6 years of High-energy starting Events in icecube Claudio Kopper, - - PowerPoint PPT Presentation

Claudio Kopper, University of Alberta

6 years of High-energy starting Events in icecube

Cosmic Rays and neutrinos

Search for the sources of Cosmic Rays

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Observation of Astrophysical Neutrinos in Six Years of IceCube Data (HESE-6year) Claudio Kopper

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Cosmic Rays

where (and how) are they accelerated?

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We know their energy spectrum

• ver 11 orders of magnitude

Their sources (especially at the highest energies) are still mostly unknown

Multi-messenger astrophysics with neutrinos

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p p Astrophysical beam dump π0 π+/π-

• Nuclei can be deflected by magnetic

fields γ γ γ

• Gamma rays can be absorbed

νμ µ e νμ νe νμ

• Neutrinos are difficult to stop and

travel in straight lines

Observation of Astrophysical Neutrinos in Six Years of IceCube Data (HESE-6year) Claudio Kopper

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Neutrinos above 1 TeV

sketch of the different expected neutrino flux components

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dominant < 100 TeV

Atmospheric neutrinos (π/K)

“prompt” ~ 100 TeV

Atmospheric neutrinos (charm)

maybe dominant > 100 TeV

Astrophysical neutrinos

>106 TeV

Cosmogenic neutrinos

Detecting neutrinos

Neutrinos are detected by looking for Cherenkovv radiation from secondary particles (muons, particle showers)

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μ νμ

Cherenkov cone Deep-inelastic scattering

The IceCube Neutrino Observatory

Deployed in the deep glacial ice at the South Pole

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IceCube Array

86 strings including 8 DeepCore strings 5160 optical sensors

DeepCore

8 strings-spacing optimized for lower energies 480 optical sensors 81 Stations 324 optical sensors

Bedrock

5160 PMTs 1 km3 volume 86 strings 17 m vertical spacing 125 m string spacing Completed 2010

Neutrino event signatures

Signatures of signal events

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CC Muon Neutrino Neutral Current / Electron Neutrino CC Tau Neutrino

track (data) factor of ≈ 2 energy resolution
 < 1° angular resolution at high energies cascade (data) ≈ ±15% deposited energy resolution
 ≈ 10° angular resolution (in IceCube)
 (at energies ⪆ 100 TeV) “double-bang” (⪆10PeV) and other signatures (simulation) (not observed yet: τ decay length is 50 m/PeV)

νµ + N → µ + X ντ + N → τ + X νe + N → e +X νx + N → νx+X

time

isolating neutrino events

two strategies

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Up-going tracks

µ-dominated ν only

Atmosphere (exaggerated) North

Active veto

μ νμ

✓

μ Veto

✘

IceCube

Air shower Air shower

νμ μ

Astrophysical source

νμ

Earth stops penetrating muons Effective volume larger than detector Sensitive to νµ only Sensitive to “half” the sky Veto detects penetrating muons Effective volume smaller than detector Sensitive to all flavors Sensitive to the entire sky

The (Very) High-Energy Tail

Update of the high-energy astrophysical flux discovery analysis

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“HISTORY”

Appearance of ~1 PeV cascades as an at-threshold background

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Two very interesting events in IceCube (between May 2010 and May 2012) 2.8σ excess over expected background in GZK analysis (PRL 111, 021103 (2013)) There should be more GZK analysis is only sensitive to very specific event topologies at these energies

“Bert”

~1.0PeV

“Ernie”

~1.1PeV

“Starting Event” Analysis

Specifically designed to find contained events.

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μ νμ

✓

μ Veto

✘

Explicit contained search at high energies (cut: Qtot>6000 p.e.) 400 Mton effective fiducial mass Use atmospheric muon veto Sensitive to all flavors in region above 60TeV deposited energy Estimate background from data

Atmospheric neutrino self-veto

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−1.0 −0.5 0.0 0.5 1.0 sin(δ) = − cos(θ) at the South Pole 10−3 10−2 10−1 100 101 Interactions km−3 sr−1 yr−1 Eν > 100 TeV astrophysical ν

Some neutrinos are absorbed in the Earth

Schönert, Resconi, Schulz, Phys.

• Rev. D, 79:043009 (2009)

Gaisser, Jero, Karle, van Santen,

• Phys. Rev. D, 90:023009 (2014)

Primary cosmic ray

νμ π- μ 1.5 km

• f ice

An active muon veto removes down-going atmospheric neutrinos.

−1.0 −0.5 0.0 0.5 1.0 sin(δ) = − cos(θ) at the South Pole 10−3 10−2 10−1 100 101 Interactions km−3 sr−1 yr−1 Eν > 100 TeV astrophysical ν

Some neutrinos are absorbed in the Earth

c

• n

v e n t i

• n

a l ν

µ

conventional νe −1.0 −0.5 0.0 0.5 1.0 sin(δ) = − cos(θ) at the South Pole 10−3 10−2 10−1 100 101 Interactions km−3 sr−1 yr−1 Eν > 100 TeV astrophysical ν

Some neutrinos are absorbed in the Earth

c

• n

v e n t i

• n

a l ν

µ

conventional νe −1.0 −0.5 0.0 0.5 1.0 sin(δ) = − cos(θ) at the South Pole 10−3 10−2 10−1 100 101 Interactions km−3 sr−1 yr−1 Eν > 100 TeV astrophysical ν

Some neutrinos are absorbed in the Earth

c

• n

v e n t i

• n

a l ν

µ

conventional νe prompt νµ + νe −1.0 −0.5 0.0 0.5 1.0 sin(δ) = − cos(θ) at the South Pole 10−3 10−2 10−1 100 101 Interactions km−3 sr−1 yr−1 Eν > 100 TeV astrophysical ν

Some neutrinos are absorbed in the Earth

c

• n

v e n t i

• n

a l ν

µ

conventional νe prompt νµ + νe

Prompt atmospheric neutrinos are vetoed, too. D- K0

−1.0 −0.5 0.0 0.5 1.0 sin(δ) = − cos(θ) at the South Pole 10−3 10−2 10−1 100 101 Interactions km−3 sr−1 yr−1 Eν > 100 TeV astrophysical ν

Some neutrinos are absorbed in the Earth

a t m

• s

p h e r i c ν

The zenith distributions of high-energy astrophysical and atmospheric neutrinos are fundamentally different. slide courtesy of J. van Santen

Effective Volume / Target Mass

Fully efficient above 100 T eV for CC electron neutrinos

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What did IceCube find? (6 years)

82 events in 2078 days

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80(+2) events observed! Estimated background: 15.6+11.4-3.9 atm. neutrinos 25.2±7.3 atm. muons Two of them are an obvious (but expected) background: coincident muons from two CR air showers

• 1
• 0.5

0.5 1 102 103 sin(Declination) Deposited EM-Equivalent Energy in Detector (TeV) IceCube Preliminary Showers Tracks

We updated the cross-section model (now “CSMS”) -> expected ~25% decrease in best-fit normalization

energy spectrum (6 years)

energy deposited in the detector (lower limit on neutrino energy)

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Compatible with benchmark single power-law model. 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-2ɸ = 2.46 ± 0.8 x 10-8 x
 (E / 100TeV)-0.92 GeV cm-2 s-1 sr-1

IceCube Preliminary

Zenith distribution (6 years)

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unfolding to neutrino energy

Fit for an arbitrary spectrum + background components (with priors) - 6 years

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assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino

IceCube Preliminary

unfolding to neutrino energy

Fit for an arbitrary spectrum + background components (with priors) - 6 years

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assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino

IceCube Preliminary

unfolding to neutrino energy

Fit for an arbitrary spectrum + background components (with priors) - 6 years

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assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino

IceCube Preliminary

IceCube Preliminary

unfolding to neutrino energy

Fit for an arbitrary spectrum + background components (with priors) - 6 years

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assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino

IceCube Preliminary

unfolding to neutrino energy

Fit for an arbitrary spectrum + background components (with priors) - 6 years

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assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino

IceCube Preliminary

unfolding to neutrino energy

Fit for an arbitrary spectrum + background components (with priors) - 6 years

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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

We are not able to make statements about the spectral shape with this analysis - stay tuned for future selections/analyses

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• law in black
• range - with a prior on the hard

between a one 1- component and a 2-component

Best-fit normalization ɸastro at 100 TeV vs. astrophysical index ɣastro 1-component power-law in black 2-component assumption in orange - with a prior on the hard component from the muon neutrino analysis This data sample can not discriminate between a 1-component and a 2-component model

skymap / clustering

No significant clustering observed (six years)

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(all p-values are post-trial)

Galactic

−180 +180

Southern Hemisphere Northern Hemisphere 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 29 30 31 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82

0.0 12.6

TS = 2 ln(L/L0)

IceCube Preliminary

Observation of Astrophysical Neutrinos in Six Years of IceCube Data (HESE-6year) Claudio Kopper

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skymap / clustering

No significant clustering observed

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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

CONCLUSIONS

and summary

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This selection still has low statistics and hence large

• fluctuations. It can not currently distinguish between

different spectral shapes, a single power law is a good fit. Lower-threshold datasets, using the full set of data collected by IceCube will become available soon. In addition, combined fits of this dataset and others like the through-going muon channel are currently in

• preparation. These should allow us to make better

statements on the astrophysical neutrino spectrum. All track-like "HESE" events are sent as public GCNs (and have been for about a year!)

THANK YOU!