The RPC charge readout system of the ARGO-YBJ experiment

The ARGO-YBJ experiment has been in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet,P.R. China, 4300 m a.s.l.). Its main fields of research are γ-astronomy with an energy threshold of a few hundred GeV and cosmic ray physics in the 1-1000 TeV energy range. The ARGO detector consists of a single layer of RPCs operated in streamer mode, covering a total instrumented area of about 10,000 m2. Signals from each RPC are picked up with 80 read-out strips 6.7 cm wide and 62 cm long (23 strips/m2) that allow the shower front reconstruction with an high space-time resolution. In order to fully investigate the PeV region, where the previous (digital) read-out saturates, an analog one has been implemented by instrumenting each RPC with two large size pads of dimension 1.39 × 1.23 m2. In this paper we describe the hardware solution that implements the real-time charge read-out in the ARGO-YBJ experiment, paying a special attention to the synchronization with the central data acquisition system, which also is described.