1. Olivier Deligny for the Pierre Auger Collaboration IPN Orsay – CNRS/IN2P3 TAUP 2007, Sendai Limit to the diffuse flux of UHE ν at EeV energies from the Pierre Auger Observatory τ

2. THE PIERRE AUGER OBSERVATORY We also have the capability to detect Ultra High Energy ν Hybrid detector: - 4 Fluorescence telescopes - 1600 Surface detectors 3000 km 2 A huge detector to study the Cosmic Rays at the highest energies (EeV). (Results and performance: Plenary 6 )

3. THE PIERRE AUGER OBSERVATORY We also have the capability to detect Ultra High Energy ν Cherenkov water tank A huge detector to study the Cosmic Rays at the highest energies (EeV). (Results and performance: Plenary 6 )

4. NEUTRINO IDENTIFICATION Principle: A shower deeply initiated by a neutrino looks like a hadronic shower BUT at high angle ! Time [µs] Signal

5. SKIMMING NEUTRINOS L int ( ν ) ~ 500 km L decay ( τ ) ~ 50 kmL Eloss ~ 10 km (at 1 EeV) θ>95, Earth opaque ( μ ), much larger (e), much smaller Pierre Auger Observatory: 50 x 50 km 2 All ν flavours can interact in the atmosphere and produce an EAS, but the earth-skimming mechanism can be used for ν : This channel is expected to produce more identified neutrinos. τ

6. LOOKING FOR NEUTRINOS IN AUGER DATA No candidate (Jan'04 - Dec'06), while ~80% identification efficiency width length Principle: Build discriminative variables sensitive to young and horizontal showers

7. ACCEPTANCE (1) Interactions in Earth Detection probability h : parameter describing the altitude of the shower center 10 km after the decay point, where the shower has the largest “trigger power” c

8. ACCEPTANCE (2) Conversion ν τ  Neutrino cross section  Tau energy losses  Tau decay τ Interactions in Earth MC vs numerical solutions

9. ACCEPTANCE (3) Detection probability Acceptance for τ showers  Depends on tau energy and altitude shower centre  Growing detector 1 EeV Acceptance

10. SYSTEMATICS Worst/Best combination of scenarios leads to a factor ~3 difference for the flux limit Theoretical knowledge All contributions

11. FLUX LIMIT 90 % CL for each flavour with the worst systematic scenario and assuming:

12. SUMMARY AND PROSPECTS The Pierre Auger Observatory has a large discriminant capacity to distinguish earth-skimming neutrinos from standard Cosmic Rays. From Jan'04 till Dec'06 (about 1 year of a full Surface Detector), ZERO ν candidates have been found, leading to spectra dependent limit to tau neutrinos of E 2 dN/dE 2·10 -7 GeV cm -2 s -1 sr -1. The Pierre Auger Observatory has its maximum sensitivity at the most relevant energy range (~ 1 EeV) for GZK neutrinos, the expected level of which will be tested in about 10 years. The Pierre Auger Observatory is also sensitive to neutrinos that interact in the atmosphere. This channel has different systematics and depends differently on neutrino properties. Studies are ongoing… τ

13. END OF TALK

14. Tau Neutrino (Monte Carlo) 0.3 EeV

15. INCLINED EVENT Real event, 80º

16. VERTICAL EVENT Noise ! doublet Real event, 20º

17. SENSITIVITY Sensitivity ≡ one event per year and decade of energy with the full SD GZK TD AGN WB

18. FLUX LIMIT 2 90 % CL for each flavour with the worst systematic scenario and assuming:

19. CONSTRAINTS ON TD MODELS