TeV Particle Astrophysics 2009Stanford Linear Accelerator

Laboratory

Sean GrullonFor the IceCube Collaboration

Searching for High Energy Diffuse Astrophysical Neutrinos with

IceCube

Sean Grullon – TeVPA 2009 2

Overview

• Astrophysical Neutrinos & Searching for a Diffuse Flux of Muon Neutrinos

• Muon Energy Estimation• 22 String Diffuse Analysis Results• Outlook for 40 Strings• Questions & Discussion

Sean Grullon – TeVPA 2009 3

Neutrinos as Cosmic Messengers

Neutrinos help answer many questions in astrophysics:

•What are the sources of highest energy cosmic rays? Are there pp and p interactions at the source?

•Can neutrino production be linked to TeV sources, GRBs, AGN?

• Can a superposition of faint neutrino sources cause a detectable signal?

Sean Grullon – TeVPA 2009 4

IceTop

InIce

Air shower detector

threshold ~ 300 TeV

80-86 Strings,

60 Optical Modules per

String

2004-2005 : 1 String

2005-2006: 8 Strings

AMANDA

19 Strings

677 Modules

first data 2005upgoing muon 18. July 2005

2006-2007:

13 Strings

2007-2008:18 Strings

Sean Grullon – TeVPA 2009 5

Astrophysical (signal)

Atmospheric

Atmospheric

Cosmic ray

Sean Grullon – TeVPA 2009 6

Downgoing Muon Rejection

• Apply quality cuts on Data, Corsika MC, and Atmospheric Neutrino MC

Sean Grullon – TeVPA 2009 8

Diffuse Analysis Strategy

• Find an excess of astrophysical neutrinos (E-2) over atmospheric neutrinos (E-3.7) at the high-energy tail of an energy distribution

Sean Grullon – TeVPA 2009 9

Energy Estimation

•Convert what is measured, Cherenkov light, to an estimate of the Muon energy.

•Simplest estimation: Number of Triggered Optical Modules (NCh)

•More Sophisticated: Muon Energy Loss (dE/dX)

e+e-

pair-creation

bremsstrahlung

photo-nuclear

Sean Grullon – TeVPA 2009 10

Reconstructing The Muon energy loss

Approximate as:

loglog}){|}({log1

NnnPk

iiiii

dust

ycl

ean

deep

shallow

Incorporate Ice Properties:

Formulate LLH:

Sean Grullon – TeVPA 2009 11

Muon Energy Correlation – 40 Strings

•dE/dX reco more linearly correlated with Muon energy

dE/dX Reco NChannel

Sean Grullon – TeVPA 2009 12

Energy Resolution – 40 Strings

Width 0.27

Width 0.43

•dE/dX reco has narrower energy resolution

Sean Grullon – TeVPA 2009 13

Energy Resolution as a Function of Muon Energy – 40 Strings

Sean Grullon – TeVPA 2009 14

The dE/dX distribution of IC22 275.7 days LiveTime

Keep

•Energy Cut > 1.4

•Background above cut = 4.1 Events

•Observed Data above cut = 4.0 Events

• Sensitivity: 2.5 x10-7

GeV cm-2 s-1 sr-1

•Find cut that minimizes average upper limit

Sean Grullon – TeVPA 2009 15

The dE/dX distribution of IC40 300 days LiveTime - MC Only

Sean Grullon – TeVPA 2009 16

Likelihood Analysis Method

• Likelihood - product over bin-by-bin Poisson probabilities:

i

i

en

nPLk

i i

ni

ii

1 !}){|}({

ieipici eNpNcN

Events observed in bin iEvents expected in bin i

Conventional Atmospheric ν Astrophysical ν Prompt ν

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Fitting Example: 1 Year IC40 - No Astrophysical or Prompt ν

•“Data” Poisson sampled from 1 year of Atm. ν MC

Sean Grullon – TeVPA 2009 18

Allowed Regions, No Astrophysical or Prompt ν : 1 Year of IC40

Preliminary IC40 Diffuse Sensitivity:

E2 < 1.1 x 10-8 GeV cm-2 s-1 sr-1

No Systematics included

Sean Grullon – TeVPA 2009 19

Models & Limits

IC22

IC40

WB

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Summary

• A reliable log-likelihood reconstruction of the muon energy loss is now available for IceCube analyses.

• The IC22 sensitivity is E2 < 2.5 x 10-8 GeV cm-2

s-1 sr-1 above a dE/dX cut of log10(dE/dX) >= 1.4• 275.7 days of IC22 data were analyzed and

compared with the Bartol + naumov RQPM atmospheric neutrino simulation. No data excess over the atmospheric neutrino prediction observed above the dE/dX cut.

• The IC40 analysis uses a likelihood method giving a preliminary sensitivity of E2 < 1.1 x 10-8 GeV cm-2 s-1 sr-1 and the incorporation of systematic errors is currently underway.

Sean Grullon – TeVPA 2009 22

Backup slides

Sean Grullon – TeVPA 2009 24

Systematics – IC22

• Observed data exceeds MC by a factor of 2 in deep ice

• Deep Ice 40% clearer.

AMANDAdepth

New from IceCube

Data Atms. Nu MC

SingleMu

Coinc. Mu

Sean Grullon – TeVPA 2009 25

Data Atms. Nu MC

Systematic Test (low energy, NCh<50)C

OG

Z

CO

GZ

Data - MC

upgoing cos(zenith) horizon upgoing cos(zenith) horizon

C

OG

Z

• Data excess is observed even with the low energy events(conventional atmospheric neutrinos)

• Divide the detector in 2 depths : upper half and lower half

Sean Grullon – TeVPA 2009 26

Systematic Test

EstimatorEnergy

cut

Sensitivity

x 10-7

Bartol+Naumov

RQPM

1e-7 E-

2

MCdata

log10(dEdX)

>=0.97

0.50 7.9 12.2 5

NCh >=68 0.41 7.9 15.0 3log10(NPe

)>=2.8

50.54 8.0 11.3 5

Upper Half

Lower Half

EstimatorEnergy

cut

Sensitivity

x 10-7

Bartol+Naumov

RQPM

1e-7 E-

2

MCdata

log10(dEdX)

>=0.91

0.58 15.5 14.0 14

NCh >=80 0.47 12.8 15.7 25log10(NPe

)>=3.1

50.64 2.4 6.4 4

Sean Grullon – TeVPA 2009 28

Sensitivities: Likelihood Method Extraterrestrial Only

Energy Estimator MRF Limit

MCν 0.04 4* 10-9

MCμ 0.066 6.6* 10-9

Photorec 0.101 1.01* 10-8

MuE 0.122 1.22* 10-8

NChan 0.125 1.25* 10-8

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Fitting Example: No Signal

Sean Grullon – TeVPA 2009 30

Fitting Example: No Signal

Sean Grullon – TeVPA 2009 31

Allowed Signal and Prompt Regions

Sean Grullon – TeVPA 2009 34

Fitting Example: Signal + Prompt + Conventional Atmospheric Neutrinos

“Data” sampled from Atm Nu background

Sean Grullon – TeVPA 2009 35

Allowed Extraterrestrial and Prompt Regions