Background
The contamination in the beam, mostly due to the prompt tauonic decay of the
produced from proton interactions in the primary target and in the hadron
stopper, is the ultimate irreducible background for a 
oscillation
search.
In the NGS, the prompt problem appears less severe
than in the WANF [9, 10]. Compared to the WANF, the NGS near
detector site is about twice
as far from both the primary target and the hadron dump. As the angular distribution
of 's is rather broad and approximately flat,
a yield lower by
about a factor 4 is qualitatively expected just from the reduction of the solid angle.
Quantitative estimates of R in the NGS have also to take into account the
different material, graphite, used here for both the target and the beam
dump. This implies a 
larger yield of (and ) than
that from the WANF
beryllium target and a 
lower yield than from the WANF iron beam dump.
Table 2: Predicted Prompt Background at the Location of TOSCA.
Results from detailed estimates of R ( the ratio of -CC to
-CC events) in the NGS
are given in Table 2.
The background level appears, therefore, tolerable for the NGS
reference proton
beam momentum of 400 GeV/c. The value of
R at 400 GeV/c proton momentum is lower than that expected for the
operation of the WANF at 350 GeV/c ( 
)