Mesons other than quark-antiquark states?

[websterling]

Mesons: hadrons with integer spin, usually quark-antiquark states

I came across this statement in a pdf of a powerpoint. Unfortunately the presentation is so badly formatted (missing images, content overlapping content, etc.) that it's hard to follow and I can't see if he ever describes mesons that are not quark-antiquark states.

Are there mesons that aren't quark-antiquark pairs? The only definition I've ever seen is: Mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. The only thing I can think of is that he might classify tetraquarks as mesons because of their integer spin?

 

[mfb]

It depends on the definition.

There are exotic states that could be tetraquarks, meson molecules or something else (and it's not clear if it makes sense to distinguish between those categories). The existence of something meson-like is clear, the interpretation is not.

Hypothetical glueballs could be called mesons as well.

 

[ohwilleke]

Are there mesons that aren't quark-antiquark pairs? The only definition I've ever seen is: Mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. The only thing I can think of is that he might classify tetraquarks as mesons because of their integer spin?

Your definition can't really be true, since many mesons are linear combinations of multiple quark-antiquark states, most prosaically, neutral pions, but also for several other light pseudo-scalar mesons. This is also the case for essentially all true scalar mesons.