The Data Pre-processing For CBM-TOF

In the last decades, our nature was deeper understood benefiting from the fast development of science and technology. The Large Hadron Collider (LHC), which is the world’s largest and highest-energy particle accelerator, brings human to enter TeV beam energy level. Like Relativistic Heavy Ion Collider (RHIC) and other high energy colliders, it helps us explore the Quantum Chromo-Dynamics (QCD) phase diagram of strongly interacting matter. These accelerators and experiments are focused on the very high energy with low baryonic density. To exploring the phase diagram in the region of very high baryonic densities, the Compressed Baryonic Matter (CBM) experiment and SIS100/300of the Facility for Antiproton and Ion Research (FAIR) are planned in Germany. As the high interaction rate is up to10MHz for the Au+Au collisions at25AGeV, an efficient fast trigger is difficult to be implemented. Thus, a free stream data acquisition (DAQ) is planned for the CBM. The Time-of-Flight (TOF) detector is one of the core detectors of the CBM experiment. It provides particle identification for all charged hadrons emitted from the beam-target interactions.In order to achieve a time resolution of80ps within the free stream DAQ system, it is important to design high time resolution detector, with fast readout electronics, and online data processing system. The TOF detector is decided to use Resistive Plate Chamber (RPC) for the whole wall. The front-end electronics with PADI (PreAm-plifier DIscriminator) chip and GET4(GSI Event-Driven TDC with4channels) chip is an option for the detector. The SysCore board is used as Readout Control (ROC) for data transferring to DAQ. All kinds of data will be readout from front-end elec-tronics and sent to DAQ for the CBM experiment operating a free streaming DAQ system. In order to reduce the bandwidth without detector performance loss, an additional function, data pre-processing, is required to be implemented in the TOF readout chain. The main work during my stay at Physikalisches Institut Heidelberg from October2010to October2012is to implement this data pre-processing in the readout chain. In this thesis, I will present the analysis of GET4chip data, design and test of data pre-processing for TOF readout chain.In the first two chapters, the CBM experiment and the TOF detector are intro-duced. Both the pad RPC and strip RPC are considered as for the TOF detector, and are described in detail for the data pre-processing is related to the geometry of the RPC detectors.Chapter3introduces the current (during my stay in Heidelberg) TOF front-end electronics and its readout. The PADI board and GET4board are described in detail. The design of data pre-processing is based on the characters of these boards. As the front-end electronics and its readout are still under developed, the new version of them is described at the end of the chapter, although they are not considered in the design of data pre-processing.As the data pre-processing is very specific to the front-end electronics and readout, the analysis and evaluation on the data pre-processing is necessary. In chapter4, a typical offline analysis on GET4data is described. The analysis is a preliminary standard way for the PADI+GET4+ROC readout chain. The ROC data rate based on the current readout chain is illustrated in this chapter and also the relation between noise rate and PADI threshold. The result from a beam test is presented. It shows that the time ordering of GET4data, data storage reduction and filtering noise should be solved before being sent to DAQ.Referred on the analysis in chapter4, we designed a data pre-processing for ROC firmware in chapter5. It is consists of three unit, a data pre-processing unit, a monitor unit and a control unit. The data pre-processing unit is the main part. It has two functions, hit filtering and cluster filtering. The goal of hit filtering is to remove useless data from GET4chip and to reduce the data rate to DAQ by transferring hits with time stamp and time-over-thrcshold (TOT) values instead of edge data from GET4chip. The cluster filtering focuses on collecting relative hits and removing useless hits. Further more, the cluster filtering is the first stage of data processing for First Level Event Selection (FLES). The monitor unit is designed to monitor the front-end electronics and ROC itself. The control unit is planned to realize the automatic threshold setting. Due to the limited resource of current FPGA used in the ROC, it has not been implemented yet.Before the data pre-processing to be implemented in the readout chain, its pa-rameters have to be found out and its performance has to be evaluated. A C/C++code for these tasks is designed under the Go4(GSI Object Oriented On-line-Offline) environment. The code can run for offline analysis and online monitoring. Specially, it uses the method as in FPGA to process the GET4data. A simulation with raw data got from a beam test as inputs is done with the code and correct parameters are determined during the simulation. The data pre-processing with the hit filtering function implemented was tested in beam in November2011in Julich in Germany. The data pre-processing with hit filtering and cluster filtering functions was tested in lab. The test setup and results are presented in chapter6.The main tasks and contributions are as followed.·Implement module on the data pre-processing into the readout controller (ROC) firmware and realized online data suppression for testing beam data of more than90%.· Developed the software for expecting streaming TOF data in offline analysis framework and transfer the codes to free streaming online environment.· Identified the main requirement for the data preprocessing of the full CBM-TOF data processing chain and implemented interface in the current ROC firmware. As the front-end electronics, readout electronics, DAQ and FLES system are still in development, the data pre-processing functions for CBM-TOF in readout chain will enter developing stage in future.