Jet vetoing and Herwig++

Understand

We investigate the simulation of events with gaps between jets with a veto on additional radiation in the gap in Herwig++.

• We discover that the currently-used random treatment of radiation in the parton shower is generating some unphysical behaviour for wide-angle gluon emission in QCD 2 to 2 scatterings.
• We explore this behaviour quantitatively by making the same assumptions as the parton shower in the analytical calculation.
• We then modify the parton shower algorithm in order to correct the simulation of QCD radiation.