- Bottom quark
name = Bottom quark
generation = Third
Leon M. Ledermanet al., 1977
mass = 4,200
MeV/c2 [ [http://pdg.lbl.gov/2007/reviews/quarks_q000.pdf PDG—Quark masses] ]
electric_charge = −frac|1|3 e
spin = frac|1|2
The bottom quark is a third-generation
quarkwith a charge of −frac|1|3"e". Although all quarks are described in a similar way by the quantum chromodynamics, the bottom quark's large mass (around 4,200 MeV(a bit more than four times the mass of a proton), combined with low values of the CKM matrixelements "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), mesonscontaining the bottom quark are the easiest particles to use to investigate the phenomenon; such experiments are being performed at BaBar and Belle. The bottom quark is also notable because it is a product in almost all top quarkdecays, and would be a frequent decay product for the hypothetical Higgs bosonif it is sufficiently light.
The bottom quark was discovered by the E288 experiment at
Fermilabin 1977 when collisions produced bottomonium[http://www.symmetrymagazine.org/cms/?pid=1000195 Discovery of the Bottom Quark] . On its discovery, there were efforts to name it "beauty", paired along with "truth", but they came to be called "bottom" and "top" instead.
The bottom quark can decay into either an up or charm quark via the
weak interaction. Both these decays are suppressed by CKM matrix, making lifetimes of most bottom particles (~10−12 s) somewhat higher than those of charmed particles (several times 10−13 s), but lower than those of strange particles (~10−10–10−8 s).
Hadrons containing bottom quarks
Some of the
hadronscontaining bottom quarks include:
B mesons contain a bottom quark (or its antiparticle) and an up or down quark.
*SubatomicParticle|Charmed B and SubatomicParticle|Strange B mesons contain a bottom quark along with a
charm quarkor strange quarkrespectively.
*There are many bottomonium states, for example the SubatomicParticle|Upsilon meson. These consist of a bottom quark and its antiparticle.
baryons have been observed, and are named in analogy with strange baryons (e.g. SubatomicParticle|Bottom Lambda0).
* [http://www.fnal.gov/pub/inquiring/physics/discoveries/bottom_quark.html Bottom quark information on Fermilab website]
* [http://pdg.lbl.gov/2007/listings/q005.pdf Technical data from Particle Data Group (pdf)]
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