Prompt nu(tau) background in wide band nu(mu) beams

To estimate the prompt background for nu(mu) --> nu(tau) oscillation search in the Chorus and Nomad experiments, two possible sources of tau-neutrinos were considered. The first is the production and (semi-)leptonic decay of heavy flavour mesons. Secondly, the Drell-Yan mechanism can lead to tau-pairs. It is shown that this last contribution is negligible. However, the decay of D-s(+/-) mesons to tau(+/-)nu(tau) gives rise to 3.3 x 10(-6) nu(tau) charged-current interactions per nu(mu) charged-current interaction. Over the course of the Chorus experiment, this corresponds to 0.1 detected nu(tau) charged-current events. This value is an upper limit and the actual background might be smaller by a factor of 2. However, it should carefully be taken into account, especially in view of future experiments, wishing to explore smaller values of mixing.