The bottom quark or b quark, also known as
the beauty quark, is a third-generation quark
with a charge of −1/3 e.
All quarks are described in a similar way
by electroweak and quantum chromodynamics,
but the bottom quark has exceptionally low
rates of transition to lower-mass quarks.
The bottom quark is also notable because it
is a product in almost all top quark decays,
and is a frequent decay product of the Higgs
boson.
== Name and history ==
The bottom quark was first described theoretically
in 1973 by physicists Makoto Kobayashi and
Toshihide Maskawa to explain CP violation.
The name "bottom" was introduced in 1975 by
Haim Harari.The bottom quark was discovered
in 1977 by the Fermilab E288 experiment team
led by Leon M. Lederman, when collisions produced
bottomonium.
Kobayashi and Maskawa won the 2008 Nobel Prize
in Physics for their explanation of CP-violation.On
its discovery, there were efforts to name
the bottom quark "beauty", but "bottom" became
the predominant usage, by analogy of "top"
and "bottom" to "up" and "down".
== Distinct character ==
The bottom quark's "bare" mass is around 4.2
GeV/c2 – a bit more than four times the
mass of a proton, and many orders of magnitude
larger than common "light" quarks.
Although it almost-exclusively transitions
from or to a top quark, the bottom quark can
decay into either an up quark or charm quark
via the weak interaction.
CKM matrix elements Vub and Vcb specify the
rates, where both these decays are suppressed,
making lifetimes of most bottom particles
(~10−12 s) somewhat higher than those of
charmed particles (~10−13 s), but lower
than those of strange particles (from ~10−10
to ~10−8 s).The combination of high mass
and low transition-rate gives experimental
collision byproducts containing a bottom quark
a distinctive signature that makes them relatively
easy to identify using a technique called
"B-tagging".
For that reason, mesons containing the bottom
quark are exceptionally long-lived for their
mass, and are the easiest particles to use
to investigate CP violation.
Such experiments are being performed at the
BaBar, Belle and LHCb experiments.
== Hadrons containing bottom quarks ==
Some of the hadrons containing bottom quarks
include:
B mesons contain a bottom quark (or its antiparticle)
and an up or down quark.
Bc and Bs mesons contain a bottom quark along
with a charm quark or strange quark respectively.
There are many bottomonium states, for example
the ϒ meson and χb(3P), the first particle
discovered in LHC.
These consist of a bottom quark and its antiparticle.
Bottom baryons have been observed, and are
named in analogy with strange baryons (e.g.
Λ0b).
== See also ==
Quark model
B-factory
B meson
