  We give an estimate of $\Xi_{cc}^{++}$ production rate and transverse
momentum spectra in relativistic heavy ion collisions. We use Boltzmann
transport equations to describe the dynamical evolution of charm quarks and
diquarks inside quark-gluon plasma. In-medium formation and dissociation rates
of charm diquarks are calculated from potential non-relativistic QCD for the
diquark sector. We solve the transport equations by Monte Carlo simulations.
For $2.76$ TeV Pb-Pb collisions with $0-10\%$ centrality, the number of
$\Xi_{cc}^{++}$ produced in the transverse momentum range $0-5$ GeV and
rapidity from $-1$ to $1$ is roughly $0.02$ per collision. We repeat the
calculation with a melting temperature $250$ MeV above which no diquarks can be
formed. The number of $\Xi_{cc}^{++}$ produced in the same kinematic region is
about $0.0125$ per collision. We discuss how to study diquarks at finite
temperature on a lattice and construct the anti-triplet free energy in a gauge
invariant but path dependent way. We also comment on extensions of the
calculation to other doubly heavy baryons and doubly heavy tetraquarks and the
feasibility of experimental measurements.
