Abstract
In this paper a generalisation of the Catani–Seymour dipole subtraction method to next-to-leading order electroweak calculations is presented. All singularities due to photon and gluon radiation off both massless and massive partons in the presence of both massless and massive spectators are accounted for. Particular attention is paid to the simultaneous subtraction of singularities of both QCD and electroweak origin which are present in the next-to-leading order corrections to processes with more than one perturbative order contributing at Born level. Similarly, embedding non-dipole-like photon splittings in the dipole subtraction scheme discussed. The implementation of the formulated subtraction scheme in the framework of the Sherpa Monte-Carlo event generator, including the restriction of the dipole phase space through the alpha -parameters and expanding its existing subtraction for NLO QCD calculations, is detailed and numerous internal consistency checks validating the obtained results are presented.
Highlights
Looking at theTeV regime, the NLO EW corrections quickly grow considerably, reducing cross sections by a few tens of percent, due to the emergence of large electroweak Sudakov corrections arising as the scattering energies Q2 m2W [2–17]. In this regime they are larger than even the NLO QCD corrections in many cases and their omission becomes the dominant uncertainty in experimental studies and searches
Besides the translation of the QCD dipole functions to the QED case, several other issues have been addressed. They include the special role photon splittings play in the formalism, embedding extermal massive emitters of spin
1 2 into the formalism and the interplay of QCD and QED subtractions for processes exhibiting both kinds of divergences
Summary
In order to be applicable to NLO EW calculations the wellknown Catani–Seymour dipole subtraction [40,41] needs to be recast in a suitable form. To highlight the changes from the original formulation for NLO QCD calculations the complete structure of the formalism is reviewed This subtraction formalism starts from the the expectation value of any infrared safe observable O described at NLO accuracy through. The virtual and real corrections, V and R, as well as the collinear counter term, C, are defined analogously. When regulating their respective divergences through dimensional regularisation, they have to be evaluated consistently in d = 4 − 2 dimensions for all singularities to cancel.
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