Tests for observing ν/sub tau/ interactions in a beam-dump experiment

We carry out a comparative analysis of three tests for the purpose of observing /sup( /nu-bar)/sup //sub tau/ in a beam-dump experiment. The main source of /sup( /nu-bar)/sup //sub tau/'s is determined to be the hadronic production of F mesons, followed by the decay F +- → tau+-/sup( /nu-bar)/sup //sub tau/. Possible signatures for various /sup( /nu-bar)/sup //sub tau/-induced processes, together with their corresponding backgrounds, are examined. The muon-trigger test proposed earlier is found to be by far the most promising method. This test identifies /sup( /nu-bar)/sup //sub tau/ events by the muonic decay mode of the tau+- produced in /sup( /nu-bar)/sup //sub tau/ charged-current interactions, together with the requirements of substantial missing transverse momentum and distinctive behavior of certain azimuthal-angle distributions describing the emission of the muon, hadron shower, and direction of missing transverse momentum. It can be applied on an event-by-event basis, can separate ν/sub tau/- and nu-bar/sub tau/-induced reactions, and is specific to /sup( /nu-bar)/sup //sub tau/. One should be able to use the test to determine directly whether ν/sub tau/ is, indeed, a new, sequential neutrino. The test relies on the ability of recently developed neutrino detectors to measure the direction of the hadron shower. In addition to this muon-trigger test, we study the possibility of using two others, one based on the identification of events with two hadron showers, due to the semileptonic decay of the produced tau, and the other based on the apparent neutral-to-charged-current event ratio. We find that neither of these two other tests seems feasible. However, it is expected that the muon-trigger test can be used in the near future to observe, for the first time, ν/sub tau/ and nu-bar/sub tau/