1. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr

2. 1) Production of secondary electrons Widening of the fluorescence volume : 2 mm Negligible impact on electron length Atm. pressure : 99 % of electrons have E ≤ 5 keV

3. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 2) Diffusion on the lead Influence on the electron spectrum simulated :

4. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 3) Retro-diffusion on the scintillator Only 10 -9 effect : negligible

5. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Gas circulation Switch

6. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Principle of the DAQ

7. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Calibration : how do the PMTs work ? electron-PMT : μ ~ 2 000 pe integral & spectro PMT : μ ~ 0.02 pe P(0) = 0 Efficiency ~1 P(0) = 0.98, P(1) ~ 0.02 single photoelectron mode Poisson law :

8. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Pure single pe in PMTs Analog signal ADC channel Photonis XP2020Q « 0 » / « 1 » ~ 50

9. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Pure single pe in PMTs ADC channel Analog signal

10. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Pure single pe in PMTs Detection inefficiency integral-PMT : 3.76 % spectro-PMT : 3.85% Analog signal ADC channel

11. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Efficiency measurement process 1.X-Y mapping 2.Absolute efficiency in (x 0, y 0 ) 3.Normalization of the map New method in 3 steps uncertainty < 2 % CNRS patent application

12. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 1) Mapping

13. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 1) Mapping integral-PMT spectro-PMT

14. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 1) Mapping spectro-PMT

15. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 2) Absolute efficiency Absolute comparison with something known  calibrated source or photodetector spatial distribution of light ~10 % accuracy NO gain ~1 when PMT have gain ~10 7

16. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 2) Absolute efficiency Integrating spheres AND diaphragms

17. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 2) Absolute efficiency Integrating Sphere NIST photodiode

18. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 2) Absolute efficiency everything stays the same but the PMT 2 Spheres + 3 diaphragms Flux reduction 2.42 × 10 6

19. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr 3) Normalization of the map 18.5 % 1.7 % uncertainty Efficiency (%) integral-PMT

20. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Result for integral-PMT Absolute efficiency measured (377 nm) Integral-PMT response adjusted to measurement Ulrich’s fluorescence spectrum Absolute efficiency of fluorescence detection 0.178 ± 0.004 Uncertainty : 2.2 % wavelength (nm) Efficiency

21. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Integral measurement QuantityUncertainty Detection inefficiency, scaler dead timenegligible geometry (L e and solid angles)1.5 % Transmission of the quartz window1 % Efficiency of the PMT2.2 % TDC4 % Statistics0.2 % TOTAL4.91 % 4.23 ± 0.22 photons / m After normalizations (P, T, E) : 5 % G. Lefeuvre et al, to be published (NIM A)

22. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Spectral measurement 3.9 ± 0.8 ph/m (Ulrich, Airlight workshop, 2003) wavelength (nm) yield (photons / m)

23. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Spectral measurement Our results Ulrich’s spectrum, convoluted with our 3 nm resolution wavelength (nm) yield (photons / m)

24. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Conclusion Bahcall & Waxman hep-ph/0206217 v5 Fly’s Eye Extra-Galactic + Galactic Galactic No GZK HiRes Fly’Eyes Yakutsk AGASA 10 20 10 19 E (eV) 10 18 J x E 2,61 (eV 1,61 /m 2. sr. s)

25. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Still much to measure... Pressure & Temperature dependences Impurities Spectrometer + CCD + light intensifier Reduction of the TDC uncertainty Flash-ADC

26. Gwenaëlle LEFEUVRE APC-Collège de France, Paris, France lefeuvre@apc.univ- paris7.fr Thank you