ar X iv : n uc l - ex / 0 50 10 10 v 1 1 7 Ja n 20 05 ρ meson production in ultraperipheral dAu collision

Ultra-peripheral heavy ion collisions involve long range electromagnetic interactions at impact parameters larger than twice the nuclear radius, where no nucleon-nucleon collisions occur. We report on the first observation of ρ meson production in dAu → dAuρ 0 and dAu → npAuρ 0. In ultraperipheral heavy-ion collisions, two nuclei geometrically " miss " each other. The impact parameter is larger than twice nuclear radius. In such conditions hadronic interactions do not occur[1]. Relativistic ions are sources of electromagnetic and pomeron fields. The electromagnetic fields have a large radius of interaction, than strong interactions. So, in ultraperipheral collisions, the nuclei interact by two photons or photon-pomeron exchange. The photon flux is proportional to the square of the nuclear charge Z 2 [2], and the forward cross section for elastic ρ 0 A scattering scales as A 4/3 for surface coupling and A 2 in the bulk. Thus the cross section for photon-pomeron interaction ∼ A 2 Z 2 for " heavy " states (as like J/psi) and Z 2 A 4/3 for lighter mesons (ρ, ω, φ). Fig.1(a) Fig.1(b) Exclusive vector meson production dAu → d(np)Auρ 0 (fig.1(a,b)) can be described by using Weizsacker-Williams approach[2] to photon and pomeron fluxes and vector dominance model. Photon emitted by one nucleus can be consider as a state of virtual photons plus some fluctuations of quark-antiquark pairs. When the nucleus absorbs " photonic " part of wave function, the quark-antiquark pairs contribution becomes dominant. This pair can elastically scatters on the other nucleus and appears as a real vector meson. In ultraperipheral deuteron gold interactions there are two mechanisms of ρ-meson production. First, a photon emitted by the gold interacts with the deuteron producing 1