Towards a common skymap based
on Antares & IceCube data
J. Brunner
24/09/2011
1
Reminder
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Proposed at MANTS 2010
Agreed test sets:
• IC22
• IC22 UHE
• Antares 2007/2008
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Unblinded data provided recently
(August 2011, Chad & Aart)
• individual analyses published
2
Data taking periods & analysis
samples
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ANTARES: analysis on 2007/2008 data
IceCube: IC22, IC22-UHE
Good overlap
144 days
740 ev S
60% 
151 days
1350 ev S
60% 
ANT-5
ANT-10-12
2007
R. Lauer
ANT-07-10
2008
IC22
Ch. Finley
A. Heijboer, C. Bogazzi
276 days
5114 ev N
785 ev S
2009
IC40
375 days
14121 ev N
22778 ev S
IC59
Problem
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Impressive analysis speed for both ANTARES &
IceCube
• Antares : 2007-2010 analysis released
• IceCube : IC40, IC59 ready
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Old data sets are not anymore competitive, even
when combined
Ch. Finley
4
What can we learn anyway ?
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Compare analysis methods
• Likelihood definitions
• Limit setting methods
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Reproduce individual results
Propose common interfaces for
possible future combined analysis
5
Normalization and differences
Important to distinguish Integral over full sky versus Integral over
Vicinity of source to build likelihood (here 5 degrees)
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Int4(F)=1
Int4(Bi)=Ntot
Ntot =Total number of
observed events in full
sky
Signal events are
added on top of Ntot
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Int5º(Si)=1
Int5º(Bi)=1 (Bi = cons)
N = total number of
observed events
inside search window
Signal events are a
fraction of N
7
Combining Samples
(Antares method)
log Ls b   log  sig rj  F j  ij  s ,  s   Bij   sig
j
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i
Add sum of j samples
Each event knows from which sample it comes
(indices ij)
Each sample has its own background PDF Bj
Each sample has its own PSF ßj
But only one sig can be fitted
Relative contributions of samples to signal
controlled by rj for each 
 r    1
j
j
8
Signal events
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Unified in bins of 10 degrees
Event per declination per reference flux
Used for signal simulation and rj
calculation
ANT07
ANT08
IC22-UHE
IC22
ALL
10
Signal events
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Fraction of events per declination band
Northern hemisphere: IC22 contributes more
than 95%
DEC<-50º: only ANTARES
-50º -0º: ok
ANT07
ANT08
IC22-UHE
IC22
Declination range where both experiments contribute more than1110%
Chance to get events from both samples close to source
Code development
Signal histos
Background
histos
PSF
histos
Small root files
Command line
Test experiments
Root executable
Fit within 5º from source
No graphics
Runs in batch mode
107 TE for BG-only
106 otherwise
Root Tree
TS,LH(S+B),LH(B),sig
Sensitivity
Discovery power
Filenames
NEXP
Nsig
Ra,Dec
Small Root Macros
Graphics output
Interactive
Flux limits
12
Example sky maps
Point source with 20 events included
IC22
IC22-UHE
ANT-2007
ANT2008
Declinationion
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Rectascension
14
Example sky maps
Point source with 20 events included
IC22
IC22-UHE
ANT-2007
ANT2008
Declinationion
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Rectascension
15
Example sky maps
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Point source with 20 events included
Reasonable mixture of both sets
IC22
IC22-UHE
ANT-2007
ANT2008
Declinationion
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Rectascension
16
Examples for TestStatistics
• DEC=-35º
 More pronounced change in TS of
Antares
0 2 4
6
8 signal events
ANTARES
0 2 4 6 8 signal events
IceCube
19
Sensitivity versus actual limits
ANTARES
Sensitivity is average of actual limit points
50% of points above, 50% below
IceCube
Sensitivity coincides with best limits
i.e. those which are most BG-like
Difference in treatment of TS=0 peak for bg-only test experiments
25
IceCube: minimal p-value 0.5 if TS=0
Antares: exploit tiny fluctuations around zero
Fluctuations around TS=0
BG-only TS
log(TS+0.001)
A. Heijboer
My analysis:
Same procedure but spread
introduced “by hand”
(random number)
TS=0
BG-only TS
Compare methods
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Compare limit setting methods
• Neyman
• CLs
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Compare TS=0 treatment difference
• Choose random value in Q1 when TS=0
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-3<Q1<-2
• Choose Fixed value at 50%/50%
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Q1=-2.5
Look at 90% C.L. event number limits
27
Comparison of limit setting methods
DEC=+35º
CLs method
Median=5.8
DEC=+35º
Neyman
Median=3.8
DEC=-35º
Neyman
Median=2.7
Neyman
2.0
DEC=-70º
Antares
When TS=0
Choose a
random
number
-3<Q1<-2
F&C
2.4
DEC=-35º
CLs method
Median=3.8
CLs
2.8
28
A. Heijboer
Comparison of limit setting methods
DEC=+35º
CLs method
Median=5.8
DEC=+35º
Neyman
Median=3.1
When TS=0
use
Q1<-2.5
DEC=-35º
Neyman
Median=2.2
Neyman
2.0
DEC=-70º
Antares
DEC=-35º
CLs method
Median=3.8
F&C
2.4
CLs
2.8
29
A. Heijboer
ANTARES 2007-2008
Present analysis
Good agreement for overfluctuating
Sky points, difference for TS=0
Results : Combined analysis
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Real skymap
IC22
IC22-UHE
ANT07/08
Discovery potential & Sensitivity
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Reproduce Antares & IC22 where one
experiment dominates
Coherent limit for whole sky
Factor 2 gain for specific declinations
5 sigma discovery
90% C.L. sensitivity
Combined
IC22
Antares
CLs method used here
33
Selected source list
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Start with source lists as specified in
Antares & IceCube papers
Recalculate individual flux limits
Compare to combined flux limits
34
Results : selected source lists
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Important improvement for limits on
Southern hemisphere when combining
samples
Marginal effect on Northern hemisphere
ANTARES source list
ANTARES
ANT & IC22-UHE
IC22 & IC22-UHE source list
IC22
ANT & IC22(UHE)
Fullsky search
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Clustering
• Individual set
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at least 4 events within 3 degrees
• Combining sets
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At least one 1 per set within 3 degrees
Fit
• 3 parameters within 5-10 degrees
36
Fullsky search - South
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ANTARES
Event within 3 degrees: 5
Ra 43.18 Dec -0.56
Signal events 3.4 Lambda 8.1
Confirmed from Antares Paper
Ra 43.21 Dec -0.50
Signal events 3.4 Lambda 6.8
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Combined
Event within 3 degrees:
4 Ant + 4 IC22-UHE
Ra 187.72 Dec -3.63
Signal events 4.6 Lambda 8.0
Find new cluster !
Compatible with background
Fullsky search - North
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IC22
Event within 3 degrees: 14
Ra 191.27 Dec 18.79
Signal events 9.5 Lambda 6.4
Different from IC22 Paper
Ra 153.4 Dec 11.4
Signal events 7.7 gamma -1.65
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Combined
Event within 3 degrees:
1 Ant + 14 IC22
Ra 191.27 Dec 18.79
Signal events 9.5 Lambda 6.2
Find same cluster !
Compatible with background
ANTARES versus IC40
differential sensitivities
Half decade bins
5 sigma discovery potential
Dashed: IceCube , Full: ANTARES
41
ANTARES versus IC40
Southern hemisphere only
Half decade bins
5 sigma discovery potential
Dashed: IceCube , Full: ANTARES
42
Summary
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Northern hemisphere
• Only marginal impact of ANTARES
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Southern hemisphere
• Interesting efficiency gain
• Improved limits
• Enhanced potential for fluxes softer
than E^-2
43
Next steps
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Wait for stable results from individual
experiments
• ANTARES 2007-201
• IceCube IC40,59,79,86 (?)
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Use public event by event data
• Already available for IC40 diffuse set
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Look at transient phenomena
44
Public Data