Abstract
In this work we present a new subtraction method for next-to-leading order calculations that is particularly convenient even when narrow resonances are present. The method is particularly suitable for the implementation of next-to-leading order calculations matched to parton shower generators. It allows at the same time for the inclusion of all finite width effects, including interferences, and for a consistent treatment of resonances in the shower approach, preserving the mass of resonances near their peak. We implement our method, in a fully general and automatic way, within the POWHEG BOX framework, and illustrate it using as a test case the process of $p p \to \mu^+ \nu_\mu j_b j$, that is dominated by $t$-channel single top production.
Highlights
Where ΦB stands for the Born phase space and ΦR is the real emission phase space
In this work we present a new subtraction method for next-to-leading order calculations that is convenient even when narrow resonances are present
We must ascribe the differences that we find to the different treatment of radiation in POWHEG and Pythia8
Summary
One introduces a parametrization of the real phase space of the form ΦR = ΦR(ΦB, Φrad), with dΦR = dΦBdΦrad,. Collinear and soft divergences cancel under the integral sign in the square bracket of the second term. The development of the subtraction method started since the very early QCD computations, already appearing in the bud in the calculation of the Drell-Yan process of ref. The subtraction method implemented in parton level generators was applied for processes initiated by hadrons [4], and it became common practice to compute the Rs term by using the collinear and the soft approximations in d dimensions (see for example [5]). [7], known as the FKS method, is instead based upon the more traditional phase space parametrizations used in refs. The formulation given in ref. [7], known as the FKS method, is instead based upon the more traditional phase space parametrizations used in refs. [2] and [4]
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