Primary cosmic ray and muon measurements with CAPRICE

The WiZard Collaboration has performed several investigations of the cosmic ray muon component in the atmosphere. In this paper, we review the most recent results from the balloon-borne CAPRICE experiment and discuss their relevance in the context of the atmospheric neutrino observations.     

Atmospheric variations in muon intensity for different zenith angles

The barometric and temperature coefficients of muon intensity for a layer of variable mass and the temperature coefficients for mass-weighted mean atmospheric temperature are found by regressions analysis from the results of continuous measurements of muon intensity at different zenith angles and atmospheric parameters. The temperature coefficients of muon intensity are determined for different atmospheric layers. Using the characteristics obtained, the changes in temperature are found for different atmospheric layers from the data on variations in muon intensity. The results obtained are compared with the observed temperature changes.     

Meteorological effects in the intensity of muon groups

The data of the experimental study of cosmic ray muon groups using the DEKOR setup for the period of 2004–2007, during which significant changes in the intensity of groups at the Earth’s surface were detected, are analyzed. It was found that these variations are caused by variations of weather conditions (temperature and atmospheric pressure); barometric and temperature coefficients were determined. It turned out that magnitudes of these coefficients for muon groups are significantly higher than available values for singlemuons. Possible physicalmechanismof the effect is discussed. Since muon groups are formed at high altitudes (of the order of several kilometers), the detected effect can be used for monitoring air temperature variations in the upper troposphere.     

Ultimate ground level enhancements of solar cosmic ray intensity

Possible values of ground level enhancements (GLEs) of the intensity of solar cosmic rays (SCRs) that can be recorded by neutron monitors (NMs) are estimated in two different ways for the ultimate spectra of solar protons. The first approach uses the statistical dependence between the maximum values of the integral proton flux >100 МeV and the GLE recorded by an NM. The second is to calculate the expected effect for the ultimate spectrum at a particular NM with known couple coefficients, atmospheric depth, and the threshold of the geomagnetic cutoff. Estimates using the first method vary from 9600 to 160000% for high-latitude NMs; estimates using the second method, from 1200 to 750000%. The obtained lower limits approximately correspond to GLE values observed earlier, and the upper limits are two orders of magnitude higher. Studies of the possible impact of solar proton events with spectra close to ultimate on the Earth’s atmosphere and biosphere should be continued.     

Narrow muon bundles from muon pair production in rock

We revise the process of muon pair production by high-energy muons in rock using the recently published cross-section. The three-dimensional Monte Carlo code MUSIC has been used to obtain the characteristics of the muon bundles initiated via this process. We have compared them with those of conventional muon bundles initiated in the atmosphere and shown that large underground detectors, capable of collecting hundreds of thousands of multiple muon events, can discriminate statistically muon induced bundles from conventional ones. However, we find that the enhancement of the measured muon decoherence function over that predicted at small distances, recently reported by the MACRO experiment, cannot be explained by the effect of muon pair production alone, unless its cross-section is underestimated by a factor of 3.     

On the structure of galactic cosmic ray intensity during its long-term variations

The structure of GCR intensity and its changes during the solar magnetic cycle are analyzed by numerically solving its transport equation. We propose a research method that allows us to use the intermediate results from numerical calculations, to resolve the intensity of galactic cosmic rays into components caused by sunspot and magnetic solar cycles, and to monitor the changes in energy in different parts of the heliosphere and different phases of the cycle. A method for dividing intensity into its components associated with the main physical processes determining the modulation of galactic cosmic rays is also proposed.     

Induction mechanism of cosmic ray production and kinks in the cosmic ray spectrum

Two kinks are observed in the energy spectrum of galactic cosmic rays. It is shown that the entire spectrum can be described, to a good approximation, by a single formula obtained on the basis of the hypothesis that the particles are produced and accelerated in plasma pinches by an induction mechanism under the assumption that three hierarchical groups of currents are present—interstellar, galactic, and metagalactic. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 225–230 (25 August 1996)     

雷暴电场对宇宙射线次级粒子μ 子的影响研究

西藏羊八井宇宙射线观测站的中子监测器主要探测宇宙射线次级粒子中能量在500 MeV—20 GeV的核子成分和少量的负μ子成分. 本文分析了2008—2010年观测站附近发生的62次雷暴期间中子监测器和大气平均电场仪的同步观测资料, 发现27次雷暴期间中子监测器计数率发生明显变化, 显著性S>5σ, 其中13次变化显著, 显著性S>10σ . 显著性S>10σ的13次个例信号变化百分比与地面电场场强幅值之间存在大体一致的变化趋势, 而显著性在5σ <S<10σ之间的14次个例信号变化百分比与地面电场场强幅值之间不存在相似的变化趋势. 较强雷暴当顶时中子监测器计数率变化一般不明显, 而中子监测器计数率变化明显的个例则多发生于雷暴云不当顶, 但探测器仍处于雷暴云下部正电荷层的控制范围之内时, 或者当顶雷暴处于形成或消散阶段. Dorman等把雷暴期间中子监测器计数率的变化归因于雷暴云内电场对宇宙射线次级粒子μ子的作用, 并建立了雷暴期间中子监测器计数率变化与雷暴地面电场相关联的理论. 本文分析发现雷暴期间羊八井中子监测器计数率变化与地面电场场强之间相关性较小或者没有相关性, 不支持Dorman的理论.     

Pulsations of the geomagnetic field associated with variations in cosmic ray intensity during thunderstorms

It was discovered that strong variations in the intensity of secondary cosmic rays observed during thunderstorms and earlier interpreted as a consequence of the cyclic generation of electrons and positrons in a strong electric field are accompanied in some cases by well-pronounced pulsations of the geomagnetic field. An experiment was performed with the CARPET array for studying extensive air showers of cosmic rays. This array, located in the Baksan Valley (North Caucasus), was used as a particle detector. Magnetic measurements were made using a high-precision magnetic variation station located deep underground in a tunnel of the Baksan Neutrino Observatory at a distance of about 4 km from the CARPET array.     

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.     

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.     

Diurnal variations in cosmic ray intensity caused by high latitude magnetospheric-ionospheric current systems

Cosmic ray intensity measurements obtained with the neutron monitors at Thule (geomagnetic latitude, 84.8°) and McMurdo (geomagnetic latitude, −79.9°) in 2007–2009 were used to test the effect of the magnetic field generated by magnetospheric currents flowing along geomagnetic field lines in the high latitude region on cosmic ray intensity. The existence of such a relation in a region where the geomagnetic field lines are virtually radial should revise our concept of the unimpeded access that cosmic ray particles have to the Earth’s atmosphere.     

Unusually low-amplitude anisotropic wave-train events of cosmic ray intensity during 1981–1994

Investigation has been made for unusually low-amplitude anisotropic wave train events (LAE) for cosmic ray intensity data of Deep River neutron monitoring station during the period 1981–94. It has been observed that the phase of diurnal anisotropy remains in the same co-rotational direction for most of the LAEs while the phase shifts to early hours for some of the LAEs in diurnal anisotropy. During minimum solar activity, LAEs have been observed to be dominant. Solar wind plasma (SWP) parameters, inter-planetary magnetic field and various features at solar disk have also been studied. The amplitude remains low continuously for most of the days while the phase shifts to earlier hours. Occurrence of LAE is independent of the nature of interplanetary magnetic field (IMF).     

Identification of the primary cosmic ray

The nature of the primary particle giving rise to an atmospheric shower may be, to some extent, inferred from the observable properties: longitudinal profile (especially position of the maximum of the number of charged particles) or shape at ground level (lateral distribution, curvature and thickness of the shower front, muonic component). Distinguishing different nuclei cannot be performed unambiguously on a single shower, because of the random fluctuations in the first steps of the cascade; however, it is possible to study the composition of the incident flux on a statistical basis: showers from heavier nuclei have a faster development, and contain more muons. The uncertainties on the hadronic interactions at the highest energies limit the reliability of the identification. Other primaries, if they exist, could be easier to distinguish. Photons would give a slower development than protons, especially at highest energies, and a very reduced muonic component; neutrinos would be characterized by deep interactions in the atmosphere, or even within the Earth, giving almost horizontal showers with a large electromagnetic component, clearly different from the muonic tail of showers induced in the upper atmosphere by nuclei. Such ‘exotic’ primaries have not yet been observed. To cite this article: P. Billoir, P. Sommers, C. R. Physique 5 (2004).     

The search for ultrashort bursts of cosmic ray intensity on the Andyrchi air shower array

A new data acquisition system that makes it possible to measure the count rate of each detector of the Andyrchi air shower array every millisecond is described. This new detection system allows us to search for ultrashort bursts of cosmic ray intensity when operating the array in the single-component detection mode. The method of data acquisition and analysis is discussed.     

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.