Upper limit on the diffuse flux of UHE tau neutrinos

The Pierre Auger Observatory is the largest Ultra High Energy (UHE) cosmic ray detector. It provides a laboratory for studying fundamental interactions at energies well beyond those available at colliders. In addition to hadrons or photons, Auger is sensitive to ultra-high energy neutrinos in the EeV range and above. Models for new physics can be explored by observing neutrino interactions at center-of-mass energies well beyond the TeV scale. By comparing the rate for quasi-horizontal, deeply penetrating air showers triggered by all types of neutrinos with the rate for slightly upgoing showers generated by Earth-skimming tau neutrinos, any deviation of the neutrino-nucleon cross-section from the Standard Model expectation can be constrained. In this talk I will present the evaluation of the sensitivity of Auger to such ``Earth-skimming" events, the procedure to discrimine them from background, and the upper limit on the diffuse flux of tau neutrinos obtained at EeV energies from Auger data.