Emulsion chamber with big radiation length for detecting neutrino oscillations

A conceptual scheme of a hybrid-emulsion spectrometer for investigating various channels of neutrino oscillations is proposed. The design emphasizes detection of τ leptons by detached vertices, reliable identification of electrons, and good spectrometry for all charged particles and photons. A distributed target is formed by layers of low-Z material, emulsion–plastic–emulsion sheets, and air gaps in which τ decays are detected. The tracks of charged secondaries, including electrons, are momentum-analyzed by curvature in magnetic field using hits in successive thin layers of emulsion. The τ leptons are efficiently detected in all major decay channels, including τ−→e−νν̄. The performance of a model spectrometer, that contains 3 t of nuclear emulsion and 20 t of passive material, is estimated for different experimental environments. When irradiated by the νμ beam of a proton accelerator over a medium baseline of 〈L/Eν〉∼1 km/GeV, the spectrometer will efficiently detect either the νμ→ντ or the νμ→νe transitions in the mass-difference region of Δm2∼1 eV2, as suggested by the results of LSND. When exposed to the neutrino beam of a muon storage ring over a long baseline of 〈L/Eν〉∼10–20 km/GeV, the model detector will efficiently probe the entire pattern of neutrino oscillations in the region Δm2∼10−2–10−3 eV2, as suggested by the data on atmospheric neutrinos.