Positioning system of the ANTARES Neutrino Telescope

📝 Abstract

Completed in May 2008, the ANTARES neutrino telescope is located 40 km off the coast of Toulon, at a depth of about 2500 m. The telescope consists of 12 detect or lines housing a total of 884 optical modules. Each line is anchored to the seabed and pulled taught by the buoyancy of the individual optical modules and a top buoy. Due to the fluid nature of the sea-water detecting medium and the flexible nature of the detector lines, the optical modules of the ANTARES telescope can suffer from deviations of up to several meters from the vertical and as such, real time positioning is needed. Real time positioning of the ANTARES telescope is achieved by a combination of an acoustic positioning system and a lattice of tiltmeters and compasses. These independent and complementary systems are used to compute a global fit to each individual detector line, allowing us to construct a 3 dimensional picture of the ANTARES neutrino telescope with an accuracy of less than 10 cm. In this paper we describe the positioning system of the ANTARES neutrino telescope and discuss its performance during the first year of 12 line data taking.

💡 Analysis

Completed in May 2008, the ANTARES neutrino telescope is located 40 km off the coast of Toulon, at a depth of about 2500 m. The telescope consists of 12 detect or lines housing a total of 884 optical modules. Each line is anchored to the seabed and pulled taught by the buoyancy of the individual optical modules and a top buoy. Due to the fluid nature of the sea-water detecting medium and the flexible nature of the detector lines, the optical modules of the ANTARES telescope can suffer from deviations of up to several meters from the vertical and as such, real time positioning is needed. Real time positioning of the ANTARES telescope is achieved by a combination of an acoustic positioning system and a lattice of tiltmeters and compasses. These independent and complementary systems are used to compute a global fit to each individual detector line, allowing us to construct a 3 dimensional picture of the ANTARES neutrino telescope with an accuracy of less than 10 cm. In this paper we describe the positioning system of the ANTARES neutrino telescope and discuss its performance during the first year of 12 line data taking.

📄 Content

arXiv:0908.0814v1 [astro-ph.IM] 6 Aug 2009 PROCEEDINGS OF THE 31st ICRC, Ł ´OD´Z 2009 1 Positioning system of the ANTARES Neutrino Telescope Anthony M Brown∗† on behalf of the ANTARES Collaboration ‡ ∗Centre de Physique des Particules de Marseille, 164 Av. de Luminy, Case 902, Marseille, France. †brown@cppm.in2p3.fr ‡http://antares.in2p3.fr Abstract. Completed in May 2008, the ANTARES neutrino telescope is located 40 km off the coast of Toulon, at a depth of about 2500 m. The telescope consists of 12 detector lines housing a total of 884 optical modules. Each line is anchored to the seabed and pulled taught by the buoyancy of the individual optical modules and a top buoy. Due to the fluid nature of the sea-water detecting medium and the flexible nature of the detector lines, the optical modules of the ANTARES telescope can suffer from deviations of up to several meters from the vertical and as such, real time positioning is needed. Real time positioning of the ANTARES telescope is achieved by a combination of an acoustic positioning system and a lattice of tiltmeters and compasses. These independent and complementary systems are used to compute a global fit to each individual detector line, allowing us to construct a 3 dimensional picture of the ANTARES neutrino telescope with an accuracy of less than 10 cm. In this paper we describe the positioning system of the ANTARES neutrino telescope and discuss its performance during the first year of 12 line data taking. Keywords: ANTARES neutrino telescope, align- ment, acoustic positioning system I. INTRODUCTION Deployed off the coast of Toulon, the ANTARES telescope is, at present, the largest neutrino detector in the Northern hemisphere [1],[2]. Utilising the Mediter- ranean Sea as a detecting medium, ANTARES consists of 12 detector lines, spaced approximately 70 meters apart, giving an overall surface area of the order of 0.1 km2. The detection principle of ANTARES relies on the observation of Cherenkov photons emitted by charged relativistic leptons, produced through neutrino interactions with the surrounding water and seabed, using a 3 dimensional lattice of photomultiplier tubes (PMTs) [3]. For ANTARES this 3 dimensional lattice of PMTs has been optimised for the detection of upward going high energy muon neutrinos and as such, each line of the detector, with the exception of Line 12, consists of 25 storeys separated by a vertical distance of 14.5 metres, each containing a triplet of Optical Modules (OMs) looking downwards at an angle of 45◦from the vertical. An important characteristic of any neutrino telescope is its angular resolution. At low energies the angular resolution is dominated by the angle between the parent neutrino and the resultant relativistic lepton. At larger energies, the angular resolution is dominated by the re- construction of the relativistic lepton’s track. Uncertainty in the reconstruction of the lepton’s track is primarily governed by (i) the timing resolution of the individual OMs and (ii) the positional accuracy of where the OMs are located. The ANTARES expected angular resolution becomes better than 0.3◦for neutrinos above 10 TeV in energy. To achieve this angular resolution, in-situ timing and positioning calibration are needed. ANTARES timing calibration is primarily achieved through the use of LED beacons deployed throughout the detector and is discussed elsewhere [4],[5]. This paper describes the po- sitioning calibration system of the ANTARES neutrino telescope and reviews its performance during the first year of 12 line operation. II. ANTARES POSITIONING CALIBRATION SYSTEM. Each of the ANTARES 12 detector lines are anchored to a bottom string socket (BSS) on the seabed and pulled taught by the buoyancy of the individual OMs and a top buoy. Due to the flexible nature of these detector lines, even a relatively small water current velocity of 5 cm/s can result in the top storeys being displaced by several meters from the vertical. Therefore, real time positioning of each line is needed. This is achieved through two independent systems: an acoustic positioning system and a lattice of tiltmeters-compasses sensors. The shape of each line is reconstructed by performing a global χ2 fit using information from both of these systems. The relative positions of each individual OM is then calculated from this line fit using the known geometry of each individual storey. A. Acoustic Positioning System The Acoustic Positioning System (APS) consists of a 3 dimensional array of emitters and receivers exchanging high frequency (40−60 kHz) acoustic signals. The use of high frequency signals allows a greater positional accuracy at the expense of a smaller acoustic attenuation length. Nonetheless, the 700−1000 meters attenuation length for 40−60 kHz signals is sufficient for the ANTARES telescope. The acoustic emitters are located on the BSS of each line, with an additional independent 2 A.M. BROWN - ANTARES POSITIONING SYSTEM Fig. 1. Radial displaceme

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