Optimization, Synchronization, Calibration and Diagnostic of the RPC PAC Muon Trigger System for the CMS detector

The Compact Muon Solenoid is one of the four experiments that will analyse the results of the collisions of the protons accelerated by the Large Hadron Collider (LHC). The collisions of proton bunches occur in the middle of the CMS detector every 25 ns, i.e. with a frequency of 40 MHz. Such a high collision frequency is needed because the probability of interesting processes, which we hope to discover at the LHC (such as production of Higgs bosons or supersymmetric particles) is very small. The objects that are the results of the proton-proton collisions are detected and measured by the CMS detector. Out of each bunch crossing the CMS produces about 1 MB of data; 40 millions of bunch collisions per second give the data stream of 40 terabytes (1013) per second. Such a stream of data is practically not possible to record on mass storage, therefore the first stage of the analysis of the detector data is performed in real time by the dedicated trigger system. Its task is to select potentially interesting events (bunch collisions) for further offline analysis and to reject events containing only standard interactions. In case of the CMS experiment the trigger system is divided into two stages: the Level-1 Trigger, realised entirely with use of the custom electronics, and Higher Level Triggers, that are implemented in the software performed by the farm of ~1000 computers. The RPC (Resistive Plate Chambers) PAC (Pattern Comparator) system, which is a subject of that thesis, is a part of the Level-1 Muon Trigger System. Its task is to identify muons and measure their transverse momentum. The works described in this thesis had one main goal: to assure best possible performance of the RPC PAC trigger system, which in turn translates into quality of the data acquired by the CMS experiment and – at the end – quality of the physic results. In the thesis, two main subjects are discussed. The first is the control and monitoring of the RPC PAC trigger system. The RPC PAC trigger is a complex, large and distributed system, composed of thousands of electronic devices of many different types. Without external control of that electronics it would be not possible to develop, build and operate the RPC PAC trigger. Therefore, the dedicated hardware, firmware and software solutions were developed, which formed an integrated system for control, configuration, monitoring and diagnostics of the PAC trigger. These solutions enable us to evaluate the state of the detector and trigger electronics and identify the malfunctions in a reliable and efficient way and appropriately present the results for users. The second part of the thesis is devoted to the issues concerning the synchronization of the data flowing thought the PAC trigger. The RPC PAC system, similarly as the whole Level-1 trigger, is a synchronous system. It means that it works synchronously to the LHC bunch collisions (i.e. is driven by the 40 MHz clock delivered by the accelerator control). In case of the PAC system, the synchronization requirement is particularly explicit: the Pattern Comparator algorithm to identify a muon requires time coincidence (within 25 ns) of signals from many different chambers. However, a particle flying with the speed of light passes only 7.5 meter (i.e. distance smaller than the length of the CMS detector) in 25 ns. The signals in the electrical or optical cables pass only 5 meters during 25 ns, while the length of the fiber cables used in the system for transmitting the detector data exceeds 100 meters. Thus, to assure that the information concerning each bunch crossing from many chambers are delivered to the trigger logic at the same moment, special methods were developed and are described in the Chapter 5.