Test results of a prototype designed to detect horizontal cosmic ray   flux
  In this paper we report test results from a prototype designed to detect muons from horizontal air shower at large zenith angle,   $86^{0}<\Theta<93^{0}$. To detect horizontal tracks and their directions we select them according the muon vertical equivalent charge and we measure the time of flight with a time resolution of 800 ps. Several measurements are collected at different zenith angles. The background studies performed with two modules show that the main source is due to tracks crossing the module at the same time. The upper limit of background flux for a single twin module is estimated to be $10^{-9} cm^{-2}$ $s^{-1}$ $sr^{-1} (90%CL)$. We estimated the size of the surface array necessary to detect the shower flux of the order of $10^{-9} cm^{-2}$ $yr^{-1}$ $sr^{-1}$ if originated by Tau Air-Showers secondaries of GZK neutrino Tau below the horizons. 
M. Iori, A. Sergi and D. Fargion