http://www-ik.fzk.de/~huege/heraeus490/Lectures.html The CODALEMA experiment hosted on the radio observatory site at Nançay (France) has been studying radio signal from UHECR showers in the frequency range from 23 to 83 MHz triggered by a ground-based particle detector array since 2002. In this poster, after a brief presentation of experimental method used in radiodetection, the main results obtained will be reported (emission mechanims, lateral ditribution of the electric field, energy calibration, etc...). The first studies of the characteristics of the radio wave front and of the calculation method (using non-linear chi2 methods) of the curvature will be then discussed as new preliminarily results.

1. Latest results of the Codalema Experiment
Rebai Ahmed
Subatech Laboratoire de physique subatomique et des technologies
associées Nantes France IN2P3/CNRS
On behalf the Codalema Collaboration
ahmed.rebai@subatech.in2p3.fr
Codalema Detectors Emission Mechanism
Since 2002, Codalema experience located Observation: NS asymmetry
on the radio observatory site at Nançay
Codalema observes a large asymmetry in the
(France) (47.3°N, 2.1°E and 137 m above
arrival directions between the North and the
sea level) aims to study the potential of the
South.
radiodetection technique of cosmic rays in
400 m
the 1016 eV energy range (detection N 322
South  Events
  0 . 188
threshold) to 1018 eV (upper limit imposed N 1708
North  Events
by the area surface).
This ratio is stable in time, with increasing
In this regard, Codalema contains: 600 m statistics (see [1]).
Scintillator array: (17 scintillator) This effect can not be due to a detector
gives the trigger signal for the bias the scintillator array has a flat azimuthal
experiment and an estimation of distribution
primary particle energy.
Geomagnetic effect
Short active antennas array: 21
The local geomagnetic field may be the main
antennas with E-W polarization & 3 cause of this asymmetry through the action of
antennas with NS polarization. The Lorentz force on the charged particles.
main array.
Suppose 2 EAS initiated by 2 primary
Decametric array: 18 groups of 8 Dipole antenna: 2*60 cm particles of the same energy interacted in the
Al arms, simple and Log-periodic antenna
same altitude. The shower from the North is ┴
log-periodic phased antennas cheap, isotropic pattern
to the geomagnetic field which gives a
studies the electric field topology at maximum |v^B|  strong radio signal that
small scale (< 100 m). Numeric filter in the exceeds the Codalema detection threshold.
23-83 MHz band
AM
FM
+ some
Corrections :
Geomagnetic Model
Time delay
E (v  B)eEW    sin( )  cos2 ( )  LobeEW

Amplitude [V]
Attenuation
Antennas gain
1 event = 2 physical quantities per
Time [s] antenna ( amplitude Vi , time ti)
Energy Calibration Radius of Curvature
The radius of curvature of the radio wave front can be a very good
discriminant variables that permet to distinguish between shower initiated by
protons, heavy ions, photons and neutrinos.
Approximation 0  a plane wave front
Approximation 1 Non planar wave front
+Emission center in a distance R
Radio signal lateral profil in the groundAllan formula : E = E0.exp(-d/d0) We use a parabolic model to fit the radius
of curvature.
Our reconstruction is not based upon
E0 on the shower axis
adjusting the wavefront shape which has a
d0 distance of the
complicated geometry dependent on the
shower decay Calibration depends on :
E0 errors shower developpement.
(X0, Y0) shower core Ep errors
E (v  B )eEW    sin( )  cos 2 ( )  LobeEW
1 event = (E0, d0, X0, Y0) ΔEp/Ep ~ 30 %
ΔE0/E0 < 10 %
The energy of the primary particle is Radius of Curvature distribution
estimated with the CIC method maximum ~ 4 km …
(Constant intensity Cut) … But interpretations difficulties (Very
N
2  
yi  (b  a  xi )2 large Radius observed)
i 1  y  a 2   x2
2
i i
E0 ~ Epα avec α ~ 1.0 
linear dependency … Next step: Chemical composition of
UHECR ? …
E0 =a Ep + b  Radio calibration EShower =(1/a)*E0 – b/a
Faisability of radiodedection with CODALEMA 2: References:
Conclusions & 

Detection of the radio signal induced by the shower developpement
Emission mechanism : geomagnetic effect
[1] D.Ardouin & al., Astro Ph 31 2009
pages 192-200 Goemagnetic origin of
Perspectives  Energy Correlation the radio emission …
 New analysis method : Rc
 Exploration of CODALEMA 3 (autonomous station) (see Diego Torres poster)