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60 lines
1.9 KiB
TeX
60 lines
1.9 KiB
TeX
%%% Local Variables: ***
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%%% mode:latex ***
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%%% TeX-master: "../document.tex" ***
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%%% End: ***
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\chapter{The Diphoton Process}%
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\label{chap:qqgg}
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Consider the scattering of quark and antiquark into two photons
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\(\qqgg\), the diphoton process. In leading order this process is
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being described by the Feynman diagrams in \cref{fig:qqggfeyn}.
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Because there is only QED involved, the color degrees of freedom
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average out and will not be considered henceforth. Furthermore a high
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energy regime will be supposed and therefor masses will be
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neglected.
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\begin{figure}[h]
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\centering
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\begin{subfigure}[c]{.4\textwidth}
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\centering
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\begin{tikzpicture}
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\begin{feynman}
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\diagram [small,horizontal=i2 to a] {
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i2 [particle=\(q\)] -- [fermion, momentum=\(p_2\)] a --
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[fermion, reversed momentum=\(q\)] b,
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i1 [particle=\(\bar{q}\)] -- [anti fermion, momentum'=\(p_1\)] b,
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i2 -- [opacity=0] i1,
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a -- [photon, momentum=\(p_3\)] f1 [particle=\(\gamma\)],
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b -- [photon, momentum'=\(p_4\)] f2 [particle=\(\gamma\)],
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f1 -- [opacity=0] f2,
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};
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\end{feynman}
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\end{tikzpicture}
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\subcaption{u channel}
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\end{subfigure}
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\begin{subfigure}[c]{.4\textwidth}
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\centering
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\begin{tikzpicture}
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\begin{feynman}
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\diagram [small,horizontal=i2 to a] {
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i2 [particle=\(q\)] -- [fermion, momentum=\(p_2\)] a --
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[fermion, reversed momentum'=\(q\)] b,
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i1 [particle=\(\bar{q}\)] -- [anti fermion, momentum'=\(p_1\)] b,
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i2 -- [opacity=0] i1,
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a -- [draw=none] f2 [particle=\(\gamma\)],
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b -- [draw=none] f1 [particle=\(\gamma\)],
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f1 -- [opacity=0] f2,
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};
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\diagram* {
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(a) -- [photon] (f1),
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(b) -- [photon] (f2),
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};
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\end{feynman}
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\end{tikzpicture}
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\subcaption{\label{fig:qqggfeyn2}t channel}
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\end{subfigure}
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\caption{First order diagrams for \(\qqgg\).}%
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\label{fig:qqggfeyn}
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\end{figure}
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