TPC readout studies at Carleton
Advances in our knowledge of the structure of matter during the past century have been made possible largely through the development of successive generations of high energy particle accelerators as well as a continued improvement in detector technologies. Starting in 2007, the Large Hadron Collider (LHC) at CERN will be able to explore physics above a TeV - an energy equivalent to one thousand times the mass of a proton. The LHC could discover the Higgs particle required to explain the very existence of the phenomenon of mass or hidden new dimensions in nature. Mankind's quest to understand nature at its deepest level will not end with the discoveries at the LHC. A world consensus has emerged recently to construct a new 500 to 1000 GeV electron-positron International Linear Collider (ILC) as the next high energy accelerator for particle physics. Particle physicists are convinced that the ILC is essential to extend and clarify LHC discoveries and to make precision measurements to reach a deeper understanding of the nature at subatomic level. An international panel of experts has recently decided that the ILC accelerating structure will be based on superconducting radio frequency technology developed at DESY in Germany. The future ILC will have a wide ranging physics program and the performance requirements for the detectors are more stringent than at previous accelerators. An electron-positron interaction at the ILC will produce a large number of energetic charged and neutral particles. Backgrounds, unrelated to physics of interest, will be higher than at previous e+ e- colliders.
A large volume Time Projection Chamber (TPC) is the favored detector for charged particle tracking at the ILC. The TPC is a fully 3-dimensional high speed electronic camera designed to measure sub-atomic charged particle tracks in a gas. The present ILC detector requirements call for the TPC to measure about 200 track points with a spatial resolution of less than 100 microns. Diffusion effects in a gas set the ultimate limit on the best achievable TPC resolution. The ILC TPC resolution goal, ambitious and close to the diffusion limit, is nearly two times better than has been achieved by existing TPCs for which the resolution limit comes from unavoidable systematic effects.
A TPC read out with a system of Micro Pattern Gas Detectors (MPGD) such as the Micromegas or the Gas Electron Multiplier (GEM) will not have the systematic problems of existing wire/pad TPCs. The MPGD-TPC could, in principle, reach the diffusion limit. However, charge position determination methods that work for the wire/pad TPC are less effective and make the MPGD TPC resolution significantly worse than the diffusion limit.
Recent R&D at Carleton has focused on developing new techniques to improve the MPGD-TPC resolution over that achievable with normal techniques. A new concept based on the phenomenon of charge dispersion in MPGDs with a resistive anode has been developed which could enable one to approach the statistical limit of resolution from transverse diffusion. Our recent studies with the GEM and the Micromegas detectors instrumented with a resistive anode are quite promising as a possible readout option for the LC TPC.