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  • 1
    ISSN: 1063-7788
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study medium modifications of the dilepton e + e − and μ+μ− mass spectra in coherent photo-and electroproduction of ρ0(1S)-and ρ′(2S)-meson resonances on nuclear targets. The analysis is performed within the coupled ρ0(1S), ρ′(2S), ... channel formalism, where nuclear modifications derive from off-diagonal rescatterings. We find that the effect of off-diagonal rescatterings on the shape of the dilepton-mass spectrum in the ρ0(1S)-meson mass region is only marginal, but it is very important in the ρ′(2S) mass region. The main off-diagonal contribution in the ρ′(2S) mass region comes from the sequential mechanism γ* → ρ0(1S) → ρ′(2S), which dominates ρ′(2S) production for heavy nuclei. Our results also show that, in the ρ′(2S) mass region, there is a considerable interference of the Breit-Wigner tail of the amplitude for the decay ρ0(1S) to e + e − and μ+μ− with the amplitude for the decay of ρ′(2S) to e + e − and μ+μ−.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 68 (1998), S. 634-640 
    ISSN: 1090-6487
    Keywords: 13.60.Hb
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We calculate the diffraction slope B D for diffractive deep inelastic scattering. We find a counterintuitive rise of B D in going from exclusive diffractive excitation of vector mesons to excitation of continuum states with M 2∼Q 2. For the small-mass continuum we predict a rapid variation of B D with M 2 on a scale of m V 2 and a sharp drop of B D for a small-mass continuum above the vector meson excitation.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 69 (1999), S. 103-109 
    ISSN: 1090-6487
    Keywords: 14.20.Dh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The HERA data on the proton structure function F 2(x,Q 2) at very small x and Q 2 show a dramatic departure of the logarithmic slope ∂F 2/∂log Q 2 from theoretical predictions based on the DGLAP evolution. We show that the running BFKL approach provides a quantitative explanation for the observed x and/or Q 2 dependence of ∂F 2/∂log Q 2.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 69 (1999), S. 294-299 
    ISSN: 1090-6487
    Keywords: 13.60.Le ; 13.88.+e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Helicity amplitudes for diffractive leptoproduction of the S and D wave states of vector mesons are derived. A dramatically different spin dependence for production of the S and D wave vector mesons is predicted. It is found that R=σL/σT is very small and that the higher twist effects in the production of longitudinally polarized D wave vector mesons are abnormally large.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1090-6487
    Keywords: 11.80.La ; 13.85.−t ; 13.87.−a ; 25.80.Hp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the salient features of the Pomeron splitting mechanism for coherent diffraction of pions into hard dijets on nuclei. Our findings include antishadowing multiple-Pomeron splitting expansion for diffractive amplitudes, exact cancellation of nuclear attenuation, and broadening/antishadowing effects to leading twist and parameter-free perturbative calculation of nuclear-rescattering-driven higher twist correction. We comment on the pQCD interpretation of the E791 results on diffractive dijets.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of experimental and theoretical physics 84 (1997), S. 421-431 
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nuclear transparency for incoherent real and virtual photoproduction of vector mesons off nuclei depends crucially on the interplay of the initial-state and final-state interactions. We develop a consistent description of initial-state and final-state interactions based on the coupled-channel multiple-scattering theory. We present detailed predictions for incoherent production of ss̄ and cc̄ mesons. The onset of initial-state interactions is controlled by the production length l P, and we find strong variations of nuclear transparency when l P rises with energy and becomes comparable to the radius of the target nucleus R A. For ss̄ mesons, the regime l P∼R A corresponds to precisely the kinematic range of the HERA-HERMES experiment, whereas for cc̄ mesons the same condition will be met at the ENC electron-nucleus collider at GSI. In spite of the subasymptotic values of Q 2 and v, we find a complex pattern of color transparency-induced effects whose experimental study may provide information on several issues relevant to the understanding of QCD, both in the perturbative and nonperturbative regimes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 69 (1999), S. 187-191 
    ISSN: 1090-6487
    Keywords: 12.38.Gc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The running BFKL equation gives rise to a series of moving poles in the complex j plane. The corresponding eigenfunctions (color dipole cross sections) are oscillatory functions of the color dipole size r. The first nodes for all subleading solutions (color dipole cross sections) are clustered at r 1∼0.1 fm. Therefore the processes dominated by dipole sizes r∼r 1 are free of subleading BFKL corrections. An example of practical importance is the leptoproduction of charm. Over a wide range of Q 2 the calculated F 2 cc (x,Q 2) is exhausted by the leading BFKL pole and gives a perfect description of the experimental data.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 66 (1997), S. 138-143 
    ISSN: 1090-6487
    Keywords: 11.55.Jy ; 12.40.Nn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We calculate the Regge trajectories of the subleading BFKL singularities and eigenfunctions for the running BFKL pomeron in the color dipole representation. We obtain a viable BFKL-Regge expansion of the proton structure function F 2p (x,Q 2) in terms of several rightmost BFKL singularities. We find large subleading contributions to F 2p (x,Q 2) in the HERA kinematical region which explain the lack of predictive power of GLDAP extrapolations of F 2p (x,Q 2) to the region of small x. We point out the relation of our early finding of precocious BFKL asymptotic behavior to the nodal structure of subleading BFKL eigenfunctions.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 68 (1998), S. 696-703 
    ISSN: 1090-6487
    Keywords: 13.60.Le ; 12.20.Ds ; 14.40.−n
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of light to heavy vector mesons in deep inelastic scattering. For large Q 2 all helicity amplitudes but the double-flip are calculable in perturbative QCD and are proportional to the gluon structure function of the proton at a similar hardness scale. We find a substantial breaking of the s-channel helicity conservation, which must persist in real photoproduction also.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of experimental and theoretical physics 86 (1998), S. 1054-1073 
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We develop the color dipole gBFKL phenomenology of a diffraction cone for photo-and electroproduction γ*N−VN of heavy vector mesons (charmonium & bottomonium) at HERA and in fixed target experiments. We predict a substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of c.m.s. energy W. The Q 2-controlled sensitivity to the color dipole size (scanning phenomenon) is shown to lead to a decrease of the diffraction slope with Q 2 (which is supported by the available experimental data). We predict an approximate flavor independence of the diffraction slope in the scaling variable Q 2+m V 2 . For diffractive production of the radially excited 2S states (Ψ′, γ′), a counterintuitive inequality of diffraction slopes B(2S)≲B(1S) is predicted, which defies the common wisdom that diffraction slopes are larger for reactions with larger size particles.
    Type of Medium: Electronic Resource
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