arXiv subjects
Publications and source records attributed to J. Alvarez-Muñiz.
Technical reports on operations and features of the Pierre Auger Observatory, including ongoing and planned enhancements and the status of the future northern hemisphere portion of the Observatory. Contributions to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009.
Reports on the atmospheric monitoring, calibration, and other operating systems of the Pierre Auger Observatory. Contributions to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009.
Studies of the composition of the highest energy cosmic rays with the Pierre Auger Observatory, including examination of hadronic physics effects on the structure of extensive air showers. Submissions to the 31st ICRC, Lodz, Poland (July 2009).
From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV (1 EeV = 10^18 eV) respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top-down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section.
In nuclear collisions, a sizable fraction of the available energy is carried away by baryons. As the baryon number is conserved, the net-baryon $B-\bar{B}$ retains information on the energy-momentum carried by the incoming nuclei. A simple and consistent model for net-baryon production in high energy proton-proton and nucleus-nucleus collisions is presented. The basic ingredients of the model are valence string formation based on standard PDFs with QCD evolution and string fragmentation via the Schwinger mechanism. The results of the model are presented and compared with data at different centre-of-mass energies and centralities, as well as with existing models. These results show that a good description of the main features of net-baryon data is possible in the framework of a simplistic model, with the advantage of making the fundamental production mechanisms manifest.
We argue that the increase of the ratio baryon/meson due to the presence of strong colour fields and percolation in ultra-high energy hadronic collisions, helps to explain some of the global features of ultra-high energy cosmic ray cascades at E>10^18 eV and, in particular the observed excess in the number of muons with respect to current models of hadronic interactions. A reasonable agreement with the small value and slope of the average depth of shower maximum Xmax vs shower energy -- as seen in data collected at the Pierre Auger Observatory -- can be obtained with a fast increase of the p-Air production cross-section compatible with the Froissart bound.
The determination of the shower development in air using fluorescence yield is subject to corrections due to the angular spread of the particles in the shower. This could introduce systematic errors in the energy determination of an extensive air shower through the fluorescence technique.
We explore the feasibility of using the Moon as a detector of extremely high energy (>10^19 eV) cosmic rays and neutrinos. The idea is to use the existing radiotelescopes on Earth to look for short pulses of Cherenkov radiation in the GHz range emitted by showers induced just below the surface of the Moon when cosmic rays or neutrinos strike it. We estimate the energy threshold of the technique and the effective aperture and volume of the Moon for this detection. We apply our calculation to obtain the expected event rates from the observed cosmic ray flux and several representative theoretical neutrino fluxes.
We present an approximation for the numerical calculation of Cherenkov radio pulses in the Fraunhofer limit from very high energy showers in dense media. We compare it to full Montecarlo simulations in ice studying its range of applicability and show how it can be extended with a simple algorithm. The approximation reproduces well the angular distribution of the pulse around the Cherenkov direction. An improved parameterization for the frequency spectrum in the Cherenkov direction is given for phenomenolgical applications. We extend the method to study the pulses produced by showers at distances at which the Fraunhofer limit does not apply, and give the ranges of distances and frequencies in which Fraunhofer approximation is good enough for interpreting future experimental data. Our results are relevant for the detection of very high energy neutrinos with this technique.
We study the longitudinal development of hadronic showers in water and ice for energies up to 100 EeV. We present results of a hybrid Monte Carlo method developed for the purpose of simulating those showers. We show parameterizations of the longitudinal development of hadronic showers in ice and we investigate the implications of the LPM effect on shower development. The results obtained are relevant for the detection of high energy cosmic rays and neutrinos in large scale detectors that use water as Cherenkov medium.
We study the Cherenkov radiopulses emitted in PeV and EeV neutrino interactions in ice. We discuss how the rich radiation pattern in the 100 MHz to 1 GHz frequency range, in principle allows the measurement of shower elongation produced in neutrino interactions opening up the possibility of flavor recognition identifying charged current electron neutrino interactions.
We discuss the recent developments in the study of alternative detection possibilites offered by the radio technique and air shower arrays.
We discuss the possibilities of detecting radio pulses from high energy showers in ice, such as those produced by PeV and EeV neutrino interactions. It is shown that the rich radiation pattern structure in the 100 MHz to few GHz allows the separation of electromagnetic showers induced by photons or electrons above 100 PeV from those induced by hadrons. This opens up the possibility of measuring the energy fraction transmitted to the electron in a charged current electron neutrino interaction with adequate sampling of the angular distribution of the signal. The radio technique has the potential to complement conventional high energy neutrino detectors with flavor information.
We study the longitudinal development of hadronic showers in ice for energies up to 100 EeV and its implications for radio and optical Cherenkov emission. A small fraction of showers induced by primaries of energy above 1 EeV is shown to display the characteristic elongation associated to the Landau Pomeranchuck Migdal (LPM) effect. The rest look like ordinary showers because the highest energy $π^0$'s interact instead of decaying in two photons. The LPM effect observed in this fraction of the showers is mainly due to $η$ and $η'$ production and decay. We give parameterizations for the total and excess charge tracklengths and for the amplitude and angular spread of the electric field spectrum in the Cherenkov direction. Implications for neutrino detection are briefly addressed.
We study the implications of the LPM effect for the Cherenkov radiation of EeV electromagnetic showers in the coherent radiowave regime for ice. We show that for showers above 100~PeV the electric field scales with shower energy but has a markedly narrower angular distribution than for lower energy showers. We give an electric field frequency and angular spectrum parameterization valid for showers having energy up to the EeV regime and discuss the implications for neutrino detectors based on arrays of radio antennas. Implications of the LPM effect for under water neutrino detectors in project are also briefly addressed.