6 years of High-energy starting Events in icecube Claudio Kopper, University of Alberta
ν Cosmic Rays and neutrinos Search for the sources of Cosmic Rays
Cosmic Rays 3 ν where (and how) are they accelerated? We know their energy spectrum over 11 orders of magnitude Their sources (especially at the highest energies) are still mostly unknown Observation of Astrophysical Neutrinos in Six Years of IceCube Data (HESE-6year) Claudio Kopper
Multi-messenger astrophysics with neutrinos 4 ν ‣ Nuclei can be deflected by magnetic fields ‣ Gamma rays can be absorbed ‣ Neutrinos are difficult to stop and travel in straight lines γ p π + / π - ν μ π 0 µ p γ γ e ν μ ν e ν μ Astrophysical beam dump
Neutrinos above 1 TeV 5 ν sketch of the different expected neutrino flux components Atmospheric neutrinos ( π /K) dominant < 100 TeV Atmospheric neutrinos (charm) “prompt” ~ 100 TeV Astrophysical neutrinos maybe dominant > 100 TeV Cosmogenic neutrinos >10 6 TeV Observation of Astrophysical Neutrinos in Six Years of IceCube Data (HESE-6year) Claudio Kopper
Detecting neutrinos 6 ν Neutrinos are detected by looking for Cherenkovv radiation from secondary particles (muons, particle showers) μ Cherenkov cone Deep-inelastic scattering ν μ
The IceCube Neutrino Observatory 7 ν Deployed in the deep glacial ice at the South Pole 81 Stations 5160 PMTs 324 optical sensors IceCube Array 1 km 3 volume 86 strings including 8 DeepCore strings 5160 optical sensors 86 strings 17 m vertical spacing DeepCore 8 strings-spacing optimized for lower energies 480 optical sensors 125 m string spacing Completed 2010 Bedrock
Neutrino event signatures 8 ν Signatures of signal events time Neutral Current / CC Muon Neutrino CC Tau Neutrino Electron Neutrino ν µ + N → µ + X ν e + N → e + X ν τ + N → τ + X ν x + N → ν x + X track (data) cascade (data) “double-bang” ( ⪆ 10PeV) and other signatures (simulation) factor of ≈ 2 energy resolution ≈ ±15% deposited energy resolution < 1° angular resolution at high ≈ 10° angular resolution (in IceCube) (not observed yet: τ decay length is energies (at energies ⪆ 100 TeV) 50 m/PeV)
isolating neutrino events 9 ν two strategies Up-going tracks Active veto IceCube Air shower Veto ν μ μ µ-dominated ν only North ν μ ν μ Atmosphere (exaggerated) μ ✓ ✘ μ Air shower Astrophysical source Earth stops penetrating muons Veto detects penetrating muons Effective volume larger than detector Effective volume smaller than detector Sensitive to ν µ only Sensitive to all flavors Sensitive to “half” the sky Sensitive to the entire sky
ν The (Very) High-Energy Tail Update of the high-energy astrophysical flux discovery analysis
“HISTORY” 11 ν Appearance of ~1 PeV cascades as an at-threshold background Two very interesting events in IceCube (between May 2010 and May 2012) 2.8 σ excess over expected background in GZK ~1.0PeV “Bert” analysis (PRL 111, 021103 (2013)) There should be more GZK analysis is only sensitive to very specific event topologies at these energies ~1.1PeV “Ernie”
“Starting Event” Analysis 12 ν Specifically designed to find contained events. Veto μ Explicit contained search at high energies (cut: ✘ Qtot>6000 p.e.) 400 Mton effective fiducial mass Use atmospheric muon veto ν μ ✓ Sensitive to all flavors in region above 60TeV deposited energy Estimate background from data μ
Atmospheric neutrino self-veto 13 The zenith An active muon veto Prompt atmospheric 10 1 10 1 10 1 10 1 10 1 10 1 Some neutrinos Some neutrinos Some neutrinos Some neutrinos Some neutrinos Some neutrinos neutrinos are vetoed, too. removes down-going astrophysical ν astrophysical ν astrophysical ν astrophysical ν astrophysical ν astrophysical ν distributions of Interactions km − 3 sr − 1 yr − 1 E ν > 100 TeV Interactions km − 3 sr − 1 yr − 1 E ν > 100 TeV Interactions km − 3 sr − 1 yr − 1 E ν > 100 TeV Interactions km − 3 sr − 1 yr − 1 E ν > 100 TeV Interactions km − 3 sr − 1 yr − 1 E ν > 100 TeV Interactions km − 3 sr − 1 yr − 1 E ν > 100 TeV are absorbed are absorbed are absorbed are absorbed are absorbed are absorbed atmospheric neutrinos. in the Earth in the Earth in the Earth in the Earth in the Earth in the Earth high-energy slide courtesy of J. van Santen Primary cosmic ray a t m o astrophysical and prompt ν µ + ν e prompt ν µ + ν e s p h 10 0 10 0 10 0 10 0 10 0 10 0 e r i c atmospheric π - ν D - K 0 neutrinos are c c c c o o o o ν μ n n n n v v v v e e e e μ n n n n fundamentally t t t t i i i i o o o o 10 − 1 10 − 1 10 − 1 10 − 1 10 − 1 10 − 1 n n n n a a a a different. l l l l ν ν ν ν 1.5 km µ µ µ µ of ice conventional ν e conventional ν e conventional ν e conventional ν e 10 − 2 10 − 2 10 − 2 10 − 2 10 − 2 10 − 2 Schönert, Resconi, Schulz, Phys. Rev. D, 79:043009 (2009) 10 − 3 10 − 3 10 − 3 10 − 3 10 − 3 10 − 3 − 1 . 0 − 1 . 0 − 1 . 0 − 1 . 0 − 1 . 0 − 1 . 0 − 0 . 5 − 0 . 5 − 0 . 5 − 0 . 5 − 0 . 5 − 0 . 5 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 5 0 . 5 0 . 5 0 . 5 0 . 5 0 . 5 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 Gaisser, Jero, Karle, van Santen, Phys. Rev. D, 90:023009 (2014) sin( δ ) = − cos( θ ) at the South Pole sin( δ ) = − cos( θ ) at the South Pole sin( δ ) = − cos( θ ) at the South Pole sin( δ ) = − cos( θ ) at the South Pole sin( δ ) = − cos( θ ) at the South Pole sin( δ ) = − cos( θ ) at the South Pole
Effective Volume / Target Mass 14 ν Fully efficient above 100 T eV for CC electron neutrinos
What did IceCube find? (6 years) 15 ν 82 events in 2078 days 1 80(+2) events observed! Showers Tracks 0.5 IceCube Preliminary Estimated background: sin(Declination) 0 15.6 +11.4-3.9 atm. neutrinos -0.5 25.2±7.3 atm. muons -1 Two of them are an obvious (but 10 2 10 3 Deposited EM-Equivalent Energy in Detector (TeV) expected) background: We updated the cross-section model coincident muons from two CR (now “CSMS”) -> expected ~25% decrease air showers in best-fit normalization
energy spectrum (6 years) 16 ν energy deposited in the detector (lower limit on neutrino energy) Compatible with benchmark single power-law model. IceCube Preliminary Things might be more complicated, but this is not the analysis to decide that. Best fit spectral index (E - ɣ ): ɣ =-2.92 +0.33-0.29 E -2 ɸ = 2.46 ± 0.8 x 10 -8 x (E / 100TeV) -0.92 GeV cm -2 s -1 sr -1
Zenith distribution (6 years) 17 ν
unfolding to neutrino energy 18 ν Fit for an arbitrary spectrum + background components (with priors) - 6 years IceCube Preliminary assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino
unfolding to neutrino energy 19 ν Fit for an arbitrary spectrum + background components (with priors) - 6 years IceCube Preliminary assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino
unfolding to neutrino energy 20 ν Fit for an arbitrary spectrum + background components (with priors) - 6 years IceCube Preliminary assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino
unfolding to neutrino energy 21 ν Fit for an arbitrary spectrum + background components (with priors) - 6 years IceCube Preliminary assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino
unfolding to neutrino energy 22 ν Fit for an arbitrary spectrum + background components (with priors) - 6 years IceCube Preliminary assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino
unfolding to neutrino energy 23 ν Fit for an arbitrary spectrum + background components (with priors) - 6 years IceCube Preliminary This data sample is not able to discriminate between a 1-component and a 2-component model
No evidence for 2 components in this analysis 24 ν We are not able to make statements about the spectral shape with this analysis - stay tuned for future selections/analyses Best-fit normalization ɸ astro at 100 TeV vs. astrophysical index ɣ astro -law in black 1-component power-law in black 2-component assumption in orange - orange - with a prior on the hard with a prior on the hard component from the muon neutrino analysis This data sample can not between a one 1- discriminate between a 1-component component and a 2-component and a 2-component model
skymap / clustering 25 ν No significant clustering observed (six years) 72 62 IceCube Preliminary 37 54 50 63 9 47 23 82 16 69 26 11 8 43 17 80 31 76 75 66 49 46 48 36 64 51 53 6 73 4 27 5 35 77 3 29 40 14 +180 � − 180 � 57 33 39 24 38 52 13 25 2 34 58 68 22 56 45 70 15 30 71 12 Northern Southern 41 81 Hemisphere Hemisphere 19 59 65 67 20 44 61 78 1 74 42 18 60 Galactic 79 7 10 21 TS = 2 ln( L / L 0 ) 0.0 12.6 (all p-values are post-trial)
skymap / clustering 26 ν No significant clustering observed Analyzed with a variant of the standard PS method (w/o energy) (i.e. scrambling in RA) Significance (p-value): 77% (not significant) Other searches (multi-cluster, galactic plane, time clustering, GRB correlations) not significant either Observation of Astrophysical Neutrinos in Six Years of IceCube Data (HESE-6year) Claudio Kopper
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