Collinear electroweak radiation in antenna parton showers
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Regular Article - Experimental Physics
Collinear electroweak radiation in antenna parton showers Ronald Kleiss1, Rob Verheyen1,2,a 1 2
Radboud University Nijmegen, 6500 GL Nijmegen, The Netherlands University College London, London WC1E 6BT, UK
Received: 28 April 2020 / Accepted: 2 October 2020 © The Author(s) 2020
Abstract We present a first implementation of collinear electroweak radiation in the Vincia parton shower. Due to the chiral nature of the electroweak theory, explicit spin dependence in the shower algorithm is required. We thus use the spinor-helicity formalism to compute helicity-dependent branching kernels, taking special care to deal with the gauge relics that may appear in computation that involve longitudinal polarizations of the massive electroweak vector bosons. These kernels are used to construct a shower algorithm that includes all possible collinear final-state electroweak branchings, including those induced by the Yang–Mills triple vector boson coupling and all Higgs couplings, as well as vector boson emissions from the initial state. We incorporate a treatment of features particular to the electroweak theory, such as the effects of bosonic interference and recoiler effects, as well as a preliminary description of the overlap between electroweak branchings and resonance decays. Some qualifying results on electroweak branching spectra at high energies, as well as effects on LHC physics are presented. Possible future improvements are discussed, including treatment of soft and spin effects, as well as issues unique to the electroweak sector.
1 Introduction Beyond the discovery of the Higgs boson [1,2], signs of new physics have yet to appear at the LHC and the Standard Model has so far survived all forms of scrutiny. It has therefore become more likely that the Standard Model continues to describe nature accurately up to very high energy scales. At these very high energies heavy particles like electroweak gauge bosons, Higgs bosons and top quarks can start to appear as constituents of jets [3,4] or otherwise contribute to radiative corrections. Virtual corrections have been shown to become sizeable even at LHC energies in exclusive observa e-mail:
[email protected] (corresponding author)
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ables [5–18]. For instance, corrections to transverse momentum at LHC energies can already reach about 10% for exclusive dijet production [14,15], and about 20% for single vector boson production [16–18], and they can be expected to grow even larger at future collider energies [19,20]. Work such as [21,22] has instead focussed on the incorporation of electroweak logarithms in the resummation of inclusive observables at high energies. However, many practical observables are not fully exclusive or fully inclusive. In most cases, the only practical solution is to instead include EW effects in a systematic way in parton shower algorithms as part of a general-purpose event generator such as Pythia [23], Sherpa [24] or Herwig [25]. These produce fully differential final states, and
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