Muon scattering at Fermilab

A review of the muon scattering program to date at Fermilab is made. Brief sections are included on muon physics at particle accelerators prior to Fermilab and on technical details of the Fermilab muon beam. A section is included on the theoretical work most closely associated with the deeply inelastic muon scattering program.     

Muon-pair production by atmospheric muons in CosmoALEPH

Data from a dedicated cosmic ray run of the ALEPH detector were used in a study of muon trident production, i.e., muon pairs produced by muons. Here the overburden and the calorimeters are the target materials while the ALEPH time projection chamber provides the momentum measurements. A theoretical estimate of the muon trident cross section is obtained by developing a Monte Carlo simulation for muon propagation in the overburden and the detector. Two muon trident candidates were found to match the expected theoretical pattern. The observed production rate implies that the nuclear form factor cannot be neglected for muon tridents.     

Influence of impurities on short range electron transport in GaAs

The influence of Cr impurities on muonium atom formation in GaAs has been studied using muon spin relaxation techniques with alternating electric fields. The results suggest that electron transport to and capture by the muon is suppressed by capture/scattering on intervening Cr centers. The length scale involved is estimated to be about 3x10(-6) cm. This offers an opportunity to study electron transport to positive centers in semiconductors on a microscopic scale.     

The motion of light interstitials in metals: Recent experiments

Recent theoretical considerations suggest, that at low temperatures the transport properties of light interstitials in metals are dominated by the interaction with the conduction electrons. After briefly surveying the state of the theory, experimental examples for the low and high temperature cases are presented. We begin with the low T regime and display first neutron scattering experiments on H trapped at O-impurities in Nb where a coherent tunneling state is observed. Its dependence on temperature and its properties in normal and superconducting Nb are discussed. Thereafter muon diffusion results in Al are examined. In Al, muon diffusion is observed via diffusion limited trapping and local properties of the impurity as well as long range diffusion are playing a role. Using a large variety of impurities it was possible to evaluate the diffusion coefficient over a large T-range. Muon motion in Al at accessible temperatures falls entirely in the hopping regime and constitutes an example for the high T regime of the theory.     

大俘获立体角的内靶超导螺线管表面muon源的设计研究

高通量μ子源是国际上μ子科学研究的重要条件。在中国散裂中子源的高能质子应用区中,运用蒙特卡罗工具Geant4和G4beamline软件设计了使用内靶超导螺线管俘获高通量表面μ子的束线。与传统的分离靶和基于四极磁铁的收集系统相比,大孔径超导螺线管可以将收集效率提高两个量级。通过对不同靶材的粒子产率进行分析得出石墨是最佳靶材,然后比较俘获螺线管与束流的不同偏转角度下收集的表面μ的产率,提出了合理的较高产率的俘获和输运螺线管的设计方案,并与常规磁铁方案比较,最终在衰变螺线管端口的表面μ通量高达108/s。     

Muon anomalous magnetic moment: A consistency check for the next-to-leading-order hadronic contributions

A duality-inspired model for verifying a consistency of the evaluation of the next-to-leadingorder hadronic contributions to the muon anomalous magnetic moment with that of the leading-order ones is proposed. A part of the next-to-leading-order hadronic contributions related to the photon vacuum polarization function is rather accurately reproduced in the model. I find a new numerical value for the light-by-light hadronic contribution that leads to the agreement of the Standard Model theoretical prediction for the muon anomalous magnetic moment with the recent experimental result.     

Local structure of isolated positively charged muonium as an analog for the hydrogen ion in p-type GaAs

We determine the local structure of isolated positively charged muonium (Mu+) in heavily doped p-type GaAs based on muon level crossing resonance and zero applied field muon spin depolarization data. These measurements provide the first direct experimental confirmation that Mu+, and by analogy H+, is located within a stretched Ga-As bond. The distances between Mu+ and the nearest neighbor Ga and As atoms are estimated to be 1.83 +/- 0.10 A; and 1.76 +/- 0.10 A, respectively. These results are compared to existing theoretical calculations on the structure of hydrogen in GaAs and additionally provide data on the induced electric field gradients.     

First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen

We report the first measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in a gaseous target, made of a H₂/O₂ mixture, exposed to a muon beam. This work sets constraints on theoretical models of muon transfer and is of fundamental importance for the measurement of the hyperfine splitting of muonic hydrogen ground state as proposed by the FAMU collaboration.     

Physical applications of muon catalysis: Muon capture in hydrogen

Results of theoretical and experimental research on capture of negative muons in hydrogen are reported with an emphasis on the accompanying phenomenon of muon catalysis in hydrogen and subtleties of the experimental method. A conclusion is drawn that precise determination of the capture rate is important for refining the standard model.     

Theoretical study ofμ + site in YBa2Cu3O x site in YBa2Cu3O x

The muon is a useful probe of magnetic fields in superconductors, but knowing the field seen by the muon is often of limited value until we know where the muon is in the crystal lattice. Here we employ two independent theoretical methods to search for candidate muon sites:the potential energy field method, which seeks the minimum of the electrostatic potential of theμ ⁺, and themagnetic dipolar field method, which compares the calculated magnetic field (due to host electronic or nuclear dipolar fields) with the observed local fields at the muon. Work supported by Canadian NRC and NSERC.     

The influence of kinetic processes at a negative muon track endpoint in doped nondegenerate silicon on the behavior of muon spin polarization

This work is aimed at creating a theoretical basis for analyzing and interpreting the results of μSR experiments in doped nondegenerate semiconductors at temperatures below 50 K, when the influence of kinetic processes at the endpoint of a muon stopping track on the behavior of its polarization is substantial. The effects related to the formation of free electrons and holes in a solid-state plasma at a muon track endpoint are shown to be responsible for the mere possibility of observing negative muon spin precession at the muon frequency in doped nondegenerate semiconductors at low temperatures. The Vangsness-Bloch equations are generalized to the case of parameters varying with time. A theory based on these generalized equations allowed us to interpret more correctly the available experimental results of mSR studies of semiconductors with the use of negative muons. We showed that the μSR method could be used to obtain information about the cross sections of exchange scattering of electrons and holes by impurity centers in the region of energies inaccessible to the other measurement techniques and to estimate the cross section of capture by a solitary charged Coulomb center at virtually all charge carrier concentrations and temperatures. Under the conditions when the Debye radius is larger than the mean distance between charged particles but smaller than the Thomson radius, the capture (recombination) cross section is described by a temperature dependence qualitatively different from that predicted by current theory.     

μ子源超导俘获线圈测试杜瓦设计与校核

根据高μ子源超导俘获线圈整体测试系统的要求,设计了μ子源超导俘获线圈测试杜瓦系统.包含液氦杜瓦、真空杜瓦及绝热冷屏,采用Solidworks软件对测试杜瓦系统进行3D建模.通过对绝热冷屏统进行了详细的传热学计算,绝热冷屏的可以满足μ子源超导俘获线圈测试过程的漏热需求;根据μ子源超导俘获线圈测试实际工况,对真空杜瓦和液氦杜瓦进行了Ansys有限元软件分析与校核,得到杜瓦详细的应力及变形结果,分析表明,测试杜瓦的设计较为合理,可以作为工程设计的理论计算依据     

Lamb shift in muonic hydrogen—II. Analysis of the discrepancy of theory and experiment

Currently, both the g factor measurement of the muon as well as the Lamb shift 2S–2P measurement in muonic hydrogen are in disagreement with theory. Here, we investigate possible theoretical explanations, including proton structure effects and small modifications of the vacuum polarization potential. In particular, we investigate a conceivable small modification of the spectral function of vacuum polarization in between the electron and muon energy scales due to a virtual millicharged particle and due to an unstable vector boson originating from a hidden sector of an extended standard model. We find that a virtual millicharged particle which could explain the muonic Lamb shift discrepancy alters theoretical predictions for the muon anomalous magnetic moment by many standard deviations and therefore is in conflict with experiment. Also, we find no parameterizations of an unstable virtual vector boson which could simultaneously explain both “muonic” discrepancies without significantly altering theoretical predictions for electronic hydrogen, where theory and experiment currently are in excellent agreement. A process-dependent correction involving electron screening is evaluated to have the right sign and order-of-magnitude to explain the observed effect in muonic hydrogen. Additional experimental evidence from light muonic atoms and ions is needed in order to reach further clarification.     

Ultra slow muon microscopy by laser resonant ionization at J-PARC, MUSE

As one of the principal muon beam line at the J-PARC muon facility (MUSE), we are now constructing a Muon beam line (U-Line), which consists of a large acceptance solenoid made of mineral insulation cables (MIC), a superconducting curved transport solenoid and superconducting axial focusing magnets. There, we can extract 2 × 10⁸/s surface muons towards a hot tungsten target. At the U-Line, we are now establishing a new type of muon microscopy; a new technique with use of the intense ultra-slow muon source generated by resonant ionization of thermal Muonium (designated as Mu; consisting of a μ ^?+? and an e^???) atoms generated from the surface of the tungsten target. In this contribution, the latest status of the Ultra Slow Muon Microscopy project, fully funded, is reported.     

宇宙线μ子的大气契仑柯夫光像

给出理想条件下聚光镜焦平面上单个μ子大气契仑柯夫光像的理论结果．简要地介绍在标定第二代大气契仑柯夫光成像望远镜中的应用．     

Detection of GLE of December 13, 2006, using the muon hodoscope

GLE of December 13, 2006, is analyzed based on the data of the muon hodoscope located at MEPhI (Moscow). The setup supermodules registered that the muon flux intensity started increasing at 0254 UTC. An increase at a maximum (0300 UTC) was 0.61 ± 0.09% (for the 10-min data), which is larger than six standard deviations. The detection of the muon flux in the hodoscope mode for the first time made it possible to obtain the two-dimensional images of an increase in the muon flux. A comparison of the muon hodoscope and neutron monitor data makes it possible to conclude that the muon event was caused by a highly collimated bunch of the solar proton fast component.     

Multiple scattering of muons in beryllium

The defocussing and the depolarization of a high energy muon beam in a beryllium filter, often used to eliminate accompanying pions, have been studied. The quantum mechanical transport equation of Waldmann, which can also be used to describe the multiple scattering of Dirac particles, is solved with a distorted wave Born approximation. Calculations are done for both the Thomas-Fermi and the Hartree-Fock potential of the beryllium atom. It is shown that the Hartree-Fock potential leads to a less divergent beam. The depolarization of a longitudinally polarized muon beam in passage through a thin beryllium foil is also studied.     

Theory of paramagnetic and critical spin fluctuations in simple magnets

Recent theoretical work on the response functions observed in magnetic neutron scattering and muon spin relaxation experiments is briefly surveyed. Coupled-mode theory is found to provide a tolerable account of experiments performed on the paramagnetic and critical regions over a wide range of frequencies and wave vectors.     

Atmospheric effects on cosmic-ray muon intensities at deep underground depths

Summary On the basis of the theoretical calculation of the atmospheric effect on the cosmic-ray muon intensity, it is demonstrated that the following two anomalous facts recently reported from muon observations at deep underground stations can be attributed to the atmospheric-temperature effect. One is the remarkable dependence of the muon intensity on the atmospheric pressure observed at Poatina (365 m w.e. in depth) and Matsushiro (250 m w.e. in depth), which is contradictory to theoretical expectations, and the other is the semi-annual variation in the muon intensity at Matsushiro, which exhibits a striking contrast to annual variations usually observed at underground stations shallower than Matsushiro. In the present paper, the barometer coefficient and the partial temperature coefficient are also provided for various combinations of parameters such as the muon threshold energy and the zenith angle to meet any requirement of observations.

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Riassunto Sulla base del calcolo teorico dell'effetto atmosferico sull'intensità dei muoni dei raggi cosmici, si dimostra che due fatti anomali riportati recentemente riguardanti osservazioni muoniche in stazioni a grande profondità si possono attribuire all'effetto della temperatura atmosferica. Uno è la notevole dipendenza dell'intensità muonica dalla pressione atmosferica osservata a Poatina (365 m w.e. di profondità) e Matsushiro (250 m w.e. di profondità), che è in contraddizione con previsioni teoriche, e l'altro è la variazione semiannuale nell'intensità muonica a Matsushiro, che mostra un contrasto stridente con le variazioni annuali osservate solitamente in stazioni sotterranee meno in profondità di Matsushiro. In questo lavoro si forniscono il coefficiente barometrico e il coefficiente parziale di temperatura per varie combinazioni di parametri come l'energia di soglia muonica e l'angolo zenitale per soddisfare ogni esigenza di osservazione.