Underwater Neutrino Detection in the Mediterranean Sea: From Present to Future

The observation of high-energy extraterrestrial neutrinos is one of the most promising future options to increase our knowledge of non-thermal processes in the universe. Neutrinos are e.g. unavoidably produced in environments where high-energy hadrons collide; in particular this is almost certainly true at astrophysical accelerators of cosmic rays, which thus could be identified unambiguously by sky observations in "neutrino light". To establish neutrino astronomy beyond the detection of single events, neutrino telescopes of km3 scale are needed. In order to obtain full sky coverage, a corresponding detector in the Mediterranean Sea is required to complement the IceCube experiment currently under construction at the South Pole. The groups pursuing the current neutrino telescope projects in the Mediterranean Sea, ANTARES, NEMO and NESTOR, have joined to prepare this future installation in a 3-year, EU-funded Design Study named KM3NeT (in the following, this name will also denote the future detector). This report highlights some scientific key questions, addresses the status of current projects and outlines the path towards the realization of KM3NeT.