Origin of the "ridge" phenomenon induced by jets in heavy ion collisions

We argue that "ridge" in two-particle correlation function associated with hard trigger at BNL Relativistic Heavy Ion Collider (RHIC) heavy ion collisions is naturally explained by an interrelation of jet quenching and hydrodynamical transverse flow. The excess particles forming the ridge are produced by QCD bremsstrahlung along the beam (and thus have wide rapidity distribution) and then boosted by transverse flow. Nontrivial correlation between directions of the jet and the radial flow is provided by jet quenching: our straightforward and basically parameter-independent calculation reproduces the angular shape, width, and other properties of the ridge.