Correlations in double parton distributions at small x

TL;DR

This paper investigates the double parton distribution in impact parameter space at small x using the Lund Dipole Cascade model, revealing large correlations and hot spots that influence double scattering processes in hadronic collisions.

Contribution

It introduces a dynamical study of double parton distributions incorporating BFKL evolution, higher order corrections, and saturation effects, highlighting correlation effects and hot spot development.

Findings

Large correlation effects break factorization in double scattering.

Hot spots develop at small transverse separation and grow with Q^2.

Distribution widens at smaller x, affecting LHC extrapolations.

Abstract

We present a dynamical study of the double parton distribution in impact parameter space, which enters into the double scattering cross section in hadronic collisions. This distribution is analogous to the generalized parton densities in momentum space. We use the Lund Dipole Cascade model, presented in earlier articles, which is based on BFKL evolution including essential higher order corrections and saturation effects. As result we find large correlation effects, which break the factorization of the double scattering process. At small transverse separation we see the development of "hot spots", which become stronger with increasing Q^2. At smaller x-values the distribution widens, consistent with the shrinking of the diffractive peak in elastic scattering. The dependence on Q^2 is, however, significantly stronger than the dependence on x, which has implications for extrapolations to LHC, e.g. for results for underlying events associated with the production of new heavy particles.