Inclusive Pseudorapidity Distributions in p(d)+A Collisions Modeled With Shifted Rapidity Distributions

We study the recent PHOBOS data on the pseudorapidity density of inclusive charged particles in centrality-binned d+Au collisions at sqrt(s_NN) = 200 GeV. It appears that one can understand the increasing forward-backward asymmetry in the data by assuming that the entire distribution "shifts" backwards in rapidity according to the initial-state kinematics, while the total multiplicity scales linearly with Npart/2. Two models are explored, both of which achieve a reasonable description of the available data for rapidities sufficiently far from the pro jectiles (|eta|< 3 at the top RHIC energy). One model uses PYTHIA as the underlying distribution, to allow a straightforward mapping of a rapidity shift back to pseudorapidity space. The other model is a simple analytic calculation based on functions inspired by Landau's hydrodynamical model. The apparent success of these simple pictures to describe the bulk of particle production over |eta|< 3 suggests that collective effects may be present even in the "small" systems created in p+p and d+Au reactions, active over the full rapidity range. The relationship between this and other theoretical approaches are discussed.