Factorization and the parton model in QCD (original) (raw)
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Perturbation theory and the parton model in QCD
Nuclear Physics B, 1979
We prove that for any process which admits a parton-model interpretation, the naive parton model can be modified to include the effects of QCD interactions to all orders in perturbation theory. This requires that the mass singularities in quark and gluon inclusive cross sections factor into universal functions which renormalize the naive parton model distribution and decay functions. We prove that this factorization takes place for all leading and non-leading logs and thus check the consistency of the parton model to all orders in perturbation theory.
New look at the QCD factorization
We show that both the k_T- and collinear factorization for the DIS structure functions can be obtained by consecutive reductions of the Compton scattering amplitude. Each of these reductions is an approximation valid under certain assumptions. In particular, the transitions to the k_T- factorization is possible when the virtualities of the partons connecting the perturbative and non-perturbative blobs are space-like. Then, if the parton distribution has a sharp maximum in k_T, the k_T factorization can be reduced to the collinear factorization.
QCD factorization at twist-3: the two parton contributions
arXiv: High Energy Physics - Phenomenology, 2007
In this paper, the twist-3 two parton corrections in charmless BtoPPB\to PPBtoPP decays are shown to be factorizable under the QCD factorization approach. The factorizability of the twist-3 two parton corrections is constructed on the following findings. Under the energetic meson limit, the pseudoscalar distribution amplitude for a light pseudoscalar meson is allowed to be non-constant by the equations of motion for the quark. The non-constant pseudoscalar distribution amplitude is then used to regularize the end-point divergences in the hard spectator corrections at twist-3 order. By retaining the momentum fraction variable of the spectator quark of the BBB meson in the propagators, the end-point divergence in the weak annihilation corrections at twist-3 order is resolved. The factorization of the O(alphas)O(\alpha_s)O(alphas) corrections under the two parton approximation is shown valid up-to O(1/mb)O(1/m_b)O(1/mb) . The hard scattering kernels of order O(alphas)O(\alpha_s)O(alphas) and O(LambdaQCD/mb)O(\Lambda_{QCD}/m_b)O(LambdaQCD/mb) are explicitly given a...
Next-to-next-to-leading order QCD corrections to the photon's parton structure
Nuclear Physics B, 2002
The next-to-next-to-leading order (NNLO) corrections in massless perturbative QCD are derived for the parton distributions of the photon and the deep-inelastic structure functions F γ 1 and F γ 2. We present the full photonic coefficient functions at order αα s and calculate the first six even-integer moments of the corresponding O(αα 2 s) photon-quark and photon-gluon splitting functions together with the moments of the αα 2 s coefficient functions which enter only beyond NNLO. These results are employed to construct parametrizations of the splitting functions which prove to be sufficiently accurate at least for momentum fractions x > ∼ 0.05. We also present explicit expressions for the transformation from the MS to the DIS γ factorization scheme and write down the solution of the evolution equations. The numerical impact of the NNLO corrections is discussed in both schemes.
Nuclear Physics B, 1989
Several recent papers attempting to apply the optimised QCD perturbation theory to reactions involving real or virtual photons are discussed with particular attention paid to the ambiguity appearing in the definition of parton distribution and fragmentation functions at the next-to-leading order (NLO). The necessity to use NLO parametrisations of quark densities is stressed and the problem with optimisation with respect to the factorisation mass M for the "physical" definition of parton densities is pointed out.
The range of validity of the QCD-improved parton model
Physics Letters B, 2000
Based on the world DIS data we extract the experimental F p 2 − F n 2 as a function of Bjorken-x and photon virtuality Q 2 , using two different methods. Both methods lead to identical results. We find that the standard PDFs fail to describe the experimental data below Q 2 < 7 GeV 2 , which is much higher than for F p 2 and F d 2 separately. The difference between PDFs and the experimental data cannot be understood as due to nuclear effects in the deuteron, and evidently suggests substantial nonsinglet higher-twist effects. The trend of the experimental data is approximately explained by a recent two-component model of the nucleon structure functions and suggests strong Q 2-dependence of the Gottfried Sum, in disagreement with the parton model interpretation. The large negative higher-twist effects can explain the difference between the value of the Gottfied integral obtained recently by the E866 Drell-Yan experiment at Fermilab and an older NMC result.
One-loop singular behaviour of QCD and SUSY QCD amplitudes with massive partons
Physics Letters B, 2001
We discuss the structure of infrared and ultraviolet singularities in on-shell QCD and supersymmetric QCD amplitudes at one-loop order. Previous results, valid for massless partons, are extended to the case of massive partons. Using dimensional regularization, we present a general factorization formula that controls both the singular ǫ-poles and the logarithmic contributions that become singular for vanishing masses. We introduce generalized Altarelli-Parisi splitting functions and discuss their relations with the singular terms in the amplitudes. The dependence on the regularization scheme is also considered.
The high-energy limit of perturbative QCD: Theory and phenomenology
arXiv (Cornell University), 2022
After a brief introduction of formal and phenomenological progresses in the study of the high-energy limit of perturbative QCD, we present arguments supporting the statement that the inclusive emission of Higgs bosons or heavy-flavored hadrons acts as fair stabilizer of high-energy resummed differential distributions. We come out with the message that the hybrid high-energy and collinear factorization, built in term of the next-to-leading logarithmic resummation à la BFKL and supplemented by collinear parton distributions and fragmentation functions, is a valid and powerful tool to gauge the feasibility of precision analyses of QCD in its high-energy limit.