Neutrino Analysis of Cosmic Ray Hot Spots
Lizz
1
Wills ,
1
Neilson for
Naoko Kurahashi
the IceCube Collaboration
1Physics Department, Drexel University, Philadelphia, PA
elizabeth.j.wills@drexel.edu
Background
Motivation
Cosmic Rays
Why should we map the sky in neutrinos?
• Electrically charged particles (protons, nuclei)
• Interact with inter-galactic magnetic fields
• Energy scale of rays helps determine distance
• Anisotropy discovered – due to magnetic fields or
sources?
1. No one has mapped the cosmic ray hot spots in noncharged particles, that don’t change direction in
magnetic fields
2. Help inform the debate over hot-spot origin – caused by
magnetic fields or local sources?
3. No analysis has been done with neutrinos or complete
data from IceCube
Data Selection
ARGO-YBJ PHYS REV D 88
Neutrinos
• Weakly interacting, almost massless, chargeless, travel at
roughly the speed of light
• Produced in stellar processes
• Point back to their astrophysical
sources
IceCube
• Neutrino detector at geographical
South Pole under 1.5km of ice
• Detect muon signature of neutrino
interaction via Cherenkov radiation
IceCube Data
• 4 years of data from 2008-2011
Preliminary Results
General:
• Burn sample data –Condenser
10% of total
• IceCube analyses are blinded
• Keeps from biasing final analysis
• Total burn events: 36,628
Region A:
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•
•
On/off region ratio = 1/6
Counts on = 995
Counts off = 5669 (avg: 944)
Significance = 1.49σ Heater
P-value = 0.13
Surplus – 11 counts over background
Point Source Data Selection
• South Sky analysis: high energy, good tracks
• North Sky analysis: no muon background
Method
Region Selection
• On regions: hot spots A and B
• Off regions: background regions, same shape areas at
same declination but different right ascensions
• 2 “null regions”: less significant hot spots, avoided to not
contaminate background
• Constant declination eliminates data background
• 1km3, 86 strings of 60 light sensors
Region B:
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•
•
•
•
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On/off region ratio = 1/5
Counts on = 904
Counts off = 4636 (avg: 927)
Significance = 0.69σ
ARGO-YBJ PHYS REV D 88
P-value = 0.31
Deficit – 35 counts less than background
Future Work
Unblinding
• Full collaboration verification approval
• Getting 100% of data allows for meaningful statistics
• Measure level of excess or set limits
References
Li-Ma Statistical Analysis
• Analysis weighted for different total areas of on site/off
site regions
Y. Ma and T. Li., The Astrophysical Journal, 272:317-324 (1983).
A. A. Abdo et al. (Milagro Collaboration), arXiv:0801.3827v3 (2008).
B. Bartoli et al. (ARGO-YBJ Collaboration), Phys. Rev. D 88, 082001
(2013).
A. U. Abeysekara et al. (HAWC Collaboration), arXiv:1408.4805v2
(2014).
P. Mertsch, S. Funk, arXiv:1408.3630v2 (2015).
M. G. Aartsen et al. (IceCube Collaboration), arXiv:1311.4767v3
(2014)