We present results of a search for neutral strange quark matter (strangelet
s) in 11.6A GeV/c Aut-Pb reactions from the 1995 run of experiment E864 at
the Brookhaven Alternating Gradient Synchrotron. We have sampled approximat
ely 1.3 billion 10% most central Au+Pb interactions and have observed no st
atistically significant signal for neutral strangelet states with baryon nu
mber in the range 6<A<100. We set upper limits on the production of these e
xotic states at the level of 8 x 10(-8) per central collision for mass >20
GeV/c(2) These limits are the first limits reported on the production of he
avy neutral strangelets. They complement searches for positively and negati
vely charged strangelets also conducted by our collaboration. We discuss th
e implications of these results on strangelet production mechanisms and the
stability of strange quark matter. [S0556-2813(99)50504-9].