Cosmic rays around the so-called knee in the spectrum at around PeV primary energy are generally galactic in origin. Observations on the form of their energy spectrum and their mass composition are ...fundamental tools to understand the origin, acceleration and propagation mechanism of high-energy cosmic rays. In addition, it is required to find signatures to clarify the transition from galactic to extragalactic sources, which are believed to be responsible for the highest-energy cosmic rays above EeV. This brief review focuses on recent experimental results around the knee of the all-particle energy spectrum and composition in the energy range of the knee up to EeV energies.
We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered ...simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the ‘ankle’ at lg(E/eV)=18.5–19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A>4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth.
We review open questions and prospects for progress in ultrahigh-energy cosmic ray (UHECR) research, based on a series of discussions that took place during the “The High-Energy Universe: Gamma-Ray, ...Neutrino, and Cosmic-ray Astronomy” MIAPP workshop in 2018. Specifically, we overview open questions on the origin of the bulk of UHECRs, the UHECR mass composition, the origin of the end of the cosmic-ray spectrum, the transition from Galactic to extragalactic cosmic rays, the effect of magnetic fields on the trajectories of UHECRs, anisotropy expectations for specific astrophysical scenarios, hadronic interactions, and prospects for discovering neutral particles as well as new physics at ultrahigh energies. We also briefly overview upcoming and proposed UHECR experiments and discuss their projected science reach.
► We review air shower data related to the mass composition of cosmic rays above 1015eV. ► We review of different approaches of composition studies with surface and optical detectors. ► We interpret ...data in terms of primary mass.
In this paper we review air shower data related to the mass composition of cosmic rays above 1015eV. After explaining the basic relations between air shower observables and the primary mass and energy of cosmic rays, we present different approaches and results of composition studies with surface detectors. Furthermore, we discuss measurements of the longitudinal development of air showers from non-imaging Cherenkov detectors and fluorescence telescopes.
The interpretation of these experimental results in terms of primary mass is highly susceptible to the theoretical uncertainties of hadronic interactions in air showers. We nevertheless attempt to calculate the logarithmic mass from the data using different hadronic interaction models and to study its energy dependence from 1015eV to 1020eV.
•Increased South Sourced Water in the mid-depth Atlantic during HS1 plays a minor role in the δ13C decrease.•Remineralization caused by the change of ventilation dominates the deglacial δ13C ...change.•Deep end-member includes additional remineralization after the surface end-member leaves the surface.
δ13C records from the mid-depth Atlantic show a pronounced decrease during the Heinrich Stadial 1 (HS1), a deglacial episode of dramatically weakened Atlantic Meridional Ocean Circulation (AMOC). Proposed explanations for this mid-depth decrease include a greater fraction of δ13C-depleted southern sourced water (SSW), a δ13C decrease in the North Atlantic Deep Water (NADW) end-member, and accumulation of the respired organic carbon. However, the relative importance of these proposed mechanisms cannot be quantitatively constrained from current available observations alone. Here we diagnose the individual contributions to the deglacial Atlantic mid-depth δ13C change from these mechanisms using a transient simulation with carbon isotopes and idealized tracers. We find that although the fraction of the low-δ13C SSW increases in response to a weaker AMOC during HS1, the water mass mixture change only plays a minor role in the mid-depth Atlantic δ13C decrease. Instead, increased remineralization due to the AMOC-induced mid-depth ocean ventilation decrease is the dominant cause. In this study, we differentiate between the deep end-members, which are assigned to deep water regions used in previous paleoceanography studies, and the surface end-members, which are from the near-surface water defined from the physical origin of deep water masses. We find that the deep NADW end-member includes additional remineralized material accumulated when sinking from the surface (surface NADW end-member). Therefore, the surface end-members should be used in diagnosing mechanisms of δ13C changes. Furthermore, our results suggest that remineralization in the surface end-member is more critical than the remineralization along the transport pathway from the near-surface formation region to the deep ocean, especially during the early deglaciation.
High-energy cosmic rays are observed indirectly by detecting the extensive air showers initiated in Earth’s atmosphere. The interpretation of these observations relies on accurate models of air ...shower physics, which is a challenge and an opportunity to test QCD under extreme conditions. Air showers are hadronic cascades, which give rise to a muon component through hadron decays. The muon number is a key observable to infer the mass composition of cosmic rays. Air shower simulations with state-of-the-art QCD models show a significant muon deficit with respect to measurements; this is called the Muon Puzzle. By eliminating other possibilities, we conclude that the most plausible cause for the muon discrepancy is a deviation in the composition of secondary particles produced in high-energy hadronic interactions from current model predictions. The muon discrepancy starts at the TeV scale, which suggests that this deviation is observable at the Large Hadron Collider. An enhancement of strangeness production has been observed at the LHC in high-density events, which can potentially explain the puzzle, but the impact of the effect on forward produced hadrons needs further study, in particular with future data from oxygen beam collisions.
In this paper we study, using Monte Carlo simulations, the possibility to discriminate the mass of the Ultra High Energy Cosmic Rays (UHECRs) by combining information obtained from the maximum Xmaxμ ...of the muon production rate longitudinal profile of Extensive Air Showers (EAS) and the number of muons, Nμ, which hit an array of detectors located in the horizontal plane. We investigate the sensitivity of the 2D distribution Xmaxμ versus Nμ to the mass of the primary particle generating the air shower. To this purpose we analyze a set of CORSIKA showers induced by protons and iron nuclei at energies of 1019 eV and 1020 eV, at five angles of incidence, 0°, 37°, 48°, 55° and 60°. Using the simulations we obtain the 2D Probability Functions Prob(Xmaxμ,Nμ|p) and Prob(Xmaxμ,Nμ|Fe) which give the probability that a shower induced by a proton or iron nucleus contributes to a specific point on the plane (Xmaxμ,Nμ). Then we construct the probability functions Prob(p|Xmaxμ,Nμ) and Prob(Fe|Xmaxμ,Nμ) which give the probability that a certain point on the plane (Xmaxμ,Nμ) corresponds to a shower initiated by a proton or an iron nucleus, respectively. Finally, a test of this procedure using a Bayesian approach, confirms an improved accuracy of the primary mass estimation in comparison with the results obtained using only the Xmaxμ distributions.
The Tunka-133 EAS Cherenkov light array: Status of 2011 Berezhnev, S.F.; Besson, D.; Budnev, N.M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2012, Letnik:
692
Journal Article
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A new EAS Cherenkov light array, Tunka-133, with ∼1km2 geometrical area has been installed at the Tunka Valley (50km from Lake Baikal) in 2009. The array permits a detailed study of cosmic ray energy ...spectrum and mass composition in the energy range 1016–1018eV with a uniform method. We describe the array construction, DAQ and methods of the array calibration. The method of energy reconstruction and absolute calibration of measurements are discussed. The analysis of spatial and time structure of EAS Cherenkov light allows to estimate the depth of the EAS maximum Xmax.
The results on the all particles energy spectrum and the mean depth of the EAS maximum Xmax vs. primary energy derived from the data of two winter seasons (2009–2011) are presented. Preliminary results of joint operation of the Cherenkov array with antennas for the detection of EAS radio signals are shown. Plans for future upgrades – deployment of remote clusters, radioantennas and a scintillator detector network and a prototype of the HiSCORE gamma-telescope – are discussed.
A method to determine the primary cosmic ray mass composition is presented. Data processing is based on the theoretical model representing the integral muon multiplicity spectrum as the superposition ...of the spectra corresponding to different kinds of primary nuclei. The method consists of two stages. In the first stage, the permissible intervals of primary nuclei fractions fi are determined on the basis of the EAS spectrum versus the total number of muons (Eμ 235 GeV). In the second stage, the permissible intervals of fi are narrowed by the fitting procedure. We use the experimental data on high multiplicity muon events (nμ 114) collected at the Baksan underground scintillation telescope. Within the framework of three components (protons, helium and heavy nuclei), the mass composition in the region 1015-1016 eV has been defined: fp = 0.235 ± 0.02, fHe = 0.290 ± 0.02, fH = 0.475 ± 0.03. The average logarithmic mass is lnA 1.93 and it is in good agreement with results before the knee energy obtained by JACEE, RUNJOB, ATIC. At energies above the knee (1015-1016 eV) our analysis supports KASCADE results and contradicts to CASA-BLANCA and DICE data.
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