Search for Neutrino-Induced Cascades in AMANDA II

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Search for Neutrino-Induced Cascades in AMANDA
II

• Marek Kowalski
• DESY-Zeuthen
• Workshop on Ultra High Energy Neutrino Telescopes
• Chiba, 29.7.2003

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Outline

• Introduction
• Reconstruction of cascade-like events
• Searching for cascade-like events in the AMANDA
  II data
• Summary

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Neutrino-Induced Cascades

• Signature of ne and nt are hadronic and
  electro-magnetic cascades.
• Neutral Current interactions of all neutrino
  flavors produce hadronic cascades
• Background consists of atmospheric muons,
  emitting energetic secondaries

Signal and Background
5 m
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Why search for Neutrino-Induced Cascades?

• Advantages
• Large Sensitivity for ne and nt
• Local events, therefore better energy resolution
• Less intrinsic background of atmospheric muons
  neutrinos
• Nearly 4 p sensitivity
• Disadvantages
• Less signal than in the muon channel due to very
  large muon range
• Worse angular resolution
• Local events, therefore
• better energy resolution
• Less background of atmospheric neutrinos

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Reconstructing Cascades Vertex Position
With scattering
Without scattering
far track
0 ?t
?t
close track
0 ?t
0 ?t
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Vertex Resolution
Reconstruction of 1 TeV EM cascades which
trigger AMANDA II
Vertex resolution of cascades in
the detector (radius 100 m, height 200 m)
s 5 m for x,y,z coordinates and
large range of energies.
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Energy Reconstruction

• Parameterization of hit-probability with MC.
  Function is random walk inspired
• Construction of Likelihood function

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Resolution of Energy Reconstruction

• Reconstruction of EM cascades of energies
  102, 103 , 104 ,105 ,106 GeV.
• Vertex within AMANDA II. (radius 100m, height
  200m) Vertex fitted with time-likelihood.

lt7.1
s(logE) lt 0.2
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Testing Reconstruction with In-Situ Light
Sources
data
Vertex reconstruction Reconstructing position of
YAG laser light emitters (position known to 1
m).
mc
Energy reconstruction LEDs (UV 370 nm) run at
different intensities. Reconstructing energy of
LED events (20 resolution) . Absolute intensity
not known, but relative Intensities reconstructed
correctly.
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The cascade filter
Starting with 1.2 x 109 events (in the 2000 data
set) 7 cuts to reduce background The full
likelihood reconstruction is performed after cut
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Final cut
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Final cut variable
Variables merged into one Bayesian
Discriminator (thereby neglecting correl.)
m
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Optimizing the Final Cut in L-logE space

• Cuts are optimized on MC to obtain best
  sensitivity.
• Sensitivity is defined as average upper limit on
  F(E) const x E-2 / (GeV s sr cm2)
• L-logE space scanned and sensitivity calculated
  (performing a counting rate experiment)

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Final energy spectrum
Energy cut chosen by MC Optimization 2 events
passed all cuts
Background Expectation
Atmospheric muons 0.45 0.5-0.3
Conventional atmospheric n 0.050.05-0.02
Prompt charm n 0.015-0.7
Sum (w/o charm) 0.50 0.5-0.3
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The highest energy event (200 TeV)
300 m
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Effective Volume for ne ,nm and nt
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Upper limits on the diffuse flux

• Nobs2 Nbg0.50.5-0.3
• Upper bounds on the diffuse flux of astrophysical
  neutrinos (at 90 CL) for different assumed
  spectras F(E) E-g g1-3
• Limit on tau neutrinos 25 - 30 worse than for
  electron neutrinos
• Glashow resonance at 6.3 PeV results in
  differential ne limit

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Comparision with other Limitsand Models
Preliminary (2000 data)
Model ne ne nm nt
1e-6 x E-2 1.8 0.9
SSDS (92) 0.86 0.41
SS QC (95) 0.43 0.21
SS BJ (95) 1.2 0.61
P pg (96) 4.7 2.4
MPR (98) 9.8 4.8

SSDS


MPR
units model rejection factor assuming
a flavor ratio 111
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Conclusions

• Cascades interacting within AMANDA can be
  reconstructed with a resolutions
• sx,y,z5 m, sq30o- 40o and
  slogE0.1-0.2
• A search for neutrino-induced cascades in the
  data of the first year of AMANDA II was
  performed. No significant excess over
  background was seen!
• Upper limits set on the diffuse flux of
  neutrinos, ruling out several AGN flux models.
• AMANDA can be considered an all flavor neutrino
  detector!

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Back Up
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Angular detector sensitivity nearly
uniform.Depletion due to propagation through the
earth.
Examplene _at_ 1 PeV
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The AMANDA detectorat the South Pole

• Detector deployed 2 km deep into Antarctic ice
  

• Instalation of 10 strings in 1996/97 (referred
  to as AMANDA-B10)
• Comissioning of AMANDA II in 2000 consisting of
  19 strings and 677 OMs

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First Level Cascade Filter
The discriminating variables are based on fast
estimate of vertex position time
Late hits (but causal) Direct hits c (ti-200
ns) lt d lt c ti Early hits (non causal!) d
gt c ti
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First Level Cascade Filter
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Final Level Cascade Filter
Energy spectrum of remaining events
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Systematic uncertainty on signal sensitivity
Type and size of uncertainty Unertainty in event rate (ne)
Variation of ice models 10
OM sensitivity (/- 20 ) 10
Energy scale (/- 20 ) 10
Cut variation 5
MC Statistics 3
Shower simulation 1
Quadratic sum 20