The Auger Observatory and UHE neutrinos

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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 ?

NO-VE 2006 Pierre Billoir, LPNHE Paris,
CNRS/univ. Paris 6 and 7 Auger Collaboration
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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
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general framework

• n oscillations equal fluxes of the 3
  flavours
• assume neutrinos weakly interacting, even at UHE
• probability of interaction in atmosphere lt
  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 data
(2004-05) (special contribution of Oscar Blanch
Bigas)
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Water Cherenkov tanks
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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
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Hybrid detection
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normal (nucleic) showers
almost vertical thick curved front muons
electromagnetic
earth
atmosphere
very inclined thin flat front High energy muons
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a real vertical event (20 deg)
Noise !
doublet
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a real horizontal event (80 deg)
single peaks fast rise exp. light decay (t
70 ns) accidental background signals are
similar
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neutrino showers
(distinguishable if almost horizontal)
downgoing (direct n interaction in atmosphere)
upgoing (n t in earth t decay in flight )
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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)

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ground spot
decay of an horizontal t of 1 EeV
enn (almost pure e.m. cascade)
pn (hadronice.m. cascade)
injected t
average level of trigger
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• Simulated t
• p (0.27 EeV) n
• 400 m above ground

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• Simulated t
• p (5.1) p0(16.1) n
• 1800 m above ground

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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 gt 1.4 single one
central one within 1500 m one within 3000 m
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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
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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
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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 gt c )
cuts L/W gt 5 0.29 lt av. Speed lt 0.31
r.m.s. lt 0.08
from years 2004-2005 no real event survived
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What can be measured ?

• direction precision better than 2deg
• (improving with Nstat)
• energy possible lower bound for a given event
• - unknown energy losses in interaction/decay
  chain
• - estimation of Eshower depends on altitude

possible strategy 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
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main sources of systematic errors

• detection triggering/selection efficiency,
  effective integrated aperture to be evaluated
  (not dominant)
• cross section of neutrinos
• energy loss of t in earth big uncertainty !
• - bremsstrahlung pair production well
  defined
• - deep inelastic scattering in
  photonuclear process
• pessimistic hypothesis from Dutta et
  al, Phys.Rev. D63 (2001)
• factor of 5 between low and high estimation
  of the acceptance

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Auger sensitivity
uncertainty range
pessimistic t energy loss
TD
preliminary
GRB
GZK
AGN
Points 1 event / year / decade of energy
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upper bounds for 1 year of full Auger(if no
candidate)
(pessimistic hypothesis for t energy loss)
Solid various models from Protheroe
(astro-ph/9809144) Dashed upper bounds at 95
C.L. for each shape if no candidate
preliminary
uncertainty range
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summary and perspectives

• the surface array of Auger 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 of criteria
• 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 (less horizontal)