Tau neutrino properties are not well known in comparison to those of muon or electron neutrinos. The tau neutrino interaction cross-section is known with large uncertainties. In particular, measured by the DONuT experiment in 2008, it has 30% statistical error and systematical error of 50% due to a poor knowledge of the tau neutrino flux in this beam dump experiment. Better known cross section would allow testing the Lepton Flavour Universality (LFU) of Standard Model in neutrino interactions. Accurate measurement of the tau neutrino interaction cross section is also needed for the future neutrino experiments.
The tau neutrinos are produced in the Ds meson decays: Ds -> tau + nu_tau, with further decay tau-> x + nu_tau. DsTau experiment has been proposed to measure the Ds production differential cross-section in p-W interaction. This will allow reducing of the uncertainty due to the tau neutrino flux in the DONUT result from 50% to 10% . The peculiar Ds cascade decay topology ("double kink") in a few mm range will be detected by nuclear emulsion tracker thanks to its excellent spatial resolution (~50nm). Large amount of charm decay events (~105) are expected to be detected as well, providing interesting by-product studies, in particular a search for intrinsic charm in a proton.
