Eur. Phys. J. C (2016) 76: 68
https://doi.org/10.1140/epjc/s10052-016-3908-0

Regular Article - Experimental Physics

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

¹ INFN Sezione Bari, Via E. Orabona 4, 70126, Bari, Italy
² INFN Sezione Bologna, V.le Berti Pichat 6/2, 40127, Bologna, Italy
³ INFN Laboratori Nazionali del Sud, Via S.Sofia 62, 95123, Catania, Italy
⁴ INFN Sezione Catania, Via S. Sofia 64, 95123, Catania, Italy
⁵ INFN Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati, Italy
⁶ INFN Sezione Genova, Via Dodecaneso 33, 16146, Genoa, Italy
⁷ INFN Sezione Napoli, Via Cintia, 80126, Naples, Italy
⁸ INFN Sezione Pisa, Polo Fibonacci, Largo Bruno Pontecorvo 3, 56127, Pisa, Italy
⁹ INFN Sezione Roma, P.le A. Moro 2, 00185, Rome, Italy
¹⁰ INFN Gruppo Collegato di Salerno, Via Giovanni Paolo II 132, 84084, Fisciano, Italy
¹¹ Dipartimento Interateneo di Fisica Università di Bari, Via E. Orabona 4, 70126, Bari, Italy
¹² Dipartimento di Fisica ed Astronomia Università di Bologna, V.le Berti Pichat 6/2, 40127, Bologna, Italy
¹³ Dipartimento di Fisica e Astronomia Università di Catania, Via S. Sofia 64, 95123, Catania, Italy
¹⁴ Dipartimento di Fisica Università di Genova, Via Dodecaneso 33, 16146, Genoa, Italy
¹⁵ Dipartimento di Scienze Fisiche Università di Napoli, Via Cintia, 80126, Naples, Italy
¹⁶ Dipartimento di Fisica Università di Pisa, Polo Fibonacci, Largo Bruno Pontecorvo 3, 56127, Pisa, Italy
¹⁷ Dipartimento di Fisica Università “Sapienza”, P.le A. Moro 2, 00185, Rome, Italy
¹⁸ Dipartimento di Fisica Università di Salerno, Via Giovanni Paolo II 132, 84084, Fisciano, Italy
¹⁹ Accademia Navale di Livorno, viale Italia 72, 57100, Livorno, Italy
²⁰ Instituto de Investigación para la Gestión Integrada de las Zonas Costeras, Universitat Politècnica de València, Gandia, Spain
²¹ IFIC-Instituto de Física Corpuscular, CSIC-Universitat de València, Valencia, Spain
²² Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
²³ Nikhef, Science Park, Amsterdam, The Netherlands

^* e-mail: piattelli@lns.infn.it

Received: 20 July 2015
Accepted: 26 January 2016
Published online: 9 February 2016

Abstract

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 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.