Roman Hiller Karlsruhe Institut für Technologie

A composition study of ultra high energy cosmic rays using risetime data from the 750m infill array of the Pierre Auger Observatory (pdf)

The determination of mass composition of ultra high energy cosmic rays is one of the main tasks of the Pierre Auger Observatory and may give important hints on their sources and accelerators. One approach to deduce it from data of the surface detector is to use the risetime, the time it takes for the integrated signal of a surface detector station to rise from 10% to 50% of its final value. For the 750m infill array, that was commissioned in 2008 as a part of the AMIGA extension of the surface detector, risetime studies have yet to be performed. To use risetime for the determination of mass composition one has to condense the information of the stations from a single event to one mass sensitive observable that can be compared with simulations. Therefore risetime has to be corrected for azimuthal asymmetry and its dependance on the distance to the shower core and zenith angle hast to be considered. The preliminary results of this analysis are presented up to the distance dependance.