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Register a new userUnderground neutron events at Tien Shan and the properties of the $10^{14}-10^{17}$ eV EAS muonic component
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The events of multiple neutron production under 2000g/cm$^2$ thick rock absorber were studied at the Tien~Shan mountain cosmic ray station, at the altitude of 3340m above the sea level. From comparison of the experimental and Geant4 simulated neutron multiplicity spectra it follows that the great bulk of these events can be explained by interaction of cosmic ray muons with internal material of the neutron detector. In synchronous operation of the underground neutron monitor with the Tien~Shan shower detector system it was found that the characteristics of the muonic component of extensive air showers which is seemingly responsible for generation of the neutron events underground do change noticeably within the energy range of the knee of primary cosmic ray spectrum. Some peculiar shower events were detected when the neutron signal reveals itself only $sim$(100--1000),$mu$s after the passage of the shower particles front which probably means an existence of corresponding delay of the muon flux in such events.
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Cosmic rays are the highest energy particles found in nature. Measurements of the mass composition of cosmic rays between 10^{17} eV and 10^{18} eV are essential to understand whether this energy range is dominated by Galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate cascades of secondary particles (air showers) in the atmosphere and their masses are inferred from measurements of the atmospheric depth of the shower maximum, Xmax, or the composition of shower particles reaching the ground. Current measurements suffer from either low precision, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique, suitable for determination of Xmax with a duty cycle of in principle nearly 100%. The radiation is generated by the separation of relativistic charged particles in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean precision of 16 g/cm^2 between 10^{17}-10^{17.5} eV. Because of the high resolution in $Xmax we can determine the mass spectrum and find a mixed composition, containing a light mass fraction of ~80%. Unless the extragalactic component becomes significant already below 10^{17.5} eV, our measurements indicate an additional Galactic component dominating at this energy range.
The average mass composition of cosmic rays with primary energies between $10^{17}$eV and $10^{18}$eV has been studied using a hybrid detector consisting of the High Resolution Flys Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum, $X_{max}$, and in the change in the muon density at a fixed core location, $rho_mu(600m)$, as a function of energy. The composition has also been evaluated in terms of the combination of $X_{max}$ and $rho_mu(600m)$. The results show that the composition is changing from a heavy to lighter mix as the energy increases.
The amplitude and phase of the cosmic ray anisotropy are well established experimentally between 10^{11} eV and 10^{14} eV. The study of their evolution into the energy region 10^{14}-10^{16} eV can provide a significant tool for the understanding of the steepening (knee) of the primary spectrum. In this letter we extend the EAS-TOP measurement performed at E_0 around 10^{14} eV, to higher energies by using the full data set (8 years of data taking). Results derived at about 10^{14} and 4x10^{14} eV are compared and discussed. Hints of increasing amplitude and change of phase above 10^{14} eV are reported. The significance of the observation for the understanding of cosmic ray propagation is discussed.
We explore the feasibility of estimating primary cosmic ray composition at high energies from the study of two parameters of Extensive Air Showers (EAS) at ground and underground level with Monte Carlo simulations using the new EPOS and QGSJETII hadronic models tuned with LHC data. Namely, the slope and density at a given distance of the muon lateral distribution function are analysed in this work. The power to discriminate primary masses is quantified in terms of merit factor for each parameter. The analysis considers three different primary particles (proton, iron and gamma), four different zenith angles (0$^{circ}$, 15$^{circ}$, 30$^{circ}$ and 45$^{circ}$) and primary energies of $10^{17.25}$ eV, $10^{17.50}$ eV and $10^{17.75}$ eV.
The energy spectrum of primary cosmic rays at energies between at 2x10$^{13}$ - 3x10$^{17}$ eV is presented according to data from the Tien Shan array on the basis of the detection of the number of electrons in extensive air showers. In the energy range 5x10$^{15}$ - 3x10$^{17}$ eV, the spectrum was obtained by means of the HADRON array and was extended to the region of lower energies from 2x10$^{13}$ eV on the basis of the results of an individual experiment. The changes in the slope of the spectrum in the energy range of 10$^{16}$ - 3x10$^{17}$ eV and a feature of this spectrum at about 1017 eV are analyzed in detail and are described. The spectrum in question is compared with the results obtained at some other arrays.
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