The bottom eta meson () or eta-b meson is a flavourless meson formed from a bottom quark and its antiparticle. It was first observed by the BaBar experiment at SLAC in 2008, and is the lightest particle containing a bottom and anti-bottom quark.
See also Eta and eta prime mesons, a similar particle with light quarks. Quarkonium, the general name for mesons formed from a quark and the corresponding antiquark. List of mesons
References