1. E.Plagnol - TA/TALE feb 2004 - 1 Acceptance and Counting Rates of EUSO ë Detecting UHECR from space ë The EUSO detector : Who does what. ë Some characteristics of UHECR ë A statistical view of clouds ë A first approach of the acceptance ë The influence of clouds on the signal ë The different Atmosphere Sounding Devices ë An "End to End" simulation ë Duty Cycle and Counting rates ë Conclusions

2. E.Plagnol - TA/TALE feb 2004 - 2 Detecting UHECR from space The study of UHECR via the observation of fluorescence is becoming a standard technique : it is used HIRES, TA/TALE, Auger and EUSO. The great interest of this method is that it allows for a " 3 dimensional" view : one observes its complete developement. This method can be used from ground (HIRES, TA/TALE, Auger), but also from space : EUSO. -Very large surface of observation ( 200 000km 2 ) -Total covering of the sky, -No proximity effect (Cerenkov), -Large transparency of the atmosphere, -Limited influence of clouds, -Less dependence on aerosols, -Night time is necessary: not too much moonlight ( D.C. 20% ) -Small solid angle…

3. E.Plagnol - TA/TALE feb 2004 - 3 The EUSO detector : Who does what ? Optics : USA  ≈ 2m Photo-detectors : Japan ≈ 200 000 pixels Mechanics : France Electronics : France - Italy Analogue - Digital Ground Segment : Portugal ASD (LIDAR) : Suisse - Italy

4. E.Plagnol - TA/TALE feb 2004 - 4 Some characteristics of UHECR A proper measurement of a shower can be performed if its development is observed up to (and a little bit beyond) its fluorescence maximum. The altitude of this maximum is strongly and mainly function of the shower inclination Note The brightness (N max ) of the shower at its maximum is a function of its energy. If sufficient p.e. statistics is available (E > 10 20 eV), an autonomous (ASD free) method of energy measurement can be used: Y.Takahashi and D.Naumov.

5. E.Plagnol - TA/TALE feb 2004 - 5 A statistical view of clouds (I) : The occurrence of clouds Cloud Presence : TOVs, between latitudes ±51° In this table, the clear sky fraction has been included (30%) A presence of 20% of subvisible clouds have been added between latitudes ±20° (SAGE observations) This is more an "educated guess than a real measurement : No precise measurements exists Different cloud databases are known and can be used : ISCCP, TOVs,…

6. E.Plagnol - TA/TALE feb 2004 - 6 A statistical view of Clouds (II) : The Clear Sky Fraction The impact of clouds on the shower signal is a 3D problem. The clear sky fraction depends on the nature of the clouds The TOVs database is NOT used statistically, but by using real cloud scenes (latitude, longitude, date, time of day,…) in coincidence with shower generation : A random cloud scenario (among 90 000) is chosen :  cloud top altitude, optical depth… (a width of 1 km is assumed) Clear Sky Fraction : TOVs, between latitudes ±51°

7. E.Plagnol - TA/TALE feb 2004 - 7 A first approach of the acceptance In this approach, the shower signal is hidden by the cloud top (whatever the OD) The Cerenkov is reflected by the cloud top (albdebo = f(OD) ) No Clouds TOVs Clouds Fluo + cerenkov detection Cerenkov alone Fluo alone

8. E.Plagnol - TA/TALE feb 2004 - 8 The influence of clouds on the signal (I) The impact of clouds on the shower signal is double : 1.The presence of clouds lead to an attenuation of the transport of photons from locus of production to EUSO -> the transmission coefficient. 2.The presence of clouds leads to a "Cerenkov overshoot" due to an excess of diffusion realted to Mie scattering

9. E.Plagnol - TA/TALE feb 2004 - 9 The influence of clouds on the signal (II) One of the difficulty is to evolve "smoothly" from Single (Mie) scattering to Multiple (Mie) scattering (albedo). This is based on the following scheme : Note 1 : This is also an "educated" guess. A complete realistic multiple scattering process is "out of bounds" for phase A. Note 2 : the exact outcome of the photon production due to clouds is a delicate balance between : -Diffusion -Intensity of the Cerenkov beam -The scattering process Extraction of physics from the Cerenkov "peak" will be difficult.

10. E.Plagnol - TA/TALE feb 2004 - 10 The different Atmosphere Sounding Devices 4 different options : The Autonomous method The PRN-cw Lidar : a sophisticated altimeter A 1 wavelength Lidar : 1064 nm  Baseline A 3 wavelengths Lidar : 1064, 532, 350 nm

11. E.Plagnol - TA/TALE feb 2004 - 11 An "End to End" simulation : What is included ? The shower; - GIL parametrisation (based on Corsika) - Cerenkov yield (approx.) - Random first interaction - Euso acceptance The detector: - Optics ray tracing - photo-detector efficiency - Trigger : p.e. threshold and persistence The atmosphere (LowTran): - Molecular (Rayleigh) scattering - Ozone absorption - Aerosol (Mie) scattering The Clouds: - TOVs cloud scenes - Mie Optical Depths - Cerenkov reflection The Procedure: - > 10 000 showers - Lidar Cloud detection - Experimental uncertainties: P, T, (X, Y, Z), , , 1st int.… Cloud top and OD - X 2 fit procedure Multiple scattering not included

12. E.Plagnol - TA/TALE feb 2004 - 12 Duty Cycle, Acceptance and Counting rates Strict cut Sun zenith < 109.18° Moon zenith < 109.18° Duty cycle = 12.87% No background from the moon with 90° < zenith < 109.18° Duty cycle = 17.96% Accepting 100ph/m 2 /ns from the moon only Duty cycle = 19.26% The background used in the calculations = 500 ph/m 2 /nsec Duty Cycle = 20% A precise study of the background and duty cycle has been performed

13. E.Plagnol - TA/TALE feb 2004 - 13 Duty Cycle, Acceptance and Counting rates : Super-GZK Acceptance (geom.) ≈ 608 000 km 2.sr Duty Cycle ≈ 20% NOT FINAL

14. E.Plagnol - TA/TALE feb 2004 - 14 Duty Cycle, Acceptance and Counting rates : A GZK spectrum E > 6 10 19 eV

15. E.Plagnol - TA/TALE feb 2004 - 15 Duty Cycle, Acceptance and Counting rates

16. E.Plagnol - TA/TALE feb 2004 - 16 Conclusions The detection of UHECR showers from space (fluorescence) has some clear advantages, A significant effort has been made to simulate the detection of showers from space, The duty cycle has been estimated at 20% ( ≈ 500 photons/m 2 /ns/sr), The geometrical efficiency of EUSO is 608 000 km 2.sr, The influence of cloud presence has been calculated using realistic cloud scenes, The impact of clouds on shower signals has been made as realistic as possible, The presence of a 1 Lidar enhances the quality and reliability of the measurements, Above 10 20 eV, more than 1000 showers per year are expected (Super_GZK hypothesis), For the GZK case, the detection of the "GZK recovery" is possible.