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14 lines
993 B
14 lines
993 B
\midheading{$Z\gamma\gamma$ production processes, 301, 306}
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Processes {\tt{301}} and {\tt{306}} represent the production of a $Z$ boson
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(or virtual photon for process {\tt 301}) in association with two photons. The $Z/\gamma^*$ subsequently decays into
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either an $e^+ e^-$ pair ({\tt nproc=301}) or neutrinos ({\tt nproc=306}).
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Since these processes include real photons, the cross section diverges
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when either of the photons is very soft or in the direction of the beam.
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Thus in order to produce sensible results, the input file must supply values for both
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{\tt gammptmin} and {\tt gammrapmax}. Moreover, when the parameters {\tt zerowidth}
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and {\tt removebr} are set to {\tt .false.} the decay $Z \to e^- e^+$ ({\tt nproc=301})
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will include photon radiation from both leptons, so that a non-zero $R(\gamma,\ell)_{min}$
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({\tt Rgalmin})
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should also be supplied. This will ensure that the cross section is well-defined.
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Anomalous couplings are not currently implemented for these processes.
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