Antenna Showers with One-Loop Matrix Elements

TL;DR

This paper enhances antenna shower algorithms by incorporating one-loop matrix element corrections, improving accuracy in simulating gluon emissions in qqbar pairs, and reducing theoretical uncertainties in event simulations.

Contribution

It introduces a method to correct antenna showers at second order in alphaS using matrix elements, improving the modeling of gluon emissions and reducing scale dependence.

Findings

Corrected shower matches second-order QCD matrix elements for Z -> 3 jets.

Including corrections reduces dependence on evolution and renormalization scales.

Impact on LEP event-shape and fragmentation observables demonstrated.

Abstract

We consider the probability for a colour-singlet qqbar pair to emit a gluon, in strongly and smoothly ordered antenna showers. We expand to second order in alphaS and compare to the second-order QCD matrix elements for Z -> 3 jets, neglecting terms suppressed by 1/NC^2. We give a prescription that corrects the shower to the matrix-element result at this order for both soft and hard emissions, thereby explicitly reducing its dependence on evolution- and renormalization-scale choices. We confirm that the choice of pT for both of these scales absorbs all logarithms through order alphaS^2, and contrast this with various alternatives. We include these corrections in the VINCIA shower generator and study the impact on LEP event-shape and fragmentation observables. An uncertainty estimate is provided for each event, in the form of a vector of alternative weights.