Both 
and white kink background from neutral current events can be
suppressed by kinematical analysis.
The white kink events were studied in detail.
In the plane perpendicular to the beam,
the direction of the hadron shower is back to back
to the 
candidate (CC interaction), but not
to the pion kink parent, due to the missing neutrino
(NC interaction).
The distribution of the angle 
for signal and
background are shown in Fig. 16.
Figure 16: Signal and background distributions of the angle between the shower direction
and the candidate in the transverse plane.
It should be noted that, since NC
do not probe the u/d valence quark composition in the same way CC do,
there is another observable difference between CC and NC interactions:
the ratio between the number of events with an odd number of charged
tracks and an even number.
For emulsion Z/A is about 0.45, therefore the expected ratios are
1:3 and 1:1 respectively.
Applying a harder cut on 
on the odd sample,
a rejection factor 23 with a detection efficiency of 70%
can be obtained.
Since this rejection criteria are not based on the decay properties
of the candidate (kink angle, daughter momentum, decay length),
similar results are expected for the background.
In Tab. 8 the number of expected background
events has been computed taking into account cuts that yield
a factor of 15 reduction of the charm sources
while retaining 70% of the signal.
The charm suppression can be achieved by a selection on 
, the transverse
momentum of the shower w.r.t. the kink parent and the angle
of the candidate w.r.t. the beam. The two-dimensional scatter plots
of these variables are shown in figure 17.
Figure 17: Signal and background distribution of
vs the angle of the candidate w.r.t. the beam direction.
Table 8: Summary of efficiencies and backgrounds after kinematical analysis.
The cuts that have been studied for the charm rejection
suppress further the white kink and viceversa. In the computation of the
sensitivity to 
,
the correlation between the two sets has
been taken into account for the white kink, which
will be reduced by a factor 30 by all selection criteria at the vertex.
These criteria result in a 55% signal reduction.
To evaluate the possible effect on the charm, higher statistics
would be needed.
For this reason the charm contributions to background
shown in the Table have to be taken as upper limits.
It has to be noted that the vertex cuts suppress the prompt 
and the signal by a similar amount.
