Partonic Pole Matrix Elements for Fragmentation

A model-independent analysis of collinear three-parton correlation functions for fragmentation is performed. By investigating their support properties it is shown, in particular, that the so-called partonic pole matrix elements vanish. This sheds new light on the understanding of transverse single spin asymmetries in various hard semi-inclusive reactions. Moreover, it gives additional strong evidence for the universality of transverse-momentum-dependent fragmentation functions.Comment: 4 pages, 2 figures; minor changes, matches journal versio

Production of K−K^--mesons in proton-proton and proton-nucleus interactions at various energies

The experimental data on the production of $K^-$-mesons in pp-collisions are analyzed and a method of the unified description of these data in a broad energy range for primary protons is proposed. The $K^-$-mesons production in pA-collisions is considered. The simple formulas for inclusive cross sections of the $K^-$ production in these collisions are given. The results of the calculations by these formulas are compared with the available experimental data.Comment: 14 pages, LaTeX, uses ws-art.sty. Figures can be requested from [email protected] or looked up in the article abov

Subthreshold K+ Meson Production in Proton-Nucleus Reactions

The inclusive K+ mesons production in proton-nucleus collisions in the near threshold and subthreshold energy regimes is analyzed with respect to the one-step (pN->K+YN, Y=Lambda,Sigma) and the two-step (pN->NNpi, NN2pi; piN->K+Y) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account the struck target nucleon removal energy and momentum distribution (nucleon spectral function), extracted from recent quasielastic electron scattering experiments and from many-body calculations with realistic models of the NN interaction. Comparison of the model calculations of the K+ double differential cross sections for the reaction p+C at 1.2, 1.5 and 2.5 GeV beam energies with the existing experimental data from the SATURNE experiment is given, illustrating both the relative role of the primary and secondary production channels at considered incident energies and those features of the cross sections which are sensitive to the high momentum and high removal energy part of the nucleon spectral function that is governed by nucleon-nucleon short-range and tensor correlations. In--medium modifications of the available for pion and hyperon production invariant energies squared due to the respective optical potentials are needed to account for the experimental data on K+ production in the energy region under consideration.Comment: 6 pages, LaTeX, uses revtex.st

Subthreshold K+K^+ Production on Nuclei by π+\pi^+ Mesons

The inclusive $K^+$ mesons production in $\pi^+$--nucleus reactions in the subthreshold energy regime is analyzed with respect to the one--step ($\pi^+n\to K^+\Lambda$) and the two--step ($\pi^+n\to \eta p_1,~ \eta p_2\to K^+\Lambda$) incoherent production processes on the basis of an appropriate folding model, which allows one to take into account the various forms of an internal nucleon momentum distribution as well as on-- and off--shell propagation of the struck target nucleon. Contrary to proton--nucleus reactions primary reaction channel is found to be significant practically at all considered energies. Detailed predictions for the $K^+$ total and invariant differential cross sections from \piC-- and \piPb--collisions at subthreshold energies are provided.Comment: 18 pages, LaTeX, uses ws-art.sty, gzip+uuencoded postscript. Figures are available by request from [email protected]

Higher twist distribution amplitudes of the pion and electromagnetic form factor Fπ(Q2)F_{\pi}(Q^2)

The pion electromagnetic form factor is calculated within the QCD light-cone sum rule method and using a renormalon model for the higher twist distribution amplitudes (DAs). The theoretical predictions are compared with the experimental data and constraints on the pion leading and twist-4 DAs are extracted. An upper bound on the twist-4 contribution to the form factor and estimates of effects due to higher conformal spins in the pion twist-4 DAs are obtained.Comment: 13 pages, 7 figures; the version to appear in Phys.Rev.

Single transverse-spin asymmetry in high transverse momentum pion production in pp collisions

We study the single-spin (left-right) asymmetry in single-inclusive pion production in hadronic scattering. This asymmetry is power-suppressed in the transverse momentum of the produced pion and can be analyzed in terms of twist-three parton correlation functions in the proton. We present new calculations of the corresponding partonic hard-scattering functions that include the so-called "non-derivative" contributions not previously considered in the literature. We find a remarkably simple structure of the results. We also present a brief phenomenological study of the spin asymmetry, taking into account data from fixed-target scattering and also the latest information available from RHIC. We make additional predictions that may be tested experimentally at RHIC.Comment: 32 pages, 14 figure

Azimuthal spin asymmetries in light-cone constituent quark models

We present results for all leading-twist azimuthal spin asymmetries in semi-inclusive lepton-nucleon deep-inelastic scattering due to T-even transverse-momentum dependent parton distribution functions on the basis of a light-cone constituent quark model. Attention is paid to discuss the range of applicability of the model, especially with regard to the scale dependence of the observables and the transverse-momentum dependence of the distributions. We find good agreement with available experimental data and present predictions to be further tested by future CLAS, COMPASS and HERMES data.Comment: 23 pages, 14 figures, 1 tabl

Sivers effect in Drell Yan at RHIC

On the basis of a fit to the Sivers effect in deep-inelastic scattering, we make predictions for single-spin asymmetries in the Drell-Yan process at RHIC.Comment: 10 pages, 7 figures, 1 table. v2: References and comments added, minor correction