Quantum Chromodynamics in Exclusive Processes

  • P. Kroll
Conference paper


According to Brodsky and Lepage[1] the helicity amplitude for an exclusive reaction ABCD at large momentum transfer is expressed by a convolution of universal process independent distribution amplitudes (DA) with an amplitude representing the scattering of constituents. The DA’s specify the distribution of the longitudinal momentum fractions the constituents carry inside their parent hadrons. They are the wave functions of constituent Fock states integrated over the intrinsic transverse (Fermi) momentum up to a soft scale. The convolution integral manifestly factorizes long (DA’s) and short (constituent scattering) distance physics. Explicitly, a helicity amplitude reads
$$ {{M}_{CDAB}}(s,t)=\int\limits_{i=A,B.C.D}{[d{{x}_{i}}]}\phi _{c}^{*}({{x}_{C}},{{Q}^{2}})\phi _{D}^{*}({{x}_{D}},{{Q}^{2}})\hat{T}({{x}_{i}},s,t){{\phi }_{A}}({{x}_{A}},{{Q}^{2}}){{\phi }_{B}}({{x}_{B}},{{Q}^{2}}) $$
where helicity labels are omitted for convenience. [dx i ] is a multi-index defined as
$$ [d{{x}_{i}}]=\prod\limits_{j=1}^{n}{d{{x}_{ij}}}\delta (1-\sum\limits_{j}{{{x}_{ij}}}) $$
x ij is the momentum fraction the constituent j of hadron i carries.


Form Factor Distribution Amplitude Compton Scattering Helicity Amplitude Electromagnetic Form Factor 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1991

Authors and Affiliations

  • P. Kroll
    • 1
  1. 1.Department of PhysicsUniversity of WuppertalWuppertalFed. Rep. of Germany

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