ALPHA(S) DEPENDENCE IN THE EQUILIBRATION IN RELATIVISTIC HEAVY-ION COLLISIONS

The dependence of the equilibration of the parton plasma on the value of the strong coupling is studied in Au+Au collisions at LHC and at RH IC energies. With increasing coupling, the following are found to happ en: (1) both thermal and chemical equilibration speed up, (2) in the f inal degree of equilibration, only quarks and antiquarks show obvious improvements but not gluons, and (3) the plasma cools much more rapidl y. The deconfinement phase transition will therefore take place sooner and it naturally results in the shortening of the parton phase of the plasma. The exact duration of this phase is, however, sensitive to th e value of the coupling. A change from alpha(s)=0.3 to alpha(s)= 0.5, for example, reduces the lifetime of the parton phase at LHC by as muc h as 4.0 fm/c. The total generated entropy is another sensitive quanti ty to the coupling. Larger values of alpha(s) will lead to entropy red uction and therefore reduction both in the duration of the mixed phase , assuming there is a first-order deconfinement phase transition, as w ell as in the final pion multiplicity. It is shown that the common cho ice of alpha(s)=0.3 is not a good value for the entire duration of the evolution given that the system undergoes substantial changes from th e beginning to the time that the deconfinement phase transition is abo ut to take place assumed to be at T-c similar to 200 MeV. Instead, by using a more consistent simple recipe, the system is allowed to decide its own strength of the interactions which evolves with the system as it should. With this approach, alpha(s) increases with time and this leads to acceleration in the equilibration even as equilibrium is near . This is opposite to the behavior of the equilibration of a molecular gas or ordinary many-body system where the interaction strength is fi xed. In such a system, the net interactions will slow down as the syst em is near equilibrium.