Muon Content Research Articles

Extensive air showers with the small muon content in the region of ultrahigh energies

Ultrahigh-energy extensive air showers registered at the Yakutsk EAS array have been considered. The showers without the muon component are detected. Almost one half of them forms the clusters, the arrival directions of which correlate with the nearest pulsars. The classification of showers by muon composition has been carried out and the existence of four classes of showers has been shown. The problem of mass composition and origin of ultrahigh-energy cosmic rays are discussed.

Percolation and high energy cosmic rays above 10 17 eV

In this work we argue that in the interpretation of the energy dependence of the depth of the shower maximum and of the muon content in high energy cosmic ray showers ( E ≳ 10 17 eV ) , other variables besides the composition may play an important role, in particular those characterising the first (high energy) hadronic collisions. The role of the inelasticity, of the nature of the leading particle, and of the particle multiplicity are discussed. A consistent interpretation of existing data within a string percolation model implemented in a hybrid, one-dimensional simulation method is given.

Classification of ultrahigh-energy extensive air showers in terms of the muon content

Ultrahigh-energy extensive air showers detected at the Yakutsk array are analyzed. Showers different in the muon content are revealed. Four classes of showers are separated.

Upper limit on the ultrahigh-energy photon flux from AGASA and Yakutsk data

We present the interpretation of the muon and scintillation signals of ultrahigh-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest-energy events with known muon content and conclude that at the 95% confidence level none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at a 95% confidence level on the fraction of primary photons in the cosmic-ray flux above ${10}^{20}\text{ }\text{ }\mathrm{eV}$. This result disfavors the $Z$-burst and superheavy dark-matter solutions to the Greisen-Zatsepin-Kuzmin--cutoff problem.

Estimation of the attenuation length of the charged particle density at 600 meters from the shower axis

Abstract The observations of the giant air showers with energies well in excess of 10 20 eV put forward a very dramatic puzzle to cosmic ray astrophysics. Billions of secondary particles produced in interactions with the atomic nuclei and decay processes in the atmosphere are spread out to distances of about a few kilometers from the shower axis at ground level. The density of charged particles at 600 m from the shower axis is used as a reliable estimator of the energy of individual showers. As giant showers are assumed to be isotropic, one needs the attenuation length of a signal in a standard scintillator at 600 m from the shower axis to recalculate the signal observed in a vertical direction. This attenuation length usually was estimated indirectly by taking cuts of constant intensity in signal spectra for showers detected at different zenith angles. The reliability of such a procedure for the total number of secondary particles was analyzed. As for the signal at 600 m this reliability is investigated in this paper. Besides, some new methods are also discussed. The first one is related to the longitudinal development of a signal and the second to calculations of signals both for vertical and inclined showers with the same energy. Calculations were carried out in terms of the quark-gluon string model for primary protons and an observation level of 1020 g/cm 2 for showers with various zenith angles. The Landau–Pomeranchuk–Migdal effect and neutral pions interactions are taken into account at high energies. The Monte Carlo method was used for primary protons while cascades from numerous charged pions were considered with the help of transport equations. Nearly 10 5 showers were simulated with various energies and zenith angles using a cluster of computers. Then signal spectra were calculated assuming the standard energy spectrum of the primary particles. Finally taking cuts of the signal spectra one can obtain the reconstructed development curve for a signal and estimate the attenuation length. The longitudinal development of a signal was calculated to estimate the attenuation length in the individual showers. The applicability of the second method is straightforward. As a result the value of 530±60 g/cm 2 was estimated for the attenuation length by the constant intensity cuts method which should be compared with 520±70 g/cm 2 found experimentally. The dependence of this calculated attenuation length on the primary particle energy agrees roughly with the experimental data excepting very inclined showers. The dependence on the zenith angle is also shown. The increase of the attenuation length with the zenith angle agrees with enlarging of the muon content of the charged particle density. The longitudinal development gives a very broad distribution of the attenuation length changing from ∼300 to 3000 g/cm 2 , while calculations for vertical and inclined showers lead to various attenuation lengths distributed mainly between 450÷ 550 g/cm 2 excepting nearly vertical showers for which the range of distributions is elongated above 3000 g/cm 2 . So the standard method of the constant intensity cuts may decrease (or increase) energy estimates of showers by a factor of 1.1–2.

Recent progress in EAS measurements and the single SNR model of the knee

New complex EAS measurements by CASA-MIA and KASCADE, which have very high statistical precision, are analysed in the light of the single SNR model ( SSM ) of the knee. It is shown that both EAS size spectra and their muon content have remarkable irregularities which coincide with the structures found by us in our ‘world survey’. There is thus strong support for our model. Estimates of the protons and helium nuclei abundance in SNR are given.

Constraints on Gamma‐Ray Emission from the Galactic Plane at 300 TeV

We describe a new search for diffuse ultrahigh energy gamma-ray emission associated with molecular clouds in the galactic disk. The Chicago Air Shower Array (CASA), operating in coincidence with the Michigan muon array (MIA), has recorded over 2.2 x 10^{9} air showers from April 4, 1990 to October 7, 1995. We search for gamma rays based upon the muon content of air showers arriving from the direction of the galactic plane. We find no significant evidence for diffuse gamma-ray emission, and we set an upper limit on the ratio of gamma rays to normal hadronic cosmic rays at less than 2.4 x 10^{-5} at 310 TeV (90% confidence limit) from the galactic plane region: (50 degrees < l < 200 degrees); -5 degrees < b < 5 degrees). This limit places a strong constraint on models for emission from molecular clouds in the galaxy. We rule out significant spectral hardening in the outer galaxy, and conclude that emission from the plane at these energies is likely to be dominated by the decay of neutral pions resulting from cosmic rays interactions with passive target gas molecules.

A limit to the rate of ultra high energy γ-rays in the primary cosmic radiation

Abstract An upper limit to the flux of Ultra High Energy (UHE) γ-rays in the primary cosmic radiation is obtained through the data of the electromagnetic and the muon detectors of the EAS-TOP Extensive Air Shower array (Campo Imperatore, National Gran Sasso Laboratories, atmospheric depth 810g cm−2). The search is performed by selecting Extensive Air Showers (EAS) with low muon content. For EAS electron sizes Ne > 6.3 · 105, no showers are observed with the core located inside a fiducial area and no muons recorded in the 140 m2 muon detector, during a live time of 8440 h. The 90% c.l. upper limit to the relative intensity of γ-ray with respect to cosmic ray (c.r.) primaries is I γ I c.r. −5 , at primary energy E0 ≥ 1015 eV: this limit is lower than reported in previous measurements.

A search for diffuse sources of ultra high energy gamma-rays

We describe a search for diffuse emission from several candidate sources of gamma-rays with energieauthor00 TeV, using the Chicago Air Shower Array / Michigan Muon Array (CASA-MIA) experiment. Since March 1990, CASA-MIA has recorded over 2.0 × 10 9 air shower events. Searches for diffuse emission are based upon the muon content of air showers. Candidate source regions include molecular clouds in the galaxy and the galactic plane. Results from CASA-MIA are compared to predicted diffuse emission.

Muons in extensive air showers. II. The muon content of EAS as a function of primary energy

For pt. I see ibid., vol. 21, p. 129 (1995). The muon content of EAS has been measured at Haverah Park over an extensive primary energy range ~5*1014<Ep<1020 eV. Above Ep~1016 eV the relative muon content has been found to decrease gradually in a smooth fashion up to ~Ep=1020 eV. This suggests to us that there is no major change in primary mass composition or the nature of nuclear interactions throughout these energies. Below 3*1015 eV, however, there does appear to be a significant change in the muon content characteristics. Observations, reported in this paper, indicate a more rapid reduction in the proportion of muons with increasing energy in the decade of primary energy below 3*1015 eV. Although some groups claim to observe no such a muon feature in this energy region, there is some support for our conclusion. If such a change is attributed to a change in primary mass composition then the implication must be a change to a smaller mean mass at energies approaching 3*1015 eV from below.

Muon content of UHE air showers: discrimination method between electromagnetic and hadronic cascades

Results from a detailed Monte Carlo simulation for the muon component of EAS, at mountain altitude (800 g cm-2), generated by vertical gamma -rays, protons, oxygen and iron primary cosmic rays, in the energy range 1012-1016 eV, are provided for muon threshold energies from 0.1 to 100 GeV. In the simulation of the different components of the shower ( mu +or-, e+or-, gamma ...), the CORSIKA (cosmic ray simulator for cascade) code has been used to allow for both, electromagnetic and hadronic interactions. Results on the variation and fluctuation of the total muon number with shower size and primary energy are obtained, as well as longitudinal developments, lateral distributions of low-energy muons in air showers and muon energy spectra. Moreover, analytical expressions are fitted to the muon lateral developments, and muon energy spectra have been parametrized to a log-normal distribution. Apart from their value as new results, they may be used for the design of current studies at mountain altitudes. We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available.

Study of the high energy cosmic ray cascades using the dual parton model

Abstract In this paper we describe an application of the two component dual parton model, for the simulation of high energy cosmic ray cascades. The DPMJET interaction model has been tuned to accelerator data for hadron-nucleus and nucleus-nucleus interactions, and its performance in the fragmentation region has been optimized. We make use of this generator inside the HEMAS shower code. Results are presented with particular emphasis on the electromagnetic component and on the high energy muon content of the showers.

Muons in extensive air showers. I. The lateral distribution of muons

The muon content of EAS detected at Haverah Park has been measured using both shielded scintillators and neon flashtube tracking arrays. The primary energy range covered was from 1015 up to 1020 eV with a muon energy threshold of 300 MeV. The lateral distributions of muon density are fitted to the observed data in each decade of primary energy over appropriate core-distance ranges. In the range 150<R<1200 m, and at energies above 1016 eV, it appears that a single representation of the lateral distribution function (LDF) can be fitted to the data. At R>1200 m the observed densities fall below the predictions of this LDF. At lower primary energies (Ep<1016 eV) and for R<150 m a simple power-law LDF fits the observed data. However, the best-fit power index increases with Ep up to approximately 3*1015 eV and then appears to remain constant at higher energies.

A Northern Sky Survey for Astrophysical Point Sources of 100 TeV Gamma Radiation

The CASA-MIA experiment is a very large extensive air shower detector with good angular resolution. A part of this instrument has been used to search the visible sky for astrophysical point sources of gamma rays with energies ≥100 TeV. Approximately 90% of the charged cosmic-ray background is rejected through measurement of the muon content of the showers. Stringent limits are placed on the flux of 100 TeV gamma rays from previously unknown point sources across a large fraction of the northern sky. The complete instrument, with significantly greater sensitivity, has been in operation for more than a year

Search for EAS excess from the direction of compact galactic x-ray sources Cygnus X-3, Hercules X-1, Cygnus X-1 and others

The Tien Shan EAS data obtained during the period 1974-82 have been analysed aiming at a search for a shower excess from the directions of compact x-ray sources: X-binaries-massive and low-mass systems, cataclismic variables, etc. Significant fluxes have been obtained by analysis of the corresponding phase curves of the local sources 4U 0115+63, V1727 Cyg and beta Per, and upper limits of the radiation from another six objects have been estimated. A search for long-term periods of the radiation from the direction of Cygnus X-3 has been carried out and a 4 sigma peak has been observed at phases 0.04-0.14 of the (321+or-3) day period. The consideration of the 5.6 day orbital period phase curve of Cygnus X-1 has shown a significant peak at phases 0.5-0.8, confirmed by a muon-poor shower selection. The analysis of the 1.7 day orbital period phase curve of Hercules X-1 has also shown a considerable peak at phases 0.86-0.96, which was confirmed by the analysis of the phase curve of showers with relatively small muon content (Nmu /(Nmu )

Search for compact sources of cosmic photons above 200 TeV.

From April 1988 to February 1990 we used a two-level array of scintillators to search in the cosmic radiation for compact sources of $\ensuremath{\gamma}$ rays above 200 TeV. Counters on the surface measured the size and direction of extensive air showers while counters buried 3 m below ground measured their muon content. Showers induced by $\ensuremath{\gamma}$ rays are expected to have many fewer muons than those initiated by hadrons so the selection of muon-poor showers should greatly reduce the background of hadronic showers. Three objects, Cygnus X-3, the Crab nebula, and Hercules X-1, were examined in detail. Searches were made on short and long time scales and source periodicity was used, where applicable, to enhance any possible signals. We found no evidence for any compact sources.

STAR CLUSTER: a tracking array for gamma-ray astronomy

A new type of extensive air shower array-telescope is being constructed, close to the GREX scintillator array at Haverah Park. The design of the new instrument is based on identification and measurement of individual shower particles by means of pattern recognition techniques applied to data from LST chambers above and below a thin sheet of high-Z material. Air showers will be detected in the range from 1014 eV to 1018 eV. The directions of the shower primaries will be reconstructed with an accuracy of a few tenths of a degree using triangulation between tracks of detected shower particles: >1 GeV electrons, photons and muons. Particle densities measured at the detector locations will be used to calculate shower sizes and core locations. Information about the height of production of the high-energy secondaries will be obtained for each shower. This information will be taken into account in calculating the primary energies. It will be used together with the observed muon content (ratio of muons to all particles), to draw conclusions about the nature of the primary particles.

Search for discrete sources of 100 TeV gamma radiation.

The Chicago Air Shower Array is a large-area ground-based detector designed to observe extensive air showers produced by primary particles with energy \ensuremath{\gtrsim} 100 TeV. It operates in coincidence with the underground Michigan Muon Array. Data taken during 1989 are examined for evidence of continuous and pulsed emission from localized regions of the sky. The x-ray sources Cygnus X-3, Hercules X-1, and the Crab Nebula and pulsar are examined for steady and periodic $\ensuremath{\gamma}$-ray emission. To search for previously unknown compact sources, the background of cosmic rays is estimated over the sky between declinations +5\ifmmode^\circ\else\textdegree\fi{} and +90\ifmmode^\circ\else\textdegree\fi{} and enhancement is sought in small angular bins. There is no evidence for a significant excess from any of these searches, and flux limits are presented as a function of declination and muon content.

The total and jet photoproduction cross sections at HERA and Fermilab energies

We show that the hadronic structure of the photon can lead to a significant rise in the total and jet photoproduction cross sections at HERA and Fermilab energies. We present our predictions for the total and jet photoproduction cross sections for the forthcoming Fermilab E683 and ZEUS and H-1 experiments at the HERA collider. We discuss the relevance of the hadronic character to the anomalous muon content recently observed in cosmic ray showers associated with point sources such as Cygnus X-3, Hercules X-1 and the Crab Nebula.

The total and jet photoproduction cross sections at HERA and Fermilab energies

We show that the hadronic structure of the photon can lead to a significant rise in the total and jet photoproduction cross sections at HERA and Fermilab energies. We present our predictions for the total and jet photoproduction cross sections for the forthcoming Fermilab E683 and ZEUS and H-1 experiments at the HERA collider. We discuss the relevance of the hadronic character to the anomalous muon content recently observed in cosmic ray showers associated with point sources such as Cygnus X-3, Hercules X-1 and the Crab Nebula.