Bottom quark
The bottom quark or b quark, also known as the beauty quark, is a third-generation quark with a charge of −⁄3 e. Although all quarks are described in a similar way by quantum chromodynamics, the bottom quark's large bare mass (around 4.2 GeV/c, a bit more than four times the mass of a proton), combined with low values of the CKM matrix elements Vub and Vcb, gives it a distinctive signature that makes it relatively easy to identify experimentally (using a technique called B-tagging). Because three generations of quark are required for CP violation (see CKM matrix), mesons containing the bottom quark are the easiest particles to use to investigate the phenomenon; such experiments are being performed at the BaBar, Belle and LHCb experiments.