Abstract
The NEMO Phase-2 tower is the first detector which was operated underwater for more than one year at the "record" depth of 3500 m. It was designed and built within the framework of the NEMO (NEutrino Mediterranean Observatory) project. The 380 m high tower was successfully installed in March 2013 80 km offshore Capo Passero (Italy). This is the first prototype operated on the site where the italian node of the KM3NeT neutrino telescope will be built. The installation and operation of the NEMO Phase-2 tower has proven the functionality of the infrastructure and the operability at 3500 m depth. A more than one year long monitoring of the deep water characteristics of the site has been also provided. In this paper the infrastructure and the tower structure and instrumentation are described. The results of long term optical background measurements are presented. The rates show stable and low baseline values, compatible with the contribution of 40K light emission, with a small percentage of light bursts due to bioluminescence. All these features confirm the stability and good optical properties of the site.
Highlights
High energy neutrinos are expected to be messengers from astrophysical objects where hadronic interactions may take place
A telescope in the Mediterranean Sea has a field of view for up-going neutrinos, that are the golden channel for neutrino astronomy, of 87 % covering a very large part of the of the Galactic Plane including the Galactic Centre
From the Ethernet FCM (EFCM), the PMT optical data-stream is routed through a 1 Gb Ethernet network to the first layer of the Trigger and Data Acquisition System (TriDAS), composed of two Hit Managers (HM) processes running on two CPUs
Summary
High energy neutrinos are expected to be messengers from astrophysical objects where hadronic interactions may take place. Since 1998, the NEMO (NEutrino Mediterranean Observatory) collaboration carried out research activities aimed at developing and validating key technologies for a km3-scale underwater neutrino telescope [7,8,9,10] as well as searching and characterizing a deep-sea site suitable for the installation of the detector. A deep-sea site at a depth of 3500 m, about 80 km offshore Portopalo di Capo Passero (Italy) (36◦ 17 48 N, 15◦ 58 42 E), was identified as optimal for the installation of the underwater neutrino telescope (Fig. 1). In the following it is indicated as the KM3NeT-It site.
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