A search for a diffuse flux of astrophysical muon neutrinos , using data collected by the ANTARES neutrino telescope is presented .
A ( 0.83 \times 2 \pi ) sr sky was monitored for a total of 334 days of equivalent live time .
The searched signal corresponds to an excess of events , produced by astrophysical sources , over the expected atmospheric neutrino background .
The observed number of events is found compatible with the background expectation .
Assuming an E ^ { -2 } flux spectrum , a 90 % c.l .
upper limit on the diffuse \nu _ { \mu } flux of E ^ { 2 } \Phi _ { 90 \% } = 5.3 \times 10 ^ { -8 } \mathrm { GeV cm ^ { -2 } s ^ { -1 } sr ^ { -1 } } in the energy range 20 TeV - 2.5 PeV is obtained .
Other signal models with different energy spectra are also tested and some rejected .