On the way to the determination of the cosmic ray mass composition by the Pierre Auger fluorescence detector: The 'minimum momentum method'

We propose a possible approach for the determination of very high energy cosmic ray primary mass A based on the information provided by the reconstruction of shower longitudinal development in the Earth atmosphere. We refer to an apparatus such as the Pierre Auger Observatory, which is a unique "hybrid" UHECR detector. The surface detector (SD) and air fluorescence detector (FD) of the observatory are designed for observation of cosmic ray showers in coincidence, with a 10% duty cycle, with resulting data expected to be superior in quality especially for the primary energy E-0 which is determined with a 5% accuracy. We present results obtained using an approach for the determination of A in the individual event based on only FD information (MMM - 'Minimum Momentum Method'). This approach shows that, if the entire information contained in the longitudinal profile is exploited, reliable results may be obtained.