As indicated above, the most likely sources of background are those which
produce a real slow track in the apparatus which did not come from the target.
If this track has the right direction, it could be interpreted as a high
rigidity (hence high mass) track from the target. If this track also points
to a region of the calorimeter where coincidentally neutral particles have
deposited substantial energy in the correct place with the correct time
and energy, then the track could simulate a high mass object. Although
such multiple overlapping processes are highly unlikely, if we want a
sensitivity of order 
such processes must be considered. We
have given a detailed analysis of interactions in the upstream detectors
above. Here we consider a decay process.
If a centrally-produced 
travels through a significant
part of the magnetic field and then decays, the decay proton will have a
similar velocity and direction to the parent . However the decay
proton will not have been bent in the magnetic field by a large enough angle
(corresponding to its low momentum) and thus will appear to be a track with
higher momentum and hence higher mass. Since the and the proton
have similar velocities and directions and the is centrally
produced, the proton track can otherwise appear to be a good late track coming
from the target in space and time.
In order to produce a proton that reconstructs as a high mass particle the
must pass through most of the magnetic field before decaying. In
particular, 's which survive to the end of the first magnet but
decay before the second magnet will only give protons that reconstruct to
about three times the proton mass. To get masses as high as 10 GeV/c 
,
which would be a background for the strangelet search, the would
have to survive more than 2/3 of the way through the second magnet or more
than 7.5m from the target. Figure 
shows the proton kinematics
from decay. The maximum rapidity of interest is 1.89,
corresponding to a 3.02 GeV proton. From Fig. one
can see that the maximum momentum for a which can produce such a
proton is less than 4 GeV. For a 4 GeV the decay distance is
=0.294m. The probability to survive 7.5m or 25.5 lifetimes is
less than . Thus even without requiring any suppression from the
calorimeter (the proton energy is wrong for a high mass particle by a large
factor) or from the fact that there is no confirming hit in S1, this process
is not a background.
Figure: decay kinematics. Horizontal axis (Theta) is lab. angle of proton
with respect to direction and vertical
axis is proton lab. momentum.
We have also considered possible backgrounds due to neutrons and protons from
electromagnetic dissociation and due to nuclear fragments. Neither of these
represent a significant background source. Coulomb dissociation products are
very peripheral in nature, hence they have the wrong velocity (beam rapidity)
and very low P 
so that they do not get into our apparatus. Heavy
nuclear fragments have a low production cross section and tend to be produced
at beam rapidity so they also pose no problem for this experiment. The
details of both of these calculations are available in ``Update to P-864:
Production of Rare Composite Objects in Relativistic Heavy Ion Collisions,''
October 1, 1990.