Dynamics of muons in the ferroelectric material KDP

Muon spin relaxation in zero field and longitudinal field was measured in single crystal samples of KH₂PO₄ (KDP) and KD₂PO₄ (DKDP) over a temperature range of 5 K to 300 K. At low temperatures, diamagnetic muons and muon substituted radicals with nuclear hyperfine coupling can be observed. For both KDP and DKDP, a minor change was observed in the dynamics of the muon below 140 K. Above 140 K, the mobility of the muon appears to increase and the diffusion rate becomes faster with increasing temperature. Only a small increase in the relaxation rate is observed in KDP due to the presence of theH ⁺, suggesting that the relaxation effects probably originate from the³¹P.     

Muon spectroscopy for studying magnetism and protons and lithium dynamics in spinel manganese oxides

Polarised positive muons can be implanted into any type of material and rapidly thermalize, then the local magnetic environment dictates the evolution of muon spin vectors and provokes the muon depolarisation. The muon spin relaxation (μSR) technique provides interesting information on magnetism and spin dynamics in spinel lithium manganates insertion compounds. In this work, we compare the behaviour of muons into a lithium-rich spinel manganese oxide and its lithium extracted product. The chemical extraction of lithium from Li_1.33Mn_1.67O₄, where all the manganese is Mn^IV, is essentially a lithium by proton ion exchange process to give a protonated manganese oxide with spinel structure, H⁺–MnO₂. Muons clearly have showed the presence of protons in H⁺–MnO₂, and the movement of lithium ions or protons at increasing temperatures in both samples. Muons are quasi-static in these compounds, and they are located both in ‘regular’ lithium and proton sites and also in interstitial sites of the spinel structure, these latter being used during diffusion of lithium ions. Below 50 K, static muons behave as in a paramagnet, where Mn magnetic spins are slowing down and ordering near 6 and 14 K in the protonated and lithiated spinels, respectively.     

The source of trimuon events in neutrino scattering

A comprehensive study indicates that equally likely sources for trimuon events neutrino scattering are (a) charged heavy lepton production (with decay to three muons) and (b) simultaneous production of a neutral lepton (with decay to two muons) and a heavy quark (with decay to one muon). The sequential decay of a heavy quark to two muons is less likely. An intriguing model yielding simultaneous M⁰ and b quark production is proposed.     

Derivation of muon spectrum at high energies from the recent JACEE primary cosmic-ray spectrum using Fermilab data on meson production

Summary The energy spectrum of sea level muons in the range (10²÷10⁴) GeV has been calculated from the latest directly measured JACEE primary spectrum using Fermilab results on pp→π^± X and pp→K^± X inclusive reactions. The conventional pion atmospheric diffusion equation after Bugaevet al. has been used in this analysis to account the flux of muons emerged from the multiple generation of mesons in air. The derived muon spectrum has been compared with the earlier magnetic spectrograph data of Durham and Kiel groups. The latest BAKSAN scintillator telescope data is well in agreement with the calculated integral spectrum originated from the meson decays in the range (1÷10⁴) GeV.     

Study of condensed nitrogen by μSR method

The temperature dependences of parameters of the muon spin relaxation in liquid and crystalline nitrogen have been studied. It has been established that in condensed nitrogen there takes place a fast depolarization of muons. An anomalous behaviour of the amplitude and phase of muon precession is found in the vicinity of the orientation phase transition in solid nitrogen. It has been shown that muon spin relaxation parameters in nitrogen do not change at reduction of the oxygen impurity content from 0.7·10⁻⁴ to 10⁻⁶. The fast depolarization of muons in condensed nitrogen is apparently due to the formation of muonium atoms. To explain the phenomena observed, a model of the muonium chemical reaction is proposed. The initial phase of the muon precession has been measured as a function of the perpendicular magnetic field to determine the state of short-lived muonium in nitrogen. It has been determined that muonium in nitrogen is in an excited state. Consideration of the nuclear hyperfine interaction of muonium in condensed nitrogen makes it possible to give a qualitative explanation for the temperature dependence of the initial amplitude of the muon precession.     

Production of high-energy muons in gamma showers

We have calculated the number of high-energy muons in gamma showers generated by photoproduction and by muon pair creation. The prompt muons have flatter energy spectrum than the muons, which come from photoproduction and contribute significant fraction of the total muon rates for E_μ ? 1 TeV. The total rate of high-energy muons in gamma showers is, however, very low.     

Cosmic ray muons at a depth of 754 hg/cm2 in the Kolar gold Mines

A telescope of area 4 m², consisting of horizontal layers of plastic scintillators, neon flash tubes and absorbers was operated at a depth of 754 hg/cm² in the Kolar Gold Mines. New values for the vertical intensities of muons have been obtained from observations of the angular distribution over the slant depths ∼ 750–2300 hg/cm² and are compared with the existing measurements. From the angular distribution observed, we conclude that muons are produced wholly through the decay of pions and kaons up to energies of the order of 1 TeV. A value of 0.3±0.2 is estimated for theK/π ratio at production, for muon energies around 500 GeV. A decoherence distribution has been obtained for parallel muon events up to distances of the order of 10 m. From this we conclude that the averageP _t of the parents of muons of energy ∼ 250 GeV is of the order of 0.3 GeV/c. From an analysis of rock showers, we obtain the cross section for inelastic interaction of muons of mean energy 100 GeV as (3.8±1.5)×10⁻³⁰ cm²/nucleon.     

The effect of uniaxial static pressure on the behavior of an aluminum acceptor impurity in silicon

The effect of uniaxial compression on the behavior of shallow aluminum acceptor centers in silicon has been studied. The _μAl impurity atoms were created by implanting negative muons into silicon single crystals doped with phosphorus to 1.6×10¹³ cm^?3 (sample 1) and 1.9×10¹³ cm^?3 (sample 2). The muon polarization was studied in the temperature range 10–300 K. Measurements were performed in a magnetic field of 2.5 kG oriented perpendicularly to the muon spin. The samples were oriented so that the selected crystal axis ([111] and [100] in samples 1 and 2, respectively), the magnetic field, and the initial muon-spin polarization were mutually perpendicular. External pressure applied to the sample along the indicated crystal axis changed both the absolute value of the acceptor magnetic-moment relaxation rate and the character of its temperature dependence.     

Direct muon production in proton-nuclear collisions at 70, 50 and 35 GeV

Direct muon yields (μ^±) in the transverse momentum range of 1.9–3.1 GeV/c on Cu and Be nuclei at the proton energies 70, 50 and 35 GeV have been measured. The yield of direct μ/π is shown to considerably decrease when proton energy varies from 70 to 35 GeV. The charge ratio of direct muon μ⁺/μ^? as well as the dependence of the yield of direct muons on the atomic number of the target have been measured.     

On the change of polarization of positive muons in alkali halides

Positive muons implanted in nonconducting solids form with high probability hydrogenlike muonium atoms (µ ⁺ e ^–) with properties similar to those ofU ₂-centers. The influence of superhyperfine interactions with neighbor nuclei on the evolution of the polarization of the muon is investigated theoretically. The resulting muon polarization in longitudinal magnetic fields is calculated for muonicU ₂-centers in some alkali halides.     

Equivalent states of muonium and implanted hydrogen in silicon (experiment)

Main experimental data on the hydrogen-like states with an anisotropic hyperfine structure forming in silicon single crystals in the implantation of high energy muons and protons are presented. The characteristics of the “anomalous” muonium (Mu^*) and hydrogen-containing silicon AA9 states studied by the muon spin rotation (μSR) and ESR techniques in silicon with a due inclusion of the isotope effect are shown to be similar, thus suggesting the existence of two equivalent structures in silicon, Mu^* and AA9, differing only in the mass of the paramagnetic center.     

The lifetime of the dimuon atom

Summary The weak decay of a muon in the ground state of a dimuon atom is analysed. Although the two muons are correlated by Fermi-Dirac statistics, it is shown that, in marked contrast to the seemingly analogous case of neutron beta-decay in³H, statistics have no effect on the muon decay rate. The distinction between the two cases is discussed. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

The study of prompt and delayed muon induced fission

The mean life times of negative muons bound to actinide nuclei have been measured by detecting the time difference between a stopped muon and the arrival of fragments from delayed fission after muon capture. The deduced capture ratesΛ _c are 1.392(4)·10⁷/s for²³⁷Np, 1.290(7)·10⁷/s for²⁴²Pu and 1.240(7)·10⁷/s for²⁴⁴Pu. The results are compared with published data for the fission and the neutron decay channels and for the electron decay of the bound muon. Including a former measurement ofΛ _c for²³⁹Pu, an isotopic dependence of the muon capture rates in the Pu isotopes is clearly observed.     

Reconstruction of cosmic and beam-halo muons with the CMS detector

The powerful muon and tracker systems of the CMS detector together with dedicated reconstruction software allow precise and efficient measurement of muon tracks originating from proton-proton collisions. The standard muon reconstruction algorithms, however, are inadequate to deal with muons that do not originate from collisions. This note discusses the design, implementation, and performance results of a dedicated cosmic muon track reconstruction algorithm, which features pattern recognition optimized for muons that are not coming from the interaction point, i.e., cosmic muons and beam-halo muons. To evaluate the performance of the new algorithm, data taken during Cosmic Challenge phases I and II were studied and compared with simulated cosmic data. In addition, a variety of more general topologies of cosmic muons and beam-halo muons were studied using simulated data to demonstrate some key features of the new algorithm.     

Solar diurnal anisotropy measured using muons in GRAPES-3 experiment in 2006

The GRAPES-3 experiment at Ooty contains a large-area (560 m²) tracking muon detector. This detector consists of 16 modules, each 35 m² in area, that are grouped into four supermodules of 140 m² each. The threshold energy of muons is sec(θ) GeV along a direction with zenith angle θ and the angular resolution of the muon detector is 6°. Typically, it records ~4×10⁹ muons every day. The muon detector has been operating uninterruptedly since 2001, thus providing a high statistics record of the cosmic ray flux as a function of time over one decade. However, prior to using these data, the muon rate has to be corrected for two important atmospheric effects, namely, variations in atmospheric pressure and temperature. Because of the near equatorial location of Ooty (11.4°N), the seasonal variations in the atmospheric temperature are relatively small and shall be ignored here. Due to proximity to the equator, the pressure changes at Ooty display a dominant 12 h periodic behaviour in addition to other seasonal changes. Here, we discuss various aspects of a novel method for accurate pressure measurement and subsequent corrections applied to the GRAPES-3 muon data to correct these pressure-induced variations. The pressure-corrected muon data are used to measure the profile of the solar diurnal anisotropy during 2006. The data, when divided into four segments, display significant variation both in the amplitude (~45%) and phase (~42 m) of the solar diurnal anisotropy during 2006, which was a period of relatively low solar activity.     

Feasibility studies of the geochemical solar neutrino experiment205Tl(v,e−)205Pb

New investigations on the signal-to-background ratio of the geochemical solar neutrino experiment²⁰⁵Tl(v,e^?)²⁰⁵Pb using thallium minerals from Allchar (Yugoslavia) are presented. The contributions of several background processes producing²⁰⁵Pb induced by natural radioacitivities, stopped negative muons and fast muons are estimated. The production rate of²⁰⁵Pb by cosmic ray muons, derived from experimental investigations with 120, 200 and 280 GeV muons at the high energy muon channel of CERN, is significantly higher than expected by former estimations. The feasibility of the geochemical²⁰⁵T1 solar neutrino experiment is discussed.     

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.     

Investigation of the zenith angle dependence of cosmic-ray muons at sea level

Angular distribution of cosmic-ray muons at sea level has been investigated using the Geant4 simulation package. The model used in the simulations was tested by comparing the simulation results with the measurements made using the Berkeley Lab cosmic ray detector. Primary particles’ energy and fluxes were obtained from the experimental measurements. Simulations were run at each zenith angle starting from θ?=?0° up to θ?=?70° with 5° increment. The angular distribution of muons at sea level has been estimated to be in the form I(θ)?=?I(0°) cos ⁿ (θ), where I(0°) is the muon intensity at 0° and n is a function of the muon momentum. The exponent n?=?1.95±0.08 for muons with energies above 1 GeV is in good agreement, within error, with the values reported in the literature.     

High-statistics study of the low-energy cosmic-muons angular distribution: Results from MICRO

Summary We present results from MICRO, a muon telescope with good angular resolution, which has collected more than 31·10⁶ cosmic muons. Upper limits are given for the flux coming from point sources and for the periodic component from Cygnus X3.     

Fluxes of high- and ultrahigh-energy cosmic-ray muons

The positive excess of cosmic-ray muons at energies higher than 1 TeV is estimated taking into account the data obtained from accelerator experiments on the production of particle and antiparticles in proton-proton interactions at energies of ～20 TeV. The fluxes of cosmic-ray muons at energies up to ～10¹¹ GeV and the production functions of muon bremsstrahlung photons at different depths in the atmosphere are calculated with due regard for the contribution from the decay of J/ψ mesons. The analysis performed is based on the accelerator data and their extrapolation to higher energies.