Analysis of the space-time microstructure of cosmic ray air showers using the HADES RPC TOF wall

Abstract

Cosmic rays have been studied, since they were discovered one centuryago, with a very broad spectrum of detectors and techniques. However,never the properties of the extended air showers (EAS) induced by highenergy primary cosmic rays had been analysed at the Earth surface witha high granularity detector and a time resolution at the 0.1 nsscale. The commissioning of the timing RPC (Resistive Plate Chambers)time of flight wall of the HADES spectrometer with cosmic rays, at theGSI (Darmstadt, Germany), opened up that opportunity. During the lastmonths of 2009, more than 500 millions of cosmic ray events wererecorded by a stack of two RPC modules, of about 1.25 m2 each, ableto measure swarms of up to ∼ 100 particles with a time resolutionbetter than 100 ps. In this document it is demonstrated how such arelative small two-plane, high-granularity timing RPC setup mayprovide significant information about the properties of the shower andhence about the primary cosmic ray properties.