Azimuthally sensitive correlations in nucleus-nucleus collisions

We define a set of model-independent observables which generally characterize the azimuthal dependence of two-particle correlations in nucleus-nucleus collisions. We explain how they can be analyzed, and show to what extent such analyses are model dependent. We discuss specific applications to the anisotropic flow of decaying particles, azimuthally sensitive Hanbury-Brown Twiss interferometry, and correlations between particles at large transverse momentum. A quantitative prediction is made for jet quenching with respect to the reaction plane.

Figure 1

Illustration of the various azimuthal angles ${\varphi }_1$, ${\varphi }_2$, ${\varphi }_{\text{pair}}$, $\Delta \varphi$, with $x=1∕2$.

Figure 2

Illustration of the prediction made in Eq. (17). The long arrows represent the momenta of trigger particles, while the shorter arrows represent the momenta of associated particles. If the modification of the correlation is due to the quenching of the associated particle, it must be unchanged under the transformation ${\varphi }_2-{\Phi }_R\to -({\varphi }_2-{\Phi }_R)$.