Large multiplicity fluctuations and saturation effects in onium collisions

This paper studies two related questions in high energy onium-onium scattering: the probability of producing an unusually large number of particles in a collision, where it is found that the cross section for producing a central multiplicity proportional to k should decrease exponentially in √ k. Secondly, the nature of gluon (dipole) evolution when dipole densities become so high that saturation effects due to dipole-dipole interactions become important: measures of saturation are developed to help understand when saturation becomes important, and further information is obtained by exploiting changes of frame, which interchange unitarity and saturation corrections. This work is supported in part by the US Department of Energy under Grant DE-FG02-94ER40819 This work is supported by the UK Particle Physics and Astronomy Research Council