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24 lines
1.3 KiB
24 lines
1.3 KiB
\midheading{$Zt{\bar t}$ production, processes 529-533}
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\label{subsec:ztt}
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These processes represent the production of a $Z$ boson in association
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with a pair of top quarks. These processes are only available at LO.
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For process {\tt 529}, neither the top quarks nor the $Z$-boson
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decays.
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In processes {\tt 530-533}, the top quarks are always
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produced on-shell, which is a necessity for a gauge invariant result
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from this limited set of diagrams.
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Switching {\tt zerowidth} from {\tt .true.} to {\tt .false.} only affects
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the $Z$ and the $W$ bosons from the top quark decay.
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In process {\tt 530} the $Z$ boson decays into an electron pair, whilst
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in {\tt 531} the decay is into a massless bottom quark pair.
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In process {\tt 532--533} the $Z$ boson decays into an electron pair, whilst
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one or other of the top quark or top anti-quark decays hadronically.
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For processes {\tt 532} and {\tt 533} the default behaviour is that the hadronic decay products
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are clustered into jets using the supplied jet
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algorithm parameters, but no cut is applied on the number of jets.
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This behaviour can be altered by changing the value of the
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variable {\tt notag} in the file {\tt src/User/setnotag.f}.
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When {\tt removebr} is true in process {\tt 530}, the top quarks and the $Z$ boson do not decay.
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