Transcript Slide 1
Limit to the diffuse flux of UHE ντ at EeV energies from the Pierre Auger Observatory Olivier Deligny for the Pierre Auger Collaboration IPN Orsay – CNRS/IN2P3 TAUP 2007, Sendai THE PIERRE AUGER OBSERVATORY A huge detector to study the Cosmic Rays at the highest energies (EeV). (Results and performance: Plenary 6 ) Hybrid detector: - 4 Fluorescence telescopes - 1600 Surface detectors 3000 km2 We also have the capability to detect Ultra High Energy ν THE PIERRE AUGER OBSERVATORY A huge detector to study the Cosmic Rays at the highest energies (EeV). (Results and performance: Plenary 6 ) Cherenkov water tank We also have the capability to detect Ultra High Energy ν NEUTRINO IDENTIFICATION Signal Principle: A shower deeply initiated by a neutrino looks like a hadronic shower BUT at high angle ! Time [µs] Time [µs] SKIMMING NEUTRINOS All ν flavours can interact in the atmosphere and produce an EAS, but the earth-skimming mechanism can be used for ντ : Lint (ν) ~ 500 km θ>95, Earth opaque Ldecay (τ) ~ 50 km (μ), much larger LEloss ~ 10 km (at 1 EeV) (e), much smaller Pierre Auger Observatory: 50 x 50 km2 This channel is expected to produce more identified neutrinos. LOOKING FOR NEUTRINOS IN AUGER DATA Principle: Build discriminative variables sensitive to young and horizontal showers d ij width tj ti length d ij v ij = t j− t i No candidate (Jan'04 - Dec'06), while ~80% identification efficiency ACCEPTANCE (1) Interactions in Earth Detection probability hc : parameter describing the altitude of the shower center 10 km after the decay point, where the shower has the largest “trigger power” ACCEPTANCE (2) Interactions in Earth Conversion ντ τ Neutrino cross section Tau energy losses Tau decay MC vs numerical solutions ACCEPTANCE (3) Detection probability Acceptance for τ showers Depends on tau energy and altitude shower centre Growing detector 1 EeV Acceptance SYSTEMATICS Source Uncertainty MC Simulations Interactions in Earth Extensive Air Shower 5% +20%, -5% Pierre Auger Observatory Acceptance Topography ± 2% +18% ± Theoretic knowledge Tau Polarisation Cross Section Energy Losses +17%, -10% +5, -9% +25%, -10% Total +132%, -45% Theoretical knowledge All contributions Worst/Best combination of scenarios leads to a factor ~3 difference for the flux limit FLUX LIMIT 90 % CL for each flavour with the worst systematic scenario and assuming: 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 τ candidates have been found, leading to spectra dependent limit to tau neutrinos of E2dN/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… END OF TALK Tau Neutrino (Monte Carlo) 0.3 EeV INCLINED EVENT Real event, 80º VERTICAL EVENT Real event, 20º Noise ! doublet SENSITIVITY Sensitivity ≡ one event per year and decade of energy with the full SD GZK TD AGN WB FLUX LIMIT 2 90 % CL for each flavour with the worst systematic scenario and assuming: dN dE = f0E −2 CONSTRAINTS ON TD MODELS