M. Ambrosio

Measurement of the depth of maximum of extensive air showers above 10(18) eV

We describe the measurement of the depth of maximum, Xmax, of the longitudinal development of air showers induced by cosmic rays. Almost four thousand events above 10^18 eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/- 0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.

Trigger and aperture of the surface detector array of the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy, from the identification of candidate showers at the level of a single detector, amongst a large background (mainly random single cosmic ray muons), up to the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above 3 x 10(18) eV, for all zenith angles between 0 degrees and 60 degrees, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance

A tracking and timing (T&T) front-end electronics for RPC detectors

Abstract The availability of a detector such as an RPC (resistive plate counter) opens new possibility on the future experiments for accelerator and non-accelerator physics. The main advantage consists on the possibility to obtain accurate tracking and timing with a low-cost detector and electronics. We report results on time resolution, signal transmission on long strips, efficiency and maintenance. A possible front-end electronics able to give tracking and timing information on each input channel operating in free-running mode will be illustrated toghether to the preliminary tests performed.

A new 63 MHz RPC parallel readout system

Abstract In the framework of the high energy physics experiments at the future accelerators a new kind of front-end and readout electronics has been developed. The system features have been optimized to handle the signals of resistive plate counters used as trigger detector. We describe here the modules and the results of a test performed on them using cosmic rays.