Atmospheric background measurement in the 300-400 NM band with a balloon borne experiment during a nocturnal flight

The balloon borne experiment, named BABY (BAckground BYpass) belongs to a wider program, AIRWATCH-OWL, intended for the observation of high energy Cosmic Rays from space, detecting the faint UV fluorescence light emitted by the atmospheric Nitrogen as final result of a complex hadronic cascade. In this framework, one of the fundamental information concern the knowledge of the background level. This is one of the main parameters that contribute to the sensitivity of any kind of instrument. The apparatus used for the BABY experiment was designed and completely built at the IFCAI-CNR in Palermo. The instrument is composed by two filtered and collimated photomultipliers (PMT) that detect the UV light in the 300-400 nm wavelength. We report a brief description of the design of the detector and the results coming from a preliminary analysis of the data taken during a nocturnal over-sea observation.