Simulations of a high-rate TPC for PANDA

The PANDA experiment at the new FAIR facility in Darmstadt, Germany, will be investigating unresolved questions of non-perturbative QCD. The experiment is designed to make use of internal targets in the p storage ring HESR (design luminosity: 2 . 10³² cm^-2 s^-1, pp-annihilation rate: 2 . 10⁷ s^-1), requiring continuous operation of all detectors. One option for its central tracking unit is a Time Projection Chamber (TPC) with Gas Electron Multiplier (GEM) readout. One of the main challenges due to the continuous operation at high rates is the buildup of ion space charge in the chamber leading to drift distortions of the electrons on their way to the readout. This compromises the track reconstruction capabilities of the detector. To be able to correct for this effect, space charge buildup has been simulated with Monte Carlo methods based on realistic models. Space charge densities of up to 60 fC cm^-3 in certain regions are reached, leading to absolute drift distortions of up to 10 mm on the readout-plane. The feasibility of a laser calibration system to correct these distortions has been investigated on simulation level. Based on full simulations of the detector physics and response (including electronics) we are able to correct for drift distortions within 300 μm precision. In this paper the effect of the drift distortions and their correction on momentum reconstruction and resolution is shown. Another important challenge at the high rates expected for the PANDA TPC is track deconvolution. Tracks from up to O(1000) events may be present in the TPC volume at the same time, requiring an efficient and fast method of track separation and event association. In this paper, two approaches for future fast online tracking are discussed: (i) a track following algorithm and (ii) a five-dimensional Fast Hough Transform (FHT) algorithm for massively parallel pattern recognition on a Graphics Processing Unit (GPU).