Shower Core Research Articles

EMMA – an underground cosmic-ray experiment

A new cosmic-ray experiment is under construction in the Pyhäsalmi mine, Finland. It aims to study the (mass) composition of cosmic rays at and above the knee region. The array, called EMMA (Experiment with MultiMuon Array), will cover approximately 130 m2 of detector area at a depth of 75 metres (~210 mwe). It is able to locate shower cores in an area of approximately 400 m2 with an accuracy better than 6 metres. The array detects underground muons and the muon multiplicity, their lateral distribution and the arrival direction of the air shower can be determined. First scientific measurements can be started during the spring 2009 with a partial-size array. The full-size array is expected to be ready by autumn 2010. The full-size array consist of two type of detectors: drift chambers and plastic scintillation detectors. Besides the composition study, it is also expected that the array contributes on the study of high-multiplicity muon bundles that were observed at the cosmic-ray experiments at the LEP detectors.

On possible role of neutrons in appearance of delayed muons in MUON-T setup at the Tien Shan high-altitude station

The MUON-T setup operated at the Tien Shan high-altitude station of the Lebedev Physical Institute (3340 m above sea level) at a soil depth of ∼10 m (∼20 m m.w.e.). Muons with delay times of 30–150 ns with respect to the extensive air shower front were observed at this setup. Calculations showed that delay times of relativistic muons, taking into account their deviations in the geomagnetic field, do not exceed ∼30 ns. To elucidate the possible role of neutrons in the appearance of delayed events due to the n-p reaction in the plastic scintillator material, the problem of neutron transport in a medium with a density of 2 g/cm3 and a humidity of 10% was solved by the Monte Carlo method. Calculations for a point source of neutrons with energies of 5, 10, and 20 MeV (such neutrons can be generated, in particular, in cascades in soil from hadrons of the shower core) showed that the neutron flux decreases more than by a factor of 104 at a distance of 2.8 m of soil from the source. Neither neutron crosses the boundary of 3m at the total statistics of 3 · 105 events. Since the MUON-T setup is at a depth of 10 m, it is clear that neutrons from the atmosphere and soil upper layer are absorbed, scattered, and do not reach the detector. Thus, the formation of delayed muons in the MUON-T setup cannot be explained by these neutrons.

Energy determination of cosmic ray showers in surface arrays using signal inference at a single distance from the core

In most high energy cosmic ray surface arrays, the primary energy is currently determined from the value of the lateral distribution function at a fixed distance from the shower core, r 0 . The value of r 0 is mainly related to the geometry of the array and is, therefore, considered as fixed independently of the shower energy or direction. We argue, however, that the dependence of r 0 on energy and zenith angle is not negligible. Therefore, in the present work we propose a new characteristic distance, which we call r opt , specifically determined for each individual shower, with the objective of optimizing the energy reconstruction. This parameter may not only improve the energy determination, but also allow a more reliable reconstruction of the shape and position of rapidly varying spectral features. We show that the use of a specific r opt determined on a shower-to-shower basis, instead of using a fixed characteristic value, is of particular benefit in dealing with the energy reconstruction of events with saturated detectors, which are in general a large fraction of all the events detected by an array as energy increases. Furthermore, the r opt approach has the additional advantage of applying the same unified treatment for all detected events, regardless of whether they have saturated detectors or not.

Radio emission of energetic cosmic ray air showers: Polarization measurements with LOPES

LOPES is a radio antenna array co-located with the Karlsruhe Shower Core and Array DEtector, KASCADE–Grande in Forschungszentrum Karlsruhe, Germany, which provides well-calibrated trigger information and air shower parameters for primary energies up to 10 18 eV . By the end of 2006, the radio antennas were re-configured to perform polarization measurements of the radio signal of cosmic ray air showers, recording in the same time both, the East–West and North–South polarization directions of the radio emission. The main goal of these measurements is to reconstruct the polarization characteristics of the emitted signal. This will allow a detailed comparison with theoretical predictions. The current status of these measurements is reported here.

Frequency spectra of cosmic ray air shower radio emission measured with LOPES

Aims. We wish to study the spectral dependence of the radio emission from cosmic-ray air showers around 100 PeV (10 17 eV). Methods. We observe short radio pulses in a broad frequency band with the dipole-interferometer LOPES (LOFAR Prototype Station), which is triggered by a particle detector array named Karlsruhe Shower Core and Array Detector (KASCADE). LOFAR is the Low Frequency Array. For this analysis, 23 strong air shower events are selected using parameters from KASCADE. The radio data are digitally beam-formed before the spectra are determined by sub-band filtering and fast Fourier transformation. Results. The resulting electric field spectra fall off to higher frequencies. An average electric field spectrum is fitted with an exponential Eν = K · exp (ν/MHz/β )a ndβ = −0.017 ± 0.004, or alternatively, with a power law � ν = K · ν α and a spectral index of α = −1 ± 0.2. The spectral slope obtained is not consistent within uncertainties and it is slightly steeper than the slope obtained from Monte Carlo simulations based on air showers simulated with CORSIKA (Cosmic Ray Simulations for KASCADE). For the analyzed sample of LOPES events, we do not find any significant dependence of the spectral slope on the electric field amplitude, the azimuth angle, the zenith angle, the curvature radius, nor on the average distance of the antennae from the shower core position. But one of the strongest events was measured during thunderstorm activity in the vicinity of LOPES and shows the longest pulse length measured of 110 ns and a spectral slope of α = −3.6. Conclusions. We show with two different methods that frequency spectra from air shower radio emission can be reconstructed on event-by-event basis, with only two dozen dipole antennae simultaneously over a broad range of frequencies. According to the obtained spectral slopes, the maximum power is emitted below 40 MHz. Furthermore, the decrease in power to higher frequencies indicates a loss in coherence determined by the shower disc thickness. We conclude that a broader bandwidth, larger collecting area, and longer baselines, as will be provided by LOFAR, are necessary to further investigate the relation of the coherence, pulse length, and spectral slope of cosmic ray air showers.

The influence of background radiation on the events registered in a neutron monitor at mountain heights

We have made an experimental check of an influence caused by external background of slow thermal neutrons on the temporal distribution of the signals from the standard NM64 supermonitor used as a detector of hadron component of extensive air showers with the energy above 1015 eV. Special attention in our study was paid to the possible connection of this background with the anomalously (up to a few milliseconds) delayed signals from the neutron monitor which were detected when the shower cores passed in its close vicinity. It has been found that in spite of the long, up to tens of milliseconds, presence of thermal neutrons nearby the shower axis, these external neutrons do not have any effect on the temporal behaviour of the neutrons diffusing inside the monitor as well as on the distribution of gamma-radiation accompanying the absorption of the latter.

Air Shower Core Observation at High Altitudes

The limitation of the original mountain emulsion chamber experiments is discussed and a way to improve the air shower (AS) core detection at high altitudes by using a hadron calorimeter plus an AS array is presented. In this report the experimental approach is considered to be used to the checking of hadronic interaction models of the forward particle production at 10TeV energy region. Assuming that a KASCADE-like hadron calorimeter is set up at the center of the ARGO array at Yangbajing, a Monte Carlo shows that a low-height interaction and near core AS event sample at 10TeV region can be selected. This sample could provide an almost direct checking on the property of hadron production in the forward region of p-air inelastic interactions.

Studying High pT Muons in Cosmic-Ray Air Showers

Most cosmic-ray air shower arrays have focused on detecting electromagnetic shower particles and low energy muons. A few groups (most notably MACRO + EASTOP and SPASE + AMANDA) have studied the high energy muon component of showers. However, these experiments had small solid angles, and did not study muons far from the core. The IceTop + IceCube combination, with its 1 km 2 muon detection area can study muons far from the shower core. IceCube can measure their energy loss ( d E / d x ), and hence their energy. With the energy, and the known distribution of production heights, the transverse momentum ( p T ) spectrum of high p T muons can be determined. The production of these muons is calculable in perturbative QCD, so the measured muon spectra can be used to probe the composition of incident cosmic-rays.

Simulation study of air shower particles near the core region

The ARGO-YBJ experiment has two kinds of signals in the shower working mode which allows coverage of the energy region from TeV to PeV region. One is the digital strip pattern, another is so-called ‘big pad’ mode, which is the analog signal counting the pulse height on half of an RPC, proportional to the number of hitting particles. In this paper by using the Monte Carlo simulation method the ARGO-YBJ sensitivity to the cosmic ray composition is discussed, by using the ‘big pad’ signal for measuring the number of particles detected close to the shower core.

Calibration of the Yangbajing Air-shower Core detector using the test beam of BEPCII

Yangbajing Air shower Core detector(YAC) has been developed for the next phase of Tibet air-shower experiment to measure the chemical composition of cosmic rays in “knee” region. A preparation is made for calibration of the linearity of the dynamic range and position dependence of light yield of YAC using test beam of BEPCII. A scraper will be used to attenuate the electron beam intensity from about 10 10 /pulse to 10 2 –10 6 /pulse. A Faraday cup, a thick ionization chamber and a thin ionization chamber are being manufactured to monitor the beam intensity covering dynamic range from 10 2 /pulse to 10 10 /pulse.

Investigations of Muons in EAS with KASCADE-Grande

KASCADE-Grande is a multi detector setup for the investigation of extensive air showers in the primary energy range of the knee including energies around the so-called second knee. With the data of the 700 ⋅ 700 m2 large Grande array shower core position, shower direction, and the total number of electrons are reconstructed for events with primary energy above 1016.5 eV. In addition, the experiment consists of different detector setups for measuring muons at various energy thresholds between 230 MeV and 2.4 GeV. These informations are used to estimate the muon shower size as well as observables sensitive to differences of hadronic interaction models embedded in shower simulation codes. We report the goals and the status of the different muon measurements at KASCADE-Grande.

Calibrated measurements of the radio emission of cosmic ray air showers

This work investigates the properties of the radio emission of cosmic ray air showers, in particular by reconstructing the lateral distribution of the emission on an event-by-event basis. The LOPES experiment is measuring the radio emission in the frequency range 40-80 MHz in coincidence with the air shower experiment KASCADE-Grande. For the present analysis a set of data is used which was measured with east-west oriented antennas. By selecting the high energy air showers the occurring short radio pulses can be observed and the lateral distribution of the radio signal for individual showers reconstructed. Based on a performed amplitude calibration of the radio signals for each antenna the absolute value of the field strength is known. Therefore the scale parameter R 0 and the field strength 1 ∈0 of the lateral behavior can be determined. The obtained most probable value of the scale parameter results in R 0 ≈ 125 m, and no significant dependence of this values on general shower parameters, like angle-of-incidence or primary energy could be found. A comparison of the field strength ∈ 0 with the value obtained by a parameterization of earlier LOPES measurements yields significant differences, whereby the field strengths determined from lateral distributions are systematically above the values of the parameterization. Using Monte Carlo simulations of the radio emission of extensive air showers, adjusted to the individual measured events by using the known individual shower parameters, direct comparisons with the measurements are performed. As a result of this, a systematically flatter lateral distribution was obtained for the measurements. In particular, measured events with large scale parameter (R 0 > 200 m) could not be reproduced by the simulations. The comparisons of the field strength at different distances with the simulations show a significant discrepancy close to the shower core. This arises from the larger scale parameters at the measurements. However, an important conclusion from the comparison of measurements with simulations results in a deviation of only ≈ 10% of the absolute values of the field strength at a distance of 75 m.

Design, performance, and calibration of CMS forward calorimeter wedges

We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region (\(3\leq|\eta|\leq5\)), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h≈5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as \(\frac{a}{\sqrt{E}}\oplus{b}\). The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.

EXOTIC PHYSICS AT THE LHC WITH CASTOR IN CMS

Cosmic-rays sometimes produce showers of unusual composition that contain particles with energy-loss profiles different from all known particles. The Large Hadron Collider (LHC) will produce, for the first time, nuclear collisions at the extremely high energy characteristic of the cosmic-ray events. The CASTOR detector, a part of the huge CMS experiment, is designed for detailed studies of the products corresponding to the cores of cosmic-ray showers. It will cover angles of 0.1° to 0.7° from the beam. It will be divided azimuthally into 16 segments and longitudinally into 18 segments. It is assumed that cosmic ray showers are caused by nuclei, protons through iron, hitting the atmosphere. If CASTOR does not find events that can be identified with the anomalous cosmic-ray events, this assumption may need to be reconsidered. Pb - Pb collisions with the LHC will have an energy 28 times that of Au - Au collisions studied at RHIC. With this huge increase in energy a wealth of new phenomena is almost assured. Because of the much larger mass number, Pb - Pb events can be expected to show exotic phenomena that is beyond the reach of cosmic rays.

HYDRA hydroacoustic antenna in the NEVOD experimental complex

The main characteristics of the HYDRA hydroacoustic antenna intended for the detection of signals generated by cores of extensive air showers in a water Cherenkov detector involved in the NEVOD experimental complex are considered. Primary attention is focused on the calibration of antenna sensors and on the selection of an optimum trigger that ensures an effective detection of acoustic signals generated by cores of extensive air showers in the water volume of the Cherenkov detector.

Methods for estimating the energy of extensive air showers

A multilevel scheme for calculating estimates of the energy of extensive air showers on the basis of signals in different detectors is considered. The numerical energy estimates at specified values of signals in scintillation detectors are smaller than the experimental ones by a factor of about 1.6. The results of the calculation confirmed that the total flux of Cherenkov light is proportional to the shower energy. The flux of fluorescent light generated within 100 m from the shower core is due to only 60% of the total energy.

Possible observations of new physics in ultrahigh-energy cosmic rays

The muon lateral structure functions in giant air showers induced by primary photons have been simulated with the help of original codes. Particularly, the densities of muons with energies above 0.5 and 1 GeV at a distance of 1000 m from the shower core have been estimated for gamma-induced showers of various energies. A comparison with the results of calculations for hadronic showers shows a considerable deficit of muons in the gamma-induced showers. The density of muons at a distance of 1000 m from the shower core happened to be ≳ 10 times larger for the hadronic showers. Some possible constraints of the source models with superheavy-dark-matter particles and topological defects are discussed.

Radio emission of highly inclined cosmic ray air showers measured with LOPES

Aims. The capability of radio antenna arrays to measure cosmic ray air showers with very large zenith angles is explored. This is important, since a possible neutrino detection has to fulfill two requirements. First: antennas should be able to detect very inclined cosmic ray air showers, and second: it should be possible to estimate the distance to the shower maximum, since neutrinos are most likely to travel far through the Earth’s atmosphere without interaction and induce air showers close to the ground. Methods. LOPES (LOFAR PrototypE Station; LOFAR – LOw Frequency ARray), an array of dipole antennas, is used for the detection of inclined cosmic ray air showers. LOPES is co-located and triggered by the KASCADE (KArlsruhe Shower Core and Array DEtector) experiment, which also provides information on air shower properties such as electron and muon numbers on the ground, as well as the arrival direction. Radio emission of nearly vertical cosmic ray air showers has been detected by LOPES. Results. LOPES-10 (the first phase of LOPES, consisting of 10 antennas) detected a significant number of cosmic ray air showers with a zenith angle larger than 50 ◦ , and many of these have very high radio field strengths. The most inclined event that has been detected with LOPES-10 has a zenith angle of almost 80 ◦ . This is proof that the new technique is also applicable for cosmic ray air showers with high inclinations, which in the case that they are initiated close to the ground, can be a signature of neutrino events. Conclusions. Our results indicate that arrays of simple radio antennas can be used for the detection of highly inclined air showers, which might be triggered by neutrinos. In addition, we found that the radio pulse height (normalized with the muon number) for highly inclined events increases with the geomagnetic angle, which confirms the geomagnetic origin of radio emission in cosmic ray air showers.

The optimum distance at which to determine the size of a giant air shower

To determine the size of an extensive air shower it is not necessary to have knowledge of the function that describes the fall-off of signal size from the shower core (the lateral distribution function). In this paper an analysis with a simple Monte Carlo model is used to show that an optimum ground parameter can be identified for each individual shower. At this optimal core distance, r opt, the fluctuations in the expected signal, S( r opt), due to a lack of knowledge of the lateral distribution function are minimised. Furthermore it is shown that the optimum ground parameter is determined primarily by the array geometry, with little dependence on the energy or zenith angle of the shower or choice of lateral distribution function. For an array such as the Pierre Auger Southern Observatory, with detectors separated by 1500 m in a triangular configuration, the optimum distance at which to measure this characteristic signal is close to 1000 m.

Progress in air shower radio measurements: Detection of distant events

Data taken during half a year of operation of 10 LOPES antennas (LOPES-10), triggered by EAS observed with KASCADE-Grande have been analysed. We report about the analysis of correlations of radio signals measured by LOPES-10 with extensive air shower events reconstructed by KASCADE-Grande, including shower cores at large distances. The efficiency of detecting radio signals induced by air showers up to distances of 700m from the shower axis has been investigated. The results are discussed with special emphasis on the effects of the reconstruction accuracy for shower core and arrival direction on the coherence of the measured radio signal. In addition, the correlations of the radio pulse amplitude with the primary cosmic ray energy and with the lateral distance from the shower core are studied.