Form Factors and Structure Functions

[Pages:52]Form Factors and Structure Functions

Yury Kolomensky

Physics 226, Fall 2010

Running of Coupling Constants

Generic property of any field theory: higher order corrections (loops) induce momentum (distance) dependence of coupling constants.

This is known as an effect of "vacuum polarization"

The magnitude and the direction of the change depends on the type of the interaction

S(Q)

Phys226

Q (GeV) = /x

YGK, Hadronic Structure

Running of Coupling Constants

? QED (electromagnetic interactions): photons have no charge, so to first order include only fermion loops

? Coupling constant depends on momentum transfer Q2 ~ 2/x2, the number of active fermions nf (with

mass (2mf)2.?)I) ''(A(+#,(&' G.#H;)!"#$%&'(#

Two regimes: quarks are asymptotically free at short distances (high energies), but are confined to hadrons when pulled apart (low energies)

!"$

!"#%

( ')

!"#

!E0 ................
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