Disentangling correlations in Multiple Parton Interactions
Giorgio Calucci, Daniele Treleani
TL;DR
The paper analyzes how double parton scattering encodes both longitudinal and transverse parton correlations and proposes proton–deuteron collisions as a clean probe to disentangle them. It develops a formal framework for DP scattering in pD, including cases with one or two active nucleons, and expresses the cross sections through two-parton densities and deuteron structure. A simple Gaussian model links the effective cross section to transverse correlation strength and multiplicity fluctuations, while longitudinal smearing is shown to be a small effect. The study concludes that light-nucleus collisions offer a model-independent avenue to map three-dimensional parton structure, with significant implications for interpreting MPI at current and future colliders.
Abstract
Multiple Parton Interactions are the tool to obtain information on the correlations between partons in the hadron structure. Partons may be correlated in all degrees of freedom and all different correlation terms contribute to the cross section. The contributions due to the different parton flavors can be isolated, at least to some extent, by selecting properly the final state. In the case of high energy proton-proton collisions, the effects of correlations in the transverse coordinates and in fractional momenta are, on the contrary, unavoidably mixed in the final observables. The standard way to quantify the strength of double parton interactions is by the value of the effective cross section and a small value of the effective cross section may be originated both by the relatively short transverse distance between the pairs of partons undergoing the double interaction and by a large dispersion of the distribution in multiplicity of the multi-parton distributions. The aim of the present paper is to show how the effects of longitudinal and transverse correlations may be disentangled by taking into account the additional information provided by double parton interactions in high energy proton-deuteron collisions.