Another possible test consists of measuring the number of
pairs of 
in the same event. As obviously shown by Eq. (8),
quantum mechanics predicts no such pair in any 
event.
That same prediction can be obtained using Eq. (7) instead,
as the result of
a 100% destructive interference effect between the
process where the 
decays into 
on the left
and 
on the right and the process where it is the other way around.
If the interference term were reduced by a factor 
,
there would be some 
events and their number
would be
To identify two-
events in the KLOE detector, the signature can be
two particles decaying or interacting at a large distance from the
interaction point. Some background is going to be generated by 
or 
events
where the 
decays via the two-
mode and the 
's from
decays get confused with a 
decay or interaction, but it is
beyond the scope of this paper to estimate this effect.
The 
background yields :
If that background and the statistical error
were the only limitations, one could detect
values of 
as low as 10
.