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Anatomy of the pQCD Approach to the Baryonic Decays
We calculate the CP-averaged branching ratios and CP-violating asymmetries
for the two-body charmless hadronic decays in the
perturbative QCD (pQCD) approach to lowest order in . The baryon
distribution amplitudes involved in the factorization formulae are considered
to the leading twist accuracy and the distribution amplitudes of the proton are
expanded to the next-to-leading conformal spin (i.e., "P" -waves), the moments
of which are determined from QCD sum rules. Our work shows that the
contributions from the factorizable diagrams in
decays are much smaller compared to the non-factorizable diagrams in the
conventional pQCD approach. We argue that this reflects the estimates of the
transition form factors in the factorization approach,
which are found typically an order of magnitude smaller than those estimated in
the light-cone sum rules and in the non-relativistic quark model. As an
alternative, we adopt a hybrid pQCD approach, in which we compute the
factorizable contributions with the form factors taken from
the light cone QCD sum rules. The non-factorizable diagrams are evaluated
utilizing the conventional pQCD formalism which is free from the endpoint
singularities. The predictions worked out here are confronted with the recently
available data from the CDF collaboration on the branching ratios and the
direct CP asymmetries for the decays , and . The asymmetry parameter relevant for the anisotropic angular
distribution of the emitted proton in the polarized baryon decays
is also calculated for the two decay modes.Comment: 47 pages, 9 figures, 8 tables; typos and references corrected;
version corresponds to the one accepted for publication in Phys. Rev.
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