Difference hard / semi-hard scattering

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Discussion Overview

The discussion centers on the differences between hard and semi-hard scattering events in the context of particle physics, particularly regarding their energy scales and the nature of the interactions involved. Participants explore the definitions and implications of these terms, referencing hadronic collisions and the role of perturbative and non-perturbative effects.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asks about the distinction between hard and semi-hard scattering events, noting that both seem to apply when s >> t.
  • Another participant requests clarification on the term "semi-hard," suggesting it relates to hadronic collisions where the virtuality of partons is large compared to lambda_QCD but small compared to s.
  • A different participant provides a source indicating that hard scattering is characterized as truly perturbative, while semi-hard scattering includes both perturbative and non-perturbative effects.
  • Another participant challenges the interpretation of a plot from the provided link, asserting that hard scattering involves non-perturbative vertex functions and emphasizes the inevitability of confinement in QCD processes.
  • This participant also clarifies that hard processes are typically associated with momentum or mass scales around several tens of GeV, while semi-hard processes involve partons with transverse momenta of a few GeV.

Areas of Agreement / Disagreement

Participants express differing interpretations of the terms hard and semi-hard scattering, particularly regarding the role of perturbative and non-perturbative effects, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

Some assumptions about the definitions of hard and semi-hard scattering may be context-dependent, and the discussion reflects varying interpretations of the relevant energy scales and processes involved.

earth2
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Hey folks,

another question.
What is the difference between hard and semi-hard scattering events?
In terms of energy I found for both s >> t, so where does the difference lie?

Thanks,
Earth's
 
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Can you be more specific, where did read "semi-hard", what was the context ? To my knowledge, this is used in hadronic collisions when the virtuality of the involved partons is large compared to lambda_QCD but small compared to s.
 
Ok, i just found the answer here: http://www-subatech.in2p3.fr/~photons/subatech/physics/potpourri/node23.html

hard: truly perturbative
semi-hard: perturbative + non-perturbative effects

Thanks anyway!
earth2
 
Last edited by a moderator:
I think the plot in your link A+B->C+X is referred to as "hard scattering" and explicitly shows vertex (or structure) functions which are non-perturbative.

No matter what you do with QCD, you will always have confinement at least on one side (that is, you may not have it only in a plasma). Confinement is non-perturbative.

Your link says
By hard processes one usually means clearly perturbative processes with momentum or mass scales of the order of several tens of GeV.
[...]
Semi-hard processes refers to QCD-processes where partons with transverse momenta of a few GeV are produced.
 

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