Search for a di ff use flux of cosmic neutrinos with the ANTARES telescope Th. Eberl*, L.A. Fusco, S. Navas, F. Versari on behalf of the ANTARES Collaboration 35th International Cosmic Ray Conference Bexco, Busan, Korea July 15th, 2017
ANTARES Collaboration Ø >100 scientists Ø 9 countries Granada Rabat 2 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
ANTARES in the Mediterranean Sea Ø >100 scientists Ø 9 countries Granada Rabat 3 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
ANTARES detector 12 Lines (885 PMTs) • Completed in 2008 • Volume: ~0.01 km 3 • ~2m - 2475 m 4 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Track-like and shower-like events credit: J. Tiffenberg, NUSKY11 shower-like track-like shower-like shower-like (17% track-like, τ à μ ) 5 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Event reconstruction algorithms arXiv:1706.01857 Angular error for Shower-like E -2 spectrum events ~ 3 deg - almost identical to shower Track-like reconstruction in KM3NeT events ~ 0.4 deg - direction resolution ~3° - energy uncertainty ~10% Energy reconstruction: Tracks: based on artificial neural network (ANN, NIM A725 (2013)) Showers: ~ 10% energy uncertainty 6 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Previous searches for a di ff use flux with ANTARES No significant excess over the atmospheric background expectation observed à 90% C.L. upper limits on E -2 spectrum: 8 GeVcm − 2 s − 1 sr − 1 5 . 3 × 10 − 8 • Track-like events, 334 days: Phys. Lett. B 696 (2011) 5 . 1 × 10 − 8 • Track-like events, 855 days: Phys. Proc. 61 (2015) 4 . 9 × 10 − 8 • Shower-like events, 1247 days Eur. Phys. J. C 77 (2017) earlier shower reconstruction algorithm 7 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Data and Monte-Carlo simulations • 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. 8 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Search method • Assumptions on cosmic neutrino flux: - flavour equipartition at Earth. - isotropic over whole sky. Φ = Φ 0 · E − Γ - single power-law spectrum: ν - spectral index: Γ = 2.0 or Γ = 2.5, close to best-fit options for the IceCube cosmic signal. • Counting experiment. • Optimise selection criteria for best upper limit, i.e. Model Rejection Factor optimisation. • Derive upper limit and confidence interval, including systematic uncertainties. 9 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Search method 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. 10 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Energy spectrum for track-like events MRF optimum 11 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Energy spectrum for shower-like events MRF optimum 12 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Results after energy cut • 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 13 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Observed events Shower-like event Track-like event 14 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Limit and confidence interval E -2 spectrum, including systematics 90% C.L. upper limit 68% Confidence Interval 15 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
E -2.5 , including systematics 9 0 % C . L . u p p e r l i m i t 6 8 % C o n f i d e n c e I n t e r v a l 16 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Summary and outlook • 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 observed by IceCube. • Further analysis of the event sample and its spectral behaviour is under way. • Data taking and analysis continues ....! 17 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Thank you!
A Storey: The Basic Detector Element LED Optical Beacon Local Control Module timing calibration (titanium cylinder) (4 per line) Optical Module: 17” glass sphere Hydrophone RX 10” PMT Ham. R7081-20 (5 per line) 19 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
Upper limits and confidence intervals 20 Th. Eberl: ANTARES di ff use flux, 35th International Cosmic Ray Conference, Busan, 15.7.2017
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