Background Light in Potential Sites for the ANTARES Undersea Neutrino Telescope

The ANTARES collaboration has performed a series of {\em in situ} measurements to study the background light for a planned undersea neutrino telescope. Such background can be caused by $^{40}$K decays or by biological activity. We report on measurements at two sites in the Mediterranean Sea at depths of 2400~m and 2700~m, respectively. Three photomultiplier tubes were used to measure single counting rates and coincidence rates for pairs of tubes at various distances. The background rate is seen to consist of three components: a constant rate due to $^{40}$K decays, a continuum rate that varies on a time scale of several hours simultaneously over distances up to at least 40~m, and random bursts a few seconds long that are only correlated in time over distances of the order of a meter. A trigger requiring coincidences between nearby photomultiplier tubes should reduce the trigger rate for a neutrino telescope to a manageable level with only a small loss in efficiency.Comment: 18 pages, 8 figures, accepted for publication in Astroparticle Physic

Sedimentation and Fouling of Optical Surfaces at the ANTARES Site

ANTARES is a project leading towards the construction and deployment of a neutrino telescope in the deep Mediterranean Sea. The telescope will use an array of photomultiplier tubes to detect the Cherenkov light emitted by muons resulting from the interaction with matter of high energy neutrinos. In the vicinity of the deployment site the ANTARES collaboration has performed a series of in-situ measurements to study the change in light transmission through glass surfaces during immersions of several months. The average loss of light transmission is estimated to be only ~2% at the equator of a glass sphere one year after deployment. It decreases with increasing zenith angle, and tends to saturate with time. The transmission loss, therefore, is expected to remain small for the several year lifetime of the ANTARES detector whose optical modules are oriented downwards. The measurements were complemented by the analysis of the ^{210}Pb activity profile in sediment cores and the study of biofouling on glass plates. Despite a significant sedimentation rate at the site, in the 0.02 - 0.05 cm.yr^{-1} range, the sediments adhere loosely to the glass surfaces and can be washed off by water currents. Further, fouling by deposits of light-absorbing particulates is only significant for surfaces facing upwards.Comment: 18 pages, 14 figures (pdf), submitted to Astroparticle Physic

Study of large hemispherical photomultiplier tubes for the ANTARES neutrino telescope

The ANTARES neutrino telescope, to be immersed depth in the Mediterranean Sea, will consist of a 3 dimensional matrix of 900 large area photomultiplier tubes housed in pressure resistant glass spheres. The selection of the optimal photomultiplier was a critical step for the project and required an intensive phase of tests and developments carried out in close collaboration with the main manufacturers worldwide. This paper provides an overview of the tests performed by the collaboration and describes in detail the features of the PMT chosen for ANTARES

An alternative architecture of the L0(æ) processor

97-024 An alternative architecture of the L0(µ) processor and its implementation are presented. The architecture of the processor is based on a strong zero­suppression in order to minimize the data flow coming from the muon detector. It can be achieved by the fast identification of the muon tracks in all muon chambers using adequately dimensioned pad sectors and by transferring the individual pad information only for the regions close to the muon tracks. The proposed solution is simple, flexible and compact. Based on present technology the processor could execute the complete L0(µ) algorithm and make its decision available within less than 3 µs

The L0(muon) processor

99-008 In this note we review the Marseille implementation for the L0(muon) processor. We describe the data flow, hardware implementation, synchronization issue as well as our first ideas on debugging and monitoring procedure. We also present the performance of the proposed architecture with an estimate of its cost

A pixel detector with large dynamic range for high photon counting rates

In this paper, results obtained from a prototype photon counting detector are presented. The pixel size is 330 ìm x 330 ìm for a total area of 16 ìm x 40 mm. The detector works at room temperature and its dynamic response ranges from 0.01 up to 106 photons pixel-1 s-1. An energy resolution of about 1.5 keV has been measured. Very encouraging small-angle X-ray scattering (SAXS) and diffraction patterns were obtained, demonstrating the success of the prototype. Plans for future developments based on this study are presented

Specification of the muon trigger processing board

In this note we establish the specification of the processing board for the Level zero muon trigger