Two-particle angular correlations in p+p and Cu+Cu collisions at PHOBOS

We present results on two-particle angular correlations in p+p and Cu+Cu collisions over a broad range of (η ,φ ). The PHOBOS detector has a uniquely large angular coverage for inclusive charged particles. This allows for the study of correlations on both long and short range pseudorapidity scales. A complex two-dimensional correlation structure emerges which is interpreted in the context of a cluster model. The cluster size and its decay width are extracted from the twoparticle pseudorapidity correlation function. Relative to p+p collisions, Cu+Cu reactions show a non-trivial decrease of cluster size with increasing centrality. These results may provide insight into the hadronization stage of the hot and dense medium created in heavy ion collisions.