Parton shower

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In particle physics, parton showers refer to cascades of radiation produced from QCD processes and interactions. These are simulated extensively in Monte Carlo event generators, in order to calibrate and interpret (and thus understand) processes in collider experiments.[1] As such, the name is also used to refer to algorithms that approximate or simulate the process.


The scattering particle only sees the valence partons. At higher energies, the scattering particles also detects the sea partons.


The parton model was proposed at Cambridge University by Richard Feynman in 1969 as a way to analyze high-energy hadron collisions.[2] Any hadron (for example, a proton) can be considered a composition of a number of point-like constituents, termed "partons". The parton model was immediately applied to electron-proton deep inelastic scattering by Bjorken and Paschos.[3] Later, with the experimental observation of Bjorken scaling, the validation of the quark model, and the confirmation of asymptotic freedom in quantum chromodynamics, partons were matched to quarks and gluons. The parton model remains a justifiable approximation at high energies, and others have extended the theory over the years.


Just as accelerated electric charges emit QED radiation (photons), the accelerated coloured partons will emit QCD radiation in the form of gluons. Unlike the uncharged photons, the gluons themselves carry colour charges and can therefore emit further radiation, leading to parton showers.[4][5][6]


Parton showers simulations are of use in computational particle physics either in automatic calculation of particle interaction or decay or event generators, and are particularly important in LHC phenomenology, where they are usually explored using Monte Carlo simulation. The scale at which partons are given to hadronization is fixed by the Shower Monte Carlo program. Common choices of Shower Monte Carlo are PYTHIA and HERWIG.[7][8]

See also: particle shower, jet (particle physics), hadronization



  1. ^ Davison E. Soper, The physics of parton showers. Accessed 17 Nov 2013.
  2. ^ Feynman, R. P. (1969). "The Behavior of Hadron Collisions at Extreme Energies". High Energy Collisions: Third International Conference at Stony Brook, N.Y. Gordon & Breach. pp. 237–249. ISBN 978-0-677-13950-0. 
  3. ^ Bjorken, J.; Paschos, E. (1969). "Inelastic Electron-Proton and γ-Proton Scattering and the Structure of the Nucleon". Physical Review. 185 (5): 1975–1982. Bibcode:1969PhRv..185.1975B. doi:10.1103/PhysRev.185.1975. 
  4. ^ Bryan Webber (2011). Parton shower Monte Carlo event generators. Scholarpedia, 6(12):10662., revision #128236.
  5. ^ *Parton Shower Monte Carlo Event Generators. Mike Seymour, MC4LHC EU Networks’ Training Event May 4th – 8th 2009.
  6. ^ *Phenomenology at collider experiments. Part 5: MC generators, Frank Krauss. HEP Summer School 31.8.-12.9.2008, RAL.
  7. ^ Johan Alwall, Complete simulation of collider events, pg 33. NTU MadGraph school, May 25–27, 2012.
  8. ^ M Moretti.Understunding events at the LHC: Parton Showers and Matrix Element tools for physics simulation at the hadronic colliders, pg 19. 28/11/2006.

This article contains material from Scholarpedia.