Search for a di ff use flux of cosmic neutrinos with the ANTARES - - PowerPoint PPT Presentation

• Th. Eberl*, L.A. Fusco, S. Navas, F. Versari 

• n behalf of the ANTARES Collaboration



 35th International Cosmic Ray Conference
 Bexco, Busan, Korea 
 July 15th, 2017


Search for a diffuse flux of cosmic neutrinos with the ANTARES telescope

ANTARES Collaboration

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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Ø >100 scientists Ø 9 countries

Granada Rabat

ANTARES in the Mediterranean Sea

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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Ø >100 scientists Ø 9 countries

Granada Rabat

~2m

ANTARES detector

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• 2475 m
• 12 Lines (885 PMTs)

• Completed in 2008

• Volume: ~0.01 km3
• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

Track-like and shower-like events

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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credit: J. Tiffenberg, NUSKY11

track-like shower-like shower-like shower-like

(17% track-like, τ à μ)

Event reconstruction algorithms

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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Energy reconstruction: Tracks: based on artificial neural network (ANN, NIM A725 (2013)) Showers: ~ 10% energy uncertainty

• almost identical to shower

reconstruction in KM3NeT

• direction resolution ~3°
• energy uncertainty ~10%

arXiv:1706.01857

~ 0.4 deg ~ 3 deg Angular error for E-2 spectrum Shower-like events Track-like events

No significant excess over the atmospheric background expectation

• bserved

à 90% C.L. upper limits on E-2 spectrum:

• Track-like events, 334 days:
• Phys. Lett. B696 (2011)
• Track-like events, 855 days:
• Phys. Proc. 61 (2015)
• Shower-like events, 1247 days
• Eur. Phys. J. C77 (2017)

earlier shower reconstruction algorithm

Previous searches for a diffuse flux with ANTARES

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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5.1 × 10−8 5.3 × 10−8 4.9 × 10−8

8GeVcm−2s−1sr−1

Data and Monte-Carlo simulations

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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• Data collected from 2007 to 2015, 2450 days of livetime.
• More than a factor of two more than in previous searches.
• Detailed Monte-Carlo simulations:
• used to define event selection criteria.
• investigate systematic uncertainties.
• reproduce temporal evolution of data acquisition

conditions in the deep sea.

• Honda et al. atmospheric neutrino flux model

+ Enberg et al. for assumed prompt component.

• Blind analysis, 10% livetime used for cross-checks.

• Assumptions on cosmic neutrino flux:
• flavour equipartition at Earth.
• isotropic over whole sky.
• single power-law spectrum:
• spectral index: Γ = 2.0 or Γ = 2.5,

close to best-fit options for the IceCube cosmic signal.

• Optimise selection criteria for best upper limit,

i.e. Model Rejection Factor optimisation.

Search method

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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• Counting experiment.
• Derive upper limit and confidence interval, including

systematic uncertainties.

Φ = Φ0 · E−Γ

ν

Search method

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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Two-step event selection procedure: 1/ suppress atmospheric muon background:

• reject downward-reconstructed events
• apply reconstruction quality cuts

à rate of remaining atmospheric neutrinos:

• track channel: 1 per day
• shower channel: 0.1 per day

2/ discriminate soft atmospheric neutrino background:

• lower energy cut: optimise ratio of cosmic signal to

atmospheric background.

Energy spectrum for track-like events

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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MRF optimum

Energy spectrum for shower-like events

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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MRF optimum

Results after energy cut

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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• Event expectations from Monte-Carlo simulation:

for background: 24 +- 7 events, i.e. 13.5 track-like + 10.5 shower-like for cosmic signal: 7 events, i.e. 3 – 3.5 track-like + 4 shower-like

• Systematic uncertainties considered:
• atmospheric neutrino and muon flux normalisation
• water properties
• optical module efficiencies
• Observation: 33 events (p=0.15)

19 track-like + 14 shower-like

Observed events

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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Shower-like event Track-like event

Limit and confidence interval
 E-2 spectrum, including systematics

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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68% Confidence Interval 90% C.L. upper limit

E-2.5, including systematics

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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6 8 % C

• n

f i d e n c e I n t e r v a l 9 % C . L . u p p e r l i m i t

Summary and outlook

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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• 2450 days of ANTARES data used to search for diffuse

cosmic neutrino flux.

• All-flavour search simultaneuosly in track-like and shower-like

event channel.

• Observed event excess over atmospheric background

expectation is not significant.

• Observation is compatible with a cosmic neutrino flux as
• bserved by IceCube.
• Further analysis of the event sample and its spectral

behaviour is under way.

• Data taking and analysis continues ....!

Thank you!

A Storey: The Basic Detector Element

Hydrophone RX (5 per line) Local Control Module (titanium cylinder) LED Optical Beacon timing calibration (4 per line) Optical Module: 17” glass sphere 10” PMT Ham. R7081-20

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• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

Upper limits and confidence intervals

• Th. Eberl: ANTARES diffuse flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017

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