Chapter 6
Summary and conclusions
In this work, after a discussion of the main astrophysical sources of high energy neutrinos and of experiments now underway for their detection, I have given a detailed description of the Antares experiment, in the framework of which this study has been carried out.
I have analysed in detail the most important noise sources affecting the exper-iment: 40K radioactive decays and bioluminescence.
Using data collected in the spring of 2003 by a prototype detector, I have analysed the time behaviour of bioluminescence and its correlation with ambient variables, like sea currents. I have developed algorithms aiming at extracting from the data isolated bursts of light emission from biological sources, and studied their frequency of occurrence and shape.
The average duration of bursts, even during periods of high biological activity, is found to be substantially shorter than half a second.
The height of bursts may exceed (as expected from biology) 5 M Hz, but small bursts of few tens of kHz above the baseline rate are 104 times more frequent.
I find that the shape of bursts can be well reproduced by a fast linear rise, followed by an exponential decay. From an analysis of the distribution of the decay time constant and its correlation with other burst variables an indication emerges that at least two distinct regions in the space of parameters are involved in the process.
This has been interpreted as due to the prevalence of two main emission mech-anisms belonging to different biological population. A comparison with data from biology may lead to the identification of the species. Since bioluminescence is highly season-dependent, and each species may probably have a different life cy-cle, this information may help in planning and optimizing the operation of the
140 CHAPTER 6. CONCLUSIONS
detector.
A first attempt has been made, using the same algorithms, to analyse Monte-Carlo generated bursts, provided by a member of the ANTARES collaboration. The very preliminary results I have obtained are still unsatisfactory. There is hope that, introducing in the MonteCarlo code the information I have obtained from real data, a more satisfactory simulation may be obtained.
In view of an envisaged future extension of the detector to one of a much bigger size, I have studied the possibility of replacing the conventional PMTs, now being used, with hybrid photodetectors (HPDs). I have designed one such HPD, checked its electro-optical and mechanical characteristics and computed, using an existing montecarlo program, the acceptance and background rejection power of a large detector using HPDs. The behaviour of such a detector has then been compared with one that uses conventional PMTs. The, still very preliminary, results obtained look promising.