Study of tau neutrino production at the CERN SPS

At the CERN SPS, the DsTau project has been proposed to study tau-neutrino production aiming at providing important information for future ν_τ measurements. Precise measurement of the ν_τ cross section would enable a search for new physics effects in ν_τ charged current interactions. It also has practical implications for neutrino oscillation experiments. The dominant source of ν_τ is the sequential decay of D_s mesons produced by proton interactions, whose uncertainty dominates current uncertainty in the ν_τ cross section measurement. The project aims at reducing the systematic uncertainty from about 50% to 10% by measuring the D_s differential production cross section. For this purpose, emulsion detectors with a nanometre-precision readout will be used to detect small kinks of the D_s → τ decay. An emulsion detector has a position resolution of 50 nm, allowing for the detection of D_s → τ → X double kinks in a few millimeter range.