Abstract
We evaluated recent CLAS Collaboration measurements for the $90^\circ$ meson photoproduction off the nucleon using a tagged photon beam spanning the energy interval $s = 3 - 11$ GeV$^2$. The results are compared with the "Quark Counting Rules" predictions.
Highlights
Binary reactions in QCD with large momentum transfer involve quark and gluon exchanges between colliding particles
We examined how the counting rules are applicable to the lightest meson photoproduction off the nucleon up to s = 11 GeV2, where modern data are available, mostly produced by the CLAS Collaboration at Jefferson Laboratory
We study the energy dependence of the 90◦ light-meson photoproduction off the nucleon
Summary
Binary reactions in QCD with large momentum transfer involve quark and gluon exchanges between colliding particles. Recall that in order to provide the exclusivity of hard scattering, we have to balance the large transferred momentum between all the quarks in the hadron. This means that, in order to get the maximum contribution, we have to consider the Fock components of the hadron wave function with the minimum number of quarks. That the quark counting rules account for the minimum numbers of elementary hard processes needed to provide a large momentum transfer to the hadron. In an exclusive hard-scattering amplitude the hadron participates as a small color-singlet configuration where its constituent quarks are at short distances This property of hadron physics suppresses gluon radiation and effects
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