Particle correlations from the initial state

Abstract

The observation in small size collision systems, $pp$ and $p$A, of strong correlations with long range in rapidity and a characteristic structure in azimuth, the ridge phenomenon, is one of the most interesting results obtained at the Large Hadron Collider. Earlier observations of these correlations in heavy ion collisions at the Relativistic Heavy Ion Collider are standardly attributed to collective flow due to strong final state interactions, described in the framework of viscous relativistic hydrodynamics. Even though data for small size systems are well described in this framework, the applicability of hydrodynamics is less well grounded and initial state based mechanisms have been suggested to explain the ridge. In this review, we discuss particle correlations from the initial state point of view, with focus on the most recent theoretical developments.

16 pages, 9 figures. Invited review for the EPJA Special Issue on "Theory of hot matter and relativistic heavy-ion collisions (THOR)". v2: Summary and discussions modified, references updated. Results and conclusions unchanged, final version

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Cited by in corpus (12)

• Mining for Gluon Saturation at Colliders
• The Dynamics of Particle-Particle Correlations and the Ridge Effect in Proton-Proton Collisions
• 3-D structure of the Glasma initial state -- Breaking boost-invariance by collisions of extended shock waves in classical Yang-Mills theory
• Multiparticle production in proton-nucleus collisions beyond eikonal accuracy
• Multi-particle production in proton-nucleus collisions in the Color Glass Condensate
• Finite width effects on the azimuthal asymmetry in proton-nucleus collisions in the Color Glass Condensate
• Angular correlations in pA collisions from CGC: multiplicity and mean transverse momentum dependence of $v_2$
• Measurement of the Sensitivity of Two-Particle Correlations in $pp$ Collisions to the Presence of Hard Scatterings
• Two-particle angular correlations in $e^{+}{e}^{-}$ collisions to hadronic final states in two reference coordinates at Belle
• Manipulating strong electromagnetic fields with the average transverse momentum of relativistic nuclear collisions
• The three point asymmetric cumulants in high multiplicity pp collisions
• Anisotropic flow and the valence quark skeleton of hadrons