Possible existence of finite formation time of strongly interacting plasma in nuclear collisions at RHIC and LHC

We argue that, on the basis of recent experimental data, there is possible existence of a finite formation time of strongly interacting plasma in nuclear collisions at RHIC. To show this, we construct a simple model based on a Monte Carlo simulation of nucleus—nucleus collisions with a realistic nuclear density distribution. The most striking feature of the experimental data—an absence of absorption of high-transverse-momentum pions in the reaction-plane direction for midperipheral collisions—points to the presence of a surface zone with no absorption and strong suppression in the inner core. A natural interpretation of such a zone could be the plasma formation time T ≃ 2–3 fm/c. With this assumption, we describe the angular anisotropy of high-transverse-momentum pions with respect to the reaction plane and the centrality dependence of the nuclear modification factor in Au + Au and Cu + Cu collisions.We present predictions for LHC. The text was submitted by the author in English.