Latest results of the Codalema ExperimentRebai 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 DetectorsSince 2002, Codalema experience located on the radio observatory site at Nançay

(France) (47.3°N, 2.1°E and 137 m above sea level) aims to study the potential of the radiodetection

technique of cosmic rays in the 1016

eV

energy range (detection threshold) to 1018

eV

(upper limit imposed by the area surface).

Emission Mechanism

Energy Calibration Radius of Curvature

600 m40

0 m

In this regard, Codalema contains:

Scintillator

array: (17 scintillator) gives the trigger signal for the experiment and an estimation of primary particle energy.

Short active antennas array: 21 antennas with E-W polarization

& 3 antennas with NS polarization. The main array.

Decametric

array: 18 groups of 8 log-periodic phased antennas studies the electric field topology at small scale (< 100 m).

Time [s]

Am

plitu

de [V

]

Numeric filter in the 23-83 MHz band

FM

AM

1 event = 2 physical quantities per antenna ( amplitude Vi

, time ti

)

+ some Corrections :

Time delay

Attenuation

Antennas gain

Dipole antenna: 2*60 cm Al arms, simple and cheap, isotropic pattern

Log-periodic antenna

Codalema observes a large asymmetry in the arrival directions between the North and the South.

This ratio is stable in time, with increasing statistics (see [1]).

This effect can not be due to a detector bias the scintillator

array has a flat azimuthal

distribution

Observation: NS asymmetry

Geomagnetic

effectThe local geomagnetic field may be the main cause of this asymmetry through the action of Lorentz force on the charged particles.

Suppose 2 EAS initiated by 2 primary particles of the same energy interacted in the same altitude. The shower from the North is ┴

to the geomagnetic field which gives a maximum |v^B| strong radio signal that exceeds the Codalema detection threshold.

188.01708

322

EventsNorth

EventsSouth

N

N

EWEW LobeeBvE )(cos)sin()( 2

EWEW LobeeBvE )(cos)sin()( 2

Geomagnetic Model

N

i xy

ii

iia

xaby

1222

22 )(

ΔEp

/Ep

~ 30 %ΔE0

/E0

< 10 %

The energy of the primary particle is estimated with the CIC method (Constant intensity Cut)

E0

~ Epα

avec α

~ 1.0

linear dependency

E0

=a Ep

+ b Radio calibration EShower

=(1/a)*E0

– b/a

Calibration depends on :E0 errorsEp errors

Radio signal lateral profil in the groundAllan formula : E = E0

.exp(-d/d0

)

E0

on the shower axisd0

distance of the shower decay(X0

, Y0

) shower core1 event = (E0

, d0

, X0

, Y0

)

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 frontApproximation 1 Non planar wave front

+Emission center in a distance R

We use a parabolic model to fit the radius of curvature. Our reconstruction is not based upon adjusting the wavefront shape which has a complicated geometry dependent on the shower developpement.

Radius of Curvature distribution maximum ~ 4 km …

… But interpretations difficulties (Very large Radius observed)

… Next step: Chemical composition of UHECR ? …

Conclusions & Perspectives

Faisability of radiodedection with CODALEMA 2:

Detection of the radio signal induced by the shower developpement

Emission mechanism : geomagnetic effect

Energy Correlation

New analysis method : Rc

Exploration of CODALEMA 3 (autonomous station) (see Diego Torres

poster)

References:

[1] D.Ardouin & al., Astro Ph 31 2009 pages 192-200 Goemagnetic origin of the radio emission …