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
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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