Shower Size Research Articles

Shower size parameter as an estimator of extensive air shower energy in fluorescence telescopes

The fluorescence technique has been successfully used to detect ultrahigh energy cosmic rays by indirect measurements. The underlying idea is that the number of charged particles in the atmospheric shower, i.e, its longitudinal profile, can be extracted from the amount of emitted nitrogen fluorescence light. However the influence of shower fluctuations and the very possible presence of different nuclear species in the primary cosmic ray spectrum makes the estimate of the shower energy from the fluorescence data analysis a difficult task. We investigate the potential of shower size at maximum depth as estimator of shower energy. The detection of the fluorescence light is simulated in detail and the reconstruction biases are carefully analyzed. We extend our calculations to both HiRes and EUSO experiments. This approach has shown some advantages to the reconstruction of the energy when compared to the standard analysis procedure.

A new study on the energy spectrum and composition of primary cosmic rays at energies ∼ 10 14–10 16 eV using the GRAPES-3 array at Ooty

Data collected with the 250-detector air shower array and the 560 m 2 area tracking muon detector, operated at Ooty in southern India by the GRAPES collaboration, have been analyzed to study the shape of the energy spectrum and the composition around the knee . It is shown that muon multiplicity distributions, observed with the highly modular muon detector, permit a relatively more reliable measurement of the composition of the primary flux which then helps in a more accurate reconstruction of the energy spectrum from the observed shower size spectrum. Some preliminary results are presented here.

A Halo Event observed by the Hybrid Experiment at Mt. Chacaltaya

An experiment using an air shower array, a hadron calorimeter and an emulsion chamber is under way at Mt. Chacaltaya (5200 m, Bolivia). One of the highest energy events, having a halo (∼ 1 cm) in the centre of the family together with many γ -ray and hadron showers, is analyzed in detail. Available data for the event are on the halo ( E h a l o = 750 TeV) and on the high energy particles of electron/photon components by the emulsion chamber, and on the characteristics of the accompanied air shower ( N e = 7.0 × 10 7 , s = 0.59 ) by the air shower array. The diagram of the air shower size and the total energy of electron/photon components in the family, which shows discrepancy between the experimental data and simulated events (QGSJET code for nuclear collisions) in our previous reports, is discussed including the present event.

PRIMARY ENERGY MEASUREMENT WITH EAS CHERENKOV LIGHT: EXPERIMENT QUEST AND CORSIKA SIMULATION

A new primary mass independent method of energy measurement has been developed by exploiting: a) the joint analysis of the shower size, obtained by EAS-TOP, and of the EAS atmospheric Cherenkov light lateral distribution, obtained by the QUEST array, and b) simulations based on the CORSIKA/QGSJET code. The method is based on the correlation between the size/energy ratio and the steepness of Cherenkov light lateral distribution and has been compared with a "classical" one based on the Cherenkov light flux at a fixed distance (175 m) from the EAS core. An absolute energy calibration of the EAS atmospheric Cherenkov light flux has been obtained.

LATERAL DISTRIBUTION OF MUONS IN EAS AS A FUNCTION OF PRIMARY ENERGY

Experimental EAS muon lateral distributions for Eμ ≥ 5 GeV at fixed primary energy at the knee region measured with the modernized muon hodoscope of the GAMMA installation (Mt. Aragats, Armenia) are presented. Comparison with the data of the previous hodoscope configuration for fixed shower sizes is made. The experimental muon lateral distributions at fixed primary energies are obtained using a new method for estimation of energy of the primary particles. Approximation function for experimental distributions is proposed. Data are compared with the simulated CORSIKA data.

A NEW STUDY ON THE ENERGY SPECTRUM AND COMPOSITION OF PRIMARY COSMIC RAY FLUX AT ENERGIES ~ 1014 – 1016 EV USING THE GRAPES-3 ARRAY AT OOTY

Data collected with the 217-detector air shower array and the 560 m2 area tracking muon detector, being operated at Ooty in southern India by the India-Japan (Tata Institute-Osaka City University) collaboration, GRAPES, have been analyzed to study the shape of the energy spectrum and the composition around the knee. It is shown that the muon multiplicity distribution, observed with the highly modular muon detector, permits a relatively reliable measurement on the composition of primary flux which then helps in a more accurate reconstruction of the energy spectrum from the observed shower size spectrum. The highlights of the GRAPES array, the analysis procedure and the results are presented.

The Electromagnetic Calorimeter of the BTeV Experiment

BTeV is a new dedicated B-physics project at Fermilab. It requires excellent photon detection which is crucial to study CP violations in B decays and rare decays of B's to explore physics beyond the standard model. Electromagnetic calorimeter (EMCAL) built of lead tungstate (PbWO4) scintillating crystals can provide excellent energy and position resolution, compact shower size, fast signal, and reasonable radiation hardness. We have carried out beam studies of a prototype of the BTeV electromagnetic calorimeter. The test took place at the Institute for High Energy Physics, Protvino, Russia. The prototype was built of 25 PbWO4 crystals, from russian and chinese manufacturers. The results of the first set of measurements have confirmed the expected good energy and position resolution of the prototype, though revealed the fact that PbWO4 was not as radiation hard as expected when irradiated with intense high energy hadron and electron beams. The next step included additional studies of radiation hardness, methods of monitoring changes of crystal signal due to radiation using LEDs with different wavelength, and possible procedures for testing PbWO4 radiation hardness without high energy beams.

Reanalysis of GU miniarray data using CORSIKA

The GU miniarray is a ultra high energy cosmic ray (UHECR) detector consisting of eight plastic scintillators of carpet area 2m2, each viewed by fast PMTs. It is used to detect Giant EAS by the method of time spread measurement of secondary particles produced in the atmosphere. The energies of the air showers have been reestimated using CORSIKA program. As in the original analysis the Cosmic Ray energy was determined via its relation to the ground level parameter Ns, the shower size. This relation was obtained previously through a best fit relation in agreement with QGS model and Yakutsk data. In this work we use CORSIKA code with QGSJET model of high energy hadronic interactions to simulate miniarray data leading to a modified relation between primary energy and shower size. A revised energy spectrum is reported for 1017–1019eV primary energy.

The cosmic ray primary composition in the “knee” region through the EAS electromagnetic and muon measurements at EAS-TOP

The evolution of the cosmic ray primary composition in the energy range 106–107 GeV (i.e. the “knee” region) is studied by means of the e.m. and muon data of the Extensive Air Shower EAS-TOP array (Campo Imperatore, National Gran Sasso Laboratories). The measurement is performed through: (a) the correlated muon number (Nμ) and shower size (Ne) spectra, and (b) the evolution of the average muon numbers and their distributions as a function of the shower size. From analysis (a) the dominance of helium primaries at the knee, and therefore the possibility that the knee itself is due to a break in their energy spectrum (at EkHe=(3.5±0.3)×106 GeV) are deduced. Concerning analysis (b), the measurement accuracies allow the classification in terms of three mass groups: light (p,He), intermediate (CNO), and heavy (Fe). At primary energies E0≈106 GeV the results are consistent with the extrapolations of the data from direct experiments. In the knee region the obtained evolution of the energy spectra leads to: (i) an average steep spectrum of the light mass group (γp,He>3.1), (ii) a spectrum of the intermediate mass group harder than the one of the light component (γCNO≃2.75, possibly bending at EkCNO≈(6–7)×106 GeV), (iii) a constant slope for the spectrum of the heavy primaries (γFe≃2.3–2.7) consistent with the direct measurements. In the investigated energy range, the average primary mass increases from 〈lnA〉=1.6–1.9 at E0≃1.5×106 GeV to 〈lnA〉=2.8–3.1 at E0≃1.5×107 GeV. The result supports the standard acceleration and propagation models of galactic cosmic rays that predict rigidity dependent cut-offs for the primary spectra of the different nuclei. The uncertainties connected to the hadronic interaction model (QGSJET in CORSIKA) used for the interpretation are discussed.

Influence of shower fluctuations and primary composition on studies of the shower longitudinal development

We study the influence of shower fluctuations, and the possible presence of different nuclear species in the primary cosmic ray spectrum, on the experimental determination of both shower energy and the proton air inelastic cross section from studies of the longitudinal development of atmospheric showers in fluorescence experiments. We investigate the potential of track length integral and shower size at maximum as estimators of shower energy. We find that at very high energy (~10^19-10^20 eV) the error of the total energy assignment is dominated by the dependence on the hadronic interaction model, and is of the order of 5%. At lower energy (~10^17-10^18 eV), the uncertainty of the energy determination due to the limited knowledge of the primary cosmic ray composition is more important. The distribution of depth of shower maximum is discussed as a measure of the proton-air cross section. Uncertainties in a possible experimental measurement of this cross section introduced by intrinsic shower fluctuations, the model of hadronic interactions, and the unknown mixture of primary nuclei in the cosmic radiation are numerically evaluated.

The cosmic ray primary composition in the ?knee? region through the EAS electromagnetic and muon measurements at EAS-TOP

The evolution of the cosmic ray primary composition in the energy range 10 6 –10 7 GeV (i.e. the “knee” region) is studied by means of the e.m. and muon data of the Extensive Air Shower EAS-TOP array (Campo Imperatore, National Gran Sasso Laboratories). The measurement is performed through: (a) the correlated muon number ( N μ ) and shower size ( N e ) spectra, and (b) the evolution of the average muon numbers and their distributions as a function of the shower size. From analysis (a) the dominance of helium primaries at the knee, and therefore the possibility that the knee itself is due to a break in their energy spectrum (at E k He =(3.5±0.3)×10 6 GeV) are deduced. Concerning analysis (b), the measurement accuracies allow the classification in terms of three mass groups: light (p,He), intermediate (CNO), and heavy (Fe). At primary energies E 0 ≈10 6 GeV the results are consistent with the extrapolations of the data from direct experiments. In the knee region the obtained evolution of the energy spectra leads to: (i) an average steep spectrum of the light mass group ( γ p,He >3.1), (ii) a spectrum of the intermediate mass group harder than the one of the light component ( γ CNO ≃2.75, possibly bending at E k CNO ≈(6–7)×10 6 GeV), (iii) a constant slope for the spectrum of the heavy primaries ( γ Fe ≃2.3–2.7) consistent with the direct measurements. In the investigated energy range, the average primary mass increases from 〈ln A 〉=1.6–1.9 at E 0 ≃1.5×10 6 GeV to 〈ln A 〉=2.8–3.1 at E 0 ≃1.5×10 7 GeV. The result supports the standard acceleration and propagation models of galactic cosmic rays that predict rigidity dependent cut-offs for the primary spectra of the different nuclei. The uncertainties connected to the hadronic interaction model (QGSJET in CORSIKA) used for the interpretation are discussed.

The cosmic ray primary composition between 10 15 and 10 16 eV from Extensive Air Showers electromagnetic and TeV muon data

The cosmic ray primary composition in the energy range between 10 15 and 10 16 eV, i.e., around the “knee” of the primary spectrum, has been studied through the combined measurements of the EAS-TOP air shower array (2005 m a.s.l., 10 5 m 2 collecting area) and the MACRO underground detector (963 m a.s.l., 3100 m w.e. of minimum rock overburden, 920 m 2 effective area) at the National Gran Sasso Laboratories. The used observables are the air shower size ( N e) measured by EAS-TOP and the muon number ( N μ) recorded by MACRO. The two detectors are separated on average by 1200 m of rock, and located at a respective zenith angle of about 30°. The energy threshold at the surface for muons reaching the MACRO depth is approximately 1.3 TeV. Such muons are produced in the early stages of the shower development and in a kinematic region quite different from the one relevant for the usual N μ− N e studies. The measurement leads to a primary composition becoming heavier at the knee of the primary spectrum, the knee itself resulting from the steepening of the spectrum of a primary light component (p, He) of Δ γ=0.7±0.4 at E 0∼4×10 15 eV. The result confirms the ones reported from the observation of the low energy muons at the surface (typically in the GeV energy range), showing that the conclusions do not depend on the production region kinematics. Thus, the hadronic interaction model used (CORSIKA/QGSJET) provides consistent composition results from data related to secondaries produced in a rapidity region exceeding the central one. Such an evolution of the composition in the knee region supports the “standard” galactic acceleration/propagation models that imply rigidity dependent breaks of the different components, and therefore breaks occurring at lower energies in the spectra of the light nuclei.

Determination of primary energy and mass in the PeV region by Bayesian unfolding techniques

The field detector array of the KASCADE experiment measures the electron and muon component of extensive air showers in the knee region with high precision. A baysian unfolding procedure is presented in which the two-dimensional shower size distribution ( N e , N μ tr ) is examined. On the arbitrary assumption that the chemical composition consists of five primary mass groups (hydrogen, helium, carbon, silicon and iron) the size distribution is deconvoluted to reconstruct the energy spectra of these mass groups in the energy range between 10 15 eV and 10 17 eV. The energy spectra of the lighter element groups result in a knee-like bending with a steepening above the knee. The topology of the individual knee positions suggest a rigidity dependence.

Muon production heights determined in the KASCADE experiment

Muon production heights in EAS provide a specific tool to investigate the longitudinal development of EAS, since muons are little affected by subsequent interactions in the atmosphere. Multiplicity of muons presents also a unique tool to investigate hadronic interaction models. The capability of the Muon Tracking Detector to measure radial and tangential angles of muon tracks in EAS, in combination with the shower direction determined by the Array of the KASCADE experiment, has been investigated. Due to different characteristics in shower development of light and heavy primary cosmic ray particles the radial angle and therefore the related production height is sensitive to the mass of them. Muon production height (MPH) and muon production depth (MPD) were studied in different bins of the muon shower size for measured data and MC simulations, which have been performed using the Monte Carlo program CORSIKA with the hadronic interaction models QGSJet and neX us. First composition studies on the basis of MPD distributions have been carried out.

Muon density spectra as a probe of the muon component predicted by air shower simulations

The KASCADE experiment measures local muon densities of air-showers in the knee region at various core distances for two different muon energy thresholds. Muon density spectra have been reconstructed for the total EAS sample, as well as for particular subsamples with enhanced light and heavy induced EAS, classified on the basis of the shower size ratio N μ/N e . By comparing these spectra for different muon energy detection thresholds and core distances with detailed Monte Carlo simulations each spectrum should result in the same primary energy spectrum. This allows a comprehensive test of the simulation procedures of the muon lateral distribution and the muon energy spectrum by various Monte Carlo codes. Different combinations of high-energy and low-energy interaction models in the frame of the CORSIKA code are used for comparisons.

Cosmic rays with the LEP detectors

The LEP detectors are well suited for different studies on cosmic ray induced muons. In here, several aspects of the muon spectrum are reported. The vertical as well as the zenith-angle dependence of both the absolute muon spectrum and the muon charge ratio have been measured. High and low muon multiplicities have been measured, the latter in combination with the electromagnetic shower size. All of this has been compared to simulations.

Measurements of attenuation and absorption lengths with the KASCADE experiment

The attenuation of the electron shower size beyond the shower maximum is studied with the KASCADE extensive air shower (EAS) experiment in the primary energy range of about 10 14–10 16 eV. Attenuation and absorption lengths are determined by applying different approaches, including the method of constant intensity, the decrease of the flux of EASs with increasing zenith angle, and its variation with ground pressure. We observe a significant dependence of the results on the applied method. The determined values of the attenuation length ranges from 175 to 196 g/cm 2 and of the absorption length from 100 to 120 g/cm 2. The origin of these differences is discussed emphasizing the influence of intrinsic shower fluctuations.

Cosmic ray air showers in the knee energy region

The cosmic ray extensive air showers in the knee energy region have been studied by the North Bengal University array. The differential size spectra at different atmospheric depths show a systematic shift of the knee towards smaller shower size with the increase in atmospheric depth. The measured values of spectral indices at below and above the knee are −2.45 ±0.03 and −2.91 ±0.05 respectively. Measurements at different atmospheric depths correspond to the same values within the error limits both for below and above the knee. The present experimental results have been compared with similar such experiments

Study of the bending component at the knee of the cosmic ray primary spectrum

The cosmic ray primary composition is studied around the knee ( E 0 ⋍ 3 · 10 15 eV) of the primary energy spectrum with the EAS-TOP array. The distribution of the number of muons recorded at r c ≈ 200 m from the core in narrow intervals of shower sizes are compared with the expectations obtained from simulations performed with the CORSIKA/QGSJET code and a three component composition model (‘p+He’, N, Fe). From the analysis of vertical showers an increase in the average primary mass in the energy range E 0 = 2 · 10 15 — 8 · 10 15 eV is deduced. This effect is associated to a bending of the light and intermediate component, while no change in the slope is observed for the Fe spectrum.

Muon density measurements with the KASCADE central detector

Frequency distributions of local muon densities in high-energy extensive air showers (EAS) are presented as signature of the primary cosmic ray energy spectrum in the knee region. Together with the gross shower variables like shower core position, angle of incidence, and the shower sizes, the KASCADE experiment is able to measure local muon densities for two different muon energy thresholds. The spectra have been reconstructed for various core distances, as well as for particular subsamples, classified on the basis of the shower size ratio N μ/ N e. The measured density spectra of the total sample exhibit clear kinks reflecting the knee of the primary energy spectrum. While relatively sharp changes of the slopes are observed in the spectrum of EAS with small values of the shower size ratio, no such feature is detected at EAS of large N μ/ N e ratio in the energy range of 1–10 PeV. Comparing the spectra for various thresholds and core distances with detailed Monte Carlo simulations the validity of EAS simulations is discussed.