Upload
gary-kelly
View
221
Download
1
Embed Size (px)
Citation preview
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
1 Point Source Searches with ANTARES
Outline: reconstruction news event selection likelihood ratio method results
full sky searchFixed point search
comparison
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
2
old functional form
Distribution ofresiduals of signalhits must be parameterised
new functional form
simple functions for peak and tail connected by a polynomial (spline)
(unrelated) bug fixed in bg normalisationworks, but complicated
Reconstruction
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
3 Reconstruction
bin 1
bin2 bin 3 bin 4 bin 5
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
4 Reconstruction II
more understandable likelihood functions~10% increase in pointing accuracy
standardAartStrategy
with improvedlikelihood functions
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
5 Signal & background samples
(94% efficient for En-2 signal events with an error < 1o)
Neutrinos:GENHEN (using MUSIC + QTEQ6GEASIM+KM3
Atmospheric Muons: 2 existing productions:HEMAS: 8 hours of minimum bias eventsHEMAS: 7.4 days of high Eprimary multi-muons
pre-selection:reconstructed muon should be upward-goingenergy must be reconstructed (using Alain Romeyer's algorithm, without the quality cuts)estimated angular error must be < 1o
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
6 Event selection
Final selection based on single variable
likelihood from reconstruction
Nhits-5number tracks compatiblewith the preferred one.
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
7 Event selection
Select events with L>5.3:~1 atmospheric muon/day (neglected in the analysis)10.0 atmospheric neutrinos /day (Bartol+RPQM)74% efficient for En
-2 signal events with an error < 1o
Contribution of mis-reconstructed atm.muons must be estimated fromextrapolation :-(
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
8
6800 events/day with good
resolution
Well reconstructed Atmospheric muons
same criteriaas before, butnow reconstructedas upward-going
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
9 Point source searching
3650 atmospheric neutrino events per year
oscillations: 3% effect after selection neglected.
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
10
flux magnitude
point spread functionknowledge of energy reconstructiondetector acceptance
source position flux spectral index
knowledge of detector
(unknown) parameters of the source
likelihood if there is signal+bg
likelihood for bg-only
likelihood is expressed as a sum over the events
As discriminating variable, we use the likelihood ratio:
Likelihood ratio method
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
11 Likelihood ratio method
background like
signal like
algorithm:find clusters of events (large cluster sizeensures we find al candidate clusters)fit source parameters for each clustercalculate likelihood ratio for each clustertest statistic l is the likelihood ratio of the 'best candidate'
For a 1-year sample, ~70 clustersare found. Each cluster takes ~3sGHz.to fit source parameters and calculatelikelihood ratio. 5x104 1-year bg-only samples have been analysed.
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
12
Discovery: finding a cluster that is so signal-like that the probability for the background to produce it is very small (i.e. 2.7´10-3/ 5.7´10-7, for 3/5 s)
Examples
Three rare examples of 'best candiate' clusters:
signal eventbackground event
true source positionfitted source position
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
13 Full sky discovery potential
1 year of data-taking 2-years of data taking
Numbers have changed since previous presentations, due to increasedbackground. Conclusion still valid: improvement over binned method
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
14 Full sky discovery potential
Same quantity, now convertedto the neutrino flux neededfor a 50% discovery prob.
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
15 Fitted source position
As an extra, we get a ML estimate of the source position
6 events seen from source
single-evt resolution/ÖNs
For pinpointing a source, ANTARES has a resolution < 0.1o !
En-2 spectrum
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
16 Fixed point searches
Suppose we have a number of candidate sourcescan reduce the 'trial factor' by not looking at the full skycan put exact source coordinates in likelihood, in steadof the ML estimates
new
1 2 3 4 5 6 sig. evtssources chosenuniform in the sky
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
17 Fixed point: discovery potential
1 candidate10 candidates100 candidates
Improvement over binnedmethod smaller than incase of full-sky search:due to larger binning efficiency
roughly:one extra signal eventneeded for every factor 10in the number of candidates
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
18 Fixed point: Upper limit
This is the kind of limit that is usually presented by other experiments!
If we look at only a single candidate source, we can derivean upper limit for the flux from that particular source.
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
19 Comparison
now: data from '97
2009
2001
90% CL averageexclusion limit
discoverableat 5 s CL
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
20 End
Reconstruction PDF updatednew selection, low contamination from atm. muonFull sky & fixed point discovery potentials and limitsSoftware will be public... beforethesis defence: June 8
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
21 Standard stuff
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
22
energy reconstruction strongly biased!
Standard stuff
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
23 Error estimates
2 2
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
24semi-analytical Binned method calculation
astrophysics working group - CERN March, 2004Point source searches, Aart Heijboer
25