The sensitivity to the 
oscillation signal
and the background estimation are shown separately
for the following single charged particle decay modes of 
:
Charged current interactions of can be
selected on the basis of their characteristic topology in
1-prong decay channels. The basic selection is
a decay vertex at a distance greater than 20 
and less
than 3.5 mm from the neutrino interaction vertex,
one negatively charged track from
this secondary vertex that gives rise to a kink angle greater that 10 mrad
and no identified muon or electron at the primary vertex.
The three-prong decay 
,
with a branching ratio of about 14%,
can further improve the efficiency of detection.
Efficiency and background studies are under way in order
to estimate the additional contribution to the sensitivity.
The decays of 
and 
produced in NC and CC neutrino interactions
can simulate the 1-prong topology. They can be easily removed
by requiring the transverse momentum of the candidate's charged daughter
relative to the parent direction,
, to be greater than 250 MeV/c.
After this cut the remaining background sources are:
contamination in the beam;
A preselection, needed to reconstruct the event and determine the charge of the decay daughter, and kink detection cuts affect in a different way both signal and background as is shown in Tab. 2, 3, 4, 5, 6, 7.
In order to enhance the signal to noise ratio, kinematical analysis at the primary and decay vertices, which exploit both the space resolution of the emulsion and the full spectrometry of the event, are exploited. These reduce the background from charm and white kinks. This analysis needs only to be performed for candidate events.
Figure 15: Energy spectra for interacting neutrinos: (a) prompt; (b)
from oscillation ( 
).
Prompt interactions and
the oscillation signal have different energy spectra,
as can be seen in Fig. 15,
where the candidate spectrum is approximated by the 
spectrum
. The difference between the spectra
is more significant at low 
, as the
from oscillation becomes softer, thus
allowing a more powerful discrimination.
In the following all efficiencies will be computed in the hypothesis
of large .