29.7.2003 M. Kowalski

Search for Neutrino-Induced Cascades in AMANDA II

Marek Kowalski

DESY-Zeuthen

Workshop on Ultra High Energy Neutrino Telescopes

Chiba, 29.7.2003

29.7.2003 M. Kowalski

Outline

• Introduction

• Reconstruction of cascade-like events

• Searching for cascade-like events in the AMANDA II data

• Summary

29.7.2003 M. Kowalski

Neutrino-Induced Cascades:

• Signature of e and are hadronic and electro-magnetic cascades.

• Neutral Current interactions of all neutrino flavors produce hadronic cascades

• Background consists of atmospheric muons, emitting energetic secondaries

S

Signal and Background

~ 5 m

29.7.2003 M. Kowalski

Advantages:• Large Sensitivity for e and

• Local events, therefore better energy resolution• Less intrinsic background of atmospheric muons & neutrinos• Nearly 4sensitivity

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

• Less signal than in the muon channel since muon range very large

Why search for Neutrino-Induced Cascades?

29.7.2003 M. Kowalski

With scattering

0 t

N

i i

ii tt

12

202 )(

t

0 t

far track

close track

0 t

),,,,,( 0 scattabsiii distttfL

Reconstructing Cascades:Vertex Position

Without scattering

29.7.2003 M. Kowalski

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)

~ 5 m for x,y,z coordinates and large range of energies.

29.7.2003 M. Kowalski

Energy Reconstruction

• Parameterization of hit-probability with MC. Function is random walk inspired:

• Construction of Likelihood

function:

//

1),(

d

hit

e

eP

dEc

Ed

)1()()( allhits nohits

hithit PPL EE

29.7.2003 M. Kowalski

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.

logE) < 0.2

<7.1

29.7.2003 M. Kowalski

Vertex reconstruction:

Reconstructing position of YAG laser light emitters (position known to ~ 1 m).

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.

Testing Reconstruction with In-Situ Light Sources

datamc

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The cascade filter

Final cut

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 # 2

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Final cut variable

BS

S

iiB

iS

iBS

BS

PP

P

PP

PP

s

//

L

Variables merged into one

“Bayesian Discriminator”

(thereby neglecting correl.)

[m]

29.7.2003 M. Kowalski

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: (E)= const x E-2 / (GeV s sr cm2)

• L-logE space scanned and sensitivity calculated (performing a counting rate experiment)

29.7.2003 M. Kowalski

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 0.05+0.05

-0.02

Prompt charm 0.015-0.7

Sum (w/o charm) 0.50 +0.5-0.3

29.7.2003 M. Kowalski

The highest energy event (~200 TeV)

300 m

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Effective Volume for e , and

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Upper limits on the diffuse flux

• Nobs=2; Nbg=0.5+0.5-0.3

• Upper bounds on the diffuse flux of astrophysical neutrinos (at 90% CL) for different assumed spectras:

• Limit on tau neutrinos 25 - 30 % worse than for electron neutrinos

• Glashow resonance at 6.3 PeV

results in differential e limit

[]

=3.0,2.5,2.0,1.5,1.0

29.7.2003 M. Kowalski

[Comparision with other Limits

and Models

Model e e

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 p(96)

4.7 2.4

MPR (98) 9.8 4.8

units: model rejection factor

* assuming a flavor ratio 1:1:1

SS

DS

MPR

Preliminary (2000 data)

[

[

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Conclusions

Cascades interacting within AMANDA can be reconstructed with a resolutions:

x,y,z=5 m, =30o- 40o and logE=0.1-0.2

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.

Example:e @ 1 PeV

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29.7.2003 M. Kowalski

The AMANDA detectorThe AMANDA detectorat the South Poleat the South Pole

• 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

• Detector deployed ~2 km deep into Antarctic ice

29.7.2003 M. Kowalski

First Level Cascade Filter

Late hits (but causal)

Direct hits: c (ti-200 ns) < d < c ti

Early hits (non causal!): d > c ti

The discriminating variables are based on fast estimate of vertex position & time

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First Level Cascade Filter

Nearly/Nhits Ndirect

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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 (e)

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 %