1. The Auger Observatory and UHE neutrinos
Why UHE neutrinos ?
What is the Auger Observatory ?
How can it see UHE neutrinos ?
How to discriminate them ?
What sensitivity ?
Systematic errors
NOW 2006
Pierre Billoir LPNHE Paris, CNRS/univ. Paris 6 and 7
Auger Collaboration
P. Billoir, Auger Collab., NOW2006

2. P. Billoir, Auger Collab., NOW2006
UHE neutrinos
expected from interaction of accelerated particles with photons in the source region or with the CMBR (GZK effect):
relatively soft spectrum
decay of ultra massive objects: harder spectrum expected:
UHE photons and neutrinos are a signature of top-down scenarii
propagation in straight line: point to the source
differences with photons :
propagation over cosmological distances
low probability to produce an observable atmospheric shower
Photons and neutrinos:
possible interesting byproducts of the Auger Observatory
P. Billoir, Auger Collab., NOW2006

3. P. Billoir, Auger Collab., NOW2006
general framework
n oscillations : ~ equal fluxes of the 3 flavours
assume neutrinos weakly interacting, even at UHE
probability of interaction in atmosphere <~ 10-4
better sensitivity to nt t in earth skimming scenario
(t emerging within a few degrees from horizontal)
This study: based on Astrop. Phys. 17 (2002) 183
(X. Bertou, P.B., O. Deligny, C. Lachaud, A. Letessier-Selvon)
+ work on first Auger Surface Detector data ( )
(special contribution of Oscar Blanch Bigas)
Studies on Fluorescence Detector exist also
P. Billoir, Auger Collab., NOW2006

4. P. Billoir, Auger Collab., NOW2006
Water Cherenkov tanks
Communications
antenna
Electronics
enclosure
Solar panels
Battery box
3 nine inch
photomultiplier
tubes
Plastic tank with 12 tons of water
GPS antenna
P. Billoir, Auger Collab., NOW2006

5. Optical system (fluorescence telescopes)
corrector lens
(aperture x2)
440 PMT camera
1.5° per pixel
segmented spherical mirror
aperture box
shutter
filter UV pass
safety curtain
P. Billoir, Auger Collab., NOW2006

6. Present status (beg. Sept.2006)
(Loma Amarilla)
Coihueco
Los Morados
central
buildings
Los Leones
P. Billoir, Auger Collab., NOW2006

7. First results: spectrum (from ICHEP06)
Error bars
at at 1020
Caveat: energy scale still uncertain !!!
P. Billoir, Auger Collab., NOW2006

8. First results: anisotropy (from ICRC05)
SUGAR region
AGASA region GC
Anisotropy around Galactic Center not confirmed
(AGASA and SUGAR results excluded)
global distribution compatible with isotropy – no clusters
P. Billoir, Auger Collab., NOW2006

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11. P. Billoir, Auger Collab., NOW2006
1 atmospere
P. Billoir, Auger Collab., NOW2006

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14. P. Billoir, Auger Collab., NOW2006
2 atmospheres
P. Billoir, Auger Collab., NOW2006

15. P. Billoir, Auger Collab., NOW2006
Hybrid detection
P. Billoir, Auger Collab., NOW2006

16. “normal” (nucleic) showers
earth
almost vertical:
thick curved front
muons + electromagnetic
atmosphere
very inclined:
thin flat front
High energy muons
P. Billoir, Auger Collab., NOW2006

17. a real vertical event (20 deg)
Noise !
doublet
P. Billoir, Auger Collab., NOW2006

18. a real horizontal event (80 deg)
“single” peaks : fast rise + exp. light decay (t ~ 70 ns)
accidental background signals are similar
P. Billoir, Auger Collab., NOW2006

19. a real “monster” (lightning event)
15 km !
Many stations triggered with abnormal signal (e.g. quasi-periodic oscillations)
easily rejected (even if pattern is not well understood !)
P. Billoir, Auger Collab., NOW2006

20. P. Billoir, Auger Collab., NOW2006
neutrino showers
(distinguishable if almost horizontal)
downgoing
(direct n interaction in atmosphere)
upgoing
(n t in earth
t decay in flight )
P. Billoir, Auger Collab., NOW2006

21. P. Billoir, Auger Collab., NOW2006
Simulation chain
inject nt at 0.1, 0.3, 1, 3, …, 100 EeV into earth crust
generate c.c. and n.c interactions (CTEQ4-DIS) , t decay and energy loss
if a t emerges: generate decay in atmosphere
(modes e, p, pp0, ppp0 , pp0p0, ppp , pppp0 , pp0p0p0 + neutrinos)
inject the products of decay into AIRES (shower simulation package)
regenerate particles entering the tank from the “ground” output file
simulate the Cherenkov response and FADC traces
apply a specific analysis (trigger + selection)
P. Billoir, Auger Collab., NOW2006

22. P. Billoir, Auger Collab., NOW2006
ground spot
decay of an horizontal t of 1 EeV
enn (almost pure e.m. cascade)
pn (hadronic+e.m. cascade)
injected t
average level of trigger
P. Billoir, Auger Collab., NOW2006

23. P. Billoir, Auger Collab., NOW2006
Simulated t
p+ (0.27 EeV) n
400 m above ground
P. Billoir, Auger Collab., NOW2006

24. P. Billoir, Auger Collab., NOW2006
Simulated t
p+ (5.1) p0(16.1) n
1800 m above ground
P. Billoir, Auger Collab., NOW2006

25. candidate selection 1. “young” showers
online local triggers (one tank):
threshold: one slot above Th
(detection of peaks)
time over threshold: N slots within 3 ms above th
(detection of long signals)
Global condition:
at least 3 t.o.th. stations satisfying
area/peak > 1.4 * “single”
one “central” + one within 1500 m + one within 3000 m
P. Billoir, Auger Collab., NOW2006

26. P. Billoir, Auger Collab., NOW2006
Trigger efficiency
Fraction of decaying t (excluding mnn channel) giving a trigger
En = 0.1 EeV
En = 1 EeV
En = 100 EeV
En = 10 EeV
1 km
2 km
P. Billoir, Auger Collab., NOW2006

27. P. Billoir, Auger Collab., NOW2006
footprint analysis
Variables defined from the footprint
(in any configuration, even aligned)
length L and width W
(major and minor axis of the ellipsoid of inertia)
“speed” for each pair of stations
(distance/difference of time) tj ti
dij
major axis
P. Billoir, Auger Collab., NOW2006

28. candidate selection 2. Discriminating variables
Search for long shaped configurations, compatible with a front moving horizontally at speed c, well contained inside the array
(background: vertical or inclined showers, d/Dt > c )
cuts: L/W > < av. Speed < r.m.s. < 0.08
from years : no real event survived…
P. Billoir, Auger Collab., NOW2006

29. Possible additional criterion: front curvature
Quasi-horizontal real events
Fitted from arrival times in stations:
radius of curvature
“center”
q > 70 deg
q > 80 deg
Shower axis a
Peak around 10 km
(lower values expected for neutrinos)
P. Billoir, Auger Collab., NOW2006

30. A nearly candidate event (rejected for shape)
trom times: “trans-horizontal” event (L/Dt = m/ns for all pairs)
rare coincidence small shower (right side) + a double accidental (left) ?
P. Billoir, Auger Collab., NOW2006

31. P. Billoir, Auger Collab., NOW2006
What can be measured ?
direction: precision better than 2 deg
(improving with Nstat)
difficult to distinguish up-going/down-going
(narrow distribution around 90 deg ?)
energy: possible lower bound for a given event
- unknown energy losses in interaction/decay chain
- estimation of Eshower depends on altitude
(possible evaluation from signal shapes, with large Nstat ?)
possible strategy in a first step:
inject in the simulation chain a spectrum with a given shape
deduce from the selected data a level (or an upper bound)
model dependent result
P. Billoir, Auger Collab., NOW2006

32. P. Billoir, Auger Collab., NOW2006
systematic errors (1)
detection: triggering/selection efficiency, effective integrated aperture: to be evaluated (not dominant)
topography (Andes, Pacific Ocean): not crucial
cross section of neutrinos
modelling of UHE hadronic interactions
(not dominant, but maybe not well known…)
t of 3 EeV (all channels except m)
AIRES/QGSJET
AIRES/SIBYLL
P. Billoir, Auger Collab., NOW2006

33. P. Billoir, Auger Collab., NOW2006
systematic errors (2)
t polarization (depends on parton distribution)
using TAUOLA
here: extreme cases (very unlikely !): difference ~ 30 %
h = -1
h = +1
h = +1
h = -1
P. Billoir, Auger Collab., NOW2006

34. systematic errors (3) energy loss of t in earth: big uncertainty !
-dE/dx = a + b(E) E
- bremsstrahlung + pair production: well defined
- deep inelastic scattering in photonuclear process:
“pessimistic” hypothesis from Dutta et al, Phys.Rev. D63 (2001)
Contrib. of dE/dx
factor ~5 between low and high estimations of the acceptance
dominant at high E
total
P. Billoir, Auger Collab., NOW2006

35. P. Billoir, Auger Collab., NOW2006
Auger sensitivity
uncertainty
range
“pessimistic” t energy loss TD
preliminary
GRB
GZK
AGN
Points: 1 event / year / decade of energy
P. Billoir, Auger Collab., NOW2006

36. upper bounds for 1 year of full Auger (if no candidate)
(“pessimistic” hypothesis for t energy loss)
Solid:
various models from Protheroe (astro-ph/ )
Dashed:
upper bounds at 95 % C.L. for each shape
if no candidate
preliminary
uncertainty range
P. Billoir, Auger Collab., NOW2006

37. Detection with fluorescence telescope ?
Can see showers well above the ground, but:
- duty cycle ~ 10 % of the time
- limited range at low energy
Potential advantages:
- can distinguish up-going showers
- direct evaluation of altitude and energy
(if large angle of view)
Acceptance studied in
C. Aramo et al., Astrop. Phys. 23 (2005) 65
G. Miele et al., Phys. Lett. B634 (2006) 137
P. Billoir, Auger Collab., NOW2006

38. summary and perspectives
the Pierre Auger Observatory is sensitive to UHE neutrinos
most promising: earth skimming (decay of t in air)
real data are clean
simple criteria allow to reject the background
still room for refinement …
constraining upper bounds expected within a few years
Ongoing studies:
other criteria to select neutrino candidates
specific trigger to enhance sensitivity at low energy
acceptance calculations
shower energy evaluation
observation with the fluorescence detector
atmospheric n interactions (down-going, less horizontal)
P. Billoir, Auger Collab., NOW2006