Down quark
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| Down Quark | |
| Composition: | Elementary particle |
|---|---|
| Family: | Fermion |
| Group: | Quark |
| Generation: | First |
| Mass: | 4 - 8 MeV/c2 |
| Electric charge: | -1/3 e |
| Spin: | ½ |
The down quark is a first-generation quark with a charge of -(1/3)e. It is the second-lightest of all quarks. Its bare mass is not well determined, but probably lies between 4 and 8 MeV. According to the Standard Model of particle physics, it and the up quark are the fundamental constituents of the nucleons; the proton contains one down quark and two up quarks, while the neutron contains two down quarks and one up quark. Note, however, that the majority of the mass in nucleons comes from the energy in the gluon field holding the quarks together, and not the quark masses themselves.
Down quarks were named when Gell-Mann and Zweig developed the quark model in 1964, and the first evidence for them was found in deep inelastic scattering experiments at SLAC in 1967.
Hadrons containing down quarks
Some of the hadrons containing down quarks include:
- Charged Pions (Template:SubatomicParticle) are mesons containing an up quark and an anti-down quark, or vice versa.
- The neutral pion (Template:SubatomicParticle) is a linear combination of up-antiup and down-antidown, as are the Template:SubatomicParticle and ω mesons.
- The Template:SubatomicParticle and Template:SubatomicParticle flavorless mesons are linear combinations of several quark-antiquark pairs, including down-antidown.
- A large number of detected baryons contain one or more down quarks. Like the nucleons, the Template:SubatomicParticle baryons are made of only up and down quarks: the Template:SubatomicParticle contains no down quark, but the Template:SubatomicParticle contains one, the Template:SubatomicParticle contains two, and the Template:SubatomicParticle contains three.
See also
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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
