Neutrinos in the cosmic ray flux with energies near 1 EeV and above are detectable with the Surface Detector array of the Pierre Auger Observatory .
We report here on searches through Auger data from 1 January 2004 until 20 June 2013 .
No neutrino candidates were found , yielding a limit to the diffuse flux of ultra-high energy neutrinos that challenges the Waxman-Bahcall bound predictions .
Neutrino identification is attempted using the broad time-structure of the signals expected in the SD stations , and is efficiently done for neutrinos of all flavors interacting in the atmosphere at large zenith angles , as well as for “ Earth-skimming ” neutrino interactions in the case of tau neutrinos .
In this paper the searches for downward-going neutrinos in the zenith angle bins 60 ^ { \circ } -75 ^ { \circ } and 75 ^ { \circ } -90 ^ { \circ } as well as for upward-going neutrinos , are combined to give a single limit .
The 90 \% C.L .
single-flavor limit to the diffuse flux of ultra-high energy neutrinos with an E ^ { -2 } spectrum in the energy range 1.0 \times 10 ^ { 17 } eV - 2.5 \times 10 ^ { 19 } eV is E _ { \nu } ^ { 2 } dN _ { \nu } / dE _ { \nu } < 6.4 \times 10 ^ { -9 } \leavevmode \nobreak { GeV% \leavevmode \nobreak cm ^ { -2 } \leavevmode \nobreak s ^ { -1 } \leavevmode \nobreak sr% ^ { -1 } } .