Speaker
Description
A systematic study of differences between NLL resummation and parton showers is presented. While large logarithms arising from the IR structure of QCD can be resummed to higher logarithmic accuracy for specific observables, numerical calculations based on parton showers are formally correct to LL only. However, they incorporate additional effects like local momentum conservation, which are beyond this formal accuracy. To investigate the numerical size of these effects, a Markovian Monte-Carlo algorithm for resummation of additive observables in electron-positron annihilation is presented. The numerical effects of individual approximations intrinsic to the pure NLL result are studied and an overall comparison is made between the parton shower and pure NLL resummation.