ENH: group decay node in decay LaTeX rendering

[redeboer]

Old

$$\begin{split}\begin{array}{c} J/\psi(1S)\left[1^-\right] \xrightarrow[S=1]{L=0} N(1720)^{+}\left[\frac{3}{2}^+\right] \xrightarrow[S=1/2]{L=1} K^{0}\left[0^-\right] \Sigma^{+}\left[\frac{1}{2}^+\right] \overline{p}\left[\frac{1}{2}^-\right] \\\ J/\psi(1S)\left[1^-\right] \xrightarrow[S=1]{L=0} \overline{\Sigma}(1660)^{-}\left[\frac{1}{2}^-\right] \xrightarrow[S=1/2]{L=1} K^{0}\left[0^-\right] \overline{p}\left[\frac{1}{2}^-\right] \Sigma^{+}\left[\frac{1}{2}^+\right] \\\ \end{array}\end{split}$$

New

$$\begin{split}\begin{array}{c} J/\psi(1S)\left[1^-\right] \xrightarrow[S=1]{L=0} \left(N(1720)^{+}\left[\frac{3}{2}^+\right] \xrightarrow[S=1/2]{L=1} K^{0}\left[0^-\right] \Sigma^{+}\left[\frac{1}{2}^+\right]\right) \overline{p}\left[\frac{1}{2}^-\right] \\\ J/\psi(1S)\left[1^-\right] \xrightarrow[S=1]{L=0} \left(\overline{\Sigma}(1660)^{-}\left[\frac{1}{2}^-\right] \xrightarrow[S=1/2]{L=1} K^{0}\left[0^-\right] \overline{p}\left[\frac{1}{2}^-\right]\right) \Sigma^{+}\left[\frac{1}{2}^+\right] \\\ \end{array}\end{split}$$