Advanced instrumentation for superheated liquid detectors in dark matter searches

Dissertação para obtenção do Grau de Doutor em Engenharia Física

The initial goal of the thesis work was to improve the performance of the instrumentation used in the SIMPLE dark matter search. Consequently, the ultimate objective is to find a possible candidate for Dark Matter or improve the knowledge of its nature. Upon a brief description of Dark Matter and the status of its search, the fundamentals of Superheated Liquid Detectors are presented. This thesis presents a robust acoustic instrumentation together with a new method for the identification of bubble nucleations in Superheated Droplet Detectors. This is accomplished through straightforward signal processing techniques applied to the acoustical recording of the nucleation events, which consists of pulse shape identification procedures. A set of tests are presented to evaluate the performance of the proposed algorithms, as well as the new and more reliable instrumentation. An effort to locate a bubble nucleation in the SDDs is accomplished through some elaborated signal processing techniques applied to the acoustical recording of the nucleation events. These include the application of wavelets, the chirp-z transform and pulse shape identification procedures to locate temporally and validate the nucleation for its spatial localization. Acoustic and SDD associated backgrounds are completely discriminated with the developed signal processing techniques. Results from systematic studies are presented for the instrumentation and SDD response,which are used in the SIMPLE dark matter search experiment and possibly in neutron dosimetry. A new bubble nucleation efficiency is drawn out, together with particle discrimination confirmation determined throughout a-n calibrations. SIMPLE's Phase-II Dark Matter results are presented with the implementation of the complete instrumentation in operation for SDDs. These results are simultaneously presented with the full characterization of the local background scenario and gained knowledge of SDD characteristics and dynamics. Interpretations of these results are laid out. The direct future is given through the R&D of a rejuvenation superheated liquid detector, the Big Droplet Chamber. A prototype of this new Bubble Chamber is shown together with its first results of a more prevailing ultrasound acoustic system. Which can possibly reveal in the near future, unseen aspects such as the bubble formation stage in superheated liquids up to now.

Fundação para a Ciência e Tecnologia - (SFRH/BD/46545/2008)