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An Untriggered Search for High Energy Neutrinos From Gamma

Ray Bursts

Brennan Hughey

University of Wisconsin - Madison

April 11th, 2007

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• High Energy Neutrino Astronomy and AMANDA

• GRBs and GRB neutrinos

• Rolling Search for GRBs

• IceCube

Overview

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Questions High Energy Neutrino Astronomy Can Help Address

• Cosmic ray acceleration sites? Cosmic ray acceleration sites? – TeV gamma-ray sources? TeV gamma-ray sources? – Gamma-ray bursts? Gamma-ray bursts?

• ““GZK” cutoff? GZK” cutoff? • Dark matter? Supersymmetry?Dark matter? Supersymmetry?• What’s out there that we haven’t even What’s out there that we haven’t even

conceived of yet?conceived of yet?

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Photons can be absorbed byInterstellar matter

Charged particles are deflected by magnetic fields in space

Neutrinos interact only through theweak force, and even then only rarelyThis makes them uniquely usefulastrophysical messengers(and makes them hard to see)

Neutrinos asAstrophysicalMessengers

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PMT noise: ~1 kHz

AMANDA-B10(inner core of AMANDA-II)

10 strings302 OMs

Data years: 1997-99

Optical Module

AMANDA-II19 strings677 OMs

Trigger rate: 80 HzData years: 2000+

The AMANDA Detector

AntarcticMuonAndNeutrinoDetectorArray

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Neutrino interacts with particle in ice

Secondary particles emit Cherenkov radiation which is detected by optical modules

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Dark sector

AMANDA

IceCube

Skiway

South Pole Station

South Pole

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High EnergyHigh EnergyNeutrino Telescope Neutrino Telescope

ProjectsProjects

NESTOR Pylos, Greece

BAIKAL Russia

DUMAND Hawaii

(cancelled 1995)

AMANDA, IceCube also ANITA, RICE, AURA Antarctica

NEMOCatania, Italy

ANTARESLa-Seyne-sur-Mer, France

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Measurements:

in-situ light sources

atmospheric muons

Dust Logger

Average optical ice parameters:

abs ~ 110 m @ 400 nmsca ~ 20 m @ 400 nm

Scattering Absorption

optical WATER parameters:

abs ~ 50 m @ 400 nmsca ~ 200 m @ 400 nm

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• Better Pointing Resolution

• Larger Effective Area

• Muon-neutrinoCC interactions

• Half-sky coverage

• Better Energy Resolution

• Better Background Rejection

• All Flavor Detection

• Full-sky coverage

Two Detection Channels

Muon Channel Cascade Channel

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Backgrounds Downgoing events from Atmosphere

Upgoing events through Earth

Atmospheric Muons- ~6 million events per day- Cascade events separated by topology - Muon events separated by direction

Atmospheric Neutrinos- ~103 events per year- Created by cosmic rays- penetrate Earth- Useful for calibration

While searching for Astrophysical Neutrinos AMANDA and IceCube must deal with two primary backgrounds:

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Significance map

AMANDA II data from 2000-2004 (1001 live days)

4282 from northern hemisphere

No significant excess observed

Highest excess: 17 events on a background of 5.8 events

Time scrambled Data

Search for neutrino clusters in the northern sky

-3-2

-1 0

1 2

3

-3-2

-1 0

1 2

3

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event selection optimized for both dN/dE ~ E-2 and E-3 spectra

sourcenr. of events

(5 years)

expectedbackground

(5 years)

flux upper limit 90%(E>10 GeV)

[10-8cm-2s-1]

Markarian 421 6 7.37 0.43

M87 6 6.08 0.50

1ES1959+650 5 4.77 0.78

SS433 4 6.14 0.27

Cygnus X-3 7 6.48 0.67

Cygnus X-1 8 7.01 0.76

Crab Nebula 10 6.74 1.01

3C273 8(1yr) 4.72(1yr) 0.99

No significant excess observed

Search for neutrinos from interesting sky spots

crab

Mk421Mk501

M87

Cyg-X3

1ES1959

Cyg-X1

SS433

3C273

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Diffuse LimitsSum of total neutrino fluxover full sky (or half sky inthe case of muon analyses)Individually unresolvable sources

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• Neutralino dark matter searches (WIMPs in sun or Earth)

• Supernova searches (rise in noise rates from MeV ’s• Ultra High Energy searches: focuses on area near

horizon searching >PeV events• Galactic plane analysis• Search for new physics (i.e. Lorentz invariance

violations) with atmospheric neutrino sample• Magnetic Monopoles• Cosmic ray composition (with SPASE array)• Gamma-ray astronomy with downgoing muons (SGR in

2004)• Studies of temperature variation using downgoing muons

Other AMANDA analyses

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• Discovered by military satellites in the 1960’s

• Occur isotropically, therefore extragalactic in origin

• Most violent, energetic explosions in known universe: at least 1051 ergs

• Observationally divided into two classes due to bimodal distribution

(although additional classes have been postulated)

• Duration measured by T90: time over which central 90% of gamma-ray flux occurs

Gamma Ray Bursts

Data from BATSE Catalog, 1991-2000

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- GRBs are very non-uniform- Rapid variability on the order of a few milliseconds

GRB Light Curves

Light curves from Swift satellite

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Central EngineRapid variability implies compact object

Central engine cannot be directly observed

Currently favored models:

Collapsar: massive star forming black hole Supported by evidence from satellites(e.g. GRB030329 and GRB060218)

Merger between two objects: Black Hole -Black Hole, Black Hole -Neutron Star, et cetera

Chandra X-ray image of NGC 6240

www.astro.ku.dk/dark

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Gamma Ray EmissionRegardless of central engine, GRBs are best described by the fireball shock model- Plasma of electrons, positrons, gamma rays rapidly expands until it becomes optically thin- Particles accelerated in collisions of mildly relativistic shock fronts

GRB believed to emit in jets rather than isotropically- Direct evidence from breaks in observed optical afterglow spectra- Reduces total energy requirement to a more believable level- Means we can only see GRBs that are on-axis

Ref: Peter Meszaros www.astro.psu.edu/users/nnp/grb.html

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Neutrinos from Gamma Ray Bursts

+ p → + → + → + + → e+ + e + +

p-p interactions also possible in certain mechanisms, resulting in equal ratioof neutrinos and antineutrinos

e:: flavor ratio is thus 1:2:0 at source

After oscillations, ratio becomes 1:1:1 at Earth(although neutrino to antineutrino ratio is not the same for each flavor)

Flavor ratio at source becomes 0:1:0 at very high energies (>PeV)due to energy losses in +Resulting flavor ratio at Earth becomes 1:1.8:1.8

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90)10ln(8 T

fFA

e

)1(2.0

,2,4

5.2

52,

zt

Lf

bMeVv

6/1,

12,52, )]1([276 ztL b

MeVv

GeVz b

MeV

b

,

25.2

2

5

)1(

107

GeVtLz vBe

b

2,

45.2

2/152,

2/12/18

)()1(

10

Prompt Emission: Collapsar ModelNeutrino spectrum can be extrapolated from observed gamma-ray spectrum Band function fit

ssb

sbb

bb

EEE

EE

EE

AdE

dNE

for )/()/(

for )/(

for )/(

2-1

1

1

2

0

0

)(

100

100

)(

100

)(

0

E

EKeV

Ee

KeV

EA

EeKeV

EA

EN b

b

bE

E

Gamma-Ray Spectrum Neutrino Spectrum

Sample burst: GRB020813

HETE data

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Prompt Emission: Diffuse Flux Limits

Waxman-Bahcall limit obtained for “diffuse” flux of GRB neutrinos using typicalburst parameters – assumed as signal spectrum in rolling analysis as well as most triggered GRBsearches conducted with AMANDA[E. Waxman and J. Bahcall, Phys. Rev. Lett. 80, 3690 1997.]

Murase and Nagataki Model Ayields a similar spectrum from somewhat different assumptions[K. Murase and S. Nagataki, Physical Review D 73, 063 2002.]

Supranova Model neutrinos result if a massive supernova precedesthe burst by ~1 week, creatinga field of matter with which theGRB jet interacts. This modelis currently strongly disfavored due to observations by the Swift satellite [S. Razzaque, P. Meszaros and E. Waxman Phys. Rev. Lett. 90, 1103 2003.]

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Additional Diffuse Flux LimitsPrecursor neutrinos: produced by the GRB jet while it is still within the stellarprogenitor ~10-100 seconds before the burst. Choked bursts, which have no prompt gamma or neutrino emission but canstill produce the equivalent of precursor neutrinos, could outnumber conventionalGRBs by as much as a factor of 100[E. Waxman and J. Bahcall, Astrophysics Journal 541, 707-711 2000.]

Afterglow neutrinos: occur Through interactions of the GRB jet with interstellar matter around the burst.[S. Razzaque, P. Meszaros and E. Waxman Physical Review D, 68, 083001 2003.]

Thermal neutrinos (not shown)are emitted isotropically at anearlier stage of burst formation.They are in the MeV range andnot likely to be detectable outside of our own galaxy.

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10 min

Blinded Window

-1 hour +1 hour

Triggered AMANDA GRB Searches

Background is measured off-time at location of burst

10 minute window is kept blinded, but time examined for neutrino signalis T90+U90+1s.

Searches performed in coincidence with 312 BATSE and 91 IPN burstswith muon channel

73 burst search performed with cascade channel (year 2000)

Precursor search performed for 2000-2003

No on-source on-time events observed so far

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Rolling Search MethodThe rolling search method uses a rolling window to search for a statistically significant cluster of events which still remain after all data selection criteria have been applied.

Disadvantages:-Less sensitive due to increased backgound-Cluster analysis rather thancounting analysis

Advantages:- Can identify bursts missed by gamma-ray satellites- Can potentially identify flux from hidden sources and un-modeled transients- Will not miss neutrino flux if there is an offset relative to prompt emission

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

BATSE

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• 2 time windows: 1 and 100 seconds• Uses cascade channel

Rolling Search

Color indicates time of hit (red earliest, violet latest)

Diameter of circle proportional to intensity

Fits performed on each event in analysis: - “direct walk” muon first guess- “Center of gravity” cascade first guess- Maximum Likelihood reconstructions formuons and cascades

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Data Reduction

1. High energy filter removes events with fewer than 160 hit optical modules and events with less than 72% of hit opticalmodules having two or more hits

2. Flare checking cuts, which Remove “unphysical” events

3. Cut on “number of direct hits” variable

4. Six variable support vector machine cut

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Flare Checking Plots

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Cut Variables

Real Data Simulated Signal Simulated Background

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Final CutFinal cut is determined by Support Vector Machine:

Support Vector Machine finds optimal cut in multidimensional cut space created by six input variables

Operates by using a mathematical kernelfunction to translate six-dimensionalphase space of variables into higherdimensional space where cut is a linearfunction of variables

Support vector machine is trained with5 days of real data as background andANIS computer simulation weighted tobroken power law as signal

Tighter or looser cuts can be obtained byadjusting a variable called the cost factor

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OptimizationOptimization of analysis performed using Monte Carlo simulation of entire 3-yearensemble of bursts (1240 bursts based on BATSE rate and adjusting for livetime)

Analysis optimized for Nlarge, the largest number of events observed in any time window throughout the year

Account for variations in event rate due to distance from Earth, overall fluence,spectral shape, Earth shadowing effect, et cetera using predictions from actualbursts

When looking for an event cluster,one strong source is better than multipleweaker ones

Two time windows (1 and 100 seconds)optimized separately Predicted events for real bursts from BATSE catalog

Astro-ph/0302524 http://www.arcetri.astro.it/~dafne/grb/

>82 2

2 2

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OptimizationTwo methods of selecting optimal supportvector machine cut:

Model Discovery Potential: Finds cut suchThat one has a 90% chance of observing asignal at a 5 sigma confidence level.

Model Rejection Potential: Finds cut suchthat, in the absence of an observed signal,the best possible 90% confidence level limits can be placed on the astrophysical neutrino flux

This analysis was optimized for discovery, but this is not too far from the best choice under limit-optimization

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Data Stability

Data is consistent with Poissonian hypothesis and shows consistentrates throughout year

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ResultsNlarge for the 100 second window was 3, Nlarge for the 1 second window was 2.

Number Observed

Number Expected

2 event windows in short burst search

311 313±18

2 event windows in long burst search

1000 1016±32

3 event windows in long burst search

20 21.6±4.8

Additionally, the distributionof bins with 2 or 3 eventsIs consistent with simulationsAssuming Poissonian background

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Limit CalculationsLimits constructed using Feldman Cousins method (90% confidence level)

90% confidence belts constructedfor each discrete signal flux

Ordering principle is likelihood ratioL(Nlarge at this flux)/L(maximum probability at any flux)

Flux upper limits read off for eachvalue of Nlarge

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50% for ice properties:Modeled clear, average and dusty ice and took spread as uncertainty (conservative approach and worse for cascades than muons) 20% for other modeling: Distribution of events among various bursts is model-dependent 5% for neutrino cross section

Uncertainties incorporated as nuisance parameters Each treated as separate flat error, numerator in likelihood ratio integrated overPDF of possible range of real signal strengthsIn practice this is done numerically as part of the monte carlo simulation

Systematic Uncertainties

)ˆ,,ˆ|(

'),ˆ|'()',,|(

sbs

ssssbs

nL

dPnLR s

Conrad, Botner, Hallgren and Perez del Los Heros (hep-ex/0202013) and Hill (physics/0302057)

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LimitsLimits were derived using the Feldman Cousins maximum likelihood ratio ordering method, with systematic uncertainties included as nuisance parameters

Limits shown for central 90% Energy ranges. Limits for various Models are shown for the rolling search and triggered cascade analysis

Waxman-Bahcall Spectrum (W03)Murase-Nagataki (MN06)Precursor/choked burst (MW01)Supranova (R03b)

Solid black lines – rolling searchDashed black lines – triggeredcascade search (2000)

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Back of the Envelope Sensitivity Check

90% chance of seeing signal = 10% chance of not seeing signalWith ~425 bursts during livetime, this means an average of .9946probability of not seeing each burst.

5 or more events from a burst would exceed the90% sensitivity bound, so the probability of notseeing each burst means four or fewer events

~1.1 events per burst~734 events per year

Scaling between predicted number of eventsFrom reference WB flux, we obtain the flux to which we are sensitive

Correcting for detector deadtime, we get the original predictionof 1.3 X 10-5 GeV/cm2ssr

Taking the simplified assumption of a flat distribution wherein all burstsare equal and the 2001 data subsample our algorithm yields a Sensitivity of 1.3 X 10-5 GeV/cm2ssr

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Effective Area

Spike at 6.3 PeVIs due to GlashowResonance (antineutrino-electron interaction)

Earth is not opaqueto high energy tauneutrinos due totau regeneration

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Expected Energy Distribution

Folding effective area with predictedspectrum gives distribution of expectedenergies. This is shown for WaxmanBahcall spectrum (above) andatmospheric neutrino spectrum (right)All plots have arbitrary normalization

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Sphere of Sensitivity

Other way to look at limit:

Distance at which burst couldbe observed given certainassumptions

(e.g. bulk Lorentz factor of burst normalized to ~300, ΛCDMcosmology assumed)

Closest observed redshift so faris z~.009, although this was ananomalous burst

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The Future

Current analysis results of both cascade channel GRBsearches to be published in July 2007 Astrophysical Journal

Rolling search can be extended to muon channel,possibly taking advantage of point source search datasets

Coincidence studies with other detectors – neutrinos, gamma-rays, gravitational waves?

Extension to other sources – mildly relativistic supernova

Substantially improved limits with IceCubeOrder of magnitude improvement with little effortImproved background rejection techniques shouldbring much greater improvements

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IceTop

InIce

Air shower detector

Threshold ~ 300 TeV

planned 80 strings of

60 optical modules

17m between modules

125m string separation

1km3 instrumented

volume

2004-2005 : 1 string

2005-2006: 8 strings

AMANDA

19 strings

677 modules

Completion by 2011

2006-2007:

13 strings deployed

IceCube

First data in 2005first upgoing muon: July 18, 2005

Altogether: 22 strings52 surface tanks

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signature signature

1013 eV (10 TeV)~90 hits

6x1015 eV (6 PeV)~1000 hits

Multi-PeV

+N+...

± (300 m!)

+hadrons

AMANDAAMANDA

Event Signatures in IceCube

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Hose reel Drill tower

IceTop tanks

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Drilling and Deployment

47/52Photomultiplier tubePhotomultiplier tube Mu metal magnetic shieldMu metal magnetic shield Glass sphereGlass sphere

Active PMT baseActive PMT base

MainboardMainboard

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Digital Optical Module Testing

Each DOM taken through extensive battery of tests

Every test run at sequence of temperatures: +25 C, -45 C, -20 C, +25 C, -45 C(-55 C runs included for IceTop DOMs since temperatures will be lower onthe surface than in deep ice)

Tests run over period over ~3 weeks in batches of 60 DOMs each

Tests include- Optical Sensitivity tests- Time resolution - Local coincidence chain testing - Long term spike monitoring- High gain monitoring- Various mainboard performance tests- Reboot tests

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Predicted 15-year DOM survival rate

0

10

20

30

4050

60

70

80

90

100

Feb-05 May-05 Sep-05 Dec-05 Mar-06 Jul-06 Oct-06 Jan-07

Date (month-year)

Su

rviv

al R

ate

(%)

Mean time between failures ~= 2 million DOM hours

76 DOMs 589 DOMs

39-22 “Liljeholmen” stops

communicating properly

30-60 “Rowan” stops communicating

properly

Plot credit: Mark Krasberg

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GRB Triggered Analysis

Scenario Events/

Burst

Flat Model

1 Event

Realistic

1 Event

Flat Model

3 events

Real Model

3 events

Muon

Predicted

0.006 407 419 984 983

Muon

WB bound

0.04 67 61 148 158

Cascades

Predicted

0.002 1220 1231 2957 2945

Cascades

WB bound

0.01 244 255 592 590

1) Could take several years to observe GRB (or we could get lucky)2) Not much difference between assuming bursts are all equivalent andmodeling realistic distribution (although difference is statistically significant)

Number of bursts required (90% C.L.)

Note that bursts which can be studied by cascade channel occur at 2X rate

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ConclusionsAMANDA is currently the most sensitive high energy neutrino physics experimentand will continue to operate as a lower energy sub-array within IceCube

The rolling search method adds another approach to the search for astrophysicalneutrinos which complements previous strategies

IceCube will produce dramatically improved limits relative to AMANDA analysesand stands to be high energy neutrino astrophysics’ first discovery instrument

The End

Acknowledgements: I would like to thank the whole IceCube collaboration forsupport: Albrecht Karle, Kael Hanson, Ignacio Taboada, Francis Halzen, Gary Hill, Mike Stamatikos, Teresa Montaruli and many others

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Backup Slides

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Murase Nagataki flux

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Flavor Ratio

____ Predicted flavor ratio- - - - 90% C.L. for

........ 90% C.L. for

E0, is energy at whichcooling time is equal todecay time (~1 PeV)

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SPASE/AMANDA

12°

SPASE

AMANDA

x=-114.67my=-346.12mz=1727.91m

South Pole Air Shower ExperimentUses surface air shower array in coincidence with AMANDA as a muon detector in order to determine Composition and energy of cosmic rays

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Bursts of low-energy (MeV) νe from SN simultaneous increase of all PMT count rates (~10s)

Since 2003: AMANDA supernova system

includes all AMANDA-II channels

Recent online analysis software upgrades– can detect 90% of SN within 9.4 kpc

Part of SuperNova Early Warning System (with Super-K, SNO, LVD, …)

AMANDA-II

AMANDA-B10

IceCube30 kpc

Supernova Search

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Neutralino-induced neutrinos

qq

l+l-

W, Z, H

“down”

“up”Searches for WIMPS with

AMANDA

Weakly Interacting Massive Particles - Leading dark matter candidate- Collect in center of sun and Earth- May produce > 10 GeV neutrinos throughWIMP-antiWIMP annihilation

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Limits on muon flux from Earth Limits on muon flux from Sun

Solar and Earth WIMP Limits

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Diffuse Analyses

Sum of total neutrino fluxover full sky (or half sky inthe case of muon analyses)Individually unresolvable sources

Best available limit from 2000-2003 muon neutrino analysis

Final energy-related cut shown on right