Cherenkov light from Horizontal Air Shower

Abstract: We present results of horizontal EAS simulations focused on the opportunity of measuring Cherenkov light from air showers at stratospheric balloon altitude (eg. EUSO-SPB2). For a 1 m2 UV light detector at a 38 km altitude, the largest horizontal distance to the edge of the Earth atmosphere is about 1000 km which represents a depth of 10000 g/cm2 of atmosphere. The Cherenkov light produced by the EAS electron component would be scattered in atmosphere on its way to the detector, and would not contribute to detected light. The most promising scenario relies on the detection of light emitted within about 300 km from the detector by EAS muons with energies above 100 GeV (required to produce Cherenkov light at high altitudes and for muons to survive over a large distance). Within this scenario we might expect to measure Cherenkov light from proton induced EAS of energy between 1e17 and 1e18 eV, the lower limit being related to the strength of a signal, and upper limit being due to the product of geometrical factor by the CR flux.