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%
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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
WHY RADIODETECTION ?
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WHY RADIODETECTION ?
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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:
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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)
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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.
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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 ?
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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
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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:
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North
South
EastWest
u. a.
INTERPRETATION
XTrigger acceptance(zenithal angle distribution)
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INTERPRETATION
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
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Carte de couverture prédite:Carte de couverture prédite:
Force de Lorentz totale (sin α)
Antenna lobe
INTERPRETATION
Hypothesis:Hypothesis:- Electric field proportional to the Lorentz force- Electric field polarization in the direction of the Lorentz force (linear polarization)
Toy model:
North
South
EastWest
X
XAntenna lobe(EZNEC simulation)
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INTERPRETATION
Trigger acceptance(zenithal angle distribution)
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
Projection on East-West axis(CODALEMA antenna polarization)
X
XAntenna lobe(EZNEC simulation)
X
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INTERPRETATION
Trigger acceptance(zenithal angle distribution)
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
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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
Hypothesis:Hypothesis:- Electric field proportional to the Lorentz force- Electric field polarization in the direction of the Lorentz force (linear polarization)
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
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datatoy model
datatoy model
NORTH-SOUTH POLARIZATION
Only 3 antennas with North-South polarization: low statistic (90 events)
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North
South
WestEast
North
South
East West
Preliminary results show good agreement with simulation
NORTH-SOUTH POLARIZATION
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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 ?
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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
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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
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Log 10
(E0c
orr)
Log10(ECIC)
(E-E0)/E0
Event by event: E0corr= E0 /(cos θ . )
PRELIMINARY
SUMMARY/OUTLOOK
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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)
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STATISTICS
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