A type of spin ½ baryon. There are three types of sigma particles, denoted Σ−, Σ0, Σ+, for the negatively charged, electrically neutral, and positively charged forms, respectively. The quark content of the sigma particles are Σ− (dds), Σ0 (dus), Σ+ (uus), where d, u, and s denote down, up, and strange, respectively. The masses of the sigma particles are 1189.36 MeV (Σ+), 1192.46 MeV (Σ0), 1197.34 MeV (Σ−); their average lifetimes are 0.8×10−10 s (Σ+), 5.8×10−20 s (Σ0), and 1.5×10−10 s (Σ−).