On intermittency in heavy-ion collisions and the importance of γ-conversion in a multi-dimensional intermittency analysis

Non-statistical fluctuations are used to probe the dynamical behaviour of multi-particle production in heavy-ion interactions at ultra-relativistic energies. In a one-dimensional analysis a 1〈ϱ〉-scaling is established and it is furthermore found that effects from higher-order particle correlations are small. In a two-dimensional analysis it is shown that a small background of particle pairs with a narrow opening angle can distort the observed signal. As an example we estimate the influence of γ-conversion and find that in our experiment γ-conversion alone gives results consistent with the experimental observations from a two-dimensional analysis. Whereas a two-dimensional analysis filters events where two particles are extremely close in phase space, the one-dimensional analysis picks out events with particles clustered in pseudorapidity, which are at the same time diluted in the azimuthal plane.