1. E.Plagnol - HENA June 2003 - 1 The EUSO Project ë An overview of the Physics of EUSO ë Detection of UHECR by fluorescence +Cerenkov ë The EUSO detector and the collaboration ë Acceptance,clouds and counting rates ë Horizontal showers and neutrinos ë Status and Summary

2. E.Plagnol - HENA June 2003 - 2 The Physics of Euso I : The GZK effect (Greisen-Zatsepin-Kuzmin) The physics of Euso : Beyond the GZK effect (10 20 -10 21 eV) Astronomy with UHECR and neutrinos

3. E.Plagnol - HENA June 2003 - 3 The Physics of Euso II The contradictory (?) measurements of Agasa and Hires: is the GZK effect observed or not ? In reality : -A Hires (GZK) type spectrum would confirm a "classical" scenario, -An Agasa (Super-GZK) type spectrum would not close the debate. A GZK spectrum Hadronic nature of UHECR (protons) Distribution of sources in the universe and in the "GZK" neighbourhood (<50Mpc) The measurement of the "GZK recovery" The physics of the GZK recovery

4. E.Plagnol - HENA June 2003 - 4 The Physics of Euso III The non observation of the GZK effect could open the way to a "new physics" : Topological defects, Super-massive particles, Lorentz invariance. But a classical scenario could still be possible : Strong magnetic fields (≈ 0.1µG et Fe, G.Sigl and M.Lemoine Astro-Ph/0209192v1 ) Magnetic fields would create isolated regions (< 10 Mpc) : No way in, no way out Isotropy Effects of caustics -> doublets. A large statistics is necessary

5. E.Plagnol - HENA June 2003 - 5 The Physics of Euso IV AUGER will resolve the Agasa-Hires enigma Its counting rate (60 evts/an pour E > 10 20 eV (if E- 2.7 )) will limit its ability to study UHECR beyond 10 20 eV. Whatever the AUGER results show : EUSO will be able to study the physics beyond GZK, EUSO will either confront New Physics (Super-GZK) or the high field physics (isotropy, correlations) with large statistics.

6. E.Plagnol - HENA June 2003 - 6 The detection of UHECR by Euso ä Euso will detect UHECR fluorescence and Cerenkov from space (430 km) ä The atmosphere will act as a huge TPC : 200 000km 2 and > 2.0 10 12 tons ä The average transparency of the atmosphere is ~ 50% ä The interesting part of the signal is created above ~ 5 km where aerosols are rare.

7. E.Plagnol - HENA June 2003 - 7 The detection method

8. E.Plagnol - HENA June 2003 - 8 UHECR detection by Fluorescence and Cerenkov An UHECR creates a particle front (velocity ~ c). A fraction (<1%) of the energy will be converted in fluorescence (N 2 ) and Cerenkov photons. The space-time correlation of the detected photons allows a measurement of the Energy (∆E ~ 30%), Direction (∆  ~ 1°) and nature (p-Fe) of the UHECR.

9. E.Plagnol - HENA June 2003 - 9 The EUSO detector : Who does what ? Optics : USA Light weight fresnel lenses  ≈ 2m Photo-détectors : Japan ≈ 200 000 pixels Mechanics : France - Italy Electronics : France - Italy Analog - Digital Ground Segment : Portugal S.A. (LIDAR) : Suisse - Italy

10. E.Plagnol - HENA June 2003 - 10 Activities in France : LAPP, LPSC et APC/PCC Analog Electronics Front End Mechanical and thermal study of the focal surface Simulations - ESAF Atmosphere Lidar analysis Communication Outreach F.Vannucci

11. E.Plagnol - HENA June 2003 - 11 Japon Italie-Alenia USA and elsewhere… ESA USA

12. E.Plagnol - HENA June 2003 - 12 Acceptances and Counting Rates An "End to End" simulation of showers, detection and Trigger : Showers : Corsika -> parametrisation GIL Photons production : Fluorescence (Kakimoto et al.) et Cerenkov Transport in the atmosphere : Rayleigh, Mie, Ozone (LOWTRAN7) optics : Throughput and aberrations Detector : Filters et quantum efficiencies Trigger : Threshold and persistency (N thre, N pers )

13. E.Plagnol - HENA June 2003 - 13 Acceptances and Counting Rates The abssolute threshold is fixed by ∆  et detection efficiency (~10 19 eV). The Trigger gives the evolution as a function of energy The asymptotic efficiency will be influenced by the cloud coverage

14. E.Plagnol - HENA June 2003 - 14 Cloud effects Cloud coverage will play an important role : Hide part of the shower development (S max ), Increase the Cerenkov reflection. Cloud properties are obtained form the ISCCP database : Pixels of 280x280 km2 : Long., lat., 3hours : altitude, albedo, cloud fraction.

15. E.Plagnol - HENA June 2003 - 15 The effect of clouds The presence of clouds reduces the efficiency ≈ 86%  ≈ 53%

16. E.Plagnol - HENA June 2003 - 16 The counting rates for 3 years of observation (25% duty Cycle) 25% -> 3000 events for E > 10 20 eV for Super GZK … 250 for GZK The asymptotic acceptance(>10 20 eV) de EUSO represents 10 times AUGER Model dependent GZK recovery

17. E.Plagnol - HENA June 2003 - 17 Horizontal showers and Neutrinos The probability of observing a quasi- horizontal hadronic shower with its maximum below de 10 km is extremely weak. This probability is maximum for neutrinos.

18. E.Plagnol - HENA June 2003 - 18 Acceptance and limiting fluxes for neutrinos The total acceptance of EUSO for neutrinos (interacting in the atmosphere) is ≈ 0.25 x 10 km 2.sr This corresponds to the observation of a J( E )*E 2 ≈ 70 eV cm -2 sr -1 flux For horizontal (>85°) showers, the acceptance decreases by a factor ~ 15 (+ clouds) The acceptance for neutrino is small, but if the fluxes are sufficient …, the observation of horizontal showers, below 10km, should sign the presence of neutrinos. The  interacting with the earth crust may have an acceptance x 10-100 Acceptance with identification

19. E.Plagnol - HENA June 2003 - 19 Status and Summary International ë The ESA phase A will end in September 2003 ë ESA committees will then decide if EUSO goes into phase B…C,D… launch in 2009 ? ë NASA is committed to participate if ESA ok ! ë Switzerland (Neuchatel) and Germany (Max Planck, Munich) have joined the collaboration. Physics The physics of EUSO is "at the frontier" of new physics and of the study of UHECR astronomy. After AUGER, EUSO will be able to study, with significant statistics, the physics of UHECR beyond 10 20 eV : flux, correlations, GZK recovery,…. High energy neutrino could be "at hand" if the fluxes are sufficient. The low energy threshold of EUSO will be lowered by a factor 2 ( ≈ 2-3 10 19 eV). The EUSO detector is the first detector to observe UHECR from above. It will not be the last : USA and Japan are already studying new generations (x10 ?). The observable mass seen by EUSO represents ≈ 2.0 10 12 tonnes with good transparency it is an opening for the future…