Astrophysics working group - CERN March, 2004 Point source searches, Aart Heijboer 1 Point Source...

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


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


3 Reconstruction

bin 1

bin2 bin 3 bin 4 bin 5


4 Reconstruction II

more understandable likelihood functions~10% increase in pointing accuracy

standardAartStrategy

with improvedlikelihood functions


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


6 Event selection

Final selection based on single variable

likelihood from reconstruction

Nhits-5number tracks compatiblewith the preferred one.


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 :-(


8

6800 events/day with good

resolution

Well reconstructed Atmospheric muons

same criteriaas before, butnow reconstructedas upward-going


9 Point source searching

3650 atmospheric neutrino events per year

oscillations: 3% effect after selection neglected.


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


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.


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


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


14 Full sky discovery potential

Same quantity, now convertedto the neutrino flux neededfor a 50% discovery prob.


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


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


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


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.


19 Comparison

now: data from '97

2009

2001

90% CL averageexclusion limit

discoverableat 5 s CL


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


21 Standard stuff


22

energy reconstruction strongly biased!

Standard stuff


23 Error estimates

2 2


24semi-analytical Binned method calculation


25

Astrophysics working group - CERN March, 2004 Point source searches, Aart Heijboer 1 Point Source...

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