it in MC@NLO; in particular, one has to apply the so-called event projection which allows one to define a unique kinematic configuration associated with all counterevents (for a given real-emission configuration) – see sect. A.4 of ref. [@Frixione:2002ik]. As discussed in that paper, although event projection is largely arbitrary, in the context of MC@NLO it turns out to be convenient to derive it from the behaviour of the Monte Carlo one interfaces to. We shall therefore discuss in the next subsection the behaviour of  relevant to this issue.

Event projection with PYTHIA
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The way in which  deals with the simulation of $V$ production is the following [@Sjostrand:2006za; @Miu:1998ju]. First, the hard process is generated. This implies the generation of the two Bjorken $x$’s entering such a process, which we shall denote by ${\zeta_1}$ and ${\zeta_2}$ for the parton coming from the left and from the right respectively. The partonic c.m. energy squared is s\_0=[\_1]{}[\_2]{}S, \[spart\] with $S$ the collider energy squared. In the case of single-$V$ production, $s_0={m_V}^2$, with ${m_V}$ the mass of $V$ (or its virtuality if lepton pair production is considered), but eq. (\[spart\]) is obviously valid regardless of the production process.  then begins the showers. Choosing 