Measurement of signal propagation in RPC readout panels for ATLAS phase 2 upgrade.

The major phase 2 upgrade of the ATLAS Muon Spectrometer involves the installation of a trigger station in the innermost part of the barrel. The trigger chambers are a new generation of RPCs with 1 mm separation between 1.4 mm thick resistive electrodes. In planar electrode detectors the gain grows exponentially with the distance traveled by the electrons in the amplification gap, so as the thickness of the gap is only 1 mm, the average charge signal that is produced is much smaller than in traditional RPCs from 2 mm gas gap. Consequently, the signal induced on the strips facing the gas gap is much smaller. This entails the need to integrally transport the induced signal to the first amplification stage of the front-end electronics. This communication focuses on the measurement of the signal propagation along the reading strips of these 1 mm gas gap RPCs with and without a metal perimeter frame inside the strip panels. The signal simulation in this type of RPC is also presented. The simulated characteristic impedance and crosstalk were compared to the measured value to validate this model. This method is applied to several RPC design geometries, including the proposed new reading scheme.