Constraining double parton correlations and interferences
Tomas Kasemets, Piet J. Mulders
TL;DR
The study addresses how to bound double parton correlations and interference effects in double parton scattering by exploiting the positive semidefinite nature of two-parton density matrices. It derives a suite of upper bounds on color, flavor, and fermion-number interference DPDs for quarks, antiquarks, and gluons, using SU(3) representation decompositions and eigenvalue positivity. A key result is the equivalence of double gluon decouplet and anti-decouplet distributions, reducing the number of independent DPDs, and the extension to mixed gluon-quark distributions. These constraints provide practical guidance for modeling DPS cross sections and understanding which correlations can be phenomenologically relevant, especially when combined with QCD evolution.
Abstract
Double parton scattering (DPS) has become very relevant as a background to interesting analyses performed by the experiments at the LHC. It encodes knowledge of correlations between the proton constituents not accessible in single parton scattering. Within perturbative QCD DPS is described in terms of partonic subprocesses and double parton distributions (DPDs). There exists a large number of different DPDs describing the different possible states of two partons inside a proton. They include correlations between the two partons and interferences between the two hard subprocesses. Taking the probability interpretation of the DPDs as starting point, we derive limits on the interference DPDs and thereby constrain the size of correlations between two partons inside an unpolarized proton.