Physics:Charm quark

Short description: Type of quark

Charm quark

Composition	Elementary particle
Statistics	Fermionic
Generation	Second
Interactions	strong, weak, electromagnetic force, gravity
Symbol	c
antiparticle	Charm antiquark (c)
Theorized	Sheldon Glashow, John Iliopoulos, Luciano Maiani (1970)
Discovered	Burton Richter et al. (SLAC, 1974) Samuel Ting et al. (BNL, 1974)
Mass	1.275+0.025 −0.035 GeV/c2
Decays into	Strange quark (~95%), down quark (~5%)
electric charge	+2/3 e
|u}}r charge	Yes
Spin	1/2
Weak isospin	LH: +1/2, RH: 0
Weak hypercharge	LH: +1/3, RH: +4/3

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. 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), but its prediction is usually credited to Sheldon Glashow, John Iliopoulos and Luciano Maiani in 1970 (see GIM mechanism). Glashow is quoted as saying, "We called our construct the 'charmed quark', for we were fascinated and pleased by the symmetry it brought to the subnuclear world." The first charmed particle (a particle containing a charm quark) to be discovered was the J/ψ meson. It was discovered in 1974 by a team at the Stanford Linear Accelerator Center (SLAC), led by Burton Richter, and one at the Brookhaven National Laboratory (BNL), led by Samuel Ting.

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.

Hadrons containing charm quarks

For a more comprehensive list, see Physics:List of baryons and Physics:List of mesons.

Some of the hadrons containing charm quarks include:

• D mesons contain a charm quark (or its antiparticle) and an up or down quark.
• D_s mesons contain a charm quark and a strange quark.
• There are many charmonium states, for example the J/ψ particle. These consist of a charm quark and its antiparticle.
• Charmed baryons have been observed, and are named in analogy with strange baryons (e.g. Λ+c).

See also

• Quark model

Further reading

• R. Nave. "Quarks". HyperPhysics. Georgia State University, Department of Physics and Astronomy. http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html. 
• A. Pickering (1984). Constructing Quarks. University of Chicago Press. pp. 114–125. ISBN 978-0-226-66799-7.