bquarks

The bottom quark, also known as the b quark or beauty quark, is a fundamental particle in the Standard Model. It is a third-generation down-type quark with electric charge −1/3 e and spin 1/2. Its mass is about 4.18 GeV/c^2 in the MSbar scheme, making it the heaviest quark typically produced as a bound state in high-energy experiments. Like other quarks, it carries color charge and participates in the strong interaction, but its most distinctive role arises from weak decays that change flavor.

Because of confinement, quarks are never observed free in nature. A bottom quark appears in hadrons such as B mesons (a bottom antiquark paired with a light quark) and bottom baryons, as well as in bottomonium states (bound pairs of a bottom quark and its antiquark). Hadronization through the strong interaction produces jets containing B hadrons. The weak decay of the bottom quark leads to relatively long lifetimes for B hadrons, on the order of 1.5 picoseconds, with dominant transitions such as b → c. These decays probe the CKM matrix and generate phenomena like CP violation in the B meson system, as well as various rare decays studied in flavor physics.

The bottom quark was established experimentally in 1977 with the discovery of bottomonium resonances, the Υ family. The term beauty has historically been used as an alternate name for the b quark. In modern research, b quarks are central to precision tests of the Standard Model and to searches for new physics, via experiments at facilities such as LHCb and Belle II.