Equilibration in Heavy Ion Collisions at LHC and at RHIC

We consider the evolution of a parton plasma created in Au+Au collisions at LHC and at RHIC energies. Using Boltzmann equation, relaxation time approximation and perturbative QCD, we show the physics of both thermal and chemical equilibration in a transparent manner. In particular, we show inelastic processes are, contrary to common assumption, more important than elastic processes, the state of equilibration of the system can compensate for some powers of $\a_s$ for the purpose of equilibration, the two-stage equilibration scenario is, barring any unknown non-perturbative effects, inevitable and is an intrinsic feature of perturbative QCD, and gluon multiplication is the leading process for entropy generation.