  We present the ground and excited state spectra of doubly charmed baryons
from lattice QCD with dynamical quark fields. Calculations are performed on
anisotropic lattices of size 16^3 X 128, with inverse spacing in temporal
direction 1/a_t = 5.67(4) GeV and with a pion mass of about 390 MeV. A large
set of baryonic operators that respect the symmetries of the lattice yet which
retain a memory of their continuum analogues are used. These operators
transform as irreducible representations of SU(3) symmetry for flavor, SU(4)
symmetry for Dirac spins of quarks and O(3) for spatial symmetry. The
distillation method is utilized to generate baryon correlation functions which
are analysed using the variational fitting method to extract excited states.
The lattice spectra obtained have baryonic states with well-defined total spins
up to 7/2 and the pattern of low lying states does not support the diquark
picture for doubly charmed baryons. On the contrary the calculated spectra are
remarkably similar to the expectations from models with an SU(6)X O(3)
symmetry. Various spin dependent energy splittings between the extracted states
are also evaluated.
