Elliptic Flow arising from Ridges due to Semi-hard Scattering

TL;DR

This paper investigates azimuthal anisotropy in heavy-ion collisions by analyzing ridges from semi-hard scattering, deriving analytical formulas that match experimental v_2 data at low transverse momentum.

Contribution

It introduces a simple analytical approach to describe azimuthal anisotropy using ridge phenomenology and thermal parton recombination, highlighting initial spatial configuration effects.

Findings

Analytical formulas match v_2 data for p_T < 1-2 GeV/c

Centrality dependence described by geometrical factors

Initial slopes of v_2 determined for pions and protons

Abstract

Azimuthal anisotropy in heavy-ion collisions is studied by taking into account the ridges generated by semi-hard scattering of intermediate-momentum partons, which can be sensitive to the initial spatial configuration of the medium in non-central collisions. In a simple treatment of the problem where the recombination of only thermal partons is considered, analytical formulas can be derived that yield results in accord with the data on v_2 for p_T <1-2 GeV/c. Centrality dependence is described by a geometrical factor. Ridge phenomenology is used to determine the initial slopes of v_2 at low p_T for both pion and proton. For higher p_T, shower partons from high-p_T jets must be included, but they are not considered here.