Parton (particle physics)
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In particle physics, the parton was a hypothetical fundamental particle considered, in the "parton model" of strong interactions, to be a constituent of the hadron. In the 1970s, quantum chromodynamics showed that hadrons are composed of quarks and gluons, but the parton model is still used to explain some aspects of short-distance interactions.
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[edit] Parton distribution functions
The parton distribution functions are the probability density for finding a particle with a certain longitudinal momentum fraction x and momentum transfer Q2. Because of the inherent non-perturbative effect in a QCD binding state, parton distribution functions cannot be obtained by perturbative QCD. Due to the limitations in present lattice QCD calculations, the known parton distribution functions are obtained by using experimental data.
Experimentally determined parton distribution functions are available from various groups worldwide. The major unpolarized data sets are:
- CTEQ, from the CTEQ Collaboration
- GRV, from M. Glück, E. Reya, and A. Vogt
- MRST, from A. D. Martin, R. G. Roberts, W. J. Stirling, and R. S. Thorne
Generalized parton distributions are a more recent approach to better understand hadron structure by representing the parton distributions as functions of more variables, such as the transverse momentum and spin of the parton. The ordinary parton distribution functions are recovered when the generalized parton distributions are integrated over the extra variables. Generalized parton distributions hope to describe more accurately the low-momentum details of collider processes.
[edit] Reference
[edit] Parton distribution functions
- CTEQ Collaboration, S. Kretzer et al., "CTEQ6 Parton Distributions with Heavy Quark Mass Effects", Phys. Rev. D69, 114005 (2004).
- M. Glück, E. Reya, A. Vogt, "Dynamical Parton Distributions Revisited", Eur. Phys. J. C5, 461–470 (1998).
- A. D. Martin et al., "Parton distributions incorporating QED contributions", Eur. Phys. J. C39, 155 161 (2005).
[edit] External links
- Parton distribution functions – from HEPDATA: The Durham HEP Databases
- CTEQ6 parton distribution functions
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