  Final-state interaction and screening have a great influence on $q \bar q$
production cross sections, which are important quantities in many problems in
quark-gluon plasma physics. They lead to an enhancement of the cross section
for a $q \bar q$ color-singlet state and a suppression for a color-octet state.
The effects are large near the production threshold. The presence of screening
gives rise to resonances for $q\bar q$ production just above the threshold at
specific plasma temperatures. These resonances, especially $c\bar c$ and $b
\bar b$ resonances, may be utilized to search for the quark-gluon plasma by
studying the temperature dependence of heavy-quark pair production just above
the threshold.
