In high energy physics, a scalar meson is a meson with total spin 0 and even parity (usually noted as JP=0+). In contrast, pseudoscalar mesons have odd parity. The first known scalar mesons have been observed since the late 1950s, with observations of numerous light states and heavier states proliferating since the 1980s. Scalar mesons are most often observed in proton-antiproton annihilation, radiative decays of vector mesons, and meson-meson scattering.