Long term monitoring of the optical background in the Capo Passero deep-sea site with the NEMO tower prototype

The NEMO Phase-2 tower is the first detector which was operated underwater for more than 1 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 1 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 K-40 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.Funded by SCOAP3Adrián Martínez, S.; Aiello, S.; Ameli, F.; Anghinolfi, M.; Ardid Ramírez, M.; Barbarino, G.; Barbarito, E.... (2016). Long term monitoring of the optical background in the Capo Passero deep-sea site with the NEMO tower prototype. European Physical Journal C: Particles and Fields. 76(68):1-11. https://doi.org/10.1140/epjc/s10052-016-3908-01117668M. Ageron et al., ANTARES: the first undersea neutrino telescope. Nucl. Instr. Methods A 656, 11 (2011)V. Aynutdnov for the Baikal Coll., The BAIKAL neutrino project: results and perspective. Nucl. Instr. Methods. A 628, 115 (2011)A. Achterberg et al., First year performance of the IceCube neutrino telescope. Astropart. Phys. 26, 155 (2006)M.G. Aartsen et al., Evidence for high-energy extraterrestrial neutrinos at the IceCube detector. Science 342, 1242856 (2013)M.G. Aartsen et al., Observation of high-energy astrophysical neutrinos in three years of IceCube data. Phys. Rev. Lett. 113, 101101 (2014)M.G. Aartsen et al., Evidence for astrophysical muon neutrinos from the northern sky with IceCube. Phys. Rev. Lett. 115, 081102 (2015)E. Migneco et al., Status of NEMO. Nucl. Instr. Methods A 567, 444 (2006)E. Migneco et al., Recent achievements of the NEMO project. Nucl. Instr. Methods A 588, 111 (2008)A. Capone et al., Recent results and perspectives od the NEMO project. Nucl. Instr. Methods A 602, 47 (2009)M. Taiuti et al., The NEMO project: a status report. Nucl. Instr. Methods A 626, S25 (2011)S. Aiello et al., Measurement of the atmospheric muon flux of the NEMO Phase-1 detector. Astropart. Phys. 33, 263 (2010)A. Capone et al., Measurements of light transmission in deep sea with the AC9 transmissometer. Nucl. Instr. Methods A 487, 423 (2002)G. Riccobene et al., Deep seawater inherent optical properties in the Southern Ionian Sea. Astropart. Phys. 27, 1 (2007)A. Rubino et al., Abyssal undular vortices in the Eastern Mediterranean basin. Nat. Commun. 3, 834 (2012)KM3NeT web site. www.km3net.orgM. Sedita for the NEMO collaboration, Electro-optical cable and power feeding system for the NEMO Phase-2 project. Nucl. Instr. Methods A 567, 531 (2006)R. Cocimano for the NEMO collaboration, A comparison of AC and DC power feeding systems based on the NEMO experiences. Nucl. Instr. Methods A 602, 171 (2009)A. Orlando for the NEMO collaboration, On line monitoring of the power control and engineering parameters systems of the NEMO Phase-2 tower. Nucl. Instr. Methods. A 602, 180 (2009)M. Musumeci for the NEMO collaboration, Construction and deployment issues for a km {3} 3 underwater detector. Nucl. Instr. Methods. A 567, 545 (2006)S. Aiello et al., The optical modules of the phase-2 of the NEMO project. JINST 8, P07001 (2013)E. Leonora, S. Aiello, Design and assembly of the optical modules for phase-2 of the NEMO project. Nucl. Instr. Methods A 725, 234 (2013)S. Aiello et al., Procedures and results of the measurements on large area photomultipliers for the NEMO project. Nucl. Instr. Methods A 614, 206 (2010)C.A. Nicolau for the NEMO collaboration, An FPGA-based readout electronics for neutrino telescopes. Nucl. Instr. Methods A 567, 552 (2006)M. Cordelli et al., PORFIDO: oceanographic data for neutrino telescopes. Nucl. Instr. Methods A 626–627, S109 (2011)F. Ameli, The data acquisition and transport design for NEMO Phase-1. IEEE Trans. Nucl. Sci. 55(1), 233 (2008)A. D’Amico for the NEMO collaboration, Design of the optical Raman amplifier for the shore station of NEMO Phase-2. Nucl. Instr. Methods A 626–627, S173 (2011)T. Chiarusi for the NEMO collaboration, Scalable TriDAS for the NEMO project. Nucl. Instr. Methods A 630, 107 (2011)S. Viola et al., NEMO-SMO acoustic array: a deep-sea test of a novel acoustic positioning system for a km $$^3$$ 3 -scale underwater neutrino telescope. Nucl. Instr. Methods A 725, 207 (2013)S. Viola et al., in Underwater acoustic positioning system for the SMO and KM3NeT-Italia projects. AIP Conference Proceedings 1630, 134 (2014)M. Circella for the NEMO collaboration, Time calibration of the NEutrino Mediterranean Observatory (NEMO). Nucl. Instr. Methods A 602, 187 (2009)S. Aiello et al., Measurement of the atmospheric muon depth intensity relation with the NEMO phase-2 tower. Astropart. Phys. 66, 1 (2015)C. Hugon for the ANTARES and KM3NeT collaborations, Step by step simulation of phototubes for the KM3NeT and ANTARES optical modules. Nucl. Instr. Methods A 787, 189 (2015)Ch. Tamburini et al., Deep-sea bioluminescence blooms after dense water formation at the ocean surface. PLOS One 8, e67523 (2013