1) Production of secondary electrons

Widening of the

fluorescence

volume : 2 mm

Negligible impacton electron length

Atm. pressure : 99 % of electronshave E ≤ 5 keV

2) Diffusion on the lead

Influence on the electron spectrumsimulated :

3) Retro-diffusion on the scintillator

Only 10-9 effect :negligible

Gas circulation

Switch

Principle of the DAQ

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

!

)exp()(

NNP

N Poisson law :

Pure single pe in PMTs

Analog signal

ADC channel

Photonis XP2020Q« 0 » /  « 1 » ~ 50

Pure single pe in PMTs

ADC channel

Analog signal

Pure single pe in PMTs

Detectioninefficiency

integral-PMT : 3.76 %spectro-PMT : 3.85%

Analog signal

ADC channel

Efficiency measurement process

1. X-Y mapping2. Absolute efficiency in (x0, y0)

3. Normalization of the map

New method in 3 stepsuncertainty < 2 %CNRS patent application

1) Mapping

1) Mapping

integral-PMT spectro-PMT

1) Mapping

spectro-PMT

2) Absolute efficiencyAbsolute comparison with something known calibrated source or photodetector

spatial distribution of light~10 % accuracyNO

gain ~1when PMT have gain ~107

2) Absolute efficiency

Integrating spheres AND diaphragms

2) Absolute efficiency

Integrating Sphere

NIST photodiode

2) Absolute efficiency

everything stays thesame but the PMT

2 Spheres+

3 diaphragms

Flux reduction2.42 × 106

3) Normalization of the map

18.5 %1.7 % uncertainty

Effi

cie

ncy

(%)

integral-PMT

Result for integral-PMT

Absolute efficiency measured (377 nm)Integral-PMT response adjusted to measurementUlrich’s fluorescence spectrumAbsolute efficiency of fluorescence detection

0.178 ± 0.004Uncertainty : 2.2 %

wavelength (nm)

Effi

cie

ncy

Integral measurementQuantity Uncertainty

Detection inefficiency, scaler dead time

negligible

geometry (Le and solid angles) 1.5 %

Transmission of the quartz window

1 %

Efficiency of the PMT 2.2 %

TDC 4 %

Statistics 0.2 %

TOTAL 4.91 %

4.23 ± 0.22 photons / m

After normalizations (P, T, E) : 5 %

G. Lefeuvre et al, to be published (NIM A)

Spectral measurement

3.9 ± 0.8 ph/m

(Ulrich, Airlight workshop, 2003)

wavelength (nm)

yie

ld (

ph

oto

ns /

m)

Spectral measurement

Our results

Ulrich’s spectrum,convoluted with our 3 nm resolution

wavelength (nm)

yie

ld (

ph

oto

ns /

m

)

Conclusion

Bahcall & Waxman hep-ph/0206217 v5

Fly’s Eye

Extra-Galactic + GalacticGalacticNo GZKHiResFly’EyesYakutskAGASA

10201019

E (eV)

1018

J x E

2,6

1 (

eV

1,6

1/m

2 . s

r . s)

Still much to measure...

• Pressure & Temperature dependences

• Impurities

• Spectrometer + CCD + light intensifier

• Reduction of the TDC uncertaintyFlash-ADC

Thank you