Light at the end of the shower

The ANTARES detector is the largest deep sea neutrino observatory to date. This thesis describes a search for cosmic neutrinosources with ANTARES. There are three different types (or flavours) of neutrinos and several possible event signatures inthe detector. Until now, most analyses solely relied on one specific detection channel: A muon neutrino transforming intoa muon through a charged current interaction. This muon induces Cherenkov radiation along its track which in turn gets recordedby the detector's sensor modules. Other neutrino interactions create short cascades (or showers) of charged particles. Usingonly muon tracks as a signal channel reduces the detector's sensitivity to a fraction of the interactions cosmic neutrinoscan undergo. In this work, for the first time, all three neutrino flavours and all interactions channels are exploited in a search forcosmic neutrino sources. As a first step, a reconstruction algorithm for electromagnetic and hadronic shower events was developed(chapter 5). Later, these shower events were combined with muon candidates from an already existing muon track reconstruction.On this superset of events, searches for significant clustering were performed (chapter 7). A detection of such a clusterwould be a hint for a cosmic neutrino source. In the end, stringent limits for point-like and extended sources could be set(chapter 8).The successor of the ANTARES detector is called KM3NeT and is currently under construction on two different sites in the deepMediterranean Sea. It will encompass several cubic kilometres of instrumented volume and consist of thousands of optical modules;each housing not one large but 31 small photomultiplier tubes. A first prototype of this multi-PMT optical module has beendeployed within ANTARES. The results from the calibration and analysis of this prototype are presented here as well (chapter4)