Analysis of Data Recorded by a Large Prototype TPC Equipped with a Two Layer GEM System

Abstract

Abstract A TPC is considered as tracking detector at a future linear collider. The LCTPC (Linear Collider TPC) collaboration has therefore constructed a prototype TPC for R&D purposes. MPGD readout structures, such as Micromegas or GEMs, are being considered for the TPC since the demands on space and momentum resolution can not be met with a traditional wire based readout. The prototype TPC is placed in a 1 Tesla magnet at DESY and tested using an electron beam. Analyses of data taken during two different measurement series, in 2009 and 2010, are presented here. The TPC was instrumented with a two layer GEM system and read out using modified electronics from the ALICE experiment, including the programmable charge sensitive preamp-shaper PCA16. The PCA16 chip has a number of programmable parameters which allows studies to determine the settings optimal to the final TPC. Here, the impact of the shaping time on the space resolution in the drift direction was studied. It was found that a shaping time of 60 ns is the best setting (of the available choices) for a sampling frequency of 20 MHz. In addition, the resolution in the bend plane was studied. Unfortunately, the measurements suffered from distortions in the electric field close to the readout, which deformed the track projections and had to be corrected for. This was done using the Millipede method. The final results obtained are a resolution of 59.1 ± 0.4 μm in the bend plane and 204 ± 9 μm in the drift direction, both extrapolated to zero drift distance. The measured values are consistent with the final goal of the ILD.