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.
Each B meson has an antiparticle that is composed
of a bottom quark and an up (B−), down (B0),
strange (B0s) or charm antiquark (B−c) respectively.
== List of B mesons ==
== B–B oscillations ==
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.On
25 September 2006, Fermilab announced that
they had claimed discovery of previously-only-theorized
Bs meson oscillation.
According to Fermilab's press release:
This first major discovery of Run 2 continues
the tradition of particle physics discoveries
at Fermilab, where the bottom (1977) and top
(1995) quarks were discovered.
Surprisingly, the bizarre behavior of the
B_s (pronounced "B sub s") mesons is actually
predicted by the Standard Model of fundamental
particles and forces.
The discovery of this oscillatory behavior
is thus another reinforcement of the Standard
Model's durability...
CDF physicists have previously measured the
rate of the matter-antimatter transitions
for the B_s meson, which consists of the heavy
bottom quark bound by the strong nuclear interaction
to a strange antiquark.
Now they have achieved the standard for a
discovery in the field of particle physics,
where the probability for a false observation
must be proven to be less than about 5 in
10 million (5/10,000,000).
For CDF's result the probability is even smaller,
at 8 in 100 million (8/100,000,000).
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.
== Rare decays ==
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.
== See also ==
B–B oscillation
