense effort, the two New Small Wheels (NSW) for the upgrade of the ATLAS Muon spectrometer is now installed in the experiment and ready for final commissioning and to collect data in LHC Run3, starting March 2022. The NSW is the largest phase-1 upgrade project of ATLAS. It is challenging completion and readiness for data taking is a remarkable achievement of the collaboration. The two wheels (10 meters in diameter) replace the first Muon stations in the high-rapidity regions of ATLAS and are equipped with multiple layers of two completely new detector technologies: the small strips Thin Gap Chambers (sTGC) and the Micromegas (MM). The latter belongs to the family of Micro Pattern Gaseous Detectors (MPGD, for the first time used in such a large scale in HEP experiment). Each detector will cover more than 1200 m2 of the active area. The new system is required to maintain the present detector’s efficiency and momentum resolution level in the expected higher background level, given the ongoing LHC luminosity upgrades. In addition, it is necessary to keep an acceptable Muon trigger rate with the same Muon momentum threshold.11Copyright 2022 CERN for the benefit of the ATLAS muon collaboration. Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 license.

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.

Constraining U(1) L μ – L τ charged dark matter model for muon g – 2 anomaly with AMS-02 electron and positron data

Very recently, the Fermi-Lab reported the new experimental combined results on the magnetic momentum of muon with a 4.2σ discrepancy compared with the expectation of the Standard Model [1]. A new light gauge boson X in the Lμ – Lτ model provides a good explanation for the g – 2 anomaly. A Dirac fermion dark matter with a large Lμ – Lτ charge can explain both the g – 2 anomaly and the dark matter relic density [2]. In this work, we focus on the case that the mass of the dark matter is larger than the mass of muon (i.e. m Ψ > m μ) for which the channel ΨΨ ⟶ μ - μ + opens. Although the cross section (σ v) μ - μ + is smaller by a factor of 1/q Ψ 2 (q Ψ represents the Lμ – Lτ charge of the dark matter) compared with the channel ΨΨ ⟶ X X ⟶ ννν̅ν̅, the resulting secondary electrons and positrons could imprint on their spectra above GeV energies due to the reacceleration effect of cosmic ray propagation. We use the AMS-02 measurements of electrons and positrons to constrain the annihilation cross section of the channel ΨΨ ⟶ μ - μ +, which rules out part of the parameter space of the large Lμ – Lτ charged dark matter model to account for the muon g – 2 anomaly.

Expected measurement precision with production at the CEPC * *Supported by the Innovative Research Program of IHEP (E2545AU210); CAS Center for Excellence in Particle Physics; Yifang Wang’s Science Studio of the Ten Thousand Talents Project; the CAS/SAFEA International Partnership Program for Creative Research Teams (H751S018S5); IHEP Innovation Grant (Y4545170Y2); Key Research Program of Frontier Sciences, CAS (XQYZDY-SSW-SLH002); Chinese Academy of

A search for the dimuon decay of the Standard Model Higgs boson is performed using Monte Carlo simulated events to mimic data corresponding to an integrated luminosity of 5.6 ab collected with the Circular Electron-Positron Collider detector in collisions at GeV. This study investigates the process, and the expected significance considering only the statistical uncertainty in the data for a background-only hypothesis for a Higgs boson with a mass of 125 GeV is found to be 6.1 , corresponding to a precision of 19%. The systematic impacts from the background Monte Carlo statistical fluctuations are estimated to be negligible. Moreover, the dependence of the measurement accuracy on the muon momentum resolution of the CEPC detector is investigated. It is found that the muon momentum resolution must be better than 204 MeV to discover the process at the nominal integrated luminosity. If the resolution is 100% worse than the designed parameter, the integrated luminosity must be greater than 7.2 ab to reach 5 significance.