1. EUSO The Extreme Universe Space Observatory Marco Pallavicini INFN Genova, Italy

2. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 2 Talk Overview  Scientific case and Science Goals  The observational approach  The detector on the ISS  The detector optics  Detector expected performances

3. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 3 Euso An Innovative Space Mission doing astronomy by looking downward from the Space Station at the Earth Atmosphere  Euso is devoted to the exploration from space of the highest energy processes present and accessible in the Universe: The extreme energy cosmic rays ( E > 4 10 19 eV)  They are directly related to the extreme boundaries of the physical world.

4. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 4 Scientific motivations  Why should we study the Extreme Energy Cosmic Radiation (EECR) From the Astroparticle Physics point of view, the EECRs have energies only a few decades below the Grand Unification Energy (10 24 - 10 25 eV), although still rather far from the Planck Mass of 10 28 eV. If protons, they show the highest Lorentz factor observed in nature (  ~ 10 11 ). What is the maximum Cosmic Ray energy, if there is any limit? There is no compelling evidence for identification of EECR sources with objects known in any astronomical channel. They may be a unique probe for Grand Unification theories and cosmological models Neutrino astronomy from the deep space (no GZK cut off)

5. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 5 Today’s knowledge: spectrum Energy spectrum decreases like ~ E -3 The spectrum extends above 10 20 eV At these extreme energies, flux is of the order of Km -2 century -1 ICRC2001 Present data is interesting and challenging Not consistent fluxes among measurements GKZ cut off ? Energy scales ?

6. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 6 Today’s knowledge: Direction Arrival direction of 59 events with energies above 4 10 19 eV observed by AGASA No large scale anisotropy Indication of point like sources (1 triplet, 6 doublets, Prob. 0.07%) Triplet in the direction of interacting galaxy VV141

7. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 7 Today’s knowledge: Direction (II)

8. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 8 Experimental problem ?  HiRes and AGASA measurements are barely compatible. Is there a problem ? The number of events detected by AGASA above 10 20 eV is quite larger than that detected by HiRES (10 events vs 2 events) for equivalent exposure. The position of the “ankle” in the Cosmic Ray spectrum for AGASA is at energies a factor 2–3 larger than the one shown by HiRES (  10 19 eV vs 3x10 18 eV). GZK: Is this a measurement of the effect or discovery of its non existence (AGASA, 2.6  )? AGASA is almost complete HiRES will go on for 5 years

9. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 9 Today’s ignorance  How the cosmic rays reach such huge energies ? Acceleration mechanisms ? Decay from super-heavy relic particles ?  What are they ? Protons ? Nuclei ? Neutrinos ?  If accelerated, from where ? Galactic sources? Extragalactic? Why GZK is not there (if AGASA is right) ?

10. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 10 Top-Down and Bottom-Up scenarios Bottom - up “Bottom-up”: with acceleration in rapidly evolving processes occurring in Astrophysical Objects with an extreme case in this class being represented by the Gamma Ray Bursts (GRBs). The observation of “direction of arrival and time coincidences” between the optical-radio transient and Extreme Energy Neutrinos could provide a crucial identification of the EECR sources. “Top-down”: processes with the cascading of ultrahigh energy particles from the decay of Topological Defects; these are predicted to be the fossil remnants of the Grand Unification phase in the vacuum of space. They go by designations, such as cosmic strings, monopoles, walls, necklaces and textures. Inside a topological defect the vestiges of the early Universe may be preserved to the present day. Top - down

11. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 11 Bottom-Up: Cosmic accelerators

12. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 12 Euso Scientific goals  Extension of the measurament of the energy spectrum of the Cosmic Radiation beyond the GZK conventional limit (E GZK  5 x 10 19 eV). How does the Cosmic Ray spectrum continues beyond the existing data? Is there a maximum energy (E max ) ?  All sky survey of the arrival direction of EECRs. Point sources? We want to identify their optical counter-part.  Observation of a possible flux of High Energy Cosmic Neutrinos. Neutrinos can arrive from very distant sources!  Systematic sounding of the Atmosphere with respect to cloud distribution and UV light absorption/emission characteristics. Investigation of Atmospheric Phenomena such as Meteors and Electrical Discharges.

13. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 13 The Euso experiment  Experiments carried out by means of ground-based observatories, Auger (hybrid) and HiRes – Telescope Array (fluorescence), are limited by practical difficulties connected to the relatively small collecting area (up to 3000 Km 2 !!) still marginal for the extremely low flux involved (order of 1 particle/100 Km 2 /sr/year for a Primary of 10 20 eV). To overcome these difficulties, an adequate solution is provided by observing the atmosphere UV induced fluorescence from space which allows to exploit up to millions Km 2 /sr

14. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 14 Euso observational approach Nitrogen Spectrum Photons per m EUSO Columbus Euso Area vs Auger EUSO Pierre-Auger

15. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 15 Geometry 30° EUSO on ISS 230 km 380 km Earth surface EUSO Geometry Detector distance 380 km Total field of view60° Geometrical factor 5  10 5 km 2 sr Target air mass 2  10 12 tons Pixel size (.8 .8) km 2

16. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 16 The instrument Fresnel lens Iris Focal surface support structure System electronics Monocular and Compact

17. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 17 Euso parameters Field of View± 30° around Nadir Lens Diameter2.5 m Entrance Pupil Diameter  2.0 m F/#< 1.25 Operating wavelengths300-400 nm Angular resolution (for event direction of arrival) ~ 1° Pixel diameter (and spot size)~ 5 mm Pixel size on ground~0.8 x 0.8 km 2 Number of pixels~ 2.5 x 10 5 Track time sampling (Gate Time Unit)833 ns (prog.) Operational Lifetime3 years

18. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 18 Optics: Fresnel lenses 1.5 Fresnel lens prototype PropertyZEONEXTPXCYTOPPMMA Refractive index1.5251.4631.3461.49 Abbe’s number56 9055 Transmittance (400 nm) 3 mm 92%92 ~ 93%92%86% Linear expansion coefficient /  C 6.0E-51.17E-47.4E-58.0E-5 Water absorption rate (%) 60  C <0.01 0.3 Density g/cm 3 1.010.8332.031.20 Tensile strength kg/cm 2 600>235 (at yield) 400490~77 0 Total weight < 200 Kg Small chromatic aberration Space environment Small F/# < 1.25 Small point-spread function Mechanical strength for launch ±30° field of view Requirements Possible materials

19. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 19 Optics: structure Mass of each Lens 20 mm PMMA 125 kg 20 mm TPX 90 kg 20 mm CYTOP 215 kg 20 mm Zenoex 105 kg 3 support rings, 24 ribs/lens, 20%Contingency 90 kg Mass of Optical Structure Graphite Fiber Re-enforced Polymer 12 metering struts with 11 cross braces, 20% Contingency 60 kg 6 mm 10 mm 50 mm 10 mm 20 mm 15 mm Ring and Rib Detail Strut Detail rings ribs struts and cross braces

20. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 20 Optics: performance De-focussing Acceptance UV Filter

21. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 21 Focal surface design  Sensitivity to single photons in the wave length region between 300 nm and 400 nm  Fast response (  10 ns ), to be able count single photons and reconstruct the EAS direction from a single observation point by using photons time distribution Each pixel must see roughly 1 Km 2 at ground level 1 Km  3 ms; at 10 21 eV you expect up to about 100 photons per ms on a single pixel The system must be able to count photons at ( peak, max ) 100 MHz in a continuous background of about 1 MHz per pixel (from night glow 3 10 11 photons m -2 s -1 sr -1 )  A few mm 2 spatial resolution on the focal plane Optics point spread function size is a few mm 2. We do not want to be worse than that.

22. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 22 Focal surface Hamamatsu R7600-M64 Light Guide or Lens Focal surface is not a plane The FS is logically divided into macrocells Detailed structure is under study Trade off among efficiency, weight, feasibility, mechanichal stability “Macrocell”

23. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 23 Photodetectors Hamamatsu R7600-03-M64 Pmts will be arranged in “microcells”, i.e. units of 4 pmts hold by a single PCB Possible option: Weakly focused R8520 Better uniformity Need additional RD 5x5 maybe

24. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 24 Optical adaptors (I): Lens Problem: Hamamatsu R7600-M64 has a large dead area Option 1: Lens Features Good collection efficiency and angular acceptance Drawbacks Weight

25. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 25 Optical adaptors (II): Light guides 2.8cm UV filter Light Guide 2cm 2.57cm 2cm Entrance Surface of Light Guide Surface of R7600-M16 7mm 4mm  2.57cm 0.3m m

26. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 26 Optical adaptors: comparison

27. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 27 Electronics MC_TRIGGER From other MCs SYSTEM TRIGGER SAVE_FRAME EUSO CONTROL & DATA HANDLING UNIT LEVEL K A PMT PIXEL Incoming UV photon M=M+1 M_thr Compare X & Y + PH_CNT RING MEMORIES MCell X Y From other pixels MACROCELL DIGITAL ELECTRONICS LEVEL MC-level Dig. Thrsh From other pixels Analog Threshold N=N+1 N_thr Compare Pixel-level Digital Thrsh ASIC X Y Enable ASIC DIGITAL/ANALOG ELECTRONICS LEVEL ANALOG memories

28. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 28 The natural detector  The atmosphere is required to produce a shower. Two source of signal for Euso:  Fluorescence  Cerenkov The amount of light is proportional to the energy of the primary particle The shape of the shower and the depth of its maximum gives information about primary particle type Both signal intensity and shape are affected by atmospheric conditions  Rayleigh scattering  Aerosol (Mie scattering)  Ozone  Water vapor and cloud reflection and absorption  Ground albedo Euso needs night-time monitoring of these variables

29. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 29 Background Background is mostly due to: Nightglow (~400 m -1 s -1 sr -1 over sea) Man made Atmospheric phenomena

30. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 30 Event reconstruction X projection TUTU TU Y p r o je ct io n  A B C to receiver CR

31. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 31 Neutrinos Protons & Nuclei Expected Performances Angular resolution vs energy Events in 1 year Proton vs neutrino separation

32. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 32 Schedule (a sort of) Phase A (preliminary study): 2002-2003 Phase B (project): 2003-2004 Phase C-D (construction):2005-2008 Phase E (operation): 2009 ?

33. Nestor Insitute, Pilos, Jun. 05-10, 2002M. Pallavicini - INFN Genova 33 Conclusion  The study of EECR may lead to important discoveries in fundamental physics and astrophysics  EUSO is an innovative mission that will collect thousands of events above 10 20 eV  The phase A has been approved by ESA and financial support has been provided by INFN and other institutions  Launch is foreseen in this decade