title: Relating high-energy Lepton-Hadron, proton-nucleus, and nucleus-nucleus collisions through geometric scaling.
abstract: A characteristic feature of small-x lepton-proton data from HERA is geometric scaling: the fact that in the region of small Bjorken variable x, x less, similar 0.01, all data can be described by a single variable Q(2)/Q(2)(s,p)(x), with all x dependence encoded in the so-called saturation momentum Q(s,p)(x). Here, we observe that the same scaling ansatz accounts for nuclear photoabsorption cross sections and favors the nuclear dependence Q(2)(s,A) proportional, variant A(alpha)Q(2)(s,p), alpha approximately 4/9. We then make the empirical finding that the same A dependence accounts for the centrality evolution of the multiplicities measured in Au+Au collisions at RHIC. It also allows one to parametrize the high-p(t) particle suppression in d+Au collisions at forward rapidities. If these geometric scaling properties have a common dynamical origin, then this A dependence of Q(2)(s,A) should emerge as a consequence of the underlying dynamical model.
authors.affiliation: Department of Physics, CERN, Theory Division, CH-1211 Genève 23, Switzerland.
authors.forename: Néstor
authors.initials: N
authors.lastname: Armesto
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Salgado
authors.forename: Urs Achim
authors.initials: UA
authors.lastname: Wiedemann