  The Coulomb scattering dynamics in graphene in energetic proximity to the
Dirac point is investigated by polarization resolved pump-probe spectroscopy
and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the
carrier distribution in k-directions pointing radially away from the Dirac
point. Our study reveals, however, that in almost intrinsic graphene full
thermalization in all directions relying on noncollinear scattering is much
slower. For low photon energies, carrier-optical-phonon processes are strongly
suppressed and Coulomb mediated noncollinear scattering is remarkably slow,
namely on a ps timescale. This effect is very promising for infrared and THz
devices based on hot carrier effects.
