arXiv subjects

Enrique Zas

Publications and source records attributed to Enrique Zas.

33 records · Page 2Linked to original sources

arXiv2012

Coherent Radiation from Extensive Air Showers in the Ultra-High Frequency Band

Using detailed Monte Carlo simulations we have characterized the features of the radio emission of inclined air showers in the Ultra-High Frequency band (300 MHz - 3 GHz). The Fourier-spectrum of the radiation is shown to have a sizable intensity well into the GHz frequency range. The emission is mainly due to transverse currents induced by the geomagnetic field and to the excess charge produced by the Askaryan effect. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground. The size of the coherently emitting volume depends on frequency, shower geometry and observer position, and is interpreted in terms of the relative time delays. At ground level, the maximum emission at high frequencies is concentrated in an elliptical ring-like region around the intersection of a Cherenkov cone with its vertex at shower maximum and the ground. The frequency spectrum of inclined showers when observed at positions that view shower maximum in the Cherenkov direction, is shown to be in broad agreement with the pulses detected by the Antarctic Impulsive Transient Antenna (ANITA) experiment, making the interpretation that they are due to Ultra-High Energy Cosmic Ray atmospheric showers consistent with our simulations. These results are also of great importance for experiments aiming to detect molecular bremsstrahlung radiation in the GHz range as they present an important background for its detection.

astro-ph.HE↗

arXiv2012

Coherent Cherenkov radio pulses from hadronic showers up to EeV energies

The Cherenkov radio pulse emitted by hadronic showers in ice is calculated for showers of energies in the EeV range. This is obtained with three dimensional simulations of both shower development and the coherent radio pulse emitted as the excess charge develops in the shower. A Monte Carlo, ZHAireS, has been developed for this purpose combining the high energy hadronic interaction capabilities of AIRES, and the dense media propagation capabilities of TIERRAS, with the precise low energy tracking and specific algorithms developed to calculate the radio emission in ZHS. A thinning technique is implemented and optimized to allow the simulation of radio pulses induced by showers up to 10 EeV in ice. The code is validated comparing the results for electromagnetic and hadronic showers to those obtained with GEANT4 and ZHS codes. The contribution to the pulse of other shower particles in addition to electrons and positrons, mainly pions and muons, is found to be below 1%. The characteristics of hadronic showers and the corresponding Cherenkov frequency spectra are compared with those from purely electromagnetic showers. The dependence of the spectra on shower energy and high-energy hadronic model is addressed and parameterizations for the radio emission in hadronic showers in ice are given for practical applications.

astro-ph.HE↗

arXiv2012

Monte Carlo simulations of radio pulses in atmospheric showers using ZHAireS

We present predictions for the radio pulses emitted by extensive air showers using ZHAireS, an AIRES-based Monte Carlo code that takes into account the full complexity of ultra-high energy cosmic-ray induced shower development in the atmosphere, and allows the calculation of the electric field in both the time and frequency domains. We do not presuppose any emission mechanism, but our results are compatible with a superposition of geomagnetic and charge excess radio emission effects. We investigate the polarization of the electric field as well as the effects of the refractive index n and shower geometry on the radio pulses. We show that geometry, coupled to the relativistic effects that appear when using a realistic n>1, play a prominent role on the radio emission of air showers.

astro-ph.HE↗

arXiv2012

Practical and accurate calculations of Askaryan radiation

An in-depth characterization of coherent radio Cherenkov pulses from particle showers in dense dielectric media, referred to as the Askaryan effect, is presented. The time-domain calculation developed in this article is based on a form factor to account for the lateral dimensions of the shower. It is computationally efficient and able to reproduce the results of detailed particle shower simulations with high fidelity in most regions of practical interest including Fresnel effects due to the longitudinal development of the shower. In addition, an intuitive interpretation of the characteristics of the Askaryan pulse is provided. We expect our approach to benefit the analysis of radio pulses in experiments exploiting the radio technique.

astro-ph.HE↗

arXiv2010

Cherenkov radio pulses from electromagnetic showers in the time-domain

The electric field of the Cherenkov radio pulse produced by a single charged particle track in a dielectric medium is derived from first principles. An algorithm is developed to obtain the pulse in the time domain for numerical calculations. The algorithm is implemented in a Monte Carlo simulation of electromagnetic showers in dense media (specifically designed for coherent radio emission applications) as might be induced by interactions of ultra-high energy neutrinos. The coherent Cherenkov radio emission produced by such showers is obtained simultaneously both in the time and frequency domains. A consistency check performed by Fourier-transforming the pulse in time and comparing it to the frequency spectrum obtained directly in the simulations yields, as expected, fully consistent results. The reversal of the time structure inside the Cherenkov cone and the signs of the corresponding pulses are addressed in detail. The results, besides testing algorithms used for reference calculations in the frequency domain, shed new light into the properties of the radio pulse in the time domain. The shape of the pulse in the time domain is directly related to the depth development of the excess charge in the shower and its width to the observation angle with respect to the Cherenkov direction. This information can be of great practical importance for interpreting actual data.

astro-ph.HE↗

arXiv2005

Coherent radio pulses from showers in different media: A unified parameterization

We study the frequency and angular dependences of Cherenkov radio pulses originated by the excess of electrons in electromagnetic showers in different dense media. We develop a simple model to relate the main characteristics of the electric field spectrum to the properties of the shower such as longitudinal and lateral development. This model allows us to establish the scaling of the electric field spectrum with the properties of the medium such as density, radiation length, Moliere radius, critical energy and refraction index. We normalize the predictions of the scaling relations to the numerical results obtained in our own developed GEANT4-based Monte Carlo simulation, and we give a unified parameterization of the frequency spectrum and angular distribution of the electric field in ice, salt, and the lunar regolith, in terms of the relevant properties of the media. Our parameterizations are valid for electromagnetic showers below the energy at which the Landau-Pomeranchuk-Migdal effect starts to be relevant in these media. They also provide an approximate estimate of radio emission in hadronic showers induced by high energy cosmic rays or neutrinos.

astro-ph↗

arXiv2005

Neutrino Detection with Inclined Air Showers

The possibilities of detecting high energy neutrinos through inclined showers produced in the atmosphere are addressed with an emphasis on the detection of air showers by arrays of particle detectors. Rates of inclined showers produced by both down-going neutrino interactions and by up-coming $τ$ decays from earth-skimming neutrinos as a function of shower energy are calculated with analytical methods using two sample neutrino fluxes with different spectral indices. The relative contributions from different flavors and charged, neutral current and resonant interactions are compared for down-going neutrinos interacting in the atmosphere. No detailed description of detectors is attempted but rough energy thresholds are implemented to establish the ranges of energies which are more suitable for neutrino detection through inclined showers. Down-going and up-coming rates are compared.

astro-ph↗

arXiv2001

Astroparticle Physics: The High Energy Tail of the Cosmic Ray Spectrum

In this article I review the main theoretical problems that are posed by the highest energy end of the observed cosmic ray spectrum, stressing the importance of establishing their composition in order to decide between proposed scenarios. I then discuss the possibilities that are opened by the detection of inclined showers with extensive air shower arrays. Recent progress in modelling magnetic deviations for these showers has allowed the analysis of inclined showers that were detected by the Haverah Park experiment. This analysis disfavours models that predict a large proportion of photons in the highest energy cosmic rays and open up new possibilities for future shower array detectors particularly those, like the Pierre Auger Observatory, using water Cherenkov detectors.

astro-ph↗

arXiv2001

Calculations of radio pulses from High Energy Showers

In this article we review the progress made in understanding the main characteristics of coherent Čerenkov radiation induced by high energy showers in dense media. A specific code developed for this purpose is described because it took a significant part in this process. Subsequent approximations developed for the calculation of radio pulses from EeV showers are reviewed. Emphasis is given to the relation between the shower characteristics and different features of the corresponding radio emission.

astro-ph↗

arXiv2001

ZeV Air Showers: The View from Auger

In this article I briefly discuss the characteristics of the Auger observatories paying particular attention to the role of inclined showers, both in the search for high energy neutrino interactions deep in the atmosphere and as an alternative tool for the study of cosmic rays, particulartly their composition.

astro-ph↗

arXiv2000

A New Approach to Mass Measurements of UHECR: Horizontal Air Showers

The role of Horizontal Showers induced by cosmic rays is discussed in detail. A new approach to the calculation of the muon component in horizontal air showers induced by protons, heavier nuclei or photons is presented which allows a simple analytical evaluation of the muon density profiles at ground level. The results of the first application of these results to horizontal air showers detected at the Haverah Park Array by the recently started {\sl Leeds-Santiago collaboration}, leading to important restrictions on composition at ultra high energies, are reported.

astro-ph↗

arXiv2000

Summary: ZeV Air Showers. Where do we Stand?

Here an attempt is made at summarizing the presentations, most of which were about the highest energy particles observed in nature. Particular attention is paid to the solutions to the Ultra High Energy Cosmic Ray particles, to the new and forthcoming data, to the new proposals for experiments and to the role of primary composition, that were amongst the most discussed subtopics.

astro-ph↗

arXiv1997

The Highest Energy Neutrinos

Some neutrino predictions at the highest energies for a number of production mechanisms are comparatively reviewed in the light of future projects for neutrino detection.

astro-ph↗

arXiv1996

Neutrino Induced Events in the Pierre Auger Detector

We study the potential of the Pierre Auger detector for horizontal air showers initiated by ultra high energy neutrino. Assuming some simple trigger requirements we obtain measurable event rates for neutrino fluxes from AGN, from topological defects and from the interactions of cosmic rays with the microwave background.

astro-ph↗

arXiv1995

NEUTRINOS FROM PRIMORDIAL BLACK HOLES

The emission of particles from black holes created in the early Universe has detectable astrophysical consequences. The most stringent bound on their abundance has been obtained from the absence of a detectable diffuse flux of 100 MeV photons. Further scrutiny of these bounds is of interest as they, for instance, rule out primordial black holes as a dark matter candidate. We here point out that these bounds can, in principle, be improved by studying the diffuse cosmic neutrino flux. Measurements of near-vertical atmospheric neutrino fluxes in a region of low geomagnetic latitude can provide a competitive bound. The most favorable energy to detect a possible diffuse flux of primordial black hole origin is found to be a few MeV. We also show that measurements of the diffuse $ν_τ$ flux is the most promising to improve the existing bounds deduced from gamma-ray measurements. Neutrinos from individual black hole explosions can be detected in the GeV-TeV energy region. We find that the kilometer-scale detectors, recently proposed, are able to establish competitive bounds.

hep-ph↗