Abstract
We present algorithms that interleave photon radiation from the final state and the initial state with the QCD evolution in the antenna-based Vincia parton shower. One of the algorithms incorporates the complete soft and collinear structure associated with photon emission, but may be computationally expensive, while the other approximates the soft structure at a lower cost. Radiation from fermions and W bosons is included, and a strategy for photon radiation off leptons below the hadronization scale is set up. We show results of the application of the shower algorithms to Drell-Yan and W+W− production at the LHC, showing the impact of the inclusion of the full soft structure and treatment of radiation off W bosons.
Highlights
Parton-shower algorithms are an essential component of Monte Carlo event generators [1], providing a means of resumming radiative corrections in a fully exclusive and universal manner
We apply the new QED shower algorithms implemented in Vincia to Drell-Yan and W + W − production at the LHC and investigate their differences
We compare to the default (DGLAP-based) Pythia QED shower, whose dipole kinematics are based on a principle of “maximum screening” similar to that of our pairing algorithm
Summary
Parton-shower algorithms are an essential component of Monte Carlo event generators [1], providing a means of resumming radiative corrections in a fully exclusive and universal manner. YFS exponentiation [10] is used in some cases [11,12] as a means of including the soft interference structure in a universal processindependent way, but the QCD and QED showers are not interleaved. In an interleaved evolution [13], different branching types (here, QED and QCD ones) are allowed to compete with each other for phase space during the shower evolution. This produces an arguably more physical relative ordering of evolution scales in the resulting joint resummation, compared to the non-interleaved case. In [14], the first algorithm allowing QCD showers to be interleaved with a fully coherent (multipole) treatment of final-state
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