As discussed above, it is impossible to fully simulate the experiment
at the desired level of sensitivity (i.e. generate and track 10 
interactions)
therefore we study enhanced background processes. We have taken a sample of 8000 full
central collisions including particles from interactions in the shielding and the detectors,
all decays, etc. and processed them to simulate the calorimeter response.
To enhance the simulated background from interactions in the upstream detectors, each central rapidity neutron which strikes the calorimeter is taken as a potential strangelet candidate. The real background tracks are, of course, protons created by an upstream interaction, but our studies show that the troublesome protons have energies in the range of the neutron sample. So we imagine that each selected neutron is a background proton, and see how often we can reject it using the calorimeter.
For each such ``candidate'' the calorimeter signals were analyzed, as
discussed above, and an energy deposit determined. The mass of the
candidate was then calculated from the energy deposit and the time of flight.
The mass error is totally dominated by the calorimeter energy resolution so we did not
``smear'' the time of flight. The resulting mass spectrum is shown in
Fig. 
. The open squares show
the reconstructed mass from calorimeter energy deposit and time of flight for
72,000 neutrons. Also shown as filled triangles is the reconstructed mass for 100
strangelets of mass 15 amu. We note that 42 strangelets survive the timing and
shape cuts described above, and that the average calculated mass is 10 GeV (uncorrected for
the energy outside the cluster size used in the analysis).
Figure shows that the calorimeter analysis has a probability
of 1/72,000 of assigning a mass greater than 5.0 GeV to a background track.
Recalling that only 2/3 of the energy is inside the clusters used in this analysis,
which is not corrected in Fig. , this corresponds to a true mass of
7.5 GeV.
Figure: Mass spectra for 72,000 late neutrons (open squares) and 100
strangelets of mass 15 amu (dark triangles)
as determined from calorimeter energy deposit
and time of flight. See text for further details.