Theta meson
Template:Short description Template:Hatnote Template:Infobox particle
The theta meson (Template:Subatomic particle)[1] is a hypothetical form of quarkonium (i.e. a flavourless meson) formed by a top quark (Template:SubatomicParticle) and top antiquark (Template:SubatomicParticle). As a P-odd and C-odd Template:SubatomicParticleTemplate:SubatomicParticle state, it is analogous to the Template:SubatomicParticle (Template:SubatomicParticleTemplate:SubatomicParticle), Template:SubatomicParticle (Template:SubatomicParticleTemplate:SubatomicParticle) and Template:SubatomicParticle (Template:SubatomicParticleTemplate:SubatomicParticle) mesons. Due to the top quark's short lifetime, the theta meson is expected to not be observed in nature.[2]
In 2025, new research from the CMS[3] and ATLAS[4] collaborations unexpectedly demonstrated the existence of a tTemplate:SubatomicParticle meson at greater than 5-sigma significance[5][6], but that is believed to be the pseudoscalar ηt meson rather than the θ meson.