Integration of the Analog Readout in the ARGO-YBJ DAQ System

The ARGO-YBJ experiment has been in stable data taking since November 2007 at the YangBaJing Cosmic Ray Lab oratory (Tibet, 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-YBJ detector consists of a single layer of RPCs operated in streamer mode, housed in a large building of about 11000 m²). Signals from each RPC are picked up with 80 readout strips 61.8 cm wide and 6.75 cm long (23 strips/m²) that allow the shower front reconstruction with a high space-time resolution. In order to fully investigate the PeV region, where the previous (digital) readout saturates, an analog one has been implemented by instrumenting each RPC with two large size electrodes of dimension 1.39 × 1.23 m². The 130 Clusters of the central carpet have been instrumented with the charge readout hardware and software since November 2009. In this paper we describe the hardware solution that implements the real-time charge readout in the ARGO-YBJ experiment, paying a special attention to the synchronization with the central data acquisition system, which is also described.