  Circular polarization resolved magneto-infrared studies of multilayer
epitaxial graphene (MEG) are performed using tunable quantum cascade lasers in
high magnetic fields up to 17.5 T. Landau level (LL) transitions in the
monolayer and bilayer graphene inclusions of MEG are resolved, and considerable
electron-hole asymmetry is observed in the extracted electronic band structure.
For monolayer graphene, a four-fold splitting of the $n=0$ to $n=1$ LL
transition is evidenced and attributed to the lifting of the valley and spin
degeneracy of the zeroth LL and the broken electron-hole symmetry. The magnetic
field dependence of the splitting further reveals its possible mechanisms. The
best fit to experimental data yields effective $g$-factors, $g^*_{VS}=6.7$ and
$g^*_{ZS}=4.8$, for the valley and Zeeman splitting, respectively.
