Feasibility of measurements of cosmic ray composition by means of RPC digital read out in ARGO-YBJ

The ARGO-YBJ experiment is currently under construction at the Yangbajing Cosmic Ray Laboratory (4300 m a.s.l.). The detector will cover 74 × 78 m 2 with a single layer of Resistive Plate Counters (RPCs), surrounded by a partially instrumented guard ring. Signals from each RPC are picked up with 80 read out strips 6.7 cm wide and 62 cm long. The strip read out allows one to count the number of secondary charged particles from air showers induced by cosmic rays with an energy threshold of a few TeV. In this paper, we show that the digital response of the RPC can be used to discriminate between different models concerning the composition of the primary cosmic rays up to an energy of a few hundreds of TeV. In order to extend the dynamical range up to PeV energies, an analog read out has been implemented by instrumenting each RPC with two large size electrodes (Big Pads).