# Charm quark

The charm quark, charmed quark or c quark (from its symbol, c) is the third most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks. Examples of hadrons containing charm quarks include the J/ψ meson (
J/ψ
), D mesons (
D
), charmed Sigma baryons (
Σ
c
), and other charmed particles.

It, along with the strange quark is part of the second generation of matter, and has an electric charge of +2/3 e and a bare mass of 1.275+0.025
−0.035
GeV/c2
.[1] Like all quarks, the charm quark is an elementary fermion with spin 1/2, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle of the charm quark is the charm antiquark (sometimes called anticharm quark or simply anticharm), which differs from it only in that some of its properties have equal magnitude but opposite sign.

The existence of a fourth quark had been speculated by a number of authors around 1964 (for instance by James Bjorken and Sheldon Glashow[4]), but its prediction is usually credited to Sheldon Glashow, John Iliopoulos and Luciano Maiani in 1970 (see GIM mechanism).[5] The first charmed particle (a particle containing a charm quark) to be discovered was the J/ψ meson. It was discovered by a team at the Stanford Linear Accelerator Center (SLAC), led by Burton Richter,[6] and one at the Brookhaven National Laboratory (BNL), led by Samuel Ting.[7]

The 1974 discovery of the
J/ψ
(and thus the charm quark) ushered in a series of breakthroughs which are collectively known as the November Revolution.

Charm quark
CompositionElementary particle
StatisticsFermionic
GenerationSecond
InteractionsStrong, weak, electromagnetic, gravity
Symbol
c
AntiparticleCharm antiquark (
c
)
TheorizedSheldon Glashow,
John Iliopoulos,
Luciano Maiani (1970)
Discovered
Mass1.275+0.025
−0.035
GeV/c2
[1]
Decays intoStrange quark (~95%), down quark (~5%)[2][3]
Electric charge+2/3 e
Color chargeYes
Spin1/2
Weak isospinLH: +1/2, RH: 0
Weak hyperchargeLH: +1/3, RH: +4/3

## Hadrons containing charm quarks

Some of the hadrons containing charm quarks include:

## Notes

1. ^ a b M. Tanabashi et al. (Particle Data Group) (2018). "Review of Particle Physics". Physical Review D. 98 (3): 030001. doi:10.1103/PhysRevD.98.030001.
2. ^ R. Nave. "Transformation of Quark Flavors by the Weak Interaction". Retrieved 2010-12-06. The c quark has about 5% probability of decaying into a d quark instead of an s quark.
3. ^ K. Nakamura et al. (Particle Data Group); et al. (2010). "Review of Particles Physics: The CKM Quark-Mixing Matrix" (PDF). Journal of Physics G. 37 (75021): 150. Bibcode:2010JPhG...37g5021N. doi:10.1088/0954-3899/37/7a/075021.
4. ^ B.J. Bjorken, S.L. Glashow; Glashow (1964). "Elementary particles and SU(4)". Physics Letters. 11 (3): 255–257. Bibcode:1964PhL....11..255B. doi:10.1016/0031-9163(64)90433-0.
5. ^ S.L. Glashow, J. Iliopoulos, L. Maiani; Iliopoulos; Maiani (1970). "Weak Interactions with Lepton–Hadron Symmetry". Physical Review D. 2 (7): 1285–1292. Bibcode:1970PhRvD...2.1285G. doi:10.1103/PhysRevD.2.1285.CS1 maint: Multiple names: authors list (link)
6. ^ J.-E. Augustin; et al. (1974). "Discovery of a Narrow Resonance in e+e Annihilation". Physical Review Letters. 33 (23): 1406. Bibcode:1974PhRvL..33.1406A. doi:10.1103/PhysRevLett.33.1406.
7. ^ J.J. Aubert; et al. (1974). "Experimental Observation of a Heavy Particle J". Physical Review Letters. 33 (23): 1404. Bibcode:1974PhRvL..33.1404A. doi:10.1103/PhysRevLett.33.1404.

## Further reading

BTeV experiment

The BTeV experiment — for B meson TeV (teraelectronvolt) — was an experiment in high-energy particle physics designed to challenge the Standard Model explanation of CP violation, mixing and rare decays of bottom and charm quark states. The Standard Model has been the baseline particle physics theory for several decades and BTeV aimed to find out what lies beyond the Standard Model. In doing so, the BTeV results could have contributed to shed light on phenomena associated with the early universe such as why the universe is made up of matter and not anti-matter.

The BTeV Collaboration was a group of about 170 physicists drawn from more than 30 universities and physics institutes from Belarus, Canada, China, Italy, Russia, and the United States of America. The BTeV experiment was designed to utilize the Tevatron proton-antiproton collider at the Fermi National Accelerator Laboratory, located in the far west suburbs of Chicago, Illinois in the USA. The experiment was scheduled to start in 2006, followed by commissioning in 2008, and data-taking in 2009.

The BTeV Project was terminated by the United States Department of Energy on 2005-02-07 after being removed from the President's Budget for the 2006 fiscal year.

B meson

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.

Benjamin W. Lee

Benjamin Whisoh Lee (Korean: 이휘소; January 1, 1935 – June 16, 1977) or Ben Lee, was a Korean-born American theoretical physicist. His work in theoretical particle physics exerted great influence on the development of the standard model in the late 20th century, especially on the renormalization of the electro-weak model and gauge theory.

He predicted the mass of the Charm quark and contributed to its search. Since his inception as a physicist, he has published 110 papers for about 20 years, of which 77 papers have been published in the journal. There are 69 papers cited more than 10 times and eight papers cited more than 500 times. As of October 2013, all of his papers are cited more than 13,400 times. As a major disciple, Kang Joo-sang, professor emeritus at the Department of Physics at Korea University, is also the motif of the fictional character Lee Yong-hu in Kim Jin-myung's novel, "The Rose of Sharon Blooms Again"

Bottom quark

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.

Charm (quantum number)

Charm (symbol C) is a flavour quantum number representing the difference between the number of charm quarks (
c
) and charm antiquarks (
c
) that are present in a particle:

${\displaystyle C=n_{\text{c}}-n_{\mathrm {\bar {c}} }\ }$

By convention, the sign of flavour quantum numbers agree with the sign of the electric charge carried by the quarks of corresponding flavour. The charm quark, which carries an electric charge (Q) of +​23, therefore carries a charm of +1. The charm antiquarks have the opposite charge (Q = −​23), and flavour quantum numbers (C = −1).

As with any flavour-related quantum numbers, charm is preserved under strong and electromagnetic interaction, but not under weak interaction (see CKM matrix). For first-order weak decays, that is processes involving only one quark decay, charm can only vary by 1 (ΔC= ±1,0). Since first-order processes are more common than second-order processes (involving two quark decays), this can be used as an approximate "selection rule" for weak decays.

Charmed baryons

Charmed baryons are a category of composite particles comprising all baryons made of at least one charm quark. Since their first observation in the 1970s, a large number of distinct charmed baryon states have been identified. Observed charmed baryons have masses ranging between 2300 and 2700 MeV/c2. In 2002, the SELEX collaboration, based at Fermilab published evidence of a doubly charmed baryon (Ξcc), containing two charm quarks) with a mass of ~3520 MeV/c2, but has yet to be confirmed by other experiments. One triply charmed baryon (Ωccc) has been predicted but not yet observed.

D meson

The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called the "F mesons" prior to 1986.

GIM mechanism

In quantum field theory, the GIM mechanism (or Glashow–Iliopoulos–Maiani mechanism) is the mechanism through which flavour-changing neutral currents (FCNCs) are suppressed in loop diagrams. It also explains why weak interactions that change strangeness by 2 (ΔS = 2 transitions) are suppressed, while those that change strangeness by 1 (ΔS = 1 transitions) are allowed, but only in charged current interactions.

The mechanism was put forth by Sheldon Lee Glashow, John Iliopoulos and Luciano Maiani in their famous paper "Weak Interactions with Lepton–Hadron Symmetry" published in Physical Review D in 1970.

At the time the GIM mechanism was proposed, only three quarks (up, down, and strange) were thought to exist. Glashow and James Bjorken predicted a fourth quark in 1964, but there was little evidence for its existence. The GIM mechanism however, required the existence of a fourth quark, and the prediction of the charm quark is usually credited to Glashow, Iliopoulos, and Maiani.

The mechanism relies on the unitarity of the charged weak current flavor mixing matrix, which enters in the two vertices of a one-loop box diagram involving W boson exchanges. Even though Z0 boson exchanges are flavor-neutral (i.e. prohibit FCNC), the box diagram induces FCNC, but at a very small level. The smallness is set by the mass-squared difference of the different virtual quarks exchanged in the box diagram, originally the u-c quarks, on the scale of the W mass. The smallness of this quantity accounts for the suppressed induced FCNC, dictating a rare decay, ${\displaystyle K_{L}\to \mu ^{+}\mu ^{-}}$, illustrated. If that mass difference were ignorable, the minus sign between the two interfering box diagrams (itself a consequence of unitarity of the Cabibbo matrix) would lead to a complete cancellation, and thus a null effect.

Gerson Goldhaber

Gerson Goldhaber (February 20, 1924 – July 19, 2010) was a German-born American particle physicist and astrophysicist. He was one of the discoverers of the J/ψ meson which confirmed the existence of the charm quark. He worked at Lawrence Berkeley National Laboratory with the Supernova Cosmology Project, and was a professor of physics emeritus at the University of California, Berkeley as well as a professor at Berkeley's graduate school in astrophysics.

J/psi meson

The J/ψ (J/psi) meson or psion is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium". The J/ψ is the most common form of charmonium, due to its spin of 1 and its low rest mass. The J/ψ has a rest mass of 3.0969 GeV/c2, just above that of the ηc (2.9836 GeV/c2), and a mean lifetime of 7.2×10−21 s. This lifetime was about a thousand times longer than expected.Its discovery was made independently by two research groups, one at the Stanford Linear Accelerator Center, headed by Burton Richter, and one at the Brookhaven National Laboratory, headed by Samuel Ting of MIT. They discovered they had actually found the same particle, and both announced their discoveries on 11 November 1974. The importance of this discovery is highlighted by the fact that the subsequent, rapid changes in high-energy physics at the time have become collectively known as the "November Revolution". Richter and Ting were rewarded for their shared discovery with the 1976 Nobel Prize in Physics.

John Iliopoulos

John Iliopoulos (Greek: Ιωάννης Ηλιόπουλος; 1940, Kalamata, Greece) is a Greek physicist and the first person to present the Standard Model of particle physics in a single report. He is best known for his prediction of the charm quark with Sheldon Lee Glashow and Luciano Maiani (the "GIM mechanism"). Iliopoulos is also known for demonstrating the cancellation of anomalies in the Standard model. He is further known for the Fayet-Iliopoulos D-term formula, which was introduced in 1974. He is currently an honorary member of Laboratory of theoretical physics of École Normale Supérieure, Paris.

Lambda baryon

The Lambda baryons are a family of subatomic hadron particles containing one up quark, one down quark, and a third quark from a higher flavour generation, in a combination where the quantum wave function changes sign upon the flavour of any two quarks being swapped (thus differing from a Sigma baryon). They are thus baryons, with total isospin of 0, and have either neutral electric charge or the elementary charge +1.

Lambda baryons are usually represented by the symbols Λ0, Λ+c, Λ0b, and Λ+t. In this notation, the superscript character indicates whether the particle is electrically neutral (0) or carries a positive charge (+). The subscript character, or its absence, indicates whether the third quark is a strange quark (Λ0) (no subscript), a charm quark (Λ+c), a bottom quark (Λ0b), or a top quark (Λ+t). Physicists do not expect to observe a Lambda baryon with a top quark because the Standard Model of particle physics predicts that the mean lifetime of top quarks is roughly 5×10−25 seconds; that is about 1/20 of the mean timescale for strong interactions, which indicates that the top quark would decay before a Lambda baryon could form a hadron.

List of mesons

This list is of all known and predicted scalar, pseudoscalar and vector mesons. See list of particles for a more detailed list of particles found in particle physics.This article contains a list of mesons, unstable subatomic particles composed of one quark and one antiquark. They are part of the hadron particle family – particles made of quarks. The other members of the hadron family are the baryons – subatomic particles composed of three quarks. The main difference between mesons and baryons is that mesons have integer spin (thus are bosons) while baryons are fermions (half-integer spin). Because mesons are bosons, the Pauli exclusion principle does not apply to them. Because of this, they can act as force mediating particles on short distances, and thus play a part in processes such as the nuclear interaction.

Since mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. They are classified according to their quark content, total angular momentum, parity, and various other properties such as C-parity and G-parity. While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and will exhibit higher-energy phenomena sooner than baryons would. For example, the charm quark was first seen in the J/Psi meson (J/ψ) in 1974, and the bottom quark in the upsilon meson (ϒ) in 1977.Each meson has a corresponding antiparticle (antimeson) where quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion (π+) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π−), is made of one up antiquark and one down quark. Some experiments show the evidence of tetraquarks – "exotic" mesons made of two quarks and two antiquarks, but the particle physics community as a whole does not view their existence as likely, although still possible.The symbols encountered in these lists are: I (isospin), J (total angular momentum), P (parity), C (C-parity), G (G-parity), u (up quark), d (down quark), s (strange quark), c (charm quark), b (bottom quark), Q (charge), B (baryon number), S (strangeness), C (charm), and B′ (bottomness), as well as a wide array of subatomic particles (hover for name).

Luciano Maiani

Luciano Maiani (born 16 July 1941, in Rome) is a Sammarinese physicist best known for his prediction of the charm quark with Sheldon Lee Glashow and John Iliopoulos (the "GIM mechanism").

Omega baryon

The omega baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol Ω and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks. Omega baryons containing top quarks are not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale for strong interactions, and therefore that they do not form hadrons.

The first omega baryon discovered was the Ω−, made of three strange quarks, in 1964. The discovery was a great triumph in the study of quark processes, since it was found only after its existence, mass, and decay products had been predicted in 1961 by the American physicist Murray Gell-Mann and, independently, by the Israeli physicist Yuval Ne'eman. Besides the Ω−, a charmed omega particle (Ω0c) was discovered, in which a strange quark is replaced by a charm quark. The Ω− decays only via the weak interaction and has therefore a relatively long lifetime. Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.Since omega baryons do not have any up or down quarks, they all have isospin 0.

R (cross section ratio)

R is the ratio of the hadronic cross section to the muon cross section in electron–positron collisions:

${\displaystyle R={\frac {\sigma ^{(0)}(e^{+}e^{-}\rightarrow \mathrm {hadrons} )}{\sigma ^{(0)}(e^{+}e^{-}\rightarrow \mu ^{+}\mu ^{-})}},}$

where the superscript (0) indicates that the cross section has been corrected for initial state radiation. R is an important input in the calculation of the anomalous magnetic dipole moment. Experimental values have been measured for center-of-mass energies from 400 MeV to 150 GeV.

R also provides experimental confirmation of the electric charge of quarks, in particular the charm quark and bottom quark, and the existence of three quark colors. A simplified calculation of R yields

${\displaystyle R=3\sum _{q}e_{q}^{2},}$

where the sum is over all quark flavors with mass less than the beam energy. eq is the electric charge of the quark, and the factor of 3 accounts for the three colors of the quarks. QCD corrections to this formula have been calculated.

Sau Lan Wu

Sau Lan Wu (Chinese: 吳秀蘭) is a Chinese American particle physicist and the Enrico Fermi Distinguished Professor of Physics at the University of Wisconsin-Madison. She made important contributions towards the discovery of the J/psi particle, which provided experimental evidence for the existence of the charm quark, and the gluon, the vector boson of the strong force in the Standard Model of physics. Recently, her team located at the European Organization for Nuclear Research (CERN), using data collected at the Large Hadron Collider (LHC), was part of the international effort in the discovery of a boson consistent with the Higgs boson.

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. Example of hadrons containing strange quarks include kaons (K), strange D mesons (Ds), Sigma baryons (Σ), and other strange particles.

According to the IUPAP the symbol s is the official name, while strange is to be considered only as a mnemonic. The name sideways has also been used because the s quark has a I3 value of 0 while the u (“up”) and d (“down”) quarks have values of +1/2 and −1/2 respectively.Along with the charm quark, it is part of the second generation of matter, and has an electric charge of −1/3 e and a bare mass of 95+9−3 MeV/c2. Like all quarks, the strange quark is an elementary fermion with spin 1/2, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle of the strange quark is the strange antiquark (sometimes called antistrange quark or simply antistrange), which differs from it only in that some of its properties have equal magnitude but opposite sign.

The first strange particle (a particle containing a strange quark) was discovered in 1947 (kaons), but the existence of the strange quark itself (and that of the up and down quarks) was only postulated in 1964 by Murray Gell-Mann and George Zweig to explain the Eightfold Way classification scheme of hadrons. The first evidence for the existence of quarks came in 1968, in deep inelastic scattering experiments at the Stanford Linear Accelerator Center. These experiments confirmed the existence of up and down quarks, and by extension, strange quarks, as they were required to explain the Eightfold Way.

T meson

T mesons are hypothetical mesons composed of a top quark and either an up (T0), down (T+), strange (T+s) or charm antiquark (T0c). Because of the top quark's short lifetime, T mesons are not expected to be found in nature. The combination of a top quark and top antiquark is not a T meson, but rather toponium. Each T meson has an antiparticle that is composed of a top antiquark and an up (T0), down (T−), strange (T−s) or charm quark (T0c) respectively.

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