On the measurement of azimuthal anisotropies in nucleus–nucleus collisions

Azimuthal distributions of particles produced in nucleus-nucleus collisions are measured with respect to an estimated reaction plane which, because of finite multiplicity fluctuations, differs in general from the true reaction plane. It follows that the measured distributions do not coincide with the true ones. I propose a general method of reconstructing the Fourier coefficients of the true azimuthal distributions from the measured ones. This analysis suggests that the Fourier coefficients are the best observables to characterize azimuthal anisotropies because, unlike other observables such as the in-plane anisotropy ratio or the squeeze-out ratio, they can be reconstructed accurately. ∗ Member of CNRS. † Laboratoire de la Direction des Sciences de la Matière du Commissariat à l’Energie Atomique.