Optimization Studies and Performance Simulations for the Time-of-Flight System of PANDA
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Tuesday, 26 June, 2018
The Panda experiment, currently under construction at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, addresses fundamental questions in hadron and nuclear physics via interactions of antiprotons with nucleus / nuclei. The High Energy Storage Ring will provide an antiproton beam with a momentum range of 1.5 – 15 GeV/c and an average collision rate of 20~MHz on a fixed target. Due to a missing hardware trigger and a continuous data acquisition in the \panda experiment, a highly advanced online analysis is needed to achieve an online data reduction of a factor 100 – 1000 before storage. A missing collision time (\t0), high interaction rates and overlapping event data in the sub detector systems further increases the difficulty of the event reconstruction. The Barrel Time-of-Flight detector (Barrel TOF) for Panda, being developed at the Stefan Meyer Institute, will be one of the key components in Panda to determine the origin time of particle tracks, to ensure a disentanglement of overlapped hits from neighboring collisions and to provide information about \t0. Another important task of the Barrel TOF is to provide particle identification (PID) for charged particles together with the Cherenkov-based PID detectors, which is especially important for particle momenta below 700 MeV. In order to achieve a time resolution of < 100 ps, required for the mentioned disentanglement of the data, while keeping a minimal material budget, the detector will be realized as a barrel-shaped scintillator tile hodoscope. It covers the central region of the detector with a diameter of about 1~m and a length of about 2~ m. The sensitive area of about 6~ m² consists of 1920 scintillating tiles with a dimension of 90 x 30 x 5 mm³ each, readout by 8 Silicon Photomultipliers (SiPMs), with 4 on each end connected in series. The signal transmission lines are embedded in a multilayer PCB backplane. It also serves as the mechanical frame to minimize the material budget. During beam tests a single tile time resolution of about 55 ps in standard deviation has been achieved. It was a crucial and challenging task to implement the Barrel TOF in the simulation framework, PandaRoot. This allowed the optimization of the detector geometry using Monte Carlo simulations and the investigation of the requirements for the readout electronics and led to the described design. In the second phase the performance of the Barrel TOF was evaluated and optimized for the entire experiment. For this purpose software algorithms based on the Barrel TOF system were developed and implemented in PandaRoot, i.e. triggering, event sorting, start time reconstruction and particle identification. Among other work this allowed the submission of the Technical Design Report for the Barrel TOF in February 2017 to FAIR, which has been accepted. After this the developed and implemented algorithms as well as the acquired knowledge were used to advance the general \panda reconstruction chain. Together with our international collaborators the first steps towards a dynamical tracking and event reconstruction algorithm, which combines the signal of all sub detector systems of Panda, were developed.