  Experimental measurement of the elliptic flow parameter $v_2$ and
hydrodynamic model together showed that thermalization in the central region at
the Relativistic Heavy Ion Collider to be perplexingly fast. This is a mystery
in itself since none of the numerical perturbative QCD models are able to
achieve such a feat. By exploiting a theoretical oversight on collinear
processes in an out-of-equilibrium system it is argued that, in the bottom-up
thermalization scenario, equilibration can proceed at a higher rate than what
is expected in the conventional perturbative QCD picture.
