Ultra-high Energy Cosmic Ray Experiment Research Articles

Using deep learning to enhance event geometry reconstruction for the telescope array surface detector

The extremely low flux of ultra-high energy cosmic rays (UHECR) makes their direct observation by orbital experiments practically impossible. For this reason all current and planned UHECR experiments detect cosmic rays indirectly by observing the extensive air showers (EAS) initiated by cosmic ray particles in the atmosphere. The world largest statistics of the ultra-high energy EAS events is recorded by the networks of surface stations. In this paper we consider a novel approach for reconstruction of the arrival direction of the primary particle based on the deep convolutional neural network. The latter is using raw time-resolved signals of the set of the adjacent trigger stations as an input. The Telescope Array (TA) Surface Detector (SD) is an array of 507 stations, each containing two layers plastic scintillator with an area of 3 m2. The training of the model is performed with the Monte-Carlo dataset. It is shown that within the Monte-Carlo simulations, the new approach yields better resolution than the traditional reconstruction method based on the fitting of the EAS front. The details of the network architecture and its optimization for this particular task are discussed.

Using Deep Learning in Ultra-High Energy Cosmic Ray Experiments

The extremely low flux of ultra-high energy cosmic rays (UHECR) makes their direct observation by orbital experiments practically impossible. For this reason all current and planned UHECR experiments detect cosmic rays indirectly by observing the extensive air showers (EAS) initiated by cosmic ray particles in the atmosphere. Various types of shower observables are analyzed in the modern UHECR experiments including a secondary radio signal and fluorescent light from the excited nitrogen molecules. Most of the data is collected by the network of surface stations which allows to measure the lateral EAS profile. The raw observables in this case are the time-resolved signals for the set of adjacent triggered stations. The Monte Carlo shower simulation is performed in order to recover the primary particle properties. In traditional techniques the MC simulation is used to fit some synthetic observables such as the shower rise time, the shower front curvature and the particle density normalized to a given distance from the core. In this talk we’ll consider an alternative approach based on the deep convolutional neural network trained on a large Monte-Carlo dataset, using the detector signal time series as an input. The above approach has proven its efficiency with the Monte-Carlo simulations of the Telescope Array Observatory surface detector. We’ll discuss in detail how the network architecture is optimized for this particular task.

Open Questions in Cosmic-Ray Research at Ultrahigh Energies

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 present upcoming and proposed UHECR experiments and discuss their projected science reach.

Ultra High Energy Cosmic Rays & Super-heavy Dark Matter: Observables and prospect of (non)detection

We reanalyse the prospects for upcoming Ultra-High Energy Cosmic Ray experiments in connection with the phenomenology of Super-heavy Dark Matter. We identify a set of observables well suited to reveal a possible anisotropy in the High Energy Cosmic Ray flux induced by the decays of these particles, and quantify their performance via Monte Carlo simulations that mimic the outcome of near-future and next-generation experiments. The spherical and circular dipoles are able to tell isotropic and anisotropic fluxes apart at a confidence level as large as 4σ or 5σ, depending on the Dark Matter profile. The forward-to-backward flux ratio yields a comparable result for relatively large opening angles of about 40°, but it is less performing once a very large number of events is considered. We also find that an actual experiment employing these observables and collecting 300 events at 60 EeV would have a 50% chance of excluding isotropy against Super-heavy Dark Matter at a significance of at least 3σ.

Expected signatures from hadronic emission processes in the TeV spectra of BL Lacertae objects

Context. The wealth of recent data from Imaging Air Cherenkov telescopes (IACTs), ultra-high energy cosmic-ray experiments and neutrino telescopes have fuelled a renewed interest in hadronic emission models for γ-loud blazars. Aims. We explore physically plausible solutions for a lepto-hadronic interpretation of the stationary emission from high-frequency peaked BL Lac objects (HBLs). The modelled spectral energy distributions are then searched for specific signatures at very high energies that could help to distinguish the hadronic origin of the emission from a standard leptonic scenario. Methods. By introducing a few basic constraints on parameters of the model, such as assuming the co-acceleration of electrons and protons, we significantly reduced the number of free parameters. We then systematically explored the parameter space of the size of the emission region and its magnetic field for two bright γ-loud HBLs, PKS 2155-304 and Mrk 421. For all solutions close to equipartition between the energy densities of protons and of the magnetic field, and with acceptable jet power and light-crossing timescales, we inspected the spectral hardening in the multi-TeV domain from proton-photon induced cascades and muon-synchrotron emission inside the source. Very-high-energy spectra simulated with the available instrument functions from the future Cherenkov Telescope Array (CTA) were evaluated for detectable features as a function of exposure time, source redshift, and flux level. Results. A range of hadronic scenarios are found to provide satisfactory solutions for the broad band emission of the sources under study. The TeV spectrum can be dominated either by proton-synchrotron emission or by muon-synchrotron emission. The solutions for HBLs cover a parameter space that is distinct from the one found for the most extreme BL Lac objects in an earlier study. Over a large range of model parameters, the spectral hardening due to internal synchrotron-pair cascades, the “cascade bump”, should be detectable for acceptable exposure times with the future CTA for a few nearby and bright HBLs.

The importance of atmospheric monitoring at the Pierre Auger Observatory

The Pierre Auger Observatory is an ultra-high energy cosmic ray experiment employing a giant surface array of particle detectors together with telescopes to image fluorescence light from extensive air showers in the atmosphere. The atmosphere is the medium in which the incoming cosmic rays deposit their energy, and as a result we must monitor the characteristics of the atmosphere, including its density profile and light transmission properties, over the Observatory area of 3000 square kilometres.

The FAST Project - A Next Generation UHECR Observatory

We present a concept for large-area, low-cost detection of ultrahigh-energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report on the first results of a FAST prototype installed at the Telescope Array (TA) site, consisting of a single 200 mm photomultiplier tube (PMT) at the focal plane of a 1 m2 Fresnel lens system taken from the prototype of the JEM-EUSO experiment. We also report on the status of the full-scale FAST prototype soon to be installed at the TA site, comprising a segmented spherical mirror of 1.6 m diameter and a 2 × 2 PMT camera.

Measurements of the proton-air cross section with high energy cosmic ray experiments

Detecting Ultra High Energy Cosmic Rays (UHECRs) enables us to measure the proton-air inelastic cross section σinel p–air at energies that we are unable to access with particle accelerators. The proton-proton cross section σp–p is subsequently inferred from the proton-air cross section at these energies. UHECR experiments have been reportingon the proton-air inelastic cross section starting with the Fly’s Eye in 1984 at √s =30 TeV and ending with the most recent result of the Telescope Array experiment at √s = 95 TeV in 2015. In this proceeding, I will summarize the most recent experimental results on the σinel p–air measurements from the UHECR experiments.

Detection of ultra-high energy cosmic ray showers with a single-pixel fluorescence telescope

We present a concept for large-area, low-cost detection of ultra-high energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report first results of a FAST prototype installed at the Telescope Array site, consisting of a single 200 mm photomultiplier tube at the focal plane of a 1 m2 Fresnel lens system taken from the prototype of the JEM-EUSO experiment. The FAST prototype took data for 19 nights, demonstrating remarkable operational stability. We detected laser shots at distances of several kilometers as well as 16 highly significant UHECR shower candidates.

The infrared camera onboard JEM-EUSO

The Extreme Universe Space Observatory on the Japanese Experiment Module (JEM-EUSO) on board the International Space Station (ISS) is the first space-based mission worldwide in the field of Ultra High-Energy Cosmic Rays (UHECR). For UHECR experiments, the atmosphere is not only the showering calorimeter for the primary cosmic rays, it is an essential part of the readout system, as well. Moreover, the atmosphere must be calibrated and has to be considered as input for the analysis of the fluorescence signals. Therefore, the JEM-EUSO Space Observatory is implementing an Atmospheric Monitoring System (AMS) that will include an IR-Camera and a LIDAR. The AMS Infrared Camera is an infrared, wide FoV, imaging system designed to provide the cloud coverage along the JEM-EUSO track and the cloud top height to properly achieve the UHECR reconstruction in cloudy conditions. In this paper, an updated preliminary design status, the results from the calibration tests of the first prototype, the simulation of the instrument, and preliminary cloud top height retrieval algorithms are presented.

An optimization of the FPGA/NIOS adaptive FIR filter using linear prediction to reduce narrow band RFI for the next generation ground-based ultra-high energy cosmic-ray experiment

The electromagnetic part of an extensive air shower developing in the atmosphere provides significant information complementary to that obtained by water Cherenkov detectors which are predominantly sensitive to the muonic content of an air shower at ground. The emissions can be observed in the frequency band between 10 and 100MHz. However, this frequency range is significantly contaminated by narrow-band RFI and other human-made distortions. The Auger Engineering Radio Array currently suppresses the RFI by multiple time-to-frequency domain conversions using an FFT procedure as well as by a set of manually chosen IIR notch filters in the time-domain. An alternative approach developed in this paper is an adaptive FIR filter based on linear prediction (LP). The coefficients for the linear predictor are dynamically refreshed and calculated in the virtual NIOS processor. The radio detector is an autonomous system installed on the Argentinean pampas and supplied from a solar panel. Powerful calculation capacity inside the FPGA is a factor. Power consumption versus the degree of effectiveness of the calculation inside the FPGA is a figure of merit to be minimized. Results show that the RFI contamination can be significantly suppressed by the LP FIR filter for 64 or less stages.

A comparison study of CORSIKA and COSMOS simulations for extensive air showers

Cosmic rays with energy exceeding ∼1018eV are referred to as ultra-high energy cosmic rays (UHECRs). Monte Carlo codes for extensive air shower (EAS) simulate the development of EASs initiated by UHECRs in the Earth’s atmosphere. Experiments to detect UHECRs utilize EAS simulations to estimate their energy, arrival direction, and composition. In this paper, we compare EAS simulations with two different codes, CORSIKA and COSMOS, presenting quantities including the longitudinal distribution of particles, depth of shower maximum, kinetic energy distribution of particle at the ground, and energy deposited to the air. We then discuss implications of our results to UHECR experiments.

AugerNext: innovative research studies for the next generation ground-based ultra-high energy cosmic ray experiment

The findings so far of the Pierre Auger Observatory and also of the Telescope Array define the requirements for a possible next generation experiment: it needs to be considerably increased in size, it needs a better sensitivity to composition, and it should cover the full sky. AugerNext aims to perform innovative research studies in order to prepare a proposal fulfilling these demands. Such R&D studies are primarily focused in the following areas

A strategy to unveil transient sources of ultra-high-energy cosmic rays

Transient generation of ultra-high-energy cosmic rays (UHECRs) has been motivated from promising candidates of UHECR sources such as gamma-ray bursts, flares of active galactic nuclei, and newly born neutron stars and magnetars. Here we propose a strategy to unveil transient sources of UHECRs from UHECR experiments. We demonstrate that the rate of UHECR bursts and/or flares is related to the apparent number density of UHECR sources, which is the number density estimated on the assumption of steady sources, and the time-profile spread of the bursts produced by cosmic magnetic fields. The apparent number density strongly depends on UHECR energies under a given rate of the bursts, which becomes observational evidence of transient sources. It is saturated at the number density of host galaxies of UHECR sources. We also derive constraints on the UHECR burst rate and/or energy budget of UHECRs per source as a function of the apparent source number density by using models of cosmic magnetic fields. In order to obtain a precise constraint of the UHECR burst rate, high event statistics above ∼ 10 20 eV for evaluating the apparent source number density at the highest energies and better knowledge on cosmic magnetic fields by future observations and/or simulations to better estimate the time-profile spread of UHECR bursts are required. The estimated rate allows us to constrain transient UHECR sources by being compared with the occurrence rates of known energetic transient phenomena.

Precise measurement of the absolute fluorescence yield of the 337 nm band in atmospheric gases

A measurement of the absolute fluorescence yield of the 337nm nitrogen band, relevant to ultra-high energy cosmic ray (UHECR) detectors, is reported. Two independent calibrations of the fluorescence emission induced by a 120GeV proton beam were employed: Cherenkov light from the beam particle and calibrated light from a nitrogen laser. The fluorescence yield in air at a pressure of 1013hPa and temperature of 293K was found to be Y337=5.61±0.06stat±0.22systphotons/MeV. When compared to the fluorescence yield currently used by UHECR experiments, this measurement improves the uncertainty by a factor of three, and has a significant impact on the determination of the energy scale of the cosmic ray spectrum.

Measurement of zero degree inclusive photon energy spectra for [formula omitted] proton–proton collisions at LHC

The inclusive photon energy spectra measured by the Large Hadron Collider forward (LHCf) experiment in the very forward region of LHC proton–proton collisions at s=900GeV are reported. The results from the analysis of 0.30 nb−1 of data collected in May 2010 in the two pseudorapidity regions of η>10.15 and 8.77<η<9.46 are compared with the predictions of the hadronic interaction models DPMJET 3.04, EPOS 1.99, PYTHIA 8.145, QGSJET II-03 and SIBYLL 2.1, which are widely used in ultra-high energy cosmic ray experiments. EPOS 1.99 and SIBYLL 2.1 show a reasonable agreement with the spectral shape of the experimental data, whereas they predict lower cross-sections than the data. The other models, DPMJET 3.04, QGSJET II-03 and PYTHIA 8.145, are in good agreement with the data below 300 GeV but predict harder energy spectra than the data above 300 GeV.The results of these comparisons exhibited features similar to those for the previously reported data for s=7TeV collisions.

THE ROLE OF STRUCTURED MAGNETIC FIELDS ON CONSTRAINING PROPERTIES OF TRANSIENT SOURCES OF ULTRA-HIGH-ENERGY COSMIC RAYS

We study how the properties of transient sources of ultra-high-energy cosmic rays (UHECRs) can be accessed by exploiting UHECR experiments, taking into account the propagation of UHECRs in magnetic structures which the sources are embedded in, i.e., clusters of galaxies and filamentary structures. Adopting simplified analytical models, we demonstrate that the structured extragalactic magnetic fields (EGMFs) play crucial roles in unveiling the properties of the transient sources. These EGMFs unavoidably cause significant delay in the arrival time of UHECRs as well as the Galactic magnetic field, even if the strength of magnetic fields in voids is zero. Then, we show that, given good knowledge on the structured EGMFs, UHECR observations with high statistics above $10^{20}$ eV allow us to constrain the generation rate of transient UHECR sources and their energy input per burst, which can be compared with the rates and energy release of known astrophysical phenomena. We also demonstrate that identifying the energy dependence of the apparent number density of UHECR sources at the highest energies is crucial as a clue to such transient sources. Future UHECR experiments with extremely large exposure are required to reveal the nature of transient UHECR sources.

Spacetime noncommutativity and ultrahigh energy cosmic ray experiments

If new physics were capable of pushing the neutrino-nucleon inelastic cross section 3 orders of magnitude beyond the standard model prediction, then ultrahigh energy (UHE) neutrinos would have already been observed at neutrino observatories. We use such a constraint to reveal information on the scale of noncommutativity (NC) ${\ensuremath{\Lambda}}_{\mathrm{NC}}$ in noncommutative gauge field theories where neutrinos possess a tree-level coupling to photons in a generation-independent manner. In the energy range of interest (${10}^{10}$ to ${10}^{11}\text{ }\text{ }\mathrm{GeV}$), the $\ensuremath{\theta}$ expansion ($|\ensuremath{\theta}|\ensuremath{\sim}1/{\ensuremath{\Lambda}}_{\mathrm{NC}}^{2}$) and, therefore, the perturbative expansion, in terms of ${\ensuremath{\Lambda}}_{\mathrm{NC}}$, retains no longer its meaningful character, forcing us to resort to those NC field theoretical frameworks involving the full $\ensuremath{\theta}$ resummation. Our numerical analysis of the contribution to the process coming from the photon exchange impeccably pins down a lower bound on ${\ensuremath{\Lambda}}_{\mathrm{NC}}$ to be as high as 900 (450) TeV, depending on the estimates for the cosmogenic neutrino flux. If, on the other hand, one considers a surprising recent result that occurred in Pierre Auger Observatory data, that UHE cosmic rays are mainly composed of highly ionized Fe nuclei, then our bounds get weaker, due to the diminished cosmic neutrino flux. Nevertheless, we show that, even for the very high fraction of heavy nuclei in primary UHE cosmic rays, our method may still yield remarkable bounds on ${\ensuremath{\Lambda}}_{\mathrm{NC}}$, typically always above 200 TeV. Albeit, in this case, one encounters a maximal value for the Fe fraction, from which any useful information on ${\ensuremath{\Lambda}}_{\mathrm{NC}}$ can be drawn, delimiting thus the applicability of our method.

AN EMPIRICAL MODEL OF PRODUCTION AND ATTENUATION OF FLUORESCENCE LIGHT IN ATMOSPHERE FOR SATELLITE-BASED ULTRA HIGH ENERGY COSMIC RAY EXPERIMENTS

In the context of detection of Ultra High Energy Cosmic Ray (UHECR) showers from space the details of fluorescence light production and transmission in the atmosphere are given. An analytical model of the fluorescence yield, in dependence on nitrogen molecular parameters and the atmospheric conditions, is presented. Seasonal and geographical variations of the total fluorescence photon yield between 300 nm and 400 nm in air excited by 0.85 MeV electrons are shown as a function of the altitude, using different atmospheric models. In the frame of a satellite-based UHECR experiment the fluorescence yield has been corrected by the overall atmospheric transmission which takes into account, in the simplest approximation, the wavelength-dependent scattering and absorption of the fluorescence light from air molecules, from stratospheric ozone, and from aerosol. The effect of the atmospheric attenuation on the fluorescence yield is shown as a function of the altitude of the emission point of light.

Studies of UHECR propagation in the galactic magnetic field

We present results of simulations of ultra-high energy cosmic ray (UHECR) propagation in the Galactic magnetic field (GMF). Different assumptions on the large-scale GMF structure and/or primary particle lead to distinctly different deflection patterns of the highest energy cosmic rays (CR). The GMF modifies the exposure of an UHECR experiment to the extragalactic sky. We estimated these effects for the Pierre Auger experiment. Further forward-tracking studies under plausible UHECR sources scenarios will allow for direct comparison with the observed correlation between the nearby active galactic nuclei (AGN) and the highest energy Auger events.