ALICE/PHOS Noise And Trigger Electronics Study

A Large Ion Collider Experiment (ALICE) is dedicated to study Quark Glu-on Plasma (QGP).The studies of the QGP are very important to understand the early evolution of our universe. High energy photon is one of most important probes of QGP; the Photon Spectrometer (PHOS) is a high precision calorime-ter for detecting photons on ALICE. The PHOS energy resolution is mainly determined by the electronics noise. Therefore, in order to achieve a high ener-gy resolution, studying PHOS electronics noise is very important. The PHOS ability for selecting valid incident photons and events have a great impact on experiment’s detecting efficiency, the PHOS trigger algorithm and circuit play an crucial role in improving PHOS detecting efficiency.The performance of Avalanche photodiode (APD) affects the precision of calorimeters directly, so it is very important to study the gain of the APD. This thesis has designed a compact PHOS detector platform. With this platform, we had compared the performance of two types APDs which used on PHOS and EMCal detectors. When applied same level of bias voltage, the APD used on PHOS detector could achieve lower and more stable gain compared to the APD used on EMCal detector.Electronics noise is one of the main reasons which affect detector perfor-mance. Thermal noise, shot noise,1/f noise and lossy dielectric noise arc the main sources of PHOS electronics noise:they affect PHOS energy and time res-olution directly. This thesis has analyzed and studied the noise come from each key components and circuits of PHOS readout electronics. By analyzing the noise sources of APD, charge sensitive pre-amplifier (CSP) circuit, shaper circuit, quan-tization noise, the thesis provides a theory method for noise calculation. And, the main noise of PHOS electronics is the APD shot noise caused by APD dark current.High efficient trigger system could help to provide more detector data for physicists. So, trigger circuit is very important in the detector. PHOS detec- tor is one of most fast detectors on ALICE, it is responsible for providing fast regional level-0 and level-1 triggers to ALICE Central Trigger Processor (CT-P) which generates global triggers for ALICE. So, the thesis presents two level-0 trigger algorithms for FPGA implementation:Direct Comparison Algorithm and Weighted Sum Algorithm, and three level-1 triggers generating algorithms:single photon trigger, collision centrality trigger and high-middle-low threshold trigger. The thesis has also analyzed the waveform function of input signal of trigger cir-cuit (Analog-Or signal), and studied various performance of trigger algorithms via simulation. The level-0 and level-1 trigger generating algorithms have been implemented in the FPGA on Trigger Region Unit (TRU) on PHOS detector. The FPGA firmware is already used on ALICE/PHOS detector successfully and works stably.