Exploration of new data acquisition and background reduction techniques for the COBRA experiment
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Date
2011-09-20
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Abstract
This work has contributed improvements to several key aspects of the COBRA
double-beta decay experiment.
A new data acquisition chain was developed for pulse-shape based readout
of the COBRA coplanar grid (CPG) detectors. Prototype electronics for detector
signal transmission and amplification were developed, as well as a software
package with algorithms for pulse shape analysis of CPG detector signals. The
pulse shape data readout has already resulted in significant improvements of the
detector energy resolution. Pulse shape analysis has added interaction depth information
to data output of the experiment, which has already shown itself to
be an effective tool to suppress part of the background. A wavelet-based data
compression technique has been developed to cope with the significant increase
of data volume inherent to the recording of the full detector pulse shapes.
A flexible data acquisition software framework was developed along with the
new DAQ hardware chain. It is designed for both research and development
applications and long-term physics data collection and is now in production use
at several sites in the COBRA collaboration. The framework was also designed to
scale up to the requirements of a large-scale experiment and its modular nature
ensures that future components can be integrated easily.
This work has contributed to the reduction of the radiation background level
by over an order of magnitude, achieved by the combination of new CPG detector
coatings and contacting methods with nitrogen flushing of the COBRA setup to
create a radon-free environment.
For the first time, low-background physics data was taken with a CdZnTe pixel
detector. The results show that pixel detectors present an exciting option for the
future of the experiment.
Work is currently under way to scale up the new CPG electronics to a high
channel count. The COBRA CPG setup at LNGS is scheduled to be upgraded to
a higher number of detectors in 2011, which will all be run using the new DAQ
system. A detailed study of the detector pulse shapes using simulations and collimated
scans, currently in progress, will yield the necessary basis for advanced
CPG pulse shape analysis. This will, in the future, enable new form of background
suppression like separation between single-site and multi-site events.
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Keywords
Background reduction, Cadmium zinc telluride, CdZnTe, COBRA experiment, CPG detector, DAQ, Data aquisition, Fast ADC, Majorana neutrino, Neutrinoless double-beta decay, Pixel detector, Pulse shape analysis