The ANTARES detector is at present the most sensitive neutrino telescope in the Northern Hemisphere .
The highly significant cosmic neutrino excess observed by the Antarctic IceCube detector can be studied with ANTARES , exploiting its complementing field of view , exposure , and lower energy threshold .
Searches for an all-flavor diffuse neutrino signal , covering 9 years of ANTARES data taking , are presented in this letter .
Upward-going events are used to reduce the atmospheric muon background .
This work includes for the first time in ANTARES both track-like ( mainly \nu _ { \mu } ) and shower-like ( mainly \nu _ { e } ) events in this kind of analysis .
Track-like events allow for an increase of the effective volume of the detector thanks to the long path traveled by muons in rock and/or sea water .
Shower-like events are well reconstructed only when the neutrino interaction vertex is close to , or inside , the instrumented volume .
A mild excess of high-energy events over the expected background is observed in 9 years of ANTARES data in both samples .
The best fit for a single power-law cosmic neutrino spectrum , in terms of per-flavor flux at 100 TeV , is \Phi _ { 0 } ^ { 1 f } ( 100 \textrm { TeV } ) = \left ( 1.7 \pm 1.0 \right ) \times 10 ^ { -18 } GeV ^ { -1 } cm ^ { -2 } s ^ { -1 } sr ^ { -1 } with spectral index \Gamma = 2.4 ^ { +0.5 } _ { -0.4 } .
The null cosmic flux assumption is rejected with a significance of 1.6 \sigma .