Transcript ppt_talkmoriond0402.ppt

Rencontres de Moriond 2009
Very High Energy Phenomena in the Universe
RADIODETECTION AND CHARACTERIZATION OF
THE COSMIC RAYS AIR SHOWER RADIO
EMISSION FOR ENERGIES HIGHER THAN 1016 eV
WITH THE CODALEMA EXPERIMENT
Thomas SAUGRIN
for the CODALEMA collaboration
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WHY 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)
Features of « classical » EAS detection methods:
Surface
detectors
Advantages
Disadvantages
- Duty cycle of 100%
- Shower model dependence
(sensibility to lateral distribution)
- Large covered area is needed
Fluorescence - Shower model independence
(sensibility to longitudinal distribution)
detectors
- Large detection volume
- Duty cycle of 10%
But… first experiments (1963-1980) failed to prove EAS radiodetection efficiency
Present experiments on radiodetection: - the LOPES experiment (Germany)
- the CODALEMA experiment (France)
04/02/2009
Thomas SAUGRIN
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WHY 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)
Theorical features of EAS radiodetection:
Advantages
Disadvantages
- Duty cycle of 100%
- Shower model independence
(sensibility to longitudinal distribution)
- Large detection volume
But… first experiments (1963-1980) failed to prove EAS radiodetection efficiency
Present experiments on radiodetection: - the LOPES experiment (Germany)
- the CODALEMA experiment (France)
04/02/2009
Thomas SAUGRIN
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EXPERIMENTAL CONFIGURATION (2008)
2 overlapping arrays:
Antenna array:
21 antennas
with EW
polarization
3 antennas
with NS polarization
Scintillator array:
17 scintillators
trigger of the antenna
array
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ACTIVE DIPOLAR ANTENNAS
Antenna lobe obtained by simulation
(EZNEC software)
1,2 m
Width
10 cm
Height
1,2 m
Gain
30 dB
Frequency bandwith
80 kHz à 230 MHz
Input impedance
10 pF
Input noise
19 µV
Mean signal (V)
Sensible to the galactic noise
Length
Equivalence voltage – electric field obtained
by the simulated antenna response
LST time
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SCINTILLATOR ARRAY
Trigger rate:
1 evt/ 7 mins
1.1015 eV
Energy threshold:
Zenithal 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
scintillators
antennas
Radiodetection threshold (~5.1016 eV) > Trigger threshold (1015 eV)
Only a few events can be detected by CODALEMA
CODALEMA can only access to a restricted energy bandwith
Maximal detection efficiency of 50% for an energy of 7.1017 eV
Source of event deficit ?
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ARRIVAL DETECTION
Sky map
Covering map
North
West
Geomagnetic
axis
North
East West
South
East
South
- Deficit of events in the geomagnetic axis area
- Uniform azimutal acceptance for the scintillator array:
Strictly a radio effect
Evidence for a geomagnetic effect in the electric field creation mechanism?
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Thomas SAUGRIN
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INTERPRETATION
Toy model:
Hypothesis:
- Electric field proportional to the Lorentz force
- Electric field polarization in the direction of the Lorentz force (linear polarization)
u. a.
Predicted covering map:
North
West
Total Lorentz force (sin α)
East
South
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INTERPRETATION
Toy model:
Hypothesis:
- Electric field proportional to the Lorentz force
- Electric field polarization in the direction of the Lorentz force (linear polarization)
Predicted covering map:
North
Total Lorentz force (sin α)
X
West
Trigger acceptance
(zenithal angle distribution)
East
South
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INTERPRETATION
Toy model:
Hypothesis:
- Electric field proportional to the Lorentz force
- Electric field polarization in the direction of the Lorentz force (linear polarization)
Carte de couverture
prédite:
Antenna
lobe
North
Force de Lorentz totale (sin α)
West
East
South
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INTERPRETATION
Toy model:
Hypothesis:
- Electric field proportional to the Lorentz force
- Electric field polarization in the direction of the Lorentz force (linear polarization)
Predicted covering map:
North
Total Lorentz force (sin α)
X
West
Trigger acceptance
(zenithal angle distribution)
East
X
Antenna lobe
(EZNEC simulation)
South
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INTERPRETATION
Toy model:
Hypothesis:
- Electric field proportional to the Lorentz force
- Electric field polarization in the direction of the Lorentz force (linear polarization)
Predicted covering map:
North
Total Lorentz force (sin α)
X
West
Trigger acceptance
(zenithal angle distribution)
East
X
Antenna lobe
(EZNEC simulation)
X
South
Projection on East-West axis
(CODALEMA antenna polarization)
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INTERPRETATION
Toy model:
Hypothesis:
- Electric field proportional to the Lorentz force
- Electric field polarization in the direction of the Lorentz force (linear polarization)
SIMULATION
DATA
North
North
Carte de couverture prédite:
Force de Lorentz totale (sin α)
X
West
East
West
Acceptance du trigger particules
East
(paramétrisation de la distribution en
angle zénithal)
X
Lobe de l’antenne dipolaire
South
(logiciel EZNEC)
South
X
Simulated covering map only relevant for radiodetection at energy threshold
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MODEL – DATA COMPARISON
data
data
toy model
toy model
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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NORTH-SOUTH POLARIZATION
Only 3 antennas with North-South polarization: low statistic (90 events)
North
North
East
West
East
West
South
South
Preliminary results show good agreement with simulation
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NORTH-SOUTH POLARIZATION
Only 3 antennas with North-South polarization: low statistic (90 events)
PRELIMINARY
Preliminary results show good agreement with simulation
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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 ?
E0
Electric field (µV/m)
Electric field (µV/m)
E0
E0/e
d0
d0
Distance to the shower axis (m)
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E0/e
Distance to the shower axis (m)
Thomas SAUGRIN
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ELECTRIC FIELD LATERAL DISTRIBUTION
Only 25% of the total events allow a relevant estimate of the E0 parameter
Experimental limitations ?
Near threshold detection, size of the antenna array, one polarization measurement
Physical limitations ?
Incomplete parameterization of the electric field ?
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ENERGY CORRELATION
PRELIMINARY
For the 44 internal events with a
relevant estimate of the E0 parameter:
Log10(E0corr)
Event by event: E0corr= E0 /(cos θ .
E0corr
)
(µV/m) = 95,7. (ECIC /1017 eV ) 1,04
σres = 34%
σmin radio ~ 16%
Log10(ECIC)
- 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
(E-E0)/E0
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SUMMARY/OUTLOOK
Experimental evidence for a geomagnetic origin of the electric field
Energy calibration promising for the future of the method
Drawback of CODALEMA present experimental set-up:
Small detection surface
Work near the detection threshold
Radiodetection energy
threshold of ~5.1016 eV
Restricted energy bandwith
May explain difficulties of results interpretation
Creation of a dense array
Extension at largest area and to higher energies
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NEXT STEPS
Autonomous stations :
- self-triggered
- measurement of the E-W
and N-S polarizations
In 2009:
- 20 stations at Nançay
dense 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
Effective data time
383 days
Number of trigger events
73 907
(trigger threshold: 1015 eV)
Antenna multiplicity ≥ 3
2225 (3%)
Antenna multiplicity ≥ 3 and
relevant reconstructed arrival
directions
1139 (1,54%)
(θant < 90°)
Radiodetected EAS (coincidence
between particle front and radio
plane)
872 (1,18%)
(antenna multiplicity≥ 3, θant < 90°,
Δt < 200 ns et δang < 25°)
Radiodetected internal events
252 (0,34%)
(known energy and shower core)
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