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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
Sean Grullon – TeVPA 2009 17
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
Sean Grullon – TeVPA 2009 21
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
Sean Grullon – TeVPA 2009 29
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