This time we have a speaker from each, the theoretical and the experimental side.
Experiment: ALICE has studied two-particle angular correlations in azimuthal direction induced by low energetic di-jets produced in proton-proton collisions. Using two-particle angular correlations with low transverse momentum thresholds, jet properties on a statistical basis down to the lowest possible jet energies are measured.
The presented results allow to optimize the parametrization of the jet
fragmentation in theoretical models down to low energies into the
non-perturbative regime. Furthermore, the analysis can give information about the contribution from multiple parton interactions.
Results are presented from proton-proton collisions at the center-of-mass energies sqrt(s) = 0.9, 2.76, and 7.0 TeV recorded by the ALICE detector. Our results are compared to Pythia6, Pythia8, and Phojet simulations.
Theory: Current multi-parton interaction models will be discussed, using a Sudakov formalism that emphasizes the similarities with bremsstrahlung resummation.
Particular focus is drawn on the current physics limitations of these models, which can be roughly categorized as: multi-parton distributions, space-time picture, and collapse of color wavefunction.
L. Cunqueiro Mendez, J.F. Grosse-Oetringhaus, N. Mahmoudi