Investigating the influence of a Forbush decrease on the detected flux of high-energy muons

The effect of Forbush decreases was studied for a flux of high-energy muons with a threshold of 220 GeV detected by the Baksan Underground Scintillation Telescope (BUST) of the Institute for Nuclear Research, Russian Academy of Sciences.     

Temperature effect of the integral flux of cosmic-ray muons at high energies

The temperature coefficients of the integral fluxes of cosmic-ray muons arriving at sea level vertically and horizontally with energies of 10², 10⁴, and 3 × 10⁶ GeV are calculated. Decays of pions, kaons, and charmed particles are considered as sources of muon generation in the atmosphere (according to current data on the generation cross sections of pions, kaons, and charmed particles in interactions between nucleons and the nuclei of atmospheric atoms, obtained in experiments on accelerators and in quantum chromodynamics models). The uncertainties in the generation cross sections of charmed particles are quite high.     

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.     

Direct production of muon pairs by high-energy muons

For ultrarelativistic muons, the cross section for the process μ+Z→μ+Z+μ⁺+μ^? is calculated with allowance for the nuclear and atomic form factors. It is shown that the nuclear form factor affects significantly the cross-section value. The transverse-momentum distribution of muons is calculated. An approximate formula determining the total cross section to within 2 to 3% is derived. The fluxes of groups of cosmic-ray muons generated by the above process are estimated at various depths. It is shown that calculations performed earlier overestimate significantly the fluxes of such groups.     

Analysis of seasonal variations of the cosmic ray muon flux and neutrons produced by muons in the LVD detector

The Russian-Italian Large Volume Detector (LVD) is located at the Gran Sasso underground laboratory at a depth of 3300 m w.e. To study the seasonal variations of the penetrating component of cosmic rays, the data on cosmic ray muons detected in 2001–2008 was analyzed, along with those associated with neutrons produced by muons since April 2003. One-year periodic variations of muons and neutrons produced by them were found. The maximum intensity is observed in July, in accord with theoretical concepts.     

Measurement of the polarization of positive muons produced in high-energy antineutrino interactions

The question whether scalar-type interactions contribute to weak interactions at large momentum transfer has been investigated by a measurement of the longitudinal polarization of positive muons produced in charged-current interactions of high-energy antineutrinos with iron. At an average momentum transfer <Q ²>=4 GeV² the muon spin is found to be oriented forward with respect to the muon momentum vector, with an average polarization of 1.10±0.24, consistent with positive helicity. A limit on scalar contributions of σ_{s, p}/σ_tot <7% at the 95% confidence level can be deduced. A search for violation of time reversal invariance which could manifest itself by a polarization component perpendicular to the muon production plane gave a limit of σ_tv/σ_tot <16% (95% c.l.). It is concluded that the weak leptonic charged current retains its dominant vector and axial vector structure at large momentum transfers.     

Direct observation of muon-pair production by high-energy muons in the liquid-argon calorimeter BARS

Experimental data accumulated over a long-term exposure of the big liquid-argon spectrometer BARS at the Institute for High Energy Physics (IHEP, Protvino) in a horizontal flux of cosmic rays are analyzed with the aim of selecting events that correspond to muon-pair production by muons in the sensitive volume of the detector. The results obtained in this way make it possible to perform, for the first time, a direct experimental test of various theoretical estimates of the total cross section for electromagnetic muon-pair production by high-energy muons.     

Strong variations of cosmic ray muons during thunderstorms

Experimental data about a strong decrease of the intensity of cosmic ray muons are presented. The event occurred during a thunderstorm on September 24, 2007 in Baksan Valley (North Caucasus). The threshold energy of muons is 100 MeV. In comparison with other events of this type detected previously, this event is remarkable by a longer duration (more than an hour and a half) and by the fact that well-pronounced correlations with lightning strokes are observed for the first time.     

Statistical properties of variations in cosmic ray muons during thunderstorms

An analysis is made of experimental data on variations in muons with a threshold of 100 MeV, detected by the CARPET air shower array in the Baksan Valley during thunderstorms of 2008. It is shown that with using a special criterion for selecting statistically significant variations (0.2%), muon intensity variations are observed in the majority of cases. Their characteristic duration is ∼8 min. Their amplitudes can have different polarities and do not exceed 1%.     

Energy losses of high-energy muons and τ-leptons in inelastic scattering by nuclei

A hybrid model is used to calculate the losses of muons and τ-leptons in inelastic scattering by nuclei in water and in ground. The model includes soft and semihard photoprocesses and also hard scattering with an exchange by a γ-photon and a Z₀-boson. In the calculations, nuclear effects, such as shading and antiscreening of nucleons, the EMC effect, and the Fermi motion of nucleons in a nucleus, are considered. The distinction in scattering between a particle and an antiparticle, conditioned by an admixture of a weak neutral current, is discussed. Comparison with other calculations is given. Formulas for the coefficients of energy losses of muons and τ-leptons in water and in ground are obtained which approximate the calculation results over a wide interval of energies: 10²–10⁹ GeV. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 82–86, March, 2006.     

Measurement of the spectral flux density of negative muons at very low energies

The spectral flux density of negative muons has been measured down to 5 eV.     

Magnetic flux distribution in the bulk of the pure type-II superconductor niobium measured with positive muons

The spin precession of positive muons in ultra-pure Nb single crystals of high perfection, cooled down in transverse magnetic fields 0.68B _c2≤B _appl≤0.84B _c2 (B _c2=upper critical field) from temperatures well above the superconducting transition temperatureT _c=9.25 K, has been investigated in the temperature range 2.6 K≤T≤8.0 K. The experiments confirm the periodic fieldB(r) of triangular flux-line lattices as calculated from numerical solutions of the microscopic BCS-Gor'kov theory. The observed broadening of the van Hove singularities in the field distribution is discussed in terms of the combined effects of muon diffusion and random perturbations of the flux-line lattice.     

Temperature coefficients for muons at different zenith angles

Differential temperature coefficients for a muon flux have been calculated for different threshold energies and zenith angles. Comparison with the results of previous investigations shows only qualitative agreement, whereas the quantitative differences are significant. Possible reasons for such a discrepancy are discussed.     

Meson cascade in the atmosphere,uncertainties in calculating the fluxes of high-energy muons,and data of direct measurements

A new calculation of the atmospheric fluxes of cosmic-ray hadrons and muons in the energy range 10–10⁴ GeV is performed on the basis of the method for solving nuclear-cascade equations with allowance for a nonscaling behavior of inclusive hadron-production cross sections, the growth of cross sections for inelastic hadron-nucleus collisions with increasing energy, and a non-power-law character of the primary spectrum. The fluxes of secondary cosmic rays at various levels in the atmosphere are calculated for three models of the spectrum and composition of primary cosmic rays. The effect of uncertainties in the spectrumand composition of primary cosmic rays on the flux of atmosphericmuons and their charge ratio at sea level is investigated. The calculated energy spectra of muons at sea level are compared with the results of previous experiments and the results of recent measurements performed by means of the L3 + Cosmic and CosmoALEPH spectrometers, as well as with the results of other calculations.     

Temperature and doping dependence of the high-energy kink in cuprates

It is shown that spectral functions within the extended t-J model, evaluated using the finite-temperature diagonalization of small clusters, exhibit the high-energy kink in single-particle dispersion consistent with recent angle-resolved photoemission results on hole-doped cuprates. The kink and waterfall-like features persist up to large doping and to temperatures beyond J; hence, the origin can be generally attributed to strong correlations and incoherent hole propagation at large binding energies. In contrast, our analysis predicts that electron-doped cuprates do not exhibit these phenomena in photoemission.     

Seasonal variations of the muon flux in the MUSTANG super telescope data

The temperature effect of the muon cosmic ray (CR) component is studied using the MUSTANG super telescope data (Greifswald, Germany) from 2007 throughout its period of operation. The original hourly data obtained with the telescope are adjusted for the temperature effect using a vertical atmospheric temperature profile at standard isobaric levels derived from the Global Forecast System (GFS) model. The model’s accuracy and applicability is evaluated using atmospheric sounding data collected over a number of years.     

On the presence of fictitious solar neutrino flux variations in radiochemical experiments

Journal of Experimental and Theoretical Physics - The currently available data on solar neutrino flux variation in radiochemical experiments and Cherenkov measurements have so far defied a simple...     

On the capture of muons in atoms

In previous calculations on the capture of negative muons in atoms we used the average energy loss per unit path length as a frictional force in the classical equations of motion. In the present note it is shown that the rare events where the muon, because of its high velocity in the inner parts of the atom, loses an energy which is larger than its total energy, are important for the average stopping power. For the calculation of capture ratios these large energy losses should be treated separately. The results differ significantly from those obtained previously, and are in better agreement with experiment.     

Investigation of the spectrum of high-energy muons by the method of multiple interactions on the basis of data from the Baksan underground scintillation telescope

Experimental data obtained with the aid of the Baksan underground scintillation telescope over a long period of its operation are analyzed with the aim of searches for an excess flux of ultrahigh-energy (≥100 TeV)muons. The multiple-interaction method, which is based on the ideas of the pair-meter technique, is used to analyze the energy spectrum of the muons. The phenomenological parameters of this method and its sensitivity to the shape of the spectrum are discussed. The experimental distributions are compared with the results of calculations for various versions of the muon spectrum. The possibility of separating ultrahigh-energy muons that fly in the vicinity of the axis of extensive air showers is assessed on the basis of the integrated number of recorded and simulated events featuring large energy depositions.