We report on measurements of a triple GEM (Gas Electron Multiplier) structure in high magnetic fields up to 5 T which were performed in the framework of the R&D work for a Time Projection Chamber at ...a future Linear Collider.
The determination of charge transfer is performed using a triple GEM structure installed into a small test chamber which is irraditated with a
55Fe source. The measurements are parametrised using a functional depen- dence on the electric setup which was motivated by detailed numerical simulations of a GEM using the programs MAXWELL and GARFIELD. This parametrisation of a single GEM foil is extended to a model which describes the performance of the triple GEM structure and allows to predict the parameter setup leading to minimum ion backdrift. Applying this setup, ion backdrift of only 2.5 permille is achieved. Also the use of MHSPs (Micro Hole Strip Plates) for ion backdrift reduction is investigated. Setting an optimised negative strip voltage, a suppression factor of approximately 4 is reached at 4 T magnetic field.
Additionally, the width of the charge cloud of individual
55Fe photons is measured using a fine segmented strip readout after the triple GEM structure. Charge widths between 0.2 and 0.3 mm RMS are observed, which appear to be dominated by the diffusion in the space between the individual GEMs. This charge broadening is partly suppressed at high magnetic fields.
We report on R&D work for a time projection chamber (TPC) at the International Linear Collider (ILC). A high resolution TPC with gas amplification based on micropattern gas detectors is one of the ...options for the main tracking system at the ILC detector. The physics to be studied and the environment at the ILC pose new challenges to the performance of all detector components. For instance the momentum resolution of the tracker should be improved by an order of magnitude with respect to LEP detectors. Significant progress towards this goal has been achieved recently and we report here on results of our groups which are studying a TPC concept with triple gas electron multiplier (GEM) structures for gas amplification. The required spatial resolution of 100 /spl mu/m has been achieved in measurements with a prototype TPC in high magnetic fields. The problem of ion backdrift has been studied and found to be significantly reduced in such GEM structures. In addition, a low mass TPC field cage has been designed and constructed demonstrating a way to minimise the total radiation length of the ILC tracker. A detailed simulation for a TPC has been developed. Simulations concerning the background at the ILC are ongoing.
The CMS Silicon Strip Tracker (SST) needs to be precisely calibrated in order to correctly interpret and reconstruct the events recorded from the detector, ensuring that the SST performance fully ...meets the physics research program of the CMS experiment. Calibration constants may be derived within several workflows, from promptly reconstructed events with particles as well as from commissioning events gathered just before the acquisition of physics runs. These calibration procedures have been exercised in summer 2008 and 2009, when the CMS detector has been commissioned using cosmic muons with and without magnetic field. In this paper the reconstruction strategies, the calibration procedures and the detector performance results from the latest CMS operation are described.
