Precise Measurement of Muon Capture on the Proton

The aim of the μCap experiment is a 1% measurement of the singlet capture rate Λ _S for the basic electro-weak reaction μ + p → n + ν_μ. This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling constant g _P . It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The present method is based on high precision lifetime measurements of μ⁻ in hydrogen gas and the comparison with the free μ⁺ lifetime. The μ⁻ experiment will be performed in ultra-clean, deuterium-depleted H₂ gas at 10 bar. Low density compared to liquid H₂ is chosen to avoid uncertainties due to ppμ formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4π. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of the Cosmic-Ray Muon Detection System for Probing Internal-Structure of a Volcano

Very high-energy cosmic-ray muons penetrating through a mountain enable us to probe the internal structure of volcanoes. An improved cosmic-ray muon detection system comprising two segmented detectors with multiplicity cut of the soft components of cosmic rays was developed. The test measurement for the volcano Mt. Asama is described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Advantages and Limitations of Solid Layer Experiments in Muon Catalyzed Fusion

Since the discovery that muonic deuterium at energies near a few eV could travel distances of the order of 1 mm in condensed hydrogen, and in particular that muonic tritium and muonic deuterium could emerge from the surface of a solid hydrogen layer, the advantages of solid targets have enabled the study of several processes important in muon catalyzed fusion. A review of the results is presented, emphasizing the strengths and limitations of the use of solid hydrogen layer targets. This revised version was published online in August 2006 with corrections to the Cover Date.     

A New High-intensity, Low-momentum Muon Beam for the Generation of Low-energy Muons at PSI

At the Paul Scherrer Institute (PSI, Villigen, Switzerland) a new high-intensity muon beam line with momentum p < 40 MeV/c is currently being commissioned. The beam line is especially designed to serve the needs of the low-energy, polarized positive muon source (LE-μ⁺) and LE-μ SR spectrometer at PSI. The beam line replaces the existing μ E4 muon decay channel. A large acceptance is accomplished by installing two solenoidal magnetic lenses close to the muon production target E that is hit by the 590-MeV PSI proton beam. The muons are then transported by standard large aperture quadrupoles and bending magnets to the experiment. Several slit systems and an electrostatic separator allow the control of beam shape, momentum spread, and to reduce the background due to beam positrons or electrons. Particle intensities of up to 3.5 × 10⁸ μ⁺/s and 10⁷ μ⁻/s are expected at 28 MeV/c beam momentum and 1.8 mA proton beam current. This will translate into a LE-μ⁺ rate of 7,000/s being available at the LE-μ SR spectrometer, thus achieving μ⁺ fluxes, that are comparable to standard μ SR facilities.     

Muon Physics Possibilities at a Muon-Neutrino Factory

New intense proton accelerators with above GeV energies and MW beam power, such as they are discussed in connection with neutrino factories, appear to be excellently suited for feeding bright muon sources for low-energy muon science. Muon rates with several orders of magnitude increased flux compared to present facilities will become available. This will allow higher precision in experiments which were statistics limited so far such as searches for rare decays, muonium spectroscopy, muon capture, muon catalyzed fusion, muon decay studies and measurements muon moments and parameters. Novel and most important experiments will become possible. For example a permanent electric dipole moment (edm_μ) of a muon could be searched with by far unprecedented accuracy and with a physics potential well beyond the possibilities of present electron, neutron and nuclear edm searches. Investigations of short lived radioactive nuclei using muonic atom spectroscopy would become feasible. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theory for Relative Strengths of Trapping of He+ Ions in Solid, Liquid and Gaseous Hydrogen

The study of trapping of He⁺ ion in solid hydrogen is important both as a problem in solid state physics and also as an applied physics problem in the field of muon catalyzed fusion (μCF). In μCF, He⁺ ion acts as a trap for μ⁻, interrupting the chain reaction aspect of the catalytic role of μ⁻ in producing fusion of deuteron and triton and of triton and triton in solid hydrogen composed of ²H–³H and ³H–³H molecules, respectively. Using the Hartree–Fock procedure, combined with procedures for including many-body effects, as well as relaxation effects associated with the He⁺–H₂ distances and the adjustment of the H–H separation, we have investigated the trapping of He⁺ in gaseous and solid state environments. For the former, the environment of He⁺ is simulated by a single hydrogen molecule and for the solid by clusters appropriately chosen to represent the hexagonal close-packed structure. Our results for the gaseous state indicate that the trapping is rather strong with a binding energy of 8.5 eV, with almost equal binding energy in the linear and triangular configurations with respect to the H–H direction. For the solid, both the likely sites for He⁺ trapping, namely the tetrahedral and octahedral interstitial sites, are also found to provide deep traps (8.6 eV) of almost equal strength, independent of the orientations of the neighboring molecules, showing that the trapping is not influenced by the orientational disorder in the surrounding hydrogen molecules. Further, the influence of next nearest neighbor hydrogen molecules is found to enhance the trapping energy for He⁺ substantially, by 0.6 eV, with the incorporation of the third nearest neighbors having a much smaller added effect, demonstrating the convergence of our results with respect to the size of the cluster chosen to simulate the solid. The substantial influence on the He⁺ trapping energy found for the neighbors beyond the nearest ones provides an explanation of the greater accumulation of helium in the solid state of hydrogen in μCF experiments as compared to the liquid. Suggestions are made regarding the possible reasons for the almost negligible accumulation of helium in the liquid state. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theory of Isotope Effects on He+ Trapping in Solid Hydrogen

We are currently investigating the influence of vibrational effects on the strength of trapping of He⁺ in solid hydrogen. Such effects can lead to an isotope dependence of the trapping energy associated with the hydrogen molecules and He⁺ ion. At the present time, our focus is on the isotope effect for ³He⁺ and ⁴He⁺, which we are studying through the vibrational motions of the trapped He⁺ ions in the potential they experience as they move about their equilibrium positions. The potential governing the vibrations has been obtained from Hartree–Fock cluster calculations of the total energy of the cluster composed of the He⁺ ion and up to the third nearest neighbor hydrogen molecules as a function of the displacement of the He⁺ ion from its trapped position. The energy eigenvalues for the ground vibrational states of ³He⁺ and ⁴He⁺ in this potential come out as 1.29 and 0.96 meV, respectively, leading to corresponding reductions by these amounts in the binding energy of 8.6 eV for both ions without vibrational effects. The difference of these reductions can be considered as an isotope shift, its value for this case being 0.33 meV. From the analysis for these results, it is suggested that isotope shift effects for deuteron and triton in solid D–T would have the same order of magnitude. A procedure for more accurate investigations of the isotope shifts is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

A New Pseudospectral Method for Calculations of Hydrogen Atom in Arbitrary External Fields

A new pseudospectral method was introduced to calculate wavefunctions and energy levels of hydrogen atom in arbitrary potential.Some results of hydrogen atom in uniform magnetic fields were presented,high accuracy of results was obtained with simple calculations,and our calculations show very fast convergence.It suggests a new method for calculations of hydrogen atom in external fields.     

Muon Motion Induced by a Superintense Laser in Muon‐Catalyzed Fusion

Considering the mixture after muon‐catalyzed fusion (μ CF) reaction as overdense plasma, we study muon motion in the plasma produced by a superintense linearly polarized femtosecond laser pulse. Muon drift along the propagation of laser radiation remains after the end of the laser pulse. At the peak laser intensity of 10²¹W/cm², muon goes from the skin layer into field‐free matter at short time which is much less than the pulse duration, before the laser pulse reaches its maximum. Besides, the influence of the laser on other particles in the plasma is less. Hence, this work can avoid muon sticking to alpha (α) effectively and reduce muon‐loss probability in μ CF. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Muon radiography technology for detecting high-Z materials

This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials. Various scenarios of threat material detection are simulated with the Geant4 toolkit. PoCA （Point of Closest Approach） algorithm reconstructing muon track gives 3D radiography images of the target material. Z-discrimination capability, effects of the placement of high-Z materials, shielding materials inside the cargo, and spatial resolution of position sensitive detector for muon radiography are carefully studied. Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection.     

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。     

KIMS地下实验中μ子本底的研究

KIMS是寻找和研究暗物质WIMP的实验组. 在WIMP寻找实验中，μ子是十分重要的一种本底. 我们对地下700m深的Yangyang实验室内的μ子通量进行了测量. 介绍了μ子探测器的结构和性能测试. 描述了对μ子入射位置和角度分布的分析，并进行了蒙特卡罗模拟. 实验室内的μ子通量测量值为(7.0±0.4))×10^-8/s/cm²/sr.     

Muon identification and pion rejection in the 4th concept

We describe a completely new way to reconstruct and identify muons with high efficiency and very high pion rejection in the 4th concept detector. The dual-solenoid magnetic field allows the reconstruction and precision momentum measurement of muons down to a few GeV (just the energy loss in the 10-λ_int calorimeter and the coil) and the dual-readout calorimeter provides a new, unique and powerful separation of muons from pions. We use test beam data for the calorimeter and calculations for the magnetic fields.      

Ab Initio Investigation of Helium Bubble Formation from Trapped He+ Ions in Solid Hydrogen

We are involved in a program aimed at a first-principles examination of the possibility of helium bubble formation in solid hydrogen. Our procedure is based on an extension of the Hartree–Fock cluster approach that we have been using for study of individual He⁺ ions in solid hydrogen. The preliminary results of our cluster investigations of a particular configuration of two He⁺ ions in neighboring tetrahedral interstitial positions are presented here. It has been found that the hydrogen molecules common to the two He⁺ ions lead to a substantial attractive force between the ions that almost overcomes their inherent repulsion, leading to a binding energy for this configuration only slightly less than the binding energy for two well separated trapped He⁺ ions. The analysis of our results have suggested future investigations of different pairs of trapping sites which appear to be more favorable for providing higher binding energies for the He⁺ pairs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muon g - 2 in the Littlest Higgs Model

In this paper the anomalous magnetic dipole moment of muon in the littlest Higgs (LH) model is studied at one-loop level. We discuss the dependence of the contributions on the global symmetry breaking scale f, mixing angles c and cˊ, and the Higgs triplet vacuum expectation value vˊ in the electroweak precision data preferring ranges. We find that the LH model can give a relatively small, but non-negligible extra weak contribution to the muon anomalous magnetic moment and can reduce the deviation of Δa_μ from 2.6σ for the SM to 2.5σ for the LH model.     

Theoretical Study of Trapping Sites for Muon in the Heme Group of Cytochrome c and Associated Shifts in Muon Spin Relaxation Frequencies

Muon Spin Relaxation (μSR) experiments are currently being conducted on the important electron transfer molecule cytochrome c (cyt c) with the goal to find out about microscopic details of the path the moving electron is taking. Simultaneously we are using the Unrestricted Hartree–Fock Cluster Procedure to determine the trapping sites for muon (μ⁺) and muonium (Mu) in the heme unit of cyt c and the associated hyperfine interactions. For the trapping sites with the highest binding energies for μ⁺, namely the nitrogen and the carbon of the pyrrole rings, we have used the available magnetic susceptibility data together with our calculated hyperfine fields to predict the Knight-shifts. At room-temperature we found 88.4 ppm and 79.0 ppm for the most attractive N- and adjacent C-site, respectively. At 150 K, these shifts increase to 172.7 ppm for the N-site and 153.7 ppm for the C-site. This revised version was published online in September 2006 with corrections to the Cover Date.     

Muon Anomalous Magnetic Moment in the Supersymmetric Models with and Without Right—Handed Neutrinos

We discuss the anomalous magnetic moment of muon in the minimal supersymmetric model with and without right-handed neutrinos.In the same framework,the decay width of τ→μγ is also evaluated.Considering the measured g-2 value of muon in the E821 experiment and other experimental constraints on the lepton-flavor-violation processes,we carry out numerical analysis on the concerned observables in the minimal supergravity scenario.     

Dai Omega, a Drastic Upgrading of the Surface Muon Channel Using a Large Solid Angle Axial Focusing Superconducting System

An axial focusing surface muon channel, Dai Omega, is under construction. This channel will be installed at KEK-MSL in the summer of 2001. It uses four large aperture superconducting coils for axial focusing to realize a high-intensity positive muon beam by improving the solid angle acceptance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimation of Sea Level Muon Energy Spectrum at High Latitude from the Latest Primary Nucleon Spectra Near the Top of the Atmosphere

The vertical muon energy spectra at sea level have been estimated from directly measured primary cosmic-ray nucleon spectrum. The hadronic energy moments have been calculated from the CERN LEBC EHS data on the Lorentz invariant cross-section results on pp ^±X and pp K^±X inclusive reactions and are duly corrected for A–A collisions. Finally, the sea level muon energy spectra have been calculated from the decay of conventional mesons, using standard formulation. The estimated muon spectra are found to be in good agreement with the directly measured muon spectra obtained from the different experiments.     

有效温度的计算和大气μ子温度效应的Monte Carlo模拟

高空大气气温变化引起地面或地下探测到的宇宙线μ强度变化.本文介绍了基于日内瓦附近Payerne气象站气球数据的大气μ子有效温度的计算,并选取代表性的8个大气样本模拟了L3+Cosmics探测器位置的宇宙线μ子温度效应,计算了温度系数,得到极端高空温度情况下可能探测到的μ子强度变化的量级,为L3+Cosmicsμ谱精细测量和温度系数的抽取提供参考.