In particle physics, B mesons are mesons composed of a bottom antiquark and either an up (B+), down (B0), strange (B0s) or charm quark (B+c). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but rather bottomonium which is something else entirely.
List of B mesons
The neutral B mesons, B0 and B0s, spontaneously transform into their own antiparticles and back. This phenomenon is called flavor oscillation. The existence of neutral B meson oscillations is a fundamental prediction of the Standard Model of particle physics. It has been measured in the B0–B0 system to be about 0.496 ps−1, and in the B0s–B0s system to be Δms = 17.77 ± 0.10 (stat) ± 0.07 (syst) ps−1 measured by CDF experiment at Fermilab. A first estimation of the lower and upper limit of the B0s–B0s system value have been made by the DØ experiment also at Fermilab.
Ronald Kotulak, writing for the Chicago Tribune, called the particle "bizarre" and stated that the meson "may open the door to a new era of physics" with its proven interactions with the "spooky realm of antimatter".
On 14 May 2010, physicists at the Fermi National Accelerator Laboratory reported that the oscillations decayed into matter 1% more often than into antimatter, which may help explain the abundance of matter over antimatter in the observed Universe. However, more recent results at LHCb with larger data samples have suggested no significant deviation from the Standard Model.
B-mesons are an important probe for exploring quantum chromodynamics. Various uncommon decay paths of the B mesons are sensitive to physics processes outside the standard model. Measuring these rare branching fractions sets limits on new particles. The LHCb experiment has observed and searched for several of these decays such as Bs → µ+µ−.
On February 21, 2017, the LHCb collaboration announced that the rare decay of a neutral B-meson into two oppositely charged kaons had been observed to a statistical significance of 5σ.