Requirements for the detector

The arguments given above show that a sensitive experiment must have the following properties.

• The product of target mass, neutrino flux and -detection efficiency has to be at least ten times larger than in the present experiments. As shown above, the optimized operation of the neutrino beam can provide a doubling of the integrated flux without loss to the other users of the SPS. An increase of a factor of (at least) three in target mass and an increase of a factor three in -detection efficiency with respect to CHORUS is then required.
• The irreducible background of prompt in the beam can be brought to an acceptable level by lowering the proton beam energy and by rejecting high energy events. This has been shown to be feasible (section 3).
• Tracking detectors must ensure an efficient event reconstruction.
• The massive target has to allow for a unique detection of the decay topology. One notes that the characteristic decay length at the SPS energy is 1 mm.
• The charge of the candidate decay daughter(s) must be determined unambiguously.
• Muons and electrons have to be efficiently identified.
• The kinematics of the event must be determined. In particular, a measurement of the magnitude and direction of the decay daughter momentum, of the missing energy, of the hadronic shower, and the parent particle direction must be obtained. This requirement leads to a design where the momenta of all charged particles are well measured, and calorimetry may be employed to have full coverage of the energy flow of neutral particles.