Coulomb dissociation of a fast pion into two jets

We calculate the electromagnetic contribution to the scattering amplitude of pion diffractive dissociation into di-jets which is described by one photon exchange. The result shows that the factorization procedure known for the description of exclusive reactions holds also for this quasi-exclusive process. We find that the longitudinal momentum distribution of di-jets does not depend on the form of the pion distribution amplitude. We discuss the magnitude of the cross section.Comment: 7 pages, 3 .eps figures, Late

QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron

Photon absorption by a quark in one nucleon followed by its high momentum transfer interaction with a quark in the other may produce two final-state nucleons with high relative momentum. We sum the relevant quark rescattering diagrams, to show that the scattering amplitude depends on a convolution between the large angle $pn$ scattering amplitude, the hard photon-quark interaction vertex and the low-momentum deuteron wave function. The computed absolute values of the cross section are in reasonable agreement with the data.Comment: 4 pages, revised version to be published in Phys. Rev. Let

Broad-band polarization-independent total absorption of electromagnetic waves by an overdense plasma

We have shown both experimentally and theoretically that polarization-independent broad-band absorption of electromagnetic waves by an overdense plasma, caused by surface plasmon-polaritons (SPP) excitation, can be achieved due to combination of two factors: a non-zero angle of incidence and a two-dimensional circular diffraction grating placed at a properly chosen distance in front of the plasma boundary. Direct detection of SPP has been achieved for the first time using a miniature antenna imbedded in the plasma.Comment: considerably broadened versio

Hard diffraction from parton rescattering in QCD

We analyze the QCD dynamics of diffractive deep inelastic scattering. The presence of a rapidity gap between the target and diffractive system requires that the target remnant emerges in a color singlet state, which we show is made possible by the soft rescattering of the struck quark. This rescattering is described by the path-ordered exponential (Wilson line) in the expression for the parton distribution function of the target. The multiple scattering of the struck parton via instantaneous interactions in the target generates dominantly imaginary diffractive amplitudes, giving rise to an "effective pomeron" exchange. The pomeron is not an intrinsic part of the proton but a dynamical effect of the interaction. This picture also applies to diffraction in hadron-initiated processes. Due to the different color environment the rescattering is different in virtual photon- and hadron-induced processes, explaining the observed non-universality of diffractive parton distributions. This framework provides a theoretical basis for the phenomenologically successful Soft Color Interaction model which includes rescattering effects and thus generates a variety of final states with rapidity gaps. We discuss developments of the SCI model to account for the color coherence features of the underlying subprocesses.Comment: 12 pages, 9 figures, REVTeX4. Somewhat expanded and modified version, two new subsections added. To appear in PR

Indication of asymptotic scaling in the reactions dd→p3dd\to p^3H, dd→n3dd\to n^3He and dp→dpdp\to dp

It is shown that the differential cross sections of the reactions $dd\to ^3He n$ and $dd\to ^3H p$ measured at c.m.s.scattering angle$\theta_{cm}=60^\circ$ in the interval of the deuteron beam energy 0.5 - 1.2 GeV demonstrate the scaling behaviour,$d\sigma/d t\sim s^{-22}$, which follows from constituent quark counting rules. It is found also that the differential cross section of the elastic $dp\to dp$ scattering at $\theta_{cm}=125^\circ-135^\circ$ follows the scaling regime $\sim s^{-16}$ at beam energies 0.5 - 5 GeV. These data are parameterized here using the Reggeon exchange.Comment: 6 pages, Latex, 2 eps figures; final version accepted by Pis'ma v ZHETF, corrected and completed reference

Quantum structure of the non-Abelian Weizsacker-Williams field for a very large nucleus

We consider the McLerran-Venugopalan model for calculation of the small-$x$ part of the gluon distribution function for a very large ultrarelativistic nucleus at weak coupling. We construct the Feynman diagrams which correspond to the classical Weizs\"{a}cker-Williams field found previously [Yu. V. Kovchegov, Phys. Rev. D 54, 5463 (1996)] as a solution of the classical equations of motion for the gluon field in the light-cone gauge. Analyzing these diagrams we obtain a limit for the McLerran-Venugopalan model. We show that as long as this limit is not violated a classical field can be used for calculation of scattering amplitudes.Comment: 13 pages, REVTeX, 9 figure

Bound states of three and four resonantly interacting particles

We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonant bound state of two fermions in a spin-singlet state, with corresponding scattering length $a_F$. Applying this approach to the calculation of the dimer-dimer scattering length $a_B$, we recover exactly the already known result $a_B=0.60 a_F$. We use the developed approach to obtain new results in 2D for fermions as well as for bosons. Namely, we calculate bound state energies for three $bbb$ and four $bbbb$ resonantly interacting bosons in 2D. For the case of resonant interaction between fermions and bosons we calculate exactly bound state energies of the following complexes: two bosons plus one fermion $bbf$, two bosons plus two fermions $bf_{\uparrow}bf_{\downarrow}$, and three bosons plus one fermion $bbbf$.Comment: 10 pages, 9 figure

Polarization observables in high-energy deuteron photodisintegration within the Quark-Gluon Strings Model

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. The model describes fairly well the recent experimental data from TJNAF in the few GeV region. Angular distributions at different $\gamma$-energies are presented and the effect of a forward-backward asymmetry is discussed. New results from the QGSM for polarization observables from 1.5 -- 6 GeV are presented and compared with the available data.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002, Juelich, June 10-14, 200

Electroproduction of Charmonia off Nuclei

In a recent publication we have calculated elastic charmonium production in ep collisions employing realistic charmonia wave functions and dipole cross sections and have found good agreement with the data in a wide range of s and Q^2. Using the ingredients from those calculations we calculate exclusive electroproduction of charmonia off nuclei. Here new effects become important, (i) color filtering of the c-cbar pair on its trajectory through nuclear matter, (ii) dependence on the finite lifetime of the c-cbar fluctuation (coherence length) and (iii) gluon shadowing in a nucleus compared to the one in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as functions of s and Q^2 are presented together with some differential cross sections. The results can be tested with future electron-nucleus colliders or in peripheral collisions of ultrarelativistic heavy ions.Comment: 21 pages of Latex including 14 figures; few misprints are fixe