Quasielastic Scattering in the Dipole Model

A series of previous papers [1] develops a dipole model in initial state impact parameter space that includes subleading effects such as running αs, unitarity, confinement and saturation. Here some recent work [2] is presented, where the model is applied to a new set of data: vector meson production in γp, DVCS and dσ/dt in pp. This allows us to tune a more realistic model of the proton wavefunction from the pp data, and confirm the predictive power of the model in high Q of DVCS and vector meson production. For low Q vector meson resonances dominate the photon wavefunction, making our predictions depend on a tuned parametrisation in this range. 1 Why Dipoles? To calculate cross sections for hadronic particles it is important to understand the evolution in the initial state. In a high energy collision, each of the two incoming particles will emit gluons before meeting and interacting. Enumerate the possible initial states with i, j and give each state a probability wi such that ∑ i wi = 1. With a scattering probability pij between state i and j the total interaction probability can be expressed as Ttot(b) = 2 ∑ ij wiwjpij . (1) That means that the expectation value of pij , weighted by wi can be measured. Similarly the diffractive, including elastic, cross section is Tdiff(b) = ∑ ij wiwjp 2 ij . (2) To get both these cross sections right, not only the expectation value of pij with respect to wi is required, but also the fluctuations. That is, it is possible to measure if the cross section is dominated by frequently occuring states with a low interaction probability, giving a low Tdiff/Ttot, or by rare states with a high interaction probability, giving a high Tdiff/Ttot. Also the elastic interaction probability can be written in this way as