Abstract
A novel algorithm to reconstruct neutrino-induced particle showers within the ANTARES neutrino telescope is presented. The method achieves a median angular resolution of 6^circ for shower energies below 100 TeV. Applying this algorithm to 6 years of data taken with the ANTARES detector, 8 events with reconstructed shower energies above 10 TeV are observed. This is consistent with the expectation of about 5 events from atmospheric backgrounds, but also compatible with diffuse astrophysical flux measurements by the IceCube collaboration, from which 2–4 additional events are expected. A 90% C.L. upper limit on the diffuse astrophysical neutrino flux with a value per neutrino flavour of text {E}^2cdot Phi ^{90%} = 4.9 cdot 10^{-8},mathrm {GeV} cdot mathrm {cm^{-2} cdot s^{-1}cdot sr^{-1}} is set, applicable to the energy range from 23 TeV to 7.8 PeV, assuming an unbroken text {E}^{-2} spectrum and neutrino flavour equipartition at Earth.
Highlights
With the discovery of a diffuse astrophysical neutrino flux by the IceCube observatory located in the deep Antarctic ice, high-energy neutrino astronomy has reported its first observation [1,2,3]
The ANTARES neutrino telescope [24] is located in the Mediterranean Sea about 40 km offshore from Toulon in a depth of about 2500 m, and comprises a three-dimensional array of 885 PMTs housed inside glass spheres, denoted as optical modules (OMs) [25]
Neutrino events generated according to a hard astrophysical spectrum are on average more energetic and induce a larger number of signal hits in the detector compared to atmospheric neutrino events, and their respective detection uncertainties are smaller
Summary
With the discovery of a diffuse astrophysical neutrino flux by the IceCube observatory located in the deep Antarctic ice, high-energy neutrino astronomy has reported its first observation [1,2,3]. Using 6 years of data, an astrophysical flux with a hard spectral index of = 2.13 ± 0.13 and a normalisation at 100 TeV of 0 = 0.9 × 10−8 GeV · cm−2 · s−1 · sr−1 has been found for neutrino energies above roughly 200 TeV [6]. This result shows a 3.3 σ tension with the normalisation value and soft spectral index obtained in a fit combining different previous IceCube analyses with mainly lower energy thresholds [8], which could be indicative of a spectral break [6]. The presented work is used as input to more advanced reconstruction algorithms based on updated simulations which are in development [23]
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