The ARGO-YBJ experiment in Tibet

The setting up of the ARGO detector at the YangBaJing Cosmic Ray Laboratory (4300ma.s.l., Tibet, P.R. China) has been completed during the last spring (2007). It consists of a central carpet made of 130 identical sub-units of 12 RPCs each (a ‘‘cluster’’), covering a surface of about 5800m2 with 93% active area, and a guard ring of 24 further clusters of the same type surrounding the centralcarpet with a lower sampling density. Signals are picked up by external electrodes of small size, thus allowing the sampling of EAS with high space-time granularity. Shower events are detected at a trigger rate of about 4 kHz. Events with a few particles detected by a singlecluster are counted in scaler mode on a time base of 500 ms. The intrinsic modularity of the ARGO detector allowed us to collect data even during the setting-up period, using only the central carpet (or even part of it). Some preliminary results from the analysis of events collected in a few months of data taking are presented.