Measurements of the integrated muon intensity at large zenith angles

Precision measurements of the zenith-angle distributions of muons in the range 61°–89° are performed using the DECOR coordinate detector. The total number of selected events is more than 20 million. The dependence of the integrated muon intensity on the zenith angle is determined for several threshold energies in the range from 1.7 to 7.2. GeV. The experimental results in these ranges of zenith angles and threshold energies are obtained for the first time. It is demonstrated that the dependence of the integrated muon intensity on the zenith angle is adequately described by a simple analytical relationship.     

Experimental observation of the effect of the Earth’s magnetic field on the EAS muon component

The dependence of the intensity of muon bundles recorded using the DECOR coordinate track detector on the angle between the directions of bundle arrival and the Earth’s magnetic field has been analyzed for several ranges of zenith angles. It is found that the intensity of muon bundles decreases with an increase in the transverse magnetic field component, in contrast to the results of the calculation performed on the assumption of flux azimuthal symmetry. The effect of coplanarity of particle tracks in the plane formed by the core of an extensive air shower and the Lorentz force vector is also observed.     

Cosmic Ray Muon on the Altitude of 5500m Above the Sea Level

215 blocks of K6,K7,K8 lead emulsion chambers on Mt.Kanbala are carefully scanned,and a total of 111 muon events are found with zenith angle M(=tgθ)>2.5.The energy of muon showers are determined by saddle-shape curves.The intensity of muon,the energy spectrum and the zenith angle distribution of muon showers on the altitude of 5500m above sea level are shown in the energy region E_μ>2TeV.Meanwhile the simulation calculation is done for the behaviour of muon inside the emulsion chamber,simulation results are basically in agreement with the experiment.     

Tau neutrinos favored over sterile neutrinos in atmospheric muon neutrino oscillations

The previously published atmospheric neutrino data did not distinguish whether muon neutrinos were oscillating into tau neutrinos or sterile neutrinos, as both hypotheses fit the data. Using data recorded in 1100 live days of the Super-Kamiokande detector, we use three complementary data samples to study the difference in zenith angle distribution due to neutral currents and matter effects. We find no evidence favoring sterile neutrinos, and reject the hypothesis at the 99% confidence level. On the other hand, we find that oscillation between muon and tau neutrinos suffices to explain all the results in hand.     

Precision measurement of neutrino oscillation parameters at INO-ICAL detector

A magnetized Iron CALorimeter (ICAL) detector at the India-based neutrino observatory (INO) is used to study neutrino oscillation sensitivity using atmospheric muon neutrino source. The ICAL detector will be able to detect muon tracks and hadron showers produced by neutrino interactions with the iron target. We have performed precision measurement analysis for the atmospheric neutrino oscillation parameters with the muon neutrino events, generated by Monte Carlo NUANCE event generator. A marginalized χ² analysis based on reconstructed neutrino energy and muon zenith angle binning scheme has been performed to determine the sensitivity for the atmospheric neutrino mixing parameters, \(\sin ^{2}\theta _{23}\) and \(| {\Delta } m^{2}_{23}|\).     

The mass hierarchy with atmospheric neutrinos at INO

We study the neutrino mass hierarchy at the magnetized Iron CALorimeter (ICAL) detector at India-based Neutrino Observatory with atmospheric neutrino events generated by the Monte Carlo event generator Nuance. We judicially choose the observables so that the possible systematic uncertainties can be reduced. The resolution as a function of both energy and zenith angle simultaneously is obtained for neutrinos and anti-neutrinos separately from thousand years un-oscillated atmospheric neutrino events at ICAL to migrate number of events from neutrino energy and zenith angle bins to muon energy and zenith angle bins. The resonance ranges in terms of directly measurable quantities like muon energy and zenith angle are found using this resolution function at different input values of θ₁₃${\theta }_{13}$. Then, the marginalized χ²s${\chi }^2\mathrm{s}$ are studied for different input values of θ₁₃${\theta }_{13}$ with its resonance ranges taking input data in muon energy and zenith angle bins. Finally, we find that the mass hierarchy can be explored up to a lower value of θ₁₃≈5°${\theta }_{13}\approx 5°$ with confidence level >95% in this set up.     

Cosmic ray sea level muon spectrum at large zenith angle derived from the latest JACEE primary spectrum

The sea level cosmic ray muon spectrum at 89° has been estimated from the primary nucleon spectrum estimated after the latest JACEE measurements. The p-A collision cross section has been considered for hadronic energy moments calculations. The meson atmospheric diffusion equations after Bugaev et al. have been used in this analysis. The calculated large zenith angle muon spectrum is well in accord with the latest MUTRON data for cosmic ray muons arriving at zenith angles 86° to 90°.On leave from Indian Association for the cultivation of Science, Calcutta 700032, India.     

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.     

Muon bundles produced by UHE cosmic rays at large zenith angles

The first experimental results on a new EAS observable, the local muon density spectra measured with a large area coordinate detector DECOR in a wide range of zenith angles, are presented. These data correspond to the interval of primary particle energies from 10¹⁵ to 10¹⁸ eV. Some features of local muon density phenomenology are considered on the basis of an analytical model. Expected distributions of the events in the muon density have been calculated by means of the CORSIKA code and compared with experimental data. The text was submitted by the authors in English.     

Coincidence analysis in ANTARES: Potassium-40 and muons

The ANTARES neutrino detector, located deep underwater in Mediterranean sea, is currently almost complete and taking physics data. The amount of data collected so far allows for several kinds of neutrino studies. Yet, presently the principal task of the collaboration is to achieve thorough and precise understanding of the detector. Therefore, detector calibration and atmospheric muon studies are currently given high priorities. A new calibration technique, based on the use of natural background light in seawater, was recently invented. The method relies on correlated coincidences produced in triplets of ANTARES optical modules by Cherenkov light of beta-particles originated from ⁴⁰K decays. Based on similar ideas of coincidence analysis, a simple but powerful approach to atmospheric muon flux studies is currently being developed. The two methods and their role in the ANTARES experiment are briefly presented.     

Wide-aperture muon detector for diagnostics of the Earth’s atmosphere and magnetosphere

A wide-aperture large-area multilayered muon hodoscope is being constructed above the water Cherenkov calorimeter NEVOD (Moscow Engineering Physics Institute). This hodoscope is aimed at studying the processes in the Earth’s atmosphere and magnetosphere that lead to variations in the muon flux at the ground level. The structure of the detector and its data acquisition and triggering systems are described. Some preliminary results of the analysis of the data obtained using the first two supermodules of the system in the continuous series of measurements during 2005–2006 are discussed.     

Performance of the muon detector A under TIBET Ⅲ array

In order to observe gamma rays in the 100 TeV energy region, the 4500 m² underground muon detector array using water Cherenkov technique is constructed, forming the TIBET Ⅲ+MD hybrid array. Because the showers induced by primary gamma rays contain much fewer muons than those induced by primary hadrons, significant improvement of the gamma ray sensitivity for TIBET Ⅲ+MD array is expected. In this paper, the design and performance of the MD-A detector with large Tyvek bag is reported.     

A proposed NEVOD-EAS installation for the detection of extensive air showers

A new installation is dedicated to the independent evaluation of extensive air shower (EAS) energies detected in the NEVOD-DECOR experiment in the knee region of the energy spectrum. The design for the measuring system of the shower installation is based on clusters of scintillation detectors that are located on the roofs of laboratory buildings at MEPhI (Moscow) and will detect the electromagnetic (for near-vertical showers) and muon (for large zenith angles) EAS components. Features of the measuring system, the system for data acquisition and processing, and the results from investigating the characteristics of a single detector are discussed, along with the algorithm for event formation by the data of separate clusters.     

Discovery of atmospheric neutrino oscillations**

Atmospheric neutrinos are produced by cosmic ray interactions in the atmosphere. The zenith‐angle and energy dependence of the muon‐ and electron‐ neutrino events are observed in atmospheric neutrino experiments. Through these studies neutrino oscillations were discovered. In this article, studies of atmospheric neutrinos in the Kamiokande and Super‐Kamiokande experiments are described.     

Increase in the absorption length of inclined extensive air showers

The dependence of the number of extensive air showers with an energy above 10¹⁸ eV on the zenith angle θ is obtained in groups with a constant solid-angle step. The number of showers first decreases with an increase in the zenith angle and then, after reaching ～5°, increases strongly. With increasing energy, the kink on the dependence of the number of showers on θ is displaced towards larger angles, i.e., in the direction corresponding to the shift of the depth of the cascade-curve maximum.     

Expected energy spectrum of cosmic ray protons and helium below4 PeV measured by LHAASO

The Large High Altitude Air Shower Observatory(LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array(KM2 A), which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array(WCDA) and wide field-of-view Cherenkov telescope array(WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from 10~(14) eV to 10~(18) eV. The hybrid observation will be employed by the LHAASO experiment, in which the lateral and longitudinal distributions of extensive air shower can be observed simultaneously. Thus, many kinds of parameters can be used for primary nuclei identification. In this paper, high purity cosmic ray simulation samples of the light nuclei component are obtained using multi-variable analysis. The apertures of 1/4 LHAASO array for pure proton and mixed proton and helium(HHe) samples are 900 m~2 Sr and1800 m~2 Sr, respectively. Prospect of obtaining proton and HHe spectra from 100 TeV to 4 PeV is discussed.     

近红外白天恒星探测对比度分析

红外波段可以探测到足够多的星体用以导航。恒星-背景对比度是白天恒星探测时的一个重要指标,分析近红外波段,6星等恒星对比度随太阳天顶角、探测器高度和探测方位角的变化情况。结果显示,恒星-背景对比度随太阳天顶角近似于指数增长,40太阳天顶角时对比度是20时的2.69倍左右;一定高度时,对比度随探测器高度的增加近似指数增加,低于15 km时对比度仍小于3, 80 km时对比度达到60左右;随着探测方位角的增大,恒星-背景对比度基本上线性增大,30探测方位角时的对比度是0探测方位角时对比度的2.38倍。     

曝光时间对上行传输光束强度起伏的影响

上行传输光束的闪烁起伏影响星地激光链路的稳定性,而利用时间平滑效应,增加光电探测器曝光时间是克服大气闪烁的有效途径之一。考虑曝光时间的平滑效应,分别导出了小天顶角和大天顶角下的时间平滑因子表达式,在此基础上,分析了接收终端离地高度和天顶角对时间平滑效应的影响。研究结果表明,随着曝光时间的增大,上行传输光束的闪烁强度显著降低;随着接收终端离地高度和天顶角的增大,大气闪烁时间平滑作用降低。     

Cosmic muon flux at shallow depths underground

The cosmic muon background has been calculated for facilities placed at shallow depths. A relatively simple formula has been proposed for the muon spectrum at sea level that ensures the calculation of the depth dependences of the vertical muon intensity and integral muon flux. Calculations show that the zenith-angle distribution of the muon flux density is almost unchanged for depths from 10 to 100 m of solid rock. The muon angular distributions are presented for all three possible cases of the arrangement of the instruments in measurements carried out on the ground and at shallow depths. It has been shown that, to eliminate the cosmic muon background, it is necessary to install an active cosmic ray shielding “umbrella” covering a zenith angle ? of no less than 80°.     

Investigation of cosmic rays above the knee by means of muon bundles detected in a wide range of zenith angles

The results of investigation of muon bundles at the Earth’s surface in a wide range of zenith angles on the basis of the new phenomenological characteristic of extensive air showers—spectra of local muon density—have been investigated. Features of the local-density spectra are considered within a simple analytical model. The expected distributions of muon density in a wide range of zenith angles and primary energies, calculated on the basis of the CORSIKA code, are compared with the experimental data.