用具有不同起点和终点的两个箭头标记一个方程的两个不同部分

Question

我想写一个公式，像附图一样，公式的两个部分有两个不同的箭头。我最终可以通过 \xymatrix 编写下面的代码。但第二个箭头的起点不正确。

%
%%-------------------------------------------------------------
%% Modern Particle Physics, Mark Thomson, Cambridge University, 2013 
%%-------------------------------------------------------------
%
\documentclass[openany,11pt]{book}

\usepackage{amsthm,amsmath,amssymb,mathrsfs,amsfonts}
%\usepackage[cmex10]{amsmath}
\usepackage[all]{xy}
\usepackage{setspace}
\usepackage{makeidx}
\usepackage{colortbl}
\usepackage{tikz}
\usepackage{graphicx}
\usepackage{graphics}





\begin{document}


%-----------------
\begin{eqnarray}
\xymatrix{
    |K_L\rangle=\frac{1}{\sqrt{2(1+|\epsilon^2|)}}[(1+\varepsilon)\mkern-25mu&\mkern-25mu|K^0\rangle \ar[rd]%
    +/d:(1,1) 5pt/\mkern-25mu&\mkern-25mu - (1 - \varepsilon)\mkern-25mu&\mkern-25mu|\bar{K^0}\ar[rd]%
    +/d:(1,1) 5pt/\rangle]. \\\nonumber
    \mkern-25mu&\mkern-25mu&\mkern-25mu\pi^-e^+\nu_e \mkern-25mu&\mkern-25mu \mkern-25mu&\mkern-25mu \pi^+e^-\bar{\nu}_e}\mkern-25mu \nonumber
\end{eqnarray}
%-----------------




\end{document}

Answer 1

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{tikzmark}

\begin{document}

    \[ 
    |K_L\rangle=\frac{1}{\sqrt{2(1+|\varepsilon^2|)}}\left[(1+\varepsilon)|
    \tikzmarknode{K1}{K^0}\rangle- (1 - \varepsilon)|
    \tikzmarknode{K2}{\overline{K}^0}\rangle\right]
    \]

    \begin{tikzpicture}[
        overlay,remember picture,
        arr/.style={-stealth,shorten <=5pt}]
    
        \draw[arr] (K1.south) |-++ (.5,-1) node[at end,right] {$\pi^-e^+\nu_e$};
        \draw[arr] (K2.south) |-++ (.5,-.5) node[at end,right] {$\pi^+e^-\overline{\nu}_e$};
    
    \end{tikzpicture}

\end{document}

Answer 2

在您的帮助下最终完成的代码：

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{tikzmark}

\newcommand{\tikzmarknode}[1]{\tikz[baseline,remember picture] \coordinate (#1) {};}

\begin{document}
    
    \begin{align*}
    |K_L\rangle =\frac1{\sqrt{2(1 + \lvert\varepsilon^2\rvert)}}
    \Bigl[(1 + \varepsilon)
    {|K\tikzmarknode{K1}^0\rangle} - (1 - \varepsilon)
    {|\bar K\tikzmarknode{K2}^0\rangle} \Bigr].
    \end{align*}
    

    \begin{tikzpicture}[overlay,remember picture,
    arr/.style={-stealth,shorten <=5pt}]
    
    \draw[arr] (K1.south) |-++ (.5,-1) node[at end,right] {$\pi^-e^+\nu_e$};
    \draw[arr] (K2.south) |-++ (.5,-.5) node[at end,right] {$\pi^+e^-\overline{\nu}_e$};
    
    \end{tikzpicture}

\end{document}

enter code here