1. RADIODETECTION AND CHARACTERIZATION OF THE COSMIC RAYS AIR SHOWER RADIO EMISSION FOR ENERGIES HIGHER THAN 10 16 eV WITH THE CODALEMA EXPERIMENT Thomas SAUGRIN 1 Rencontres de Moriond 2009 Very High Energy Phenomena in the Universe for the CODALEMA collaboration

2. WHY RADIODETECTION ? AdvantagesDisadvantages 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% 04/02/20092Thomas 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

3. WHY RADIODETECTION ? 04/02/20093Thomas SAUGRIN WHY RADIODETECTION ? AdvantagesDisadvantages 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% 04/02/20093Thomas SAUGRIN 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

4. EXPERIMENTAL CONFIGURATION (2008) 21 antennas with EW polarization 3 antennas with NS polarization 17 scintillators trigger of the antenna array 2 overlapping arrays: Antenna array: Scintillator array: 04/02/20094Thomas SAUGRIN

5. ACTIVE DIPOLAR ANTENNAS Gain30 dB Frequency bandwith80 kHz à 230 MHz Input impedance10 pF Input noise19 µV Length1,2 m Width10 cm Height1,2 m Sensible to the galactic noise Antenna lobe obtained by simulation (EZNEC software) 04/02/20095Thomas SAUGRIN LST time Mean signal (V) Equivalence voltage – electric field obtained by the simulated antenna response

6. SCINTILLATOR ARRAY Trigger rate: 1 evt/ 7 mins Energy threshold: 1.10 15 eV Zenithal acceptance: 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. 04/02/20096Thomas SAUGRIN

7. DETECTION EFFICIENCY Radiodetection threshold ( ~ 5.10 16 eV) > Trigger threshold (10 15 eV) Maximal detection efficiency of 50% for an energy of 7.10 17 eV Source of event deficit ? 04/02/20097Thomas SAUGRIN scintillators antennas Only a few events can be detected by CODALEMA CODALEMA can only access to a restricted energy bandwith

8. ARRIVAL DETECTION Geomagnetic axis - 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 04/02/20098Thomas SAUGRIN North South EastWest North South EastWest Sky map Covering map

9. Hypothesis: - Electric field proportional to the Lorentz force - Electric field polarization in the direction of the Lorentz force (linear polarization) Predicted covering map: Total Lorentz force (sin α) Toy model: 04/02/20099Thomas SAUGRIN North South East West u. a. INTERPRETATION

10. X Trigger acceptance ( zenithal angle distribution ) 04/02/200910Thomas SAUGRIN INTERPRETATIONHypothesis: - Electric field proportional to the Lorentz force - Electric field polarization in the direction of the Lorentz force (linear polarization) Predicted covering map: Total Lorentz force (sin α) Toy model: North South East West

11. 04/02/200911Thomas SAUGRIN Carte de couverture prédite: Force de Lorentz totale (sin α) Antenna lobe INTERPRETATIONHypothesis: - Electric field proportional to the Lorentz force - Electric field polarization in the direction of the Lorentz force (linear polarization) Toy model: North South East West

12. X X Antenna lobe (EZNEC simulation) 04/02/200912Thomas SAUGRIN INTERPRETATION Trigger acceptance ( zenithal angle distribution ) Hypothesis: - Electric field proportional to the Lorentz force - Electric field polarization in the direction of the Lorentz force (linear polarization) Predicted covering map: Total Lorentz force (sin α) Toy model: North South East West

13. Projection on East-West axis (CODALEMA antenna polarization) X X Antenna lobe (EZNEC simulation) X 04/02/200913Thomas SAUGRIN INTERPRETATION Trigger acceptance ( zenithal angle distribution ) Hypothesis: - Electric field proportional to the Lorentz force - Electric field polarization in the direction of the Lorentz force (linear polarization) Predicted covering map: Total Lorentz force (sin α) Toy model: North South East West

14. 04/02/200914Thomas SAUGRIN Carte de couverture prédite: Force de Lorentz totale (sin α) X X Lobe de l’antenne dipolaire (logiciel EZNEC) Acceptance du trigger particules (paramétrisation de la distribution en angle zénithal) X SIMULATIONDATA North South EastWest North South East West INTERPRETATIONHypothesis: - 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

15. 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 04/02/200915Thomas SAUGRIN data toy model data toy model

16. NORTH-SOUTH POLARIZATION Only 3 antennas with North-South polarization: low statistic (90 events) 04/02/200916Thomas SAUGRIN North South WestEast North South East West Preliminary results show good agreement with simulation

17. NORTH-SOUTH POLARIZATION 04/02/200917Thomas SAUGRIN PRELIMINARY Only 3 antennas with North-South polarization: low statistic (90 events) Preliminary results show good agreement with simulation

18. ELECTRIC FIELD LATERAL DISTRIBUTION Electric field exponential parameterization (Allan): E(d) α E P. sin α. cos θ. exp(-d/d 0 ) E0E0 E 0 radio estimator of shower energy ? 04/02/200918Thomas SAUGRIN E0E0 E0E0 E 0 /e d0d0 d0d0 Electric field (µV/m) Distance to the shower axis (m)

19. ELECTRIC FIELD LATERAL DISTRIBUTION Only 25% of the total events allow a relevant estimate of the E 0 parameter 04/02/200919Thomas SAUGRIN Experimental limitations ? Physical limitations ? Near threshold detection, size of the antenna array, one polarization measurement Incomplete parameterization of the electric field ?

20. ENERGY CORRELATION For the 44 internal events with a relevant estimate of the E 0 parameter: E 0corr (µV/m) = 95,7. (E CIC /10 17 eV ) 1,04 σ res = 34%σ min radio ~ 16% - Linear relation between E 0corr and E CIC - Radio detector resolution seems to be better than particle detector resolution In case of exponential lateral distribution, E 0 is a relevant estimator of the shower energy 04/02/200920Thomas SAUGRIN Log 10 (E 0corr ) Log 10 (E CIC ) (E-E 0 )/E 0 Event by event: E 0corr = E 0 /(cos θ. ) PRELIMINARY

21. SUMMARY/OUTLOOK 04/02/200921Thomas SAUGRIN 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 Radiodetection energy threshold of ~ 5.10 16 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

22. 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 km 2 ) 04/02/200922Thomas SAUGRIN

23. STATISTICS 04/02/200923Thomas SAUGRIN