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33 lines
1.5 KiB
33 lines
1.5 KiB
\midheading{$Z+2$~jets production, processes 44, 46}
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\label{subsec:z2jets}
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These processes represents the production of a $Z$ boson and $2$ jets,
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including also the effect of a virtual photon ({\tt nproc=44} only). The $Z/\gamma^*$ decays
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to an $e^+ e^-$ pair ({\tt nproc=44}) or into three species of neutrino ({\tt nproc=46}).
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Virtual amplitudes are taken from ref.~\cite{Bern:1997sc}.
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For more details on this calculation, please see
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Refs.~\cite{Campbell:2002tg,Campbell:2003hd}.
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The calculation may be performed up to NLO.
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For $Z+2$~jet production
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the next-to-leading order matrix elements are
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particularly complex and so they have been divided into two groups.
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The division is according to the lowest order diagrams from which they
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originate:
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\begin{enumerate}
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\item Diagrams involving two external quark lines and two external gluons,
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the ``{\tt Gflag}'' contribution. The real diagrams in this case thus
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involve three external gluons.
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\item Diagrams where all four external lines are quarks,
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the ``{\tt Qflag}'' contribution. The real diagrams in this case
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involve only one gluon.
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\end{enumerate}
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By specifying {\tt Gflag} and {\tt Qflag} in the file {\tt input.ini} one may
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select one of these options at a time. The full result may be obtained
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by straightforward addition of the two individual pieces, with no
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meaning attached to either piece separately.
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The default is that both of these are set to {\tt .true.} simultaneously.
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When {\tt removebr} is true, the $Z$ boson does not decay.
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