The bottom quark, beauty quark, or b quark, is an

elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. The Standard Model presently recognizes seventeen distinct particles—twelve fermions and five bosons. As a c ...

of the third

generation A generation is all of the people born and living at about the same time, regarded collectively. It also is "the average period, generally considered to be about 20–⁠30 years, during which children are born and grow up, become adults, and b ...

. It is a heavy

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...

with a charge of − ''e''. All quarks are described in a similar way by

electroweak interaction In particle physics, the electroweak interaction or electroweak force is the unified description of two of the fundamental interactions of nature: electromagnetism (electromagnetic interaction) and the weak interaction. Although these two force ...

and

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the study of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of ...

, 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 The top quark, sometimes also referred to as the truth quark, (symbol: t) is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs field. This coupling is very close to unity; in the Standard ...

decays, and is a frequent decay product of the

Higgs boson The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the excited state, quantum excitation of the Higgs field, one of the field (physics), fields in particl ...

Name and history

The bottom quark was first described theoretically in 1973 by physicists

Makoto Kobayashi is a Japanese physicist known for his work on CP-violation who was awarded one-fourth of the 2008 Nobel Prize in Physics "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quar ...

and

Toshihide Maskawa was a Japanese theoretical physicist known for his work on CP-violation who was awarded one quarter of the 2008 Nobel Prize in Physics "for the discovery of the origin of the broken symmetry which predicts the existence of at least three fam ...

to explain

CP violation In particle physics, CP violation is a violation of CP-symmetry (or charge conjugation parity symmetry): the combination of C-symmetry (charge conjugation symmetry) and P-symmetry ( parity symmetry). CP-symmetry states that the laws of physics s ...

. The name "bottom" was introduced in 1975 by

Haim Harari use both this parameter and , birth_date to display the person's date of birth, date of death, and age at death) --> , death_place = , death_cause = , body_discovered = , resting_place = , resting_place_coordinates ...

. The evidence for the bottom quark was first obtained in 1977 by the

Fermilab Fermi National Accelerator Laboratory (Fermilab), located in Batavia, Illinois, near Chicago, is a United States Department of Energy United States Department of Energy National Labs, national laboratory specializing in high-energy particle phys ...

E288 experiment E, or e, is the fifth letter and the second vowel letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plu ...

team led by

Leon M. Lederman Leon Max Lederman (July 15, 1922 – October 3, 2018) was an American experimental physicist who received the Nobel Prize in Physics in 1988, along with Melvin Schwartz and Jack Steinberger, for research on neutrinos. He also received the Wolf Pr ...

, when proton-nucleon collisions produced

bottomonium In particle physics, quarkonium (from quark and -onium, pl. quarkonia) is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it both a neutral particle and its own antiparticle. The name "quarkonium" is analogo ...

decaying to pairs of

muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of ''ħ'', but with a much greater mass. It is classified as a ...

s. The discovery was confirmed about a year later by the PLUTO and DASP2 Collaborations at the electron-positron collider DORIS at

DESY DESY, short for Deutsches Elektronen-Synchrotron (English: ''German Electron Synchrotron''), is a national research centre for fundamental science located in Hamburg and Zeuthen near Berlin in Germany. It operates particle accelerators used to ...

. It was reported at the time that DESY scientists were in favor of the name "beauty", while the American scientists tended towards "bottom". Kobayashi and Maskawa won the 2008

Nobel Prize in Physics The Nobel Prize in Physics () is an annual award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions to mankind in the field of physics. It is one of the five Nobel Prizes established by the ...

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 A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

, and many orders of magnitude larger than common "light" quarks. Although it almost exclusively transitions from or to a

, the bottom quark can decay into either an

up quark The up quark or u quark (symbol: u) is the lightest of all quarks, a type of elementary particle, and a significant constituent of matter. It, along with the down quark, forms the neutrons (one up quark, two down quarks) and protons (two up quark ...

charm quark The charm quark, charmed quark, or c quark is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including th ...

via the

weak interaction In nuclear physics and particle physics, the weak interaction, weak force or the weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, and gravitation. It is th ...

. CKM matrix elements and 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). The combination of high mass and low transition rate gives experimental

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great for ...

byproducts containing a bottom quark a distinctive signature that makes them relatively easy to identify using a technique called "

B-tagging b-tagging is a method of particle jet, jet flavor tagging used in modern particle physics experiments. It is the identification (or "tagging") of jets originating from bottom quarks (or b quarks, hence the name). Importance b-tagging is important ...

". For that reason,

meson In particle physics, a meson () is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles, the ...

s containing the bottom quark are exceptionally long-lived for their mass, and are the easiest particles to use to investigate

. Such experiments are being performed at the

BaBar Babar (), also variously spelled as Baber, Babur, and Babor is a male given name of Persian language, Persian origin, and a popular male given name in Pakistan. It is generally taken in reference to the Persian language, Persian ''babr'' (Persian ...

, Belle and

LHCb The LHCb (Large Hadron Collider beauty) experiment is a particle physics detector collecting data at the Large Hadron Collider at CERN. LHCb specializes in the measurements of the parameters of CP violation in the interactions of b- and c-hadro ...

experiments.

Hadrons containing bottom quarks

Some of the

hadron In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...

s containing bottom quarks include: *

B meson In particle physics, B mesons are mesons composed of a bottom antiquark and either an up (), down (), strange () or charm quark (). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark' ...

s contain a bottom quark (or its

antiparticle In particle physics, every type of particle of "ordinary" matter (as opposed to antimatter) is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the ...

) and an up or

down quark The down quark (symbol: d) is a type of elementary particle, and a major constituent of matter. The down quark is the second-lightest of all quarks, and combines with other quarks to form composite particles called hadrons. Down quarks are most ...

. * and mesons contain a bottom quark along with a

strange quark The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons (), ...

respectively. * There are many

states, for example the meson and χ_b(3P), the first particle discovered in

LHC The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, and ...

. These consist of a bottom quark and its antiparticle. * Bottom

baryon In particle physics, a baryon is a type of composite particle, composite subatomic particle that contains an odd number of valence quarks, conventionally three. proton, Protons and neutron, neutrons are examples of baryons; because baryons are ...

s have been observed, and are named in analogy with strange baryons (e.g. ).

References

External links

History of the discovery of the bottom quark / Upsilon meson
{{DEFAULTSORT:Bottom Quark Elementary particles Quarks

Name and history

Distinct character

Hadrons containing bottom quarks

See also

References

Further reading

External links