The J Pc = 0 ++ Scalar Meson Nonet and Glueball of Lowest Mass

The evidence for the low mass J = 0 states is reconsidered. We suggest classifying the isoscalars f0(980) and f0(1500) as members of the 0 ++ nonet, with a mixing rather similar to that of the pseudoscalars η′ and η. The broad state called f0(400− 1200) or “sigma” and the state f0(1370) are considered as different signals from a single broad resonance, which we take to be the lowest-lying 0 glueball. The main arguments in favor of these hypotheses are presented and compared with theoretical expectations.