Interleaved resonance decays and electroweak radiation in the Vincia parton shower
Helen Brooks, Peter Skands, Rob Verheyen
Abstract
We propose a framework for high-energy interactions in which resonance decays and electroweak branching processes are interleaved with the QCD evolution in a single common sequence of decreasing resolution scales. The interleaved treatment of resonance decays allows for a new treatment of finite-width effects in parton showers. At scales above their offshellness (i.e., typically Q > \Gamma <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>Q</mml:mi> <mml:mo>></mml:mo> <mml:mi>Γ</mml:mi> </mml:mrow> </mml:math> ), resonances participate explicitly as incoming and outgoing states in branching processes, while they are effectively ``integrated out’’ of the description at lower scales. We implement this formalism, together with a full set of antenna functions for branching processes involving electroweak ( W/Z/H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>W</mml:mi> <mml:mi>/</mml:mi> <mml:mi>Z</mml:mi> <mml:mi>/</mml:mi> <mml:mi>H</mml:mi> </mml:mrow> </mml:math> ) bosons in the Vincia shower module in Pythia 8.3, and study some of the consequences.