1,992 research outputs found

    Mass dependence of nuclear shadowing at small Bjorken-x from diffractive scattering

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    We calculate the nuclear shadowing ratio for a wide range of nuclei at small Bjorken-x in the framework of Gribov theory. The coherent contribution to the (virtual) photon-nucleon cross section is obtained in terms of the diffractive dissociation cross section. Information on diffraction from FNAL and HERA is used. Our results are compared to available experimental data from the NMC and E665 experiments at x ~ 10^{-4}.Comment: To be published in Phys. Rev.

    Photon parton distributions in nuclei and the EMC effect

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    Photons as well as quarks and gluons are constituents of the infinite momentum frame (IMF) wave function of an energetic particle. They are mostly equivalent photons whose amplitude follows from the Lorentz transformation of the particle rest frame Coulomb field into the IMF and from the conservation of the electromagnetic current. We evaluate in a model independent way the dominant photon contribution \propto \alpha_{em}(Z^2/A^{4/3})\ln(1/R_{A}m_{N}x) to the nuclear structure functions as well as the term \propto \alpha_{em}Z/A. In addition we show that the definition of x consistent with the exact kinematics of eA scattering (with exact sum rules) works in the same direction as the nucleus field of equivalent photons. Combined, these effects account for the bulk of the EMC effect for x\le 0.5 where Fermi motion effects are small. In particular for these x the hadronic mechanism contribution to the EMC effect does not exceed \sim 3% for all nuclei. Also the A-dependence of the hadronic mechanism of the EMC effect for x > 0.5 is significantly modified.Comment: 14 pages, 3 figures, final version published in Phys.Rev.

    Nuclear shadowing in inclusive and tagged deuteron structure functions and extraction of F_2^p-F_2^n at small x from electron-deuteron collider data

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    We review predictions of the theory of leading twist nuclear shadowing for inclusive unpolarized and polarized deuteron structure functions F_2^D, g_1^D and b_1^D and for the tagged deuteron structure function F_2^D(x,Q^2,\vec{p}). We analyze the possibility to extract the neutron structure function F_2^n from electron-deuteron data and demonstrate that an account of leading twist nuclear shadowing leads to large corrections for the extraction of F_2^n from the future deuteron collider data both in the inclusive and in the tagged structure function modes. We suggest several strategies to address the extraction of F_2^n and to measure at the same time the effect of nuclear shadowing via the measurement of the distortion of the proton spectator spectrum in the semi-inclusive e D \to e^{\prime}NX process. We address the issue of the final state interactions in the e D \to e^{\prime}NX process and examine how they affect the extraction of F_2^n.Comment: 19 pages, 7 figures. Published in Mod. Phys. Lett.

    A unitarized model of inclusive and diffractive DIS with Q2-evolution

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    We discuss the interplay of low-x physics and QCD scaling violations by extending the unified approach describing inclusive structure functions and diffractive production in γp\gamma* p interactions proposed in previous papers, to large values of Q2. We describe the procedure of extracting, from the non-perturbative model, initial conditions for the QCD evolution that respect unitarity. Assuming Regge factorization of the diffractive structure function, a similar procedure is proposed for the calculation of hard diffraction. The results are in good agreement with experimental data on the proton structure function F2F_2 and the most recent data on the reduced diffractive cross section, x_P \sigma_r^{\D(3)}. Predictions for both F2F_2 and FLF_L are presented in a wide kinematical range and compared to calculations within high-energy QCD.Comment: 22 pages, 12 figure

    Transverse target spin asymmetry in inclusive DIS with two-photon exchange

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    We study the transverse target spin dependence of the cross section for inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a "parton-like" mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark helicity flip due to interactions with non-perturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, mu_chiral^2 >> Lambda_QCD^2. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10^{-4}, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.Comment: 22 pages, 14 figures; uses revtex

    Probing coherent charmonium photoproduction off light nuclei at medium energies

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    We demonstrate how the elementary amplitudes γNΨN\gamma N\to \Psi N, the amplitude of the nondiagonal J/ψNψNJ/\psi N\Leftrightarrow \psi' N transition, and the total J/ψNJ/\psi N and ψN\psi' N cross sections can be determined from measurements of the coherent J/ψJ/\psi and ψ\psi' photoproduction off light nuclei at moderate energies. For this purpose we provide a detailed numerical analysis of the coherent charmonium photoproduction off silicon within the generalized vector dominance model (GVDM) adjusted to account for the physics of charmonium models and color transparency phenomenon.Comment: 8 pages, 5 figures (color

    Active-to-absorbing state phase transition in the presence of fluctuating environments: Weak and strong dynamic scaling

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    We investigate the scaling properties of phase transitions between survival and extinction (active-to-absorbing state phase transition, AAPT) in a model, that by itself belongs to the directed percolation (DP) universality class, interacting with a spatio-temporally fluctuating environment having its own non-trivial dynamics. We model the environment by (i) a randomly stirred fluid, governed by the Navier-Stokes (NS) equation, and (ii) a fluctuating surface, described either by the Kardar-Parisi-Zhang (KPZ) or the Edward-Wilkinson (EW) equations. We show, by using a one-loop perturbative field theoretic set up, that depending upon the spatial scaling of the variance of the external forces that drive the environment (i.e., the NS, KPZ or EW equations), the system may show {\em weak} or {\em strong dynamic scaling} at the critical point of active to absorbing state phase transitions. In the former case AAPT displays scaling belonging to the DP universality class, whereas in the latter case the universal behavior is different.Comment: 17 pages, 2 figures, accepted in PR