Air Shower Data Research Articles

Measurement of the proton-air cross-section with the Pierre Auger Observatory

We present the procedure to measure the proton-air cross-section at a center-of-mass energy per nucleon of 57TeV developed by the Pierre Auger Collaboration. The conversion from proton-air to inelastic proton-proton cross-section with an extended Glauber calculation is discussed. The systematic uncertainties of the analysis are summarized and the final result compared to accelerator data and model predictions. The growth of hadronic cross-sections towards ultra-high energies reflects changes in the internal structure of the colliding particles. Due to the nature of QCD it is still not possible to calculate hadronic cross-sections at ultra-high energies from first principles. It is thus of paramount importance to measure hadronic cross-sections in order to guide the development of phenomenological models needed to describe secondary multiparticle production at ultra-high energies. Such models are crucial, for example, for a detailed interpretation of available cosmic-ray air-shower data in terms of the primary mass composition. Without a better understanding of the cosmic-ray mass composition it will be very difficult to distinguish between different scenarios of cosmic-ray acceleration and propagation. We present the measurement of the proton-air cross-section with data of the Pierre Auger Observatory (1). The Pierre Auger Observatory is located close to the town of Malargue in Argentina. It consist of about 1660 water Cherenkov particle detector spread over a surface area of 3000km 2 .D uring clear and moonless nights the atmosphere on top of the surface array is overlooked by 27 fluorescence telescopes. This analysis is based on the observation of the longitudinal air-shower development with the telescopes. By combining the timing data of the surface detectors with that of the fluorescence telescopes a very precise reconstruction of the geometry is achieved (2). This technique is called hybrid reconstruction. It allows us a very accurate measurement of Xmax, the position at which an air-shower deposits the maximum energy per unit of mass of atmosphere traversed (3). With the precise observation of longitudinal air-shower fluctuations it is possible to achieve high sensitivity to the mean free path of the primary cosmic-ray particles and thus to the cross-section. This technique is well known and has been first applied by the Fly's Eye experiment (4). We also discuss systematic uncertainties and limitations of the cross-section measurement. In a last step, the proton-air cross-section measurement is converted into a proton-proton cross-section. This conversion makes use of a Glauber calculation, which has been extended to account for inelastic screening effects.

Cosmic rays in the knee energy range

In the energy range of the so called 'knee' be- tween 100 TeV and 1 EeV one expects to identify the end of the galactic origin of cosmic rays. Only for the lowest energies a direct detection with instruments on high-altitude, long-flying balloons are possible. Measurements of the high- energy particles are performed indirectly via the detection of extensive air showers by extended arrays of particle or Cherenkov light sensitive detectors. Multidimensional anal- yses of the air shower data indicate a distinct knee in the energy spectra of light primary cosmic rays at few PeV and an increasing dominance of heavy ones towards higher ener- gies. This provides implications for discriminating astro- physical models of the origin of the knee and of the physics of the transition from galactic to extragalactic cosmic ray ori- gin. Where around 1 PeV many experiments were in oper- ation and have given valuable results in the last decade, at higher energies there was a lack of experimental efforts. To improve the reconstruction quality and statistics at energies from 10 to 1000 PeV, where the transition can be expected, presently several experiments are in operation or going to be in operation. First results of these experiments, as well as perspectives of future efforts in this energy range will be dis- cussed.

Hadronic multiparticle production at ultrahigh energies and extensive air showers

Studies of the nature of cosmic ray particles at the highest energies are based on the measurement of extensive air showers. Most cosmic ray properties can therefore be obtained only from the interpretation of air shower data and are thus dependent on predictions of hadronic interaction models at ultrahigh energies. We discuss different scenarios of model extrapolations from accelerator data to air shower energies and investigate their impact on the corresponding air shower predictions. To explore the effect of different extrapolations by hadronic interaction models we developed an ad hoc model. This model is based on the modification of the output of standard hadronic interaction event generators within the air shower simulation process and allows us to study the impact of changing interaction features on the air shower development. In a systematic study we demonstrate the resulting changes of important air shower observables and also discuss them in terms of the predictions of the Heitler model of air shower cascades. It is found that the results of our ad hoc modifications are, to a large extent, independent of the choice of the underlying hadronic interaction model.

Test of the hadronic interaction model EPOS with KASCADE air shower data

The description of high-energy hadronic interactions plays an important role in the (astrophysical) interpretation of air shower data. The parameter space important for the development of air showers (energy and kinematical range) extends well beyond todays accelerator capabilities. Therefore, accurate measurements of air showers are used to constrain modern models to describe high-energy hadronic interactions. The results obtained are complementary to information gained at accelerators and add to our understanding of high-energy hadronic interactions.

The Constant Intensity Cut Method applied to the KASCADE-Grande muon data

The constant intensity cut method is a very useful tool to reconstruct the cosmic ray energy spectrum in order to combine or compare extensive air shower data measured for different attenuation depths independently of the MC model. In this contribution the method is used to explore the muon data of the KASCADE-Grande experiment. In particular, with this technique, the measured muon number spectra for different zenith angle ranges are compared and summed up to obtain a single muon spectrum for the measured showers. Preliminary results are presented, along with estimations of the systematic uncertainties associated with the analysis technique.

Proton-Air Cross Section and Extensive Air Showers

Hadronic cross sections at ultra-high energy have a significant impact on the development of extensive air shower cascades. Therefore the interpretation of air shower data depends critically on hadronic interaction models that extrapolate the cross section from accelerator measurements to the highest cosmic ray energies. We discuss how extreme scenarios of cross section extrapolations can affect the interpretation of air shower data. We find that the theoretical uncertainty of the extrapolated proton-air cross section at ultra-high energies is much larger than suggested by the existing spread of available Monte Carlo model predictions. The impact on the depth of the shower maximum is demonstrated.

On the measurement of the proton-air cross section using air shower data

The analysis of high-energy air shower data allows one to study the proton-air cross section at energies beyond the reach of fixed target and collider experiments. The mean depth of the first interaction point and its fluctuations are a measure of the proton-air particle production cross section. Since the first interaction point in air cannot be measured directly, various methods have been developed in the past to estimate the depth of the first interaction from air shower observables in combination with simulations. As the simulations depend on assumptions made for hadronic particle production at energies and phase space regions not accessible in accelerator experiments, the derived cross sections are subject to significant systematic uncertainties. The focus of this work is the development of an improved analysis technique that allows a significant reduction of the model dependence of the derived cross section at very high energy. Performing a detailed Monte Carlo study of the potential and the limitations of different measurement methods, we quantify the dependence of the measured cross section on the hadronic interaction model used. Based on these results, a general improvement of the analysis methods is proposed by introducing the actually derived cross section already in the simulation of reference showers. The reduction of the model dependence is demonstrated for one of the measurement methods.

A test of the hadronic interaction model EPOS with air shower data

Predictions of the hadronic interaction model EPOS 1.61 as implemented in the air shower simulation program CORSIKA are compared to observations with the KASCADE experiment. The investigations reveal that the predictions of EPOS are not compatible with KASCADE measurements. The discrepancies seen are most likely due to use of a set of inelastic hadronic cross sections that are too high.

HIGH ENERGY NEUTRINOS FROM ACCELERATORS OF COSMIC RAY NUCLEI

Ongoing experimental efforts to detect cosmic sources of high energy neutrinos are guided by the expectation that astrophysical accelerators of cosmic ray protons also generate high energy neutrinos through their interactions with ambient matter and/or photons. However the predicted neutrino flux is reduced if cosmic ray sources accelerate not only protons but also a significant number of heavier nuclei, as is indicated by recent air shower data. I consider two plausible extragalactic class of sources, active galactic nuclei and gamma-ray bursts, and demand consistency with the observed cosmic ray composition and energy spectrum at Earth after allowing for propagation through intergalactic radiation fields. This allows me to calculate the degree of photo-disintegration and pion production expected to occur in these sources, and hence the neutrino fluxes from them.

Energy spectra and elemental composition of primary nuclei in the knee region: Recent results from the GAMMA experiment

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 1 – 100 PeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach with the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The rigidity-dependent knee feature of the primary energy spectra is displayed at the rigidities E R ≃ 2.5 ± 0.2 PeV/Z and E R ≃ 3.1 – 4.2 PeV/Z for the SIBYLL and QGSJET interaction models respectively. Using the event-by-event method of the primary energy evaluation from the measured N c h , N μ and shower age (s) parameters, the all-particle energy spectrum is also obtained.

High energy neutrinos from astrophysical accelerators of cosmic ray nuclei

Ongoing experimental efforts to detect cosmic sources of high energy neutrinos are guided by the expectation that astrophysical accelerators of cosmic ray protons would also generate neutrinos through interactions with ambient matter and/or photons. However, there will be a reduction in the predicted neutrino flux if cosmic ray sources accelerate not only protons but also significant numbers of heavier nuclei, as is indicated by recent air shower data. We consider plausible extragalactic sources such as active galactic nuclei, gamma ray bursts and starburst galaxies and demand consistency with the observed cosmic ray composition and energy spectrum at Earth after allowing for propagation through intergalactic radiation fields. This allows us to calculate the expected neutrino fluxes from the sources, normalized to the observed cosmic ray spectrum. We find that the likely signals are still within reach of next generation neutrino telescopes such as IceCube.

Mutually compensative pseudo solutions of primary energy spectra in the knee region

The problem of the uniqueness of solutions during the evaluation of primary energy spectra in the knee region using an extensive air shower (EAS) data set and the EAS inverse approach is investigated. It is shown that the unfolding of primary energy spectra in the knee region leads to mutually compensative pseudo solutions. These solutions may be the reason for the observed disagreements in the elementary energy spectra of cosmic rays in the 1–100 PeV energy range obtained from different experiments.

The accuracy of signal measurement with the water Cherenkov detectors of the Pierre Auger Observatory

The Auger Surface Detector consists of a large array of water Cherenkov detector tanks each with a volume of 12,000 l, for the detection of high energy cosmic rays. The accuracy in the measurement of the integrated signal amplitude of the detector unit has been studied using experimental air shower data. It can be described as a Poisson-like term with a normalization constant that depends on the zenith angle of the primary cosmic ray. This dependence reflects the increasing contribution to the signal of the muonic component of the shower, both due to the increasing muon/electromagnetic ( e ± and γ ) ratio and muon track length with zenith angle.

Rigidity-dependent cosmic ray energy spectra in the knee region obtained with the GAMMA experiment

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 10 3 – 10 5 TeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach in the framework of the SIBYLL2.1 and QGSJET01 interaction models and the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The energy spectra of primary H, He, O-like and Fe-like nuclei obtained with the SIBYLL interaction model agree with corresponding extrapolations of the balloon and satellite data to ∼10 3 TeV energies. The energy spectra obtained from the QGSJET model show a predominantly proton composition in the knee region. The rigidity-dependent knee feature of the primary energy spectra for each interaction model is displayed at the following rigidities: E R ≃ 2500 ± 200 TV (SIBYLL) and E R ≃ 3100 – 4200 TV (QGSJET). All the results presented are derived taking into account the detector response, the reconstruction uncertainties of the EAS parameters, and fluctuations in the EAS development.

A review of experimental results at the knee

Results of experiments investigating air showers in the energy region of the knee are summarized. The all-particle energy spectrum, the mean logarithmic mass, and the average depth of the shower maximum will be discussed. Spectra for groups of elements from air shower data are compared to results from direct measurements.

The data acquisition system of the Stockholm educational air shower array

The Stockholm Educational Air Shower Array (SEASA) project is deploying an array of plastic scintillator detector stations on school roofs in the Stockholm area. Signals from GPS satellites are used to time synchronise signals from the widely separated detector stations, allowing cosmic ray air showers to be identified and studied. A low-cost and highly scalable data acquisition system has been produced using embedded Linux processors which communicate station data to a central server running a MySQL database. Air shower data can be visualised in real-time using a Java-applet client. It is also possible to query the database and manage detector stations from the client. In this paper, the design and performance of the system are described

INDIRECT MEASUREMENTS AROUND THE KNEE — RECENT RESULTS FROM KASCADE

In the presented analysis of air shower data measured with the KASCADE experiment energy spectra for five mass groups are reconstructed. The results show a change of composition towards heavier elements across the knee but also demonstrate an insufficient description of the data by the used hadronic interaction models QGSJet and SIBYLL.

The nature of the ‘knee’ in the cosmic ray energy spectrum

In view of recent developments, attention is directed again at two aspects of the well-known ‘knee’ in the cosmic ray energy spectrum at 3 PeV: the mass of the predominant particles at this energy and their source. It is inevitable in a subject such as this that ideas—and conclusions—evolve. Earlier, we had used a particular acceleration model and the nature of the ISM in the local ISM to infer that the particles are mainly oxygen nuclei; direct measurements, when extrapolated (by at least a decade in energy), gave a similar result. Initially, no specific source was identified. More recently, however, we have specified the Monogem Ring supernova remnant as the likely source; this is at just the right distance and age and the energies are reasonable. Concerning the mass composition at the knee, a quantity more difficult to determine, recent direct measurements, which extend to higher energies than hitherto, show a likely flattening in the spectrum above ∼104 GeV/nucleon for He-nuclei, a flattening which, if extrapolated to higher energies, would meet the measured spectrum in the knee region. The other nuclei do not show this feature. He-nuclei in the knee region would also be marginally more consistent with KASCADE extensive air shower data, although there are serious problems with EAS mass estimates in that experiment. Concerning the acceleration, recent models applied to the Monogem Ring SNR allow a satisfactory explanation in terms of either oxygen or helium, but with the latter being a distinct possibility and perhaps more likely.

Flux upper limits of diffuse TeV gamma rays from the Galactic plane using the effective area of the Tibet-II and -III arrays

We obtained new upper limits on the diffuse gamma rays from the inner Galactic (IG) and outer Galactic (OG) planes in 3–10 TeV region, using the Tibet air shower data and new Monte Carlo simulation results. A difference of the effective area of the air-shower array for observing gamma rays and cosmic rays was carefully taken into account in this analysis, resulting in that the flux upper limits of the diffuse TeV gamma rays were reduced by factors of 4.0–3.7 for 3–10 TeV than those in our previous results (Amenomori, M., Ayabe, S., Cui, S.W., et al. Observation of multi-TeV diffuse gamma rays from the Galactic plane with the Tibet air shower array. Astrophys. J. 580, 887–895, 2002.). This new result suggests that the inverse power index of the energy spectrum of source electrons responsible for generating diffuse TeV gamma rays through inverse Compton effect should be steeper than 2.2 and 2.1 for IG and OG planes, respectively, with 99%C.L.

KASCADE measurements of energy spectra for elemental groups of cosmic rays: Results and open problems

A composition analysis of KASCADE air shower data is performed by means of unfolding the two-dimensional frequency spectrum of electron and muon numbers. Aim of the analysis is the determination of energy spectra for elemental groups representing the chemical composition of primary cosmic rays. Since such an analysis depends crucially on simulations of air showers the two different hadronic interaction models QGSJet and SIBYLL are used for their generation. The resulting primary energy spectra show that the knee in the all particle spectrum is due to a steepening of the spectra of light elements but, also, that neither of the two simulation sets is able to describe the measured data consistently over the whole energy range with discrepancies appearing in different energy regions.