The LHCb RICH PMTs Readout Electronics and the Monitoring of the HPDs Quantum Efficiency

LHCb is one of the four main experiments under construction on the Large Hadron Collider at CERN. Its purpose is to study CP violation in B mesons and to look for new physics effects in rare decays of b-hadrons. Particle identification will be essential to enhance the signal/background ratio in the selection of physics channels. For this reason, the Ring Imaging Cherenkov technique has been implemented: two RICH detectors (RICH1 and RICH2) have been designed to cover the wide momentum range 1-150 GeV/c. The produced Cherenkov photons will be focused on two planes of Hybrid PhotoDetectors (HPDs), which are sensitive to external magnetic fields and then need to be shielded. Despite the shielding, however, there will be some fringe field inside the HPDs volume and so it is necessary to experimentally check what is the behaviour of each photodetector when the LHCb dipole magnet is on and the HPDs are illuminated by test patterns. In RICH2, two LED projectors based on the Digital Light Processing technology are exploited to generate the test patterns, which have to be precisely aligned on the two HPD planes. The matching procedure is carried out using six PMTs permanently placed inside the HPD matrices. The work described in this thesis concerns the design, realization and test of the PMTs readout system, both on the HW and SW level. In the last chapter, I will also try to evaluate the possibility to periodically monitor the HPDs Q.E. using the same beamer selected for the magnetic distortion tests. Chapter 1 is an introduction to CERN and the LHCb experiment. Paragraph 1.2 focuses on the two RICH sub-systems, while in 1.3 the HPD working principle is described. In paragraph 2.1 I describe the PMTs installed in the RICH2, while the rest of the chapter is dedicated to the DLP projectors to be used during the magnetic distortion tests. In particular, 2.2 illustrates the DLP technology, while 2.4 and 2.5 are about the beamers tests. Chapter 3 is dedicated to the PMTs readout electronics design, realization and test. After a theoretical study carried out in paragraph 3.1, in 3.2 I describe the realized shaper amplifier prototype. In 3.3 the choice of the digitiser to be installed in cascade to the shaper is discussed and the DAQ software program is described, while 3.4 summarizes the results obtained testing the prototype with the real signals. In 3.5 the final six-channel shaper amplifier + ADC is presented and tested, while 3.6 describes the installation of this module in the pit environment. Finally, in chapter 4 I estimate the sensitivity of the HPD Q.E. monitoring based on the magnetic distortion test apparatus.