Two-particle interferometry for noncentral heavy-ion collisions

In noncentral heavy-ion collisions, identical two-particle Hanbury-Brown–Twiss (HBT) correlations $C(\mathbf{K},\mathbf{q})$ depend on the azimuthal direction of the pair momentum K. We investigate the consequences for a harmonic analysis of the corresponding HBT radius parameters $R_{\mathrm{ij}}^2.$ Our discussion includes both, a model-independent analysis of these parameters in the Gaussian approximation, and the study of a class of hydrodynamical models which mimic essential geometrical and dynamical properties of peripheral heavy-ion collisions. Also, we discuss the additional geometrical and dynamical information contained in the harmonic coefficients of $R_{\mathrm{ij}}^2.$ The leading contribution of their first and second harmonics are found to satisfy simple constraints. This allows for a minimal, azimuthally sensitive parametrization of all first and second harmonic coefficients in terms of only two additional fit parameters. We determine to what extent these parameters can be extracted from experimental data despite finite multiplicity fluctuations and the resulting uncertainty in the reconstruction of the reaction plane.