The bottom quark is the fifth quark in the Standard Model of particle physics. Together with the sixth and heaviest quark, the top quark, they form a pair, like the up and down quarks, or the charm and the strange quarks.
Bottom quarks, like the lighter quarks, form bound states. They mostly bind to a single other quark, creating the so-called B mesons. These hadrons, after being created, fly a few millimetres before decaying into a shower of particles. This is due to their relatively long lifetime. We exploit this feature to identify B hadrons: by precisely measuring the trajectories of the decay products, we can identify the position of the so-called “secondary vertex”, where the B meson has decayed, and label the decaying particle as a B hadron.
The study of B hadrons is promising for exploring fundamental symmetries of physics. We expect the laws of physics to be identical for matter and antimatter, and to not change in reflections in space and time. However, we observe violations of individual symmetries in the study of B hadrons, thus they may be a key element in explaining why the observable Universe is mainly made of matter and we do not see galaxies made of antimatter.
The sign shows a schematic representation of the B hadron decay in a particle physics experiment. Due to its relatively long lifetime, this particle moves a few millimetres away from its point of origin, before decaying. The decay products remain in a cone, also called a particle jet.
