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RADIODETECTION AND CHARACTERIZATION OF THE COSMIC RAYS AIR SHOWER RADIO EMISSION FOR ENERGIES HIGHER THAN 1016 eV WITH THE CODALEMA EXPERIMENT

Thomas SAUGRIN

1

Rencontres de Moriond 2009

Very High Energy Phenomena in the Universe

for the CODALEMA collaboration

WHY RADIODETECTION ?

Advantages Disadvantages

Surface detectors

- Duty cycle of 100% - Shower model dependence (sensibility to lateral distribution)- Large covered area is needed

Fluorescence detectors

- Shower model independence (sensibility to longitudinal distribution)- Large detection volume

- Duty cycle of 10%

04/02/2009 2Thomas SAUGRIN

Features of « classical » EAS detection methods:

EAS electric field creation mechanisms:

- negative charge excess (Askar’yan, 1962) - geomagnetic mechanism (Kahn and Lerche, 1965):

- geosynchrotron model (Huege and Falcke, 2000)- transversal current model (Lasty, Scholten and Werner, 2005)

Present experiments on radiodetection: - the LOPES experiment (Germany) - the CODALEMA experiment (France)

But… first experiments (1963-1980) failed to prove EAS radiodetection efficiency





Theorical features of EAS radiodetection:

EAS electric field creation mechanisms:

- negative charge excess (Askar’yan, 1962) - geomagnetic mechanism (Kahn and Lerche, 1965):

- geosynchrotron model (Huege and Falcke, 2000)- transversal current model (Lasty, Scholten and Werner, 2005)

Present experiments on radiodetection: - the LOPES experiment (Germany) - the CODALEMA experiment (France)

But… first experiments (1963-1980) failed to prove EAS radiodetection efficiency

EXPERIMENTAL CONFIGURATION (2008)

21 antennaswith EW polarization

3 antennaswith NS polarization

17 scintillatorstrigger of the antenna array

2 overlapping arrays:

Antenna array:

Scintillator array:


ACTIVE DIPOLAR ANTENNAS

Gain 30 dB

Frequency bandwith 80 kHz à 230 MHz

Input impedance 10 pF

Input noise 19 µV

Length 1,2 m

Width 10 cm

Height 1,2 m

Sensible to the galactic noise

Antenna lobe obtained by simulation (EZNEC software)


LST time

Mea

n si

gnal

(V)

Equivalence voltage – electric field obtained by the simulated antenna response

SCINTILLATOR ARRAY

Trigger rate: 1 evt/ 7 mins

Energy threshold: 1.1015 eV

Zenithal acceptanceZenithal acceptance: : 0° < <60°

Informations on EAS:- Arrival direction- Shower core position- Energy estimate (CIC method)

2 different classes of trigger events (5 central stations in coincidence) :

- Internal events: Station with the maximum signal is not on the border of the array. Correct estimate of shower energy and core position.

- External events: Unreliable estimate of shower energy and core position.


DETECTION EFFICIENCY

Radiodetection threshold (~5.1016 eV) > Trigger threshold (1015 eV)

Maximal detection efficiency of 50% for an energy of 7.1017 eV

Source of event deficit ?


scintillators

antennas

Only a few events can be detected by CODALEMA

CODALEMA can only access to a restricted energy bandwith

ARRIVAL DETECTION

Geomagneticaxis

- Deficit of events in the geomagnetic axis area- Uniform azimutal acceptance for the scintillator array:

Evidence for a geomagnetic effect in the electric field creation mechanism?

Strictly a radio effect


North

South

EastWest

North

South

EastWest

Sky map Covering map

Hypothesis:Hypothesis:- Electric field proportional to the Lorentz force- Electric field polarization in the direction of the Lorentz force (linear polarization)

Predicted covering map:Predicted covering map:

Total Lorentz force (sin α)

Toy model:


North

South

EastWest

u. a.

INTERPRETATION

XTrigger acceptance(zenithal angle distribution)


INTERPRETATION




Toy model:

North

South

EastWest


Carte de couverture prédite:Carte de couverture prédite:

Force de Lorentz totale (sin α)

Antenna lobe

INTERPRETATION


Toy model:

North

South

EastWest

X

XAntenna lobe(EZNEC simulation)


INTERPRETATION

Trigger acceptance(zenithal angle distribution)




Toy model:

North

South

EastWest

Projection on East-West axis(CODALEMA antenna polarization)

X

XAntenna lobe(EZNEC simulation)

X


INTERPRETATION

Trigger acceptance(zenithal angle distribution)




Toy model:

North

South

EastWest


Carte de couverture prédite:Carte de couverture prédite:

Force de Lorentz totale (sin α)X

XLobe de l’antenne dipolaire(logiciel EZNEC)

Acceptance du trigger particules(paramétrisation de la distribution en angle zénithal)

X

SIMULATION DATANorth

South

EastWest

North

South

EastWest

INTERPRETATION


Toy model:

Simulated covering map only relevant for radiodetection at energy threshold

MODEL – DATA COMPARISON

Geomagnetic toy model fits correctly experimental data:- in zenithal angle- in azimuthal angle (notably the local maximum in the South direction)

Relevant experimental evidence for a geomagnetic effect in the electric field creation mechanism


datatoy model

datatoy model

NORTH-SOUTH POLARIZATION

Only 3 antennas with North-South polarization: low statistic (90 events)


North

South

WestEast

North

South

East West

Preliminary results show good agreement with simulation

NORTH-SOUTH POLARIZATION


PRELIMINARY

Only 3 antennas with North-South polarization: low statistic (90 events)

Preliminary results show good agreement with simulation

ELECTRIC FIELD LATERAL DISTRIBUTION

Electric field exponential parameterization (Allan):

E(d) α EP . sin α . cos θ. exp(-d/d0)

E0

E0 radio estimator of shower energy ?


E0E0

E0/e E0/e

d0 d0

Elec

tric

fiel

d (µ

V/m

)

Elec

tric

fiel

d (µ

V/m

)

Distance to the shower axis (m) Distance to the shower axis (m)

ELECTRIC FIELD LATERAL DISTRIBUTION

Only 25% of the total events allow a relevant estimate of the E0 parameter


Experimental limitations ?

Physical limitations ?

Near threshold detection, size of the antenna array, one polarization measurement

Incomplete parameterization of the electric field ?

ENERGY CORRELATION

For the 44 internal events with a For the 44 internal events with a relevant estimate of the Erelevant estimate of the E00 parameter: parameter:

E0corr (µV/m) = 95,7. (ECIC /1017 eV ) 1,04

σres = 34% σmin radio ~ 16%

- Linear relation between E0corr and ECIC

- Radio detector resolution seems to be better than particle detector resolution

In case of exponential lateral distribution, E0 is a relevant estimator of the shower energy


Log 10

(E0c

orr)

Log10(ECIC)

(E-E0)/E0

Event by event: E0corr= E0 /(cos θ . )

PRELIMINARY

SUMMARY/OUTLOOK


Experimental evidence for a geomagnetic origin of the electric fieldExperimental evidence for a geomagnetic origin of the electric field

Energy calibration promising for the future of the methodEnergy calibration promising for the future of the method

Drawback of CODALEMA present experimental set-up:Drawback of CODALEMA present experimental set-up:

Small detection surface

Radiodetection energy threshold of ~5.1016 eV

Work near the detection threshold

Restricted energy bandwith

May explain difficulties of results interpretation

Creation of a dense array

Extension at largest area and to higher energies

NEXT STEPS

Autonomous stations :- self-triggered- measurement of the E-W and N-S polarizations

In 2009:

- 20 stations at Nançaydense array of 600m x

600m with 44 antennas

- Available for the radio@Auger project

large array with a step of ~300m

In 2010:

Extension of CODALEMA with 100 stations (1 km2)


STATISTICS
