Speaker
Hans Martin LJUNGGREN
(Lund University)
Description
The LCTPC-collaboration studies the technical aspects of a TPC with MPGD readout structures for a detector at a future Linear Collider such as the ILC or CLIC. For this a test facility with a 1 Tesla magnet and a large prototype TPC was set up at DESY. An analysis of data taken in 2010 at the DESY test beam T24, using this TPC equipped with a two layer GEM system, has been performed. Three GEM modules, out of maximum seven, were used in a geometry that allowed the recording of tracks, which traversed the full radial distance (about 60 cm track length) of the TPC. More than 7000 pads, of size 1.1 x 5.26 mm2, were read out by a modified version of the ALTRO-electronics, used in the ALICE experiment, containing the programmable charge sensitive preamplifier PCA16. The sampling rate was 20 MHz. The main purpose of the measurements was to study the performance of the GEM system and to determine the resolution in space and momentum. Straight tracks, taken with zero magnetic field, were used for mechnanical alignment of the modules using the Millipede method, which however suffered from the non-existing external silicon detectors as reference. An inhomogeneous electric field in the gas amplification system, the magnitude of which was dependent on the impact position of the beam, also had to be corrected for. Tracks recorded with a magnetic field were fitted to a second order polynomial in the transverse plane and analysed with the same method to account for the E x B distortions. After all corrections had been done the residuals in all cases are nicely clustered around zero along the full length of a track. The final results obtained are σrφ = 0.0613 ± 0.0006 mm and σz = 0.259 ± 0.002 mm, respectively, both extrapolated to zero drift distance. These values are consistent with the final goal of the ILD.
Author
Hans Martin LJUNGGREN
(Lund University)
