1. The showers Induced be e with LPM effect included (red stars) look very different from showers without LPM effect (blue stars).The showers are more elongated and sometimes even a double peak event can be seen in the detector focal surface. The EUSO project aims to detect from space the fluorescence and the ground-reflected cherenkov light emitted by extreme high energy air-showers.The experiment will be accommodated on the ISS and having a field of view of 60 deg will be able to monitor from space an atmospheric mass close to 1.5x10 18 g with energy threshold close to 3x10 19 eV. Such enormous amount of target mass will offer the unique opportunity to detect cosmic neutrino events at extreme high energy where the predicted neutrino fluxes are generally too small to detect with other thecniques. The positive detection of such neutrinos will give probably a strong support to the top-down solution of GZK problem. EUSO: Characterization of Neutrino Induced Showers (HE180) S. Bottai, F. Becattini, L. Haroyan and M. Tognetti (EUSO Team) University of Florence and INFN Florence, Italy bottai@fi.infn.it This poster has been prepared for the EUSO Team by S. Bottai See correlated posters HE 178, 179, 181, 182. Vincent Van Gogh, “The starry nigth” 30° EUSO 230 km 400 km Earth surface Artist view Čerenkov Cosmic ray fluorescence The simulation of shower formation and development, fluorescence and cherenkov light generation and transmission, and detector response has been performed here using UNISIM simulation package. The UNISIM package includes the LPM effect and it is able to simulate each kind of neutrino interactions inside the target mass seen by the detector. CC and NC differential cross sections used in the simulation have been calculated in the framework of QCD improved parton model using the CTEQ3 DIS parton distribution set. Due to the weekness of neu- trino cross sections, neutrino showers develop maximum at very high slant depth (XMAX) respect to proton showers. The XMAX distribution can be used to discriminate neutrinos from other less penetrating particles. The figure shows the XMAX distribution for 1 year of proton events and an arbitrary number of neutrino events. Selection on XMAX > 1100 g/cm 2 could be enough to disentangle neutrinos from protons. CC and NC current e interactions inside the 10 19 g·sr atmospheric target mass have been simulated. We required to trigger the apparatus, detect the cherenkov light and develop XMAX > 1100 g/cm 2. Showers developing maximum below the ground, decreasing of particles at XMAX due to LPM and loss of cherenkov light for almost hori- zontal events are the main sources of inefficiencies. Angular distribution of selected events 3 Years (pupil diameter = 2 m) 10% duty cycle TD1TD2TD3GZK1GZK2GZK3AGN1AGN2 INTERACTIONS INSIDE EUSO TARGET · 0.1 90 21801 0.5 4.6 26 1 11 EVENTS DETECTED AND SELECTED 21 6184 0.1 0.7 3.50.16 2.1 ( TD1 : Protheroe&Stanev ; TD2 : Sigl. Et al ; GZK1&GZK2 : Proteroe&Johnson ; GZK3 : Hill&Schramm ; AGN1&AGN2 : Mannheim ) from ref. R.J. Protheroe Nucl.Phys.Proc.Suppl.77:465-473,1999 ( TD3 ) [p=1.5] from ref. P. Battacharjee et al. Phys. Rev. Lett. 69 (1992) E =3x10 20 eV  zen =80 o