European Commission logo
English English
CORDIS - EU research results
Content archived on 2024-05-29

Signal processing, data analysis, and computation in European Astroparticle physics experiments

Final Activity Report Summary - SPACE-APEX (Signal Processing, Data Analysis, and Computation in European Astroparticle Physics Experiments)

The SPACE-APEX proposer had an unusual combination of experience and skills in the field of particle astrophysics. SPACE-APEX proposed to import data analysis techniques, previously used by the author on gravitational wave search experiments, into the efforts to analyse data from European experiments searching for gravitational waves and weakly interacting dark matter.

Firstly, I discussed work on the GEO600 gravitational wave detector. SPACE-APEX supported the application of a Multiplicative Fourier transform (MFT) relationship, derived by the proposer, between the Fourier transforms of overlapping data sets. MFT allowed for real time time-domain tracking of multiple Fourier components of arbitrary data. Moreover, MFT eliminated noise glitches at the boundaries between successive Fourier transforms.

The first application of MFT was the removal of excess noise in narrow lines polluting the GEO600 strain spectrum. Improvement of a factor of ten in the noise from these sources was demonstrated. The application of MFT to close vibration modes of mirror suspensions was under investigation by the time of the project completion. This work added significant value to the available tools for the analysis of gravitational wave data. Investigations into related techniques showed promising results in the frequency analysis of data with irregularly spaced time samples, which was another problem of great importance not only in gravitational wave data analysis research, but also elsewhere.

The second research domain was the subtraction of broadband noise due to alignment fluctuations from strain GEO600 data. A noise subtraction scheme was developed and used to demonstrate a reduction, by a factor of at least ten, in projected noise from this source. Based on the output of this simulation noise subtraction was implemented in GEO600. Moreover, research was conducted on dark matter experiments, namely ZEPLIN II, DRIFT II and EURECA.

ZEPLIN-II was a liquid xenon based ionisation-scintillation detector for dark matter. The SPACE-APEX project enabled the design and writing of a software package, unzap, used to parameterise target pulses. The software had a sophisticated graphical user interface and ran in a client-server mode allowing remote data. This software was crucial to the success of the ZEPLIN II experiment. The relevant work contributed significantly to several submitted papers.

DRIFT II was a gas time projection chamber aiming to achieve sensitivity to the direction of Weakly interacting massive particles (WIMPs). System identification was applied to the DRIFT II experiment data and shaping amplifiers were used to remove baseline fluctuations from the detector wires. Models of the shaping amplifiers were also developed. Software written by the author for LIGO was used to convert these models into working digital filters. These models allowed for inversion of the filtering operation. The resulting 'anti-filtered' pulses recovered key information, such as pulse duration. Moreover, inverse filtering removed a poorly understood high frequency ringing close to the pulse rising edge. This suggested that the cause of these pulses was at the input of the shaping amplifiers. Finite element modelling was underway, following the project completion, in order to investigate this idea.

Regarding further detector characterisation work, Dr Pawel Majewski, working under the SPACE-APEX grant, carried out a parallel programme of modelling the passage of charged ions in the DRIFT II time projection chambers. Dr Majewski generated detailed models for the electric fields in the drift chambers, the collection of charge on the anode and gate wires and the formation of pulses at the inputs of the front end charge amplifiers.

Finally, EURECA was a proposed one tonne WIMP detector planned to be developed by a multinational, i.e. French, German and British, collaboration in the following decade. The author applied his experience in vibration isolation in LIGO to the EURECA design. SPACE-APEX supported early studies into options for vibration isolation, work towards surveying of the vibration environment of the EURECA site and gathering of information on the specific vibration isolation issues.