neutrino point source search strategies for amanda-ii and results from 2005
DESCRIPTION
Neutrino Point Source Search Strategies for AMANDA-II and Results from 2005. J. Braun, A. Karle, T. Montaruli. For the IceCube Collaboration. Motivation. No extraterrestrial high energy neutrino source yet observed Need larger detectors and more sophisticated analysis methods - PowerPoint PPT PresentationTRANSCRIPT
Neutrino Point Source Search Strategies for AMANDA-II and Results from 2005
J. Braun, A. Karle, T. Montaruli
For the IceCubeCollaboration
ICRC 2007 2005 Neutrino Point Source Search with AMANDA-II 2
Motivation
• No extraterrestrial high energy neutrino source yet observed– Need larger detectors and more sophisticated
analysis methods
• Current searches: Use event direction (time)
• Construct a search to fully utilize– Event energy estimation– Event direction– Detector angular resolution
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• Model the detector point spread function as a 2D Gaussian
Method
• Energy correlated observable: Number of hit channels
• For each event at position xi, assign a probability of belonging to a source at xo
with spectral index
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• A ±5o declination band centered on the source location contains N total events and is modeled as a mixture of signal and background in a likelihood function:
• The Background PDF Bi depends on• Minimize –log(L) with respect to number of signal events and spectral index• Significance is measured by the ratio of best likelihood and background-only likelihood:
Method
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Discovery Potential
90% of sources with the given E-2 flux are detectedat 5 (3) significance
90% Chance of Discovery
35% less events requiredfor 5 detection at = 42.5o
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Sensitivity
90% confidence level sensitivity to E-2 spectra
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Results for 2005
• 1.8 billion raw events recorded in 2005
• 6001 events survive quality cuts, 887 above = 10o
• Search in range -5o < < 82o
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2005 All-Sky Results
69 out of 100 sky maps randomized in RA contain an excess of at least 3.6
Largest Excess: 3.6=48o , =2.75h
Log10(p-value)
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Results for Candidate Sources
Object RAo Dec.o P-value 90
Mrk 421 166.1 38.2 ~1 5.9
Mrk 501 253.5 39.8 0.184 18.1
Cyg. X-1 299.6 35.2 0.414 12.9
Cyg. X-3 308.1 41.0 0.458 11.0
NGC 1275 50.0 41.5 0.064 22.4
Crab 83.6 22.0 ~1 9.24
MGRO J2109+37 304.8 36.8 0.152 20.1
E2 < 90.10-11 TeV cm-2 s-1
• The method is applied separately to a list of 26 candidate sources to enhance discovery potential
• No striking excesses found
• Most significant source is NGC 1275 (Perseus A), p = 0.064– 3 events near source
location (~1.5 expected)
– 80% chance of randomly observing this significance from a source on the list
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What if a Source is Observed?
• Suppose Markarian 421 produces 8 signal events in AMANDA following an E-2 spectrum and the background is well described by atmospheric neutrinos
• >50% probability of 5 detection, assuming no trial penalty.
• Minimization of with respect to signal strength and spectral index yields an estimate of both parameters
• Approximate as a 2 distribution with two degrees of freedom
)ˆ/log(2 LL
)log(L8 E-2 Signal Events
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What if a Source is Observed?
• Suppose Markarian 421 produces 8 signal events in AMANDA following an E-2 spectrum and the background is well described by atmospheric neutrinos
• >50% probability of 5 detection, assuming no trial penalty.
• Minimization of with respect to signal strength and spectral index yields an estimate of both parameters
• Approximate as a 2 distribution with two degrees of freedom
)ˆ/log(2 LL
)log(L50 E-2 Signal Events
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Benefit of Likelihood Method
• Other benefits:
– Position confidence contours can be drawn similarly using information from the likelihood function
– Data from detectors with different angular resolution can be combined more efficiently
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Conclusions
• New methods enhance point source sensitivity and discovery potential by 30%
• Adding an energy correlated observable additionally allows estimation of signal spectral index in the case of discovery
• No significant excess observed in 2005