Shower Maximum Research Articles

Directed flow of identified particles from Au+Au collisions at RHIC

We present the measurement of directed flow (v1) for the identified particles, namely, Λ, \( \bar \Lambda \) and Ks0, as a function of rapidity and centrality in Au+Au collisions at \( \sqrt {s_{NN} } \) = 200 GeV and 62.4 GeV. The measurement is based on the run IV data obtained by the STAR experiment at RHIC. In order to enhance event plane resolution, we use tracks reconstructed from the Forward Time Projection Chambers (FTPCs), together with the sideward deflection of spectator neutrons measured by the STAR’s Shower Maximum Detector at Zero Degree Calorimeters (ZDC-SMDs). We find that for 200 GeV, proton and antiproton v1 is less than 1%, the Ks0Λ, \( \bar \Lambda \)v1 is less than 2%; for 62 GeV, proton v1 is less than 1% and antiproton is less than 2%, v1 for Ks0, Λ, \( \bar \Lambda \) is less than 2% in Au+Au collisions at 200 GeV.

The Balloon-the-Shower programme of the Pierre Auger Observatory

The southern part of the Pierre Auger Observatory in Argentina investigates cosmic rays with energies above about 5·1017 eV. High-energy events which have been recorded with both detector components, surface water Cherenkov tanks and fluorescence telescopes, are crucial for the energy calibration of the entire detector system. Using this method, the energy reconstruction of extensive air showers relies on a proper fluorescence light reconstruction which depends on the knowledge of atmospheric conditions like pressure, temperature and water vapour. These properties of the atmosphere vary with altitude and in time. Therefore, a dedicated monitoring programme has operated since March 2009 to measure an actual atmospheric profile with meteorological radio soundings shortly after the detection of a high-energy air shower with E0 > 2·1019 eV. We will present the technical implementation of this programme as well as a reconstruction analysis using the data obtained. The reconstructed primary energy of air showers and the position of the shower maximum are compared with those results using either monthly models for the local atmospheric conditions or global meteorological models.

The impact of the air-fluorescence yield on the reconstructed shower parameters of ultra-high energy cosmic rays

An accurate knowledge of the fluorescence yield and its dependence on atmospheric properties such as pressure, temperature or humidity is essential to obtain a reliable measurement of the primary energy of cosmic rays in experiments using the fluorescence technique. In this work, several sets of fluorescence yield data (i.e. absolute value and quenching parameters) are described and compared. A simple procedure to study the effect of the assumed fluorescence yield on the reconstructed shower parameters (energy and shower maximum depth) as a function of the primary features has been developed. As an application, the effect of water vapor and temperature dependence of the collisional cross section on the fluorescence yield and its impact on the reconstruction of primary energy and shower maximum depth has been studied.

Mass composition and cross-section from the shape of cosmic ray shower longitudinal profiles

Abstract The longitudinal development of extreme energy cosmic ray showers has a characteristic “Universal Shower Profile” when normalized and translated to the shower maximum. Experimentally accessible observables can be defined to parametrize the average shape and characterize each event. By describing the full shape of the profile, information related to the first hadronic interactions and primary particle type can be extracted. A shape variable which measures the distance from the first interaction to the depth of maximum can lead to a cosmic ray composition analysis with independent extraction of the primary cross-sections.

Precise determination of muon and electromagnetic shower contents from a shower universality property

We consider two new aspects of Extensive Air Shower development universality allowing to make accurate estimation of muon and electromagnetic (EM) shower contents in two independent ways. In the first case, to get muon (or EM) signal in water Cherenkov tanks or in scintillator detectors it is enough to know the vertical depth of shower maximum and the total signal in the ground detector. In the second case, the EM signal can be calculated from the primary particle energy and the zenith angle. In both cases the parametrizations of muon and EM signals are almost independent on primary particle nature, energy and zenith angle. Implications of the considered properties for mass composition and hadronic interaction studies are briefly discussed. The present study is performed on 28000 of proton, oxygen and iron showers, generated with CORSIKA 6.735 for $E^{-1}$ spectrum in the energy range log(E/eV)=18.5-20.0 and uniformly distributed in cos^2(theta) in zenith angle interval theta=0-65 degrees for QGSJET II/Fluka interaction models.

Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeV

We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (X(max)), for air shower events collected by the High-Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d<X(max)>/d[log(E)] of 47.9+/-6.0(stat)+/-3.2(syst) g/cm2/decade for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at 4x10(18) eV.

Measurement of the Depth of Maximum of Extensive Air Showers above1018 eV

We describe the measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10;{18} eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106{-21}{+35}) g/cm{2}/decade below 10{18.24+/-0.05} eV, and (24+/-3) g/cm{2}/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm{2}. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.

On the heavy chemical composition of the ultra-high energy cosmic rays

The Pierre Auger Observatory’s (PAO) shower profile measurements can be used to constrain the chemical composition of the ultra-high energy cosmic ray (UHECR) spectrum. In particular, the PAO’s measurements of the average depth of shower maximum and the fluctuations of the depth of shower maximum indicate that the cosmic ray spectrum is dominated by a fairly narrow distribution (in charge) of heavy or intermediate mass nuclei at the highest measured energies ( E ≳ 10 19 eV ) , and contains mostly lighter nuclei or protons at lower energies ( E ∼ 10 18 eV ) . In this article, we study the propagation of UHECR nuclei with the goal of using these measurements, along with those of the shape of the spectrum, to constrain the chemical composition of the particles accelerated by the sources of the UHECRs. We find that with modest intergalactic magnetic fields, 0.3 nG in strength with 1 Mpc coherent lengths, good fits to the combined PAO data can be found for the case in which the sources accelerate primarily intermediate mass nuclei (such as nitrogen or silicon). Without intergalactic magnetic fields, we do not find any composition scenarios that can accommodate the PAO data. For a spectrum dominated by heavy or intermediate mass nuclei, the Galactic (and intergalactic) magnetic fields are expected to erase any significant angular correlation between the sources and arrival directions of UHECRs.

A parameterization of cosmic ray shower profiles based on shower width

Cosmic ray (CR) air showers, detected via the air fluorescence technique, are reconstructed in part using functions that parameterize the longitudinal profile of each shower. The profile parameterization yields the position of shower maximum, Xmax in gm cm−2, which is sensitive to the incident CR particle type: e.g. p, C/N/O, Fe or γ. The integral of the profile is directly related to the shower energy. The Pierre Auger fluorescence reconstruction uses the Gaisser–Hillas (GH) four-parameter form [5]. The HiRes group has used both the Gaisser–Hillas form and a three-parameter Gaussian in age form [7]. Historically analytic shower theory suggested yet other forms; the best known is a three-parameter form popularized by Greisen [6]. Our work now uses the shower full width half-maximum, fwhm, and shower asymmetry parameter, f, to unify the parameterization of all three profile functions. Furthermore, shower profiles expressed in terms of the new parameters: fwhm, f, have correlations greatly reduced over e.g. Gaisser–Hillas parameters X0, λ. This allows shower profile reconstructions to add constraints (if needed) on the mostly uncorrelated parameters fwhm, f.

A study of the effect of molecular and aerosol conditions in the atmosphere on air fluorescence measurements at the Pierre Auger Observatory

The air fluorescence detector of the Pierre Auger Observatory is designed to perform calorimetric measurements of extensive air showers created by cosmic rays of above 10 18 eV . To correct these measurements for the effects introduced by atmospheric fluctuations, the Observatory contains a group of monitoring instruments to record atmospheric conditions across the detector site, an area exceeding 3000 km 2. The atmospheric data are used extensively in the reconstruction of air showers, and are particularly important for the correct determination of shower energies and the depths of shower maxima. This paper contains a summary of the molecular and aerosol conditions measured at the Pierre Auger Observatory since the start of regular operations in 2004, and includes a discussion of the impact of these measurements on air shower reconstructions. Between 10 18 and 10 20 eV , the systematic uncertainties due to all atmospheric effects increase from 4% to 8% in measurements of shower energy, and 4 g cm - 2 to 8 g cm - 2 in measurements of the shower maximum.

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.

Heavy Cosmic Ray Nuclei from Extragalactic Sources above ‘The Ankle '

A recent observation by the Auger Observatory group presents evidence for cosmic rays above 5.6� 10 19 eV -(56 EeV) being 'predominantly protons' coming from Active Galactic Nuclei. If, as would be expected, the particles above the ankle at about 2 EeV are almost all of Extragalactic origin then it follows that the characteristics of the nuclear interac- tions of such particles would need to be very different from conventional expectation - a result that follows from the measured positions of 'shower maximum' at somewhat lower energies where mass measurements using conventional nu- clear interaction models indicate (ln A)≃ 2.5. Such a claim is rather dramatic. In our own analysis we study to what extent the Auger results could, indeed, give such a mean value for (ln A)rather than a much smaller one. We conclude that they can, and the need for a dramatic change in the nuclear physics disappears.

The Cosmic Ray Mass Composition in the Energy Range [formula omitted] measured with the Tunka Array: Results and Perspectives

The final analysis of the Extensive Air Shower (EAS) maximum ( X m a x ) depth distribution derived from the data of Tunka-25 atmospheric Cherenkov light array in the energy range 3 ⋅ 10 15 – 3 ⋅ 10 16 eV is presented. The perspectives of X m a x studies with the new Cherenkov light array Tunka-133 of 1 km 2 area, extending the measurements up to 10 18 eV, are discussed.

Method for measuring the PCR proton spectrum in the energy range of &gt; 1016 eV

Criteria for selecting proton events among the total sequence of events from primary nuclei of cosmic rays with zenith angles θ 10 PeV; at lower energies, the average mass composition is almost unchanged. The method used in (3, 4) is based on the correlation of the Cherenkov light (CL) pulse halfwidth at a long distance from the shower axis with the shower maximum position. It is well known that the CL transverse distribution function (TDF) is also sensitive to the primary nucleus mass. However, CL detectors of ground-based installations collect light from only a small fraction of the shower area; therefore, detailed reconstruction of the CL TDF is complicated. In the SPHERE-2 experiment, it is intended to use the shape of CL TDF to determine the PCR composition, since detectors of this installation can survey about half the shower area. The operating principle of this telescope is based on the idea to measure CL produced by extended atmospheric showers (EAS) and reflected from the snow surface (7). The optical scheme of the SPHERE-2 installation represents a Schmidt camera with a mirror 1.5 m in diameter and a mosaic of 109 photomultipliers in the mirror focal surface. Thus, this system allows measurements of the quantity proportional to the total CL amount within the field of view of each detector of the mosaic. In this paper, the criteria allowing separation of a certain known proton fraction from the total number of PCR nuclei are studied using the Monte Carlo method. The Lake Baikal level (H0 = 455 m above sea level) and the detector spatial resolution δr =8 0m corresponding to the SPHERE-2 installation position at a height of 1 km over the snow surface of Lake Baikal are considered. In this case, the diameter

Composition Studies with the Pierre Auger Observatory

We report on studies of the composition of ultra high energy cosmic rays with the Pierre Auger Observatory. The detection of longitudinal air shower profiles with the fluorescence detector is described and the measurement of the average shower maximum as a function of energy is presented. Furthermore, mass sensitive parameters that can be obtained from the observatory's surface detector data are discussed.

Modified fragmentation function in heavy ion collisions at RHIC via direct γ-jet measurements

The presented results are the first measurements at RHIC for direct γ-charged hadron azimuthal correlations in heavy ion collisions. We use these correlations to study the color charge density of the medium through the medium-induced modification of high-p T parton fragmentation. Azimuthal correlations of direct photons at high transverse energy (8<p T <16 GeV) with away-side charged hadrons of transverse momentum (3<p T <6 GeV/c) have been measured over a broad range of centrality for Au+Au collisions and p+p collisions at \(\sqrt{s_{NN}}=200\) GeV in the STAR experiment. A transverse shower shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum Detector is used to discriminate between the direct photons and photons from the decays of high p T π 0. The per-trigger away-side yield of direct γ is smaller than from π 0 trigger at the same centrality class. Within the current uncertainty the I CP of direct γ and π 0 are similar.

Universality of electron–positron distributions in extensive air showers

Using a large set of simulated extensive air showers, we investigate universality features of electron and positron distributions in very-high-energy cosmic-ray air showers. Most particle distributions depend only on the depth of the shower maximum and the number of particles in the cascade at this depth. We provide multi-dimensional parameterizations for the electron–positron distributions in terms of particle energy, vertical and horizontal momentum angle, lateral distance, and time distribution of the shower front. These parameterizations can be used to obtain realistic electron–positron distributions in extensive air showers for data analysis and simulations of Cherenkov radiation, fluorescence signal, and radio emission.

Depth of the maximum of extensive air showers and mass composition of primary cosmic radiation at an energy of 4 × 1017 eV according to data on radioemission from extensive air showers

The results of a reanalysis of experimental data on extensive-air-shower radioemission that were obtained previously at the Moscow State University array for studying extensive air showers are presented. The lateral distribution of radioemission is given for showers characterized by a primary energy of 4 × 1017 eV and a zenith angle of θ = 35°. On the basis of an analysis of a lateral distribution of radioemission, the average value of the shower-maximum depth at a primary energy of 4 × 1017 eV is estimated at X max = 655 ± 13 g/cm2. Estimates of themass content of primary radiation that were obtained from an analysis of the distribution of X max are compatible with the hypothesis that the role of light nuclei becomes more pronounced at energies above 1017 eV.

Influence of the scattered Cherenkov light on the width of shower images as measured in the EAS fluorescence experiments

We calculate the lateral distribution of Cherenkov light at different levels of shower development. The calculations use the universal characteristics of large showers. We derive that the angular and lateral distributions of Cherenkov photons emitted by a shower path element depend only on the shower age and height in the atmosphere of this element. The width of a shower image in the Cherenkov scattered light also depends, however, on the zenith angle and X max . We also show that below shower maximum it is considerably wider than the width in the fluorescence light.

A new numerical technique to determine primary cosmic ray composition in the ankle region

In this paper we introduce a new multiparametric technique that attempts to tackle simultaneously the problems of composition determination and hadronic interaction uncertainty. Employing simulations of a real world detector under its planned operational conditions, and disregarding systematics, we can asses that the present technique should be able to determine the composition of a binary mixture of p and Fe with a statistical confidence of few percent, in a way that is independent of the assumed hadronic interaction model. Moreover, the combination of real data with the tools developed and presented here should give an indication of the reliability of the various hadronic interaction models in current use in the area. We center our study in the region of the ankle, where composition carries critical astrophysical information, and use two main parameters: the number of muons at 600 m from the shower axis and the depth of the shower maximum obtained from the hybrid operation of the planned muon counters and high elevation fluorescence telescopes of the AMIGA and HEAT Auger enhancements.