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تسجيل مستخدم جديدRadio Detection of Extensive Air Showers with CODALEMA
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The principle and performances of the CODALEMA experimental device, set up to study the possibility of high energy cosmic rays radio detection, are presented. Radio transient signals associated to cosmic rays have been identified, for which arrival directions and showers electric field topologies have been extracted from the antenna signals. The measured rate, about 1 event per day, corresponds to an energy threshold around 5.10^16 eV. These results allow to determine the perspectives offered by the present experimental design for radiodetection of UHECR at a larger scale.
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Studies of the radio detection of Extensive Air Showers is the goal of the demonstrative experiment CODALEMA. Previous analysis have demonstrated that detection around $5.10^{16}$ eV was achieved with this set-up. New results allow for the first time
to study the topology of the electric field associated to EAS events on a event by event basis.
Radio detection of extensive air showers initiated in the Earths atmosphere has made tremendous progress in the last decade. Today, radio detection is routinely used in several cosmic-ray observatories. The physics of the radio emission in air shower
s is well-understood, and analysis techniques have been developed to determine the arrival direction, the energy and an estimate for the mass of the primary particle from the radio measurements. The achieved resolutions are competitive with those of more traditional techniques. In this article, I shortly review the most important achievements and discuss the potential for future applications.
Based on a new approach to the detection of radio transients associated with extensive air showers induced by ultra high energy cosmic rays, the experimental apparatus CODALEMA is in operation, measuring about 1 event per day corresponding to an ener
gy threshold ~ 5. 10^16 eV. Its performance makes possible for the first time the study of radio-signal features on an event-by-event basis. The sampling of the magnitude of the electric field along a 600 meters axis is analyzed. It shows that the electric field lateral spread is around 250 m (FWHM). The possibility to determine with radio both arrival directions and shower core positions is discussed.
Some performances of the present CODALEMA experiment, set up to analyse radio-detected Extensive Air Shower (EAS) events, are presented. Characteristics of the EAS electric field distribution sampled on a 600~m long axis are discussed.
We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly $99%$, and that the angle between the polarization direction of the electric
field and the Lorentz force acting on the particles, depends on the observer location in the shower plane. This can be understood as a superposition of the radially polarized charge-excess emission mechanism, first proposed by Askaryan and the geomagnetic emission mechanism proposed by Kahn and Lerche. We calculate the relative strengths of both contributions, as quantified by the charge-excess fraction, for $163$ individual air showers. We find that the measured charge-excess fraction is higher for air showers arriving from closer to the zenith. Furthermore, the measured charge-excess fraction also increases with increasing observer distance from the air shower symmetry axis. The measured values range from $(3.3pm 1.0)%$ for very inclined air showers at $25, mathrm{m}$ to $(20.3pm 1.3)%$ for almost vertical showers at $225, mathrm{m}$. Both dependencies are in qualitative agreement with theoretical predictions.
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