Pion photoproduction on3He including final-state interaction

Coherent ⁰ and ⁺ photoproduction and elastic and charge-exchange pion scattering on³He has ben calculated in a consistent model. Realistic three-body Faddeev wave functions have been used and full nonlocal DWIA results for pion photoproduction are obtained. Furthermore, two-step processes such as³He(, ⁰)³He(⁰, ⁺)³H are included giving rise to unexpected large results. The comparison with experimental data is very good over a wide range of photon energies and nuclear momentum transfers. A long-time discrepancy between previous impulse-approximation calculations and experimental data has been removed.Supported by the Deutsche Forschungsgemeinschaft (SFB 201)     

Hyperon-nucleon final-state interaction in kaon photoproduction on a deuteron

Final state hyperon-nucleon (Y N) interaction in strangeness photoproduction on a deuteron is investigated by making use of the covariant reaction formalism and the P-matrix approach to the Y N system. A remarkably simple analytic expression for the amplitude is obtained. Pronounced effects due to final-state interaction are predicted, including a manifestation of the 2.13-GeV resonance.     

Ultrasoft contribution to heavy-quark pair production near threshold

We compute the third-order correction to the heavy-quark current correlation function due to the emission and absorption of an ultrasoft gluon. Our result supplies a missing contribution to top-quark pair production near threshold and the determination of the bottom quark mass from QCD sum rules.     

Investigation of heavy-quark production in proton-nucleus collisions with the HERA-B detector

Results obtained with the aid of the HERA-B detector, which operated at an internal target in a 920-GeV proton beam of the HERA storage ring at DESY (Hamburg, Germany), are discussed. About 164 million dilepton-triggered and 210 million minimum-bias events were collected over the data-taking time. These vast statistics made it possible to study in detail charmonium production in proton—nucleus collisions. Inclusive cross sections for open-charm, open-beauty, and ?-meson production weremeasured. The results are compared with the respective predictions of theoretical models.     

Study of the nd-breakup reaction in the kinematical region of the nn final-state interaction

The neutron neutron (nn) final-state interaction has been studied in the n + d → p + n + n reaction at 40 ± 5 MeV. Data on the dependence of reaction yield on the relative energy of two neutrons emitted in a narrow cone of angles are obtained. The value of the nn-scattering length deduced from a comparison of the shape of FSI peak with simulation data is a _nn = −17.9 ± 1.0 fm, where the error indicates the statistical uncertainty. Original Russian Text ? S.V. Zuyev, E.S. Konobeevski, M.V. Mordovskoy, S.I. Potashev, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 6, pp. 843–845.     

Deep-inelastic heavy-quark production at the HERA collider within the QCD semihard approach

Deep-inelastic heavy-quark production in electron-proton interactions at the HERA collider energies is considered within the QCD semihard (k _T-factorization) approach. The dependence of the total and differential cross sections for the production of b quarks (and for muons arising in the subsequent semileptonic decay of B mesons) on the choice of unintegrated distributions of gluons in the proton is investigated. In particular, the gluon distributions obtained by solving the Catani-Ciafaloni-Fiorani-Marchesini evolution equation and the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-Balitsky-Fadin-Kuraev-Lipatov combined equation are used in numerical calculations. The results of the theoretical calculations are compared with latest experimental data obtained by the H1 and ZEUS Collaborations at the HERA collider.     

On the next-to-next-to-leading order QCD corrections to heavy-quark production in deep-inelastic scattering

The contribution of quarks with masses m?_ΛQCD$m?{\Lambda }_{\mathrm{QCD}}$ is the only part of the structure functions in deep-inelastic scattering (DIS) which is not yet known at the next-to-next-to-leading order (NNLO) of perturbative QCD. We present improved partial NNLO results for the most important structure function _F2(x,Q²)$F_2(x,Q^2)$ near the partonic threshold, in the high-energy (small-x  ) limit and at high scales Q²?m²$Q^2?m^2$; and employ these results to construct approximations for the gluon and quark coefficient functions which cover the full kinematic plane. The approximation uncertainties are carefully investigated, and found to be large only at very small values, x?10⁻³$x?{10}^{-3}$, of the Bjorken variable.     

Equal-sign dileptons and heavy-quark detection

The production of the t-quark should be associated with a large rate of equal-sign lepton pairs. We estimate the (single and double) angular distributions of events weighted by powers of the leptonic energies, in e⁺e^? → ?⁺?⁺ (?^??^?) … . These quantities provide interesting information on heavy-quark decay and fragmentation in a transparent way.     

Light-quark and heavy-quark fragmentation functions

We discuss the shape of the leading-fragment momentum distribution function in light- and heavy-quark fragmentation. The features of the u-quark and s-quark leading fragmentation functions extrapolated to higher quark masses lead to the conclusion that as the quark mass increases the average momentum 〈z〉 carried by the heavy meson increases and the fragmentation function becomes narrower. This result fully supports Bjorken's proposal for heavy quark decay. Predictions are given for the shape of the c, b, … quark fragmentation functions.