The quark structure of the bottom eta meson. The color assignment of individual quarks is arbitrary, but the net color charge must be zero. Forces between quarks are mediated by gluons.
The bottom eta meson ( η b) or eta-b meson is a flavourlessmeson 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.