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\title{\boldmath{ $\sigma$}\ \ \ \ \ \ \ $**$}
\maketitle
 The $\sigma$ is the lightest scalar meson. It has been observed by a number of experiments but due to its large width it properties are poorly measured. It is only included as the external particle in a small number of decays to represent two pions in a $s$-wave state. However it is the intermediate particle in a number of hadronic matrix elements where the mass and width are determined by the matrix element. The mass and width used here are taken from \cite{Tornqvist:1995kr}  which is also used by some of the hadronic matrix elements. The lower limit on the mass is choosen above the two pion threshold to avoid inefficiency problems and given the large width we use twice the width as the upper limit.
The $\sigma$ has mass $860$~MeV and is unstable. The $\sigma$ has spin $0$, charge $0$ and is colour neutral.
 The $\sigma$ is a mesonThe $\sigma$ has width $880$~MeV. The lower limit on the mass of the particle is $550$~MeV and the upper limit is $1760$~MeV. These are the deviations from the on-shell value. The branching ratios are fixed.
The properties of the particle and its antiparticle are taken to be charge-conjugate to each other.
 The PDG code is 9000221.
\setlongtables
\begin{longtable}[t]{|c|c|c|p{1in}|p{2.5in}|c|}
\hline
Branching & Rating & On/ & Outgoing  & Description & Decayer  \\ 
Ratio     &                                 & Off & Particles &             &         \\ 
\hline
\endhead
\caption{The decay modes of the $\sigma$ (continues).}
\endfoot
\caption{The decay modes of the $\sigma$.}
\endlastfoot
\label{tab:9000221decaymodes}
0.666667 & $***$ & on & $ \pi^+, \pi^- $  & The decay of the $\sigma$ to two pions has been observed but the branching ratio is calculated assuming that the sigma only decays to two pions and the identical particle symmetry factor for the $\pi^0\pi^0$ channel.   & Herwig::ScalarScalarScalar::ScalarSS \\ 
\hline
0.333333 & $***$ & on & $ \pi^0, \pi^0 $  & The decay of the $\sigma$ to two pions has been observed but the branching ratio is calculated assuming that the sigma only decays to two pions and the identical particle symmetry factor for the $\pi^0\pi^0$ channel.   & Herwig::ScalarScalarScalar::ScalarSS \\ 
\hline
\end{longtable}The $\sigma$ decay modes are given in Table~\ref{tab:9000221decaymodes} and the total branching ratio is $1$.


The mass generator is \verb|sigmamass| for the $\sigma$.
The width generator is \verb|sigmawidth| for the $\sigma$.

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 The particle was checked by Peter Richardson at 9:10:6 on the 10th of August 2007. The most recently changed decay mode was modified at 23:10:55 on the 3rd of April 2005. The particle data was last modified at 16:24:39 on the 10th of October 2006.

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