Background light in potential sites for the ANTARES undersea neutrino telescope

The ANTARES collaboration has performed a series of in-situ measurements to study the background light for a planned undersea neutrino telescope. Such background can be caused by K-40 decays or by biological activity. We repo rt on measurements at two sites in the Mediterranean Sea at depths of 2400 m and 2700 m, respectively. Three photomultiplier tubes were used to measur e single counting rates and coincidence rates for pairs of tubes at various distances. The background rate is seen to consist of three components: a c onstant rate due to K-40 decays, a continuum rate that varies on a time sca le 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 dist ances of the order of a meter. A trigger requiring coincidences between nea rby photomultiplier tubes should reduce the trigger rate for a neutrino tel escope to a manageable level with only a small loss in efficiency. (C) 2000 Elsevier Science B.V. All rights reserved.