Effects of minijets on hadronic spectra and azimuthal harmonics in Au-Au collisions at 200 GeV

The production of hadrons in heavy-ion collisions at the Relativistic Heavy-Ion Collider in the low-transverse-momentum (p(T)) region is investigated in the recombination model with emphasis on the effects of minijets on the azimuthal anisotropy. Since the study is mainly focused on the hadronization of partons at late time, the fluid picture is not used to trace the evolution of the system. The inclusive distributions at low p(T) are determined as the recombination products of thermal partons. The p(T) dependencies of both the pion and the proton have a common exponential factor apart from other dissimilar kinematic and resonance factors, because they are inherited from the same pool of thermal partons. Instead of the usual description based on hydrodynamics, the azimuthal anisotropy of the produced hadrons is explained as the consequence of the effects of minijets, either indirectly through the recombination of enhanced thermal partons in the vicinity of the trajectories of the semihard partons or directly through thermal-shower recombination. Although our investigation is focused on the single-particle distribution at midrapidity, we give reasons why a component in that distribution can be identified with the ridge, which, together with the second harmonic upsilon(2), is due to the semihard partons created near the medium surface that lead to calculable anisotropy in phi. It is shown that the higher azimuthal harmonics, upsilon(n), can also be well reproduced without reference to flow. The p(T) and centrality dependencies of the higher harmonics are prescribed by the interplay between thermal-thermal (TT) and thermal-shower (TS) recombination components. The implication of the success of this drastic departure from the conventional approach is discussed.