Theta meson

{{Short description|Hypothetical form of quarkonium}}

{{Hatnote|Not to be confused with the θ⁺ of the τ–θ puzzle, which is now identified as kaon, or with the Θ⁺ and {{Physics particle|Θ|TR=+|BR=c}}, formerly thought to be pentaquarks.}}

{{Infobox particle

| name = Theta meson

| image = Quark structure toponium.svg

| caption = Quark structure of the theta meson

| num_types =

| composition = {{SubatomicParticle|Top quark}}{{SubatomicParticle|Top antiquark}}

| statistics = bosonic

| group =

| interaction = strong, weak, gravitational, electromagnetic

| antiparticle = self

| status = hypothetical

| theorized =

| discovered =

| symbol =

| mass =

| mean_lifetime =

| decay_particle =

| electric_charge = 0 e

| spin =

| strangeness =

| charm =

| bottomness =

| topness =

| isospin = 0

| hypercharge = 0

| parity = −1

| c_parity = −1

}}

The theta meson ({{Subatomic particle|Theta meson}}){{cite web |last1=Roos |first1=M. |last2=Wohl |first2=C.G. |title=Naming Scheme for Hadrons |url=http://pdg.lbl.gov/2014/reviews/rpp2014-rev-naming-scheme-hadrons.pdf |website=lbl.gov |access-date=23 March 2022}} is a hypothetical form of quarkonium (i.e. a flavourless meson) formed by a top quark ({{SubatomicParticle|Top quark}}) and top antiquark ({{SubatomicParticle|Top antiquark}}). As a P-odd and C-odd {{SubatomicParticle|Top quark}}{{SubatomicParticle|Top antiquark}} state, it is analogous to the phi meson ({{SubatomicParticle|Strange quark}}{{SubatomicParticle|Strange antiquark}}), J/psi meson ({{SubatomicParticle|Charm quark}}{{SubatomicParticle|Charm antiquark}}) and upsilon meson ({{SubatomicParticle|Bottom quark}}{{SubatomicParticle|Bottom antiquark}}) mesons. Due to the top quark's short lifetime, the theta meson is expected to not be observed in nature.{{cite journal|doi=10.1007/s100520050144|arxiv=hep-ph/9704261|title=Top mesons|first=N.|last=Fabiano|journal=European Physical Journal C|volume=2|pages=345–350|year=1998|issue=2|bibcode=1998EPJC....2..345F |s2cid=17321939}}