The need for a multicomponent UHECR Observatory

Laboratoire de Physique Nucléaire et des Hautes Énergies, 4 place Jussieu, 75252 Paris, France

^a e-mail: antoine.Letessier-Selvon@in2p3.fr

Abstract

In the past fifteen years, UHECR hybrid detection systems – combinations of fluorescence techniques with very large ground arrays (over 10³km²) – have provided data sets of unprecedented statistics and quality However, the paucity of events above the GZK cut-off combined with the limited duty cycle of the fluorescence detectors calls for further progress in the detection techniques and larger aperture. Above 50 EeV the current world data sets are of the order of 200 events out of which only a handful have been observed in hybrid mode. Hence, while the spectrum feature as well as anisotropy studies can be performed, although with limitation, a proper identification of the primary particle is out of reach. I argue here that the next generation observatory should reach an aperture of several 10⁴km² using detectors able to measure both the muonic and electromagnetic component of each individual extensive air shower in order to provide the necessary information to pin down the primary cosmic ray nature and possibly point back at their sources.