Status:

1. UHE Cosmic Ray Flux: The Auger ResultsC. Di Giulio for the Pierre Auger Collaborationa)Università degli Studi di Roma Tor Vergata b)INFN Roma Tor Vergata.

2. 0 4km AGASA 100 km2 Status: 10 events above GZK γ = 5.1 ± 0.7 J = J0 E - γ HiRes Group: astro-ph/0703099 LOW STATISTIC!!

3. Czech Republic France Germany Italy Netherlands Poland Portugal Slovenia Spain United Kingdom Argentina Australia Brazil Bolivia* Mexico USA Vietnam* *Associate Countries ~300 PhD scientists from ~70 Institutions and 17 countries The Pierre Auger Collaboration Aim: To measure properties of UHECR with unprecedented statistics and precision.

4. The Pierre Auger Observatory: Hybrid Detector! Fluorescence Detector (FD): • fluorescence light: 300-400 nm light from the de-excitation of atmospheric nitrogen (~ 4 /m/electron)‏ (+) Longitudinal shower development calorimetric measurement of E (Xmax)‏ (-) Duty cicle ~ 10% FD Surface Detector (SD): • detection of the shower front at ground (-) Shower size at ground  E‏ (+) Duty cicle ~ 100% (important for UHECR)‏ SD

5. The Pierre Auger Observatory: Malargue - Argentina Pampa Amarilla Lat.: 35oS Long.:69o W 1400 m a.s.l. 875 g/cm2 • Low population density (< 0.1 / km2)‏ • Good atmospheric conditions (clouds, aerosol…)‏

6. 50 km The Auger Hybrid Detector Total area 3000 km2 SD 1600 water Cherenkov detectors on a 1.5 km triangolar grid ~ 1550 are operational FD 4 x 6 fluorescence telescopes

7. A surface array station Communications antenna GPS antenna Electronics enclosure Solar panels Battery box 3 photomultiplier tubes looking into the water collect light left by the particles Plastic tank with 12 tons of very pure water Online calibration with background muons.

8.  , e± PMT  Cerenkov light shower front 1.2 m ~ 3 Xo water 1.5 km Vertical Muon PMT scintillator SD: shower reconstruction The calibration of the water Cherenkov detector is provided by the muons entering the tanks in the vertical direction (VEM: vertical equivalent muon). diffusive Tyvek The tanks activated by the event record the particle density in unit of VEM and the time of arrival. This data are used to determine the axis of the shower.

9. distance from the core size parameter slope parameter (β) 2-2.5)‏ Signal (VEM)‏ vertical equivalent muon = VEM S(1000)‏ distance from the core (m)‏ SD: shower reconstruction The dependence of the particle density on the distance from the shower axis is fitted by a lateral distribution function (LDF). core 34 tanks The fit allows determining the particle density S(1000) at the distance of 1000 m from the axis. This quantity is our energy estimator.

10. SD: shower energy estimator S(1000): is the energy estimator for the Auger array less sensible to signal fluctuations Simulation (?)‏ S(1000)‏ FD calorimetric measurement Energy In the Auger Detector the energy scale is determined from the data and does not depend on a knowledge of interaction models or of the primary composition – except at level of few %.

11. FD Telescope Schmidt optics Camera (sferical surface) 30ox30oFOV 440 PMTs 1.5o light spot: 15 mm (0.5o) Spherical mirror, 3.4m radius of curvature 2.2 m diameter diaphragm, corrector ring + UV optical filter

12. FD Event: bin=100 ns

13. Edep Nγ(λ)‏ T(λ)‏ A Ri Edep Photons in FD FOV Photons at diaphragm Nγ(λ)‏ ADC counts Geometry Fluorescence yield (from laboratory measurements)‏ Detector calibration Atmosphere A Ri2 T(λ)‏ FD Longitudinal Profile 5.05 ± 0.71 photons/MeV Lidar, CLF, ballon lunch etc etc... Drum.

14. FD Absolute Calibration Drum Drum: a calibrate light source uniformly illuminates the FD camera Mirror reflectivity, PMT sensitivity etc., are all included! ~ 5 /ADC 10% error

15. Atmospheric Monitoring 355 nm steerable laser Central laser facility ~30 km CLF laser track seen by FD Many instruments to check the atmosphere. Estimation of the aerosol content of the atmosphere Balloon launches (p, T, humidity..) 1 LIDAR per eye Aerosols: clouds, dust, smoke and other pollutants

16. SD hybrid fit FD mono fit Hybrid Geometry: Ttank TFD Rtank Ttank + Rtank / c ≈ TFD

17. co Light Profile Expected photons fluorescence cherenkov • The signal, after correcting for attenuation of fluorescence light due to Rayleigh and aerosol scattering, is proportional to the number of fluorescence photons emitted in the field of view of the pixel. • Cherenkov light produced at angles close to the shower axis can be scattered towards the FDs and this contamination is accounted in the reconstruction procedure. • Using the Fluorescence Yield information we convert the light profile in the energy deposit profile.

18. Longitudinal Profile Etot E ~ 3.5 1019 eV Ecal Xmax~ 810 g/cm2 Nucl. Instr. Meth. A588 (2008) 433-441. Only a 10% model dependent correction • A Gaisser-Hillas function is fitted to the reconstructed shower profile which provides the measurement of the energy of the shower deposited in the atmosphere. • The estimate of this missing energy depends on the mass of the primary cosmic ray and on the hadronic model used for its computation. • The systematic uncertainty due to the lack of knowldege of the mass composition and of the hadronic interaction model is 4%.

19. Systematics on the Absolute Energy Scale Note: Activity on several fronts to reduce these uncertainties

20. SD Calibration using FD Energy Due to the attenuation in the atmosphere for the same energy and mass S(1000;vertical)< S(1000 vertical shower inclined shower Xg/cos Xg Attenuation curve derived with constant intensity cut technique. ground for each shower determine S38 = S(1000,380)‏ S38, represents the signal at 1000m the very same shower would have produced if it had arrived from a zenith angle of 38°

21. SD Calibration using FD Energy 50 VEM ~ 1019 eV 661 hybrid events FD syst. uncertainty (22%) dominates 19% measurement of the energy resolution 16%-S38 8%-EFD

22. SD Aperture geometric quantity! Full efficiency above 3x1018 eV 1 January 2004 to 31 August 2007 ~20.000 events above 3 1018 eV Aperture 7000 km2 sr yr (3% error) (~ 1 year Auger completed 4 x AGASA)‏

23. UHECR Auger Flux (<600)‏ Exp. Observed > 4x1019 167±3 69 > 1020 35±1 1 Evidence of GZK cutoff

24. UHECR Auger Flux (<600)‏ Detailed features of the spectrum better seen by taking difference with respect to reference shape Js = A x E-2.69 γ = 2.69 ± 0.02(stat) Fit E-γ GZK cut off Slope γ above 4x1019 eV: 4.2 ± 0.4(stat) HiRes: 5.1 ± 0.7

25. Conclusion: • Auger results reject the hypothesis that the cosmic-ray spectrum continues with a constant slope above 4 × 1019 eV, with a significance of 6 standard deviations. • The flux suppression, as well as the correlation of the arrival directions of the highest-events with the position of nearby extragalactic objects, supports the GZK prediction. • A full identification of the reasons for the suppression will come from knowledge of the mass spectrum in the highest-energy region and from reductions of the systematic uncertainties in the energy scale.

27. Composition from hybrid data • UHECR: observatories detect induced showers in the atmosphere • Nature of primary: look for diferences in the shower development • Showers from heavier nuclei develop earlier in the atm with smaller fluctuations • They reach their maximum development higher in the atmosphere (lower cumulated grammage, Xmax ) • Xmax is increasing with energy (more energetic showers can develop longer before being quenched by atmospheric losses)

28. Composition from hybrid data <A> = 5 Xmax resolution ~ 20 g/cm2 Larger statistics or independent analysis of the fluctuations of Xmax and SD mass composition estimators are needed..

29. Composition from hybrid data • The results of all three experiments are compatible within their systematic uncertainties. • The statistical precision of Auger data already exceed that of preceeding experiments ( data taken during construction of the observatory)

30. muon peakVEM peak Vertical Muon PMT scintillator The Surface Detector Unit Calibration Online calibration with background muons (2 kHz)‏ 1 VEM ≈ 100 p.e.

31. The Surface Detector Unit  , e± PMT  Cerenkov light 1.2 m ~ 3 Xo water • -response ~ track • e/-response ~ energy diffusive Tyvek 1019 eV simulated showers  sign. ~ e.m. sign.

32. shower front 1.5 km The Shower direction using SD Fit of the particle arrival times with a model for the shower front (not exactly plane) Vertical shower of energy 1019 eV activates 7-8 tanks very good time resolution (~ 12 ns)‏

33. FD Shower direction: 1) Shower detector plane (SDP)‏ Camera pixels 2) Shower axis within the SDP ≈ line but 3 free parameters (Rp,o)‏ ti monocular geometry t(χi) = t0 + Rp· tan [(χ0 - χi)/2] Large uncertainties (10-200)‏ χi extra free parameter

34. Fluorescence Yield in Air Air Fluorescence spectrum Excitation of the nitrogen molecules and their radiative dexcitation . Collisional quenching AIRFLY 3 MeV e- beam 337 nm • p and T dependenceYield vs altitudine AIRFLY Several groups working on the measurement of the absolute yield Goal: uncert. close to 5% 357 nm 391 nm

35. Shower profile reconstruction SD hybrid fit FD mono fit Pulse finding SDP reconstruction (pixel selection) Drum calibration Time vs χ fit Light at diaphragm

36. Auger (Feb 07) compared to Hires and Agasa Fairly agreement within systematic uncertainties Dip explained by CMB-interactions (e+e-) of extragalactic protonts Berezinsky et al., Phys.Lett. B612 (2005) 147.

37. UHECR Auger Flux Comparison of the three Auger spectra - consistency 0-60 degrees 60-80 degrees ICRC 07

38. Astrophysical models and the Auger spectrum models assume: an injection spectral index, an exponential cutoff at an energy of Emax times the charge of the nucleus, and a mass composition at the acceleration site as well as a distribution of sources. Auger data: sharp suppression in the spectrum with a high confidence level! Expected GZK effect or a limit in the acceleration process?