Bottom quark

Name and history

The bottom quark was first described theoretically in 1973 by physicists Makoto Kobayashi and Toshihide Maskawa to explain CP violation.

The evidence for the bottom quark was first obtained in 1977 by the Fermilab E288 experiment team led by Leon M. Lederman, when proton-nucleon collisions produced bottomonium decaying to pairs of muons. |archive-url=https://web.archive.org/web/20061004101845/http://www.symmetrymagazine.org/cms/?pid=1000195 |archive-date=4 October 2006 |display-authors=etal |url-access=subscription

Kobayashi and Maskawa won the 2008 Nobel Prize in Physics for their explanation of CP-violation.

While the name "beauty" is sometimes used, "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 – 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 V and V specify the rates, where both these decays are suppressed, making lifetimes of most bottom particles (~10−12 s) somewhat longer than those of charmed particles (~10−13 s), but shorter than those of strange particles (from ~10−10 to ~10−8 s). | editor-last=Nave | editor-first=C.R.

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

Main article: list of baryons, list of mesons

Some of the hadrons containing bottom quarks include:

• B mesons contain a bottom quark (or its antiparticle) and an up or down quark.
• and mesons contain a bottom quark along with a charm quark or strange quark respectively.
• There are many bottomonium states, for example the 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. ).

References

References

1. G. Flügge. (1978). "Particle Spectroscopy". Proceedings of the 19th International Conference on High Energy Physics (Tokyo).
2. Arthur L. Robinson. (1978). "Particle Physics: New Evidence from Germany for Fifth Quark". Science.
3. [http://nobelprize.org/nobel_prizes/physics/laureates/2008/kobayashi-lecture.html 2008 Physics Nobel Prize lecture by Makoto Kobayashi]
4. [http://nobelprize.org/nobel_prizes/physics/laureates/2008/maskawa-lecture.html 2008 Physics Nobel Prize lecture by Toshihide Maskawa]