arXiv subjects

P. Allison

Publications and source records attributed to P. Allison.

103 records · Page 6Linked to original sources

arXiv2010

Observation of Ultra-high-energy Cosmic Rays with the ANITA Balloon-borne Radio Interferometer

We report the observation of sixteen cosmic ray events of mean energy of 1.5 x 10^{19} eV, via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present the first ultra-wideband, far-field measurements of the radio spectral density of geosynchrotron emission in the range from 300-1000 MHz. The emission is 100% linearly polarized in the plane perpendicular to the projected geomagnetic field. Fourteen of our observed events are seen to have a phase-inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon.

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arXiv2010

Discrepant hardening observed in cosmic-ray elemental spectra

The balloon-borne Cosmic Ray Energetics And Mass (CREAM) experiment launched five times from Antarctica has achieved a cumulative flight duration of about 156 days above 99.5% of the atmosphere. The instrument is configured with complementary and redundant particle detectors designed to extend direct measurements of cosmic-ray composition to the highest energies practical with balloon flights. All elements from protons to iron nuclei are separated with excellent charge resolution. Here we report results from the first two flights of ~70 days, which indicate hardening of the elemental spectra above ~200 GeV/nucleon and a spectral difference between the two most abundant species, protons and helium nuclei. These results challenge the view that cosmic-ray spectra are simple power laws below the so-called knee at ~1015 eV. This discrepant hardening may result from a relatively nearby source, or it could represent spectral concavity caused by interactions of cosmic rays with the accelerating shock. Other possible explanations should also be investigated.

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arXiv2010

Elemental Spectra from the CREAM-I Flight

The Cosmic Ray Energetics And Mass (CREAM) is a balloon-borne experiment designed to measure the composition and energy spectra of cosmic rays of charge Z = 1 to 26 up to an energy of ~ 10^15 eV. CREAM had two successful flights on long-duration balloons (LDB) launched from Mc- Murdo Station, Antarctica, in December 2004 and December 2005. CREAM-I achieves a substantial measurement redundancy by employing multiple detector systems, namely a Timing Charge Detector and a Silicon Charge Detector (SCD) for particle identification, and a Transition Radiation Detector and a sampling tungsten/scintillating-fiber ionization calorimeter (CAL) for energy measurement. In this paper, preliminary energy spectra of various elements measured with CAL/SCD during the first 42-day flight are presented.

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arXiv2010

Elemental energy spectra of cosmic rays measured by CREAM-II

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment CREAM (Cosmic Ray Energetics And Mass). The instrument (CREAM-II) was comprised of detectors based on different techniques (Cherenkov light, specific ionization in scintillators and silicon sensors) to provide a redundant charge identification and a thin ionization calorimeter capable of measuring the energy of cosmic rays up to several hundreds of TeV. The data analysis is described and the individual energy spectra of C, O, Ne, Mg, Si and Fe are reported up to ~ 10^14 eV. The spectral shape looks nearly the same for all the primary elements and can be expressed as a power law in energy E^{-2.66+/-0.04}. The nitrogen absolute intensity in the energy range 100-800 GeV/n is also measured.

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arXiv2010

Measurements of cosmic-ray energy spectra with the 2nd CREAM flight

During its second Antarctic flight, the CREAM (Cosmic Ray Energetics And Mass) balloon experiment collected data for 28 days, measuring the charge and the energy of cosmic rays (CR) with a redundant system of particle identification and an imaging thin ionization calorimeter. Preliminary direct measurements of the absolute intensities of individual CR nuclei are reported in the elemental range from carbon to iron at very high energy.

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arXiv2009

Energy spectra of cosmic-ray nuclei at high energies

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment Cosmic Ray Energetics And Mass (CREAM). The instrument included different particle detectors to provide redundant charge identification and measure the energy of CRs up to several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg, Si, and Fe are presented up to $\sim 10^{14}$ eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an $E^{-2.66 \pm 0.04}$ power law in energy. Moreover, a new measurement of the absolute intensity of nitrogen in the 100-800 GeV/$n$ energy range with smaller errors than previous observations, clearly indicates a hardening of the spectrum at high energy. The relative abundance of N/O at the top of the atmosphere is measured to be $0.080 \pm 0.025 $(stat.)$ \pm 0.025 $(sys.) at $\sim $800 GeV/$n$, in good agreement with a recent result from the first CREAM flight.

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arXiv2009

The Fluorescence Detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detector. Finally, we evaluate the detector performance and precision of shower reconstructions.

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arXiv2009

Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory

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.

astro-ph.HE↗

arXiv2009

IceRay: An IceCube-centered Radio-Cherenkov GZK Neutrino Detector

We discuss design considerations and simulation results for IceRay, a proposed large-scale ultra-high energy (UHE) neutrino detector at the South Pole. The array is designed to detect the coherent Askaryan radio emission from UHE neutrino interactions in the ice, with the goal of detecting the cosmogenic neutrino flux with reasonable event rates. Operating in coincidence with the IceCube neutrino detector would allow complete calorimetry of a subset of the events. We also report on the status of a testbed IceRay station which incorporates both ANITA and IceCube technology and will provide year-round monitoring of the radio environment at the South Pole.

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arXiv2008

New Limits on the Ultra-high Energy Cosmic Neutrino Flux from the ANITA Experiment

We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmic neutrinos above energies of 3 EeV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. We report here on our initial analysis, which was performed as a blind search of the data. No neutrino candidates are seen, with no detected physics background. We set model-independent limits based on this result. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In a background horizontal-polarization channel, we also detect six events consistent with radio impulses from ultra-high energy extensive air showers.

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arXiv2008

The Antarctic Impulsive Transient Antenna Ultra-high Energy Neutrino Detector Design, Performance, and Sensitivity for 2006-2007 Balloon Flight

We present a detailed report on the experimental details of the Antarctic Impulsive Transient Antenna (ANITA) long duration balloon payload, including the design philosophy and realization, physics simulations, performance of the instrument during its first Antarctic flight completed in January of 2007, and expectations for the limiting neutrino detection sensitivity. Neutrino physics results will be reported separately.

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arXiv2005

The trigger system of the Pierre Auger Surface Detector: operation, efficiency and stability

The trigger system of the Surface Detector (SD) of the Pierre Auger Observatory is described, from the identification of candidate showers ($E>1$ EeV) at the level of a single station, among a huge background (mainly single muons), up to the selection of real events and the rejection of random coincidences at a higher central trigger level (including the reconstruction accuracy). Efficiency of a single station trigger is evaluated using real data , and the high performance of event selection hierarchy will be demonstrated.

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arXiv2005

Observing muon decays in water Cherenkov detectors at the Pierre Auger Observatory

Muons decaying in the water volume of a Cherenkov detector of the Pierre Auger Observatory provide a useful calibration point at low energy. Using the digitized waveform continuously recorded by the electronics of each tank, we have devised a simple method to extract the charge spectrum of the Michel electrons, whose typical signal is about 1/8 of a crossing vertical muon. This procedure, moreover, allows continuous monitoring of the detector operation and of its water level. We have checked the procedure with high statistics on a test tank at the Observatory base and applied with success on the whole array.

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