Philipp Leitl

2015
Max-Planck-Institute for Physics Munich

Abstract: The High Energy Accelerator Research Organization (KEK) is operating Japans largest particle physics laboratory. The particle accelerator KEKB, which is located in Tsukuba, collides electrons and positrons with a center of mass energy of about 11 GeV. These colli- sions produce a lot of different new particles. Some of them are able to leave the beam pipe, others decay before they even reach it. Two of these short living particles are of special interest: the neutral B meson and its anti-particle, the anti B meson. A different behavior of particle and anti-particle breaks the CP-symmetry. The understanding of this CP violation may help explain the origin of the universe, where matter and anti-matter were created in equal parts, but after a process of annihilation the today visible universe remained as surplus. It was the objective of the Belle experiment to study the influence of CP violation on this observed asymmetry between matter and antimatter. For this purpose the collision products of KEKB were recorded by a detector system also called Belle. During its runtime from 1999 to 2010 the experiment provided first proof of CP-violation in the B meson system, measured a lot of decay channels of these particles and observed a number of new particles. The BaBar experiment at SLAC was built for the same purpose and could confirm the Belle data. After the successful verification through the experimental results, Makoto Kobayashi and Toshihide Maskawa received the 2008 Nobel Prize in Physics for their work on CP violation. To continue the research on this field the accelerator at KEK is at the moment upgraded to SuperKEKB to reach a new design luminosity of 8 × 10^35 per cm^2 s. This means, that the upgraded accelerator will have a much higher collision rate. In combination with the aim to make measurements with even more precision, it became necessary to upgrade the detector as well. The new Belle II detector is a combination of improvements of the Belle detector and the introduction of new technologies. One of the new parts will be the innermost subdetector, the Pixel Vertex Detector, which will help to measure decay vertices with a resolution of about 20 μm. This detector is currently under construction at the Max Planck Institute for Physics in Munich in collaboration with several institutes all over Europe. The sensors are produced at the semiconductor laboratory of the Max Planck Institute in Munich. The detector consists in total of almost 8 million DEPFET pixels. This new technology requires specific electronics for controlling and readout. Therefore three different kinds of ASICs are mounted very close to the sensors. Because of space limitations ball grid arrays are used for the contacts to the electronic circuitry. For placing the ASICs onto the sensor module a so called flip chip method is used. After the mounting process a quality assurance is needed to verify that the integration was done correctly and that the circuitry and the electronics are working properly. The designers and the production crew decided to use boundary-scan tests, an industrial standard, as part of the quality assurance. The task of the author was to prepare a testing setup and to implement boundary-scan in time for the series production of the sensor modules. It was necessary to prepare the basic conditions in terms of hardware and software. To gain access to the required nets a breakout board was designed and produced. The description of the boundary-scan implementation in the ASICs, so called BSDL files, were missing or not complete. Also the netlist file, which describes the circuitry, had to be adapted to match the different versions of sensor modules and the ASIC description in the BSDL files. These files were created following the guidelines of the relevant IEEE standard and the special requirements of the acquired commercial boundary-scan software. After the completion of the single parts, the combined system was tested and further optimized. The available preproduction modules of the senor were used for the first measurements. From these results a dedicated boundary-scan project file was created for the series production modules. Also a test setup for the quality assurance during the series production was prepared including a probe station with needle cards. For the final design of the sensor modules no changes are expected, which would have influence on the performance of the boundary-scan system. In this way it is now capable to contribute its part to the quality assurance process during the production of the sensor modules for the Pixel Vertex Detector.

Note: Presented on 01 12 2015
Note: MSc