Muon decay channel

The search for decays into muon takes advantage of a clear topology and a low background. Preliminary results have been presented [54] by the CHORUS experiment and they allow to estimate the expected efficiency of the proposed experiment on an experimental basis, as shown in Tab. 2.

  
Table 6: Sensitivity to .

The increase of the sensitivity, by a factor close to 3 compared to CHORUS, is achieved by:

• higher kink finding efficiency, obtained by:
  • better tracking, so that the muon assignment is unambiguous;
  • analysis of the ``video image'' at the vertex for kink finding;
  • higher resolution on ;
    
  • reduction of decays outside the stack by a factor 2 owing to the increased stack thickness;
• higher scanning efficiency, mainly achieved by:
  • larger relative fiducial volume, 95% (80% in CHORUS);
  • smaller losses at the emulsion interface due to precision external detectors, 10% (30% CHORUS). It should be noted that the silicon-emulsion track finding inside a magnetic field will be studied in a test beam;
  • higher target scanning efficiency, 90% (84% in CHORUS);
• detectors with better time response, improving pattern recognition by reduction of overlay hits and decreasing dead time.

For the muon decay mode the main background channel is given by single charm production in antineutrino CC interactions:

when the decays into a negative muon and neutral particles.

The calculation of the ratio of background events over the number of  charged current interactions is given in Tab. 3, where the last column represents the prompt  contribution.

The associated production in neutral and charged currents interactions can be neglected because the cross-section is small and the background can be suppressed by the detection of the second decay vertex and through kinematical analysis. Kinematical cuts are very selective for the NC case due to the of the primary neutrino.

  
Table 3: Main sources of background for the muon decay channel normalized to the number of CC events.