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M. Strikman

Publications and source records attributed to M. Strikman.

At least 217 records · Page 12Linked to original sources
arXiv1998

Coherent Vector Meson Production from Deuterons

In this paper we discuss coherent photo- and leptoproduction of vector mesons from deuterons at intermediate (virtual) photon energies, 3 < nu < 30 GeV. We consider the scattering from unpolarized and polarized targets as well as processes where the polarization of the recoil deuteron is measured. Our main motivation results from the need for a quantitative analysis of the space-time structure of photon-induced processes. In this respect we suggest several possibilities to explore the characteristic longitudinal interaction length in coherent vector meson production. Furthermore, we outline methods for an investigation of color coherence effects. In addition to the presentation of benchmark values for the maximal possible color coherence effect in various kinematic regions, we illustrate the anticipated phenomena within the color diffusion model. Finally we recall that the determination of vector meson-nucleon cross sections is not a closed issue. Besides being not known to a satisfying accuracy, they can be used to determine the strength of the D-state in low mass vector mesons.

nucl-th↗
arXiv1997

Cross Section Fluctuations of Photon Projectile in Generalized Vector Meson Dominance Model

We explain that the generalized vector meson dominance (GVMD) model is successful in describing hard high energy processes because it contains expected in QCD Color Coherent Phenomena. Within the model, which reproduces Bjorken scaling and nuclear shadowing for deep inelastic processes, we calculate $P_γ(σ,Q^2)$, the probability for the photon to interact with a target with the cross section $σ$. We find that within the GVMD model the virtual photon has two main components: the ''hard'' one with the small cross section of the order of $1/Q^2$ and the high probability and the ''soft'' one with a typical hadronic cross section with the probability suppressed by the factor of $1/Q^2$. Thus the GVDM model produces $P_γ(σ,Q^2)$ similar to that within the parton model and suggests the conspiracy between hard and soft QCD at $Q^2 > 1$ GeV$^2$. We study the limit $σ\to 0$ and show, that $P_γ(σ,Q^2) \propto 1/ σ$ in both GVMD model and QCD. Thus similarly to the parton model the GVMD model predicts the Color Transparency phenomenon. This is an indirect indication that Bjorken scaling, Color Transparency and shadowing in nuclei in DIS are closely related.

hep-ph↗
arXiv1997

Diffractive Heavy Quarkonium Photo- and Electroproduction in QCD

Hard diffractive photo- and electroproduction of heavy vector mesons ($J/ψ$ and $Υ$) is evaluated within the leading $α_s\ln{Q^2 \overΛ_{QCD}^2}$ approximation of QCD. In difference from our earlier work on that subject, also the production of transversely polarized vector mesons is calculated. Special emphasis is placed on the role of the vector meson's $q\bar q$ light-cone wave function. In that context, conventional non-relativistic quarkonium models and a light-front QCD bound state calculation are critically examined and confronted with QCD expectations. Our numerical analysis finds a significant high momentum tail in the latter wave functions and a deviation from the expected asymptotic behavior of $ϕ_V(z,b=0)\propto z(1-z)$. We then design an interpolation to match the quarkonium models at large inter-quark separations with QCD expectations at small distances. We use these results to compare our predictions for the forward differential cross section of $J/ψ$ photo- and electroproduction with recent experimental results from HERA. In addition, our earlier discussion of $ρ^o$ electroproduction is updated in light of recent experimental and theoretical enhancements.

hep-ph↗
arXiv1997

Soft-hard interplay and factorization for baryon production in the target fragmentation region in ep collisions

We discuss baryon production in the nucleon fragmentation region in deep inelastic scattering. The dependence of the nucleon spectra on Bjorken-$x$ is evaluated within the parton model and in QCD, and ways to look for the break-down of the DGLAP approximation via baryon production are suggested. We argue also that the leading neutron production in these small $x$ processes is rather insensitive to the pion parton densities of the nucleon.

hep-ph↗
arXiv1997

The Limiting Curve of Leading Particles from Hadron-Nucleus Collisions at Infinite A

We argue that as the atomic number of the target nucleus $A \to \infty$, the multiplicity of leading particles in hadron-nucleus collisions tends to a finite limit. The limiting multiplicities for various particle production are computed for both proton and pion projectiles. Signatures at finite A are discussed. Data from 100 GeV/c central hadron-nucleus collisions are analyzed and found to be in qualitative agreement with this picture.

hep-ph↗
arXiv1997

Probing the Origin of the EMC Effect via Tagged Structure Functions of the Deuteron

We demonstrate that measurement of tagged structure functions of the deuteron in (e,e'N) semi-inclusive reactions can discriminate between different hypotheses on the origin of the nuclear EMC effect. By choosing extreme backward kinematics for the spectator nucleon to minimize effects from the deuteron wave function and final state interactions, one can isolate the modifications in the structure of the bound nucleon within the impulse approximation. The same reaction can be used to extract the large-x neutron to proton structure function ratio.

nucl-th↗
arXiv1997

Coherent Photo- and Leptoproduction of Vector Mesons from Deuterium

We discuss the coherent photo- and leptoproduction of vector mesons from deuterium at intermediate (virtual) photon energies, 3 GeV < nu < 30 GeV. These processes provide several options to explore the space-time evolution of small size quark-gluon configurations. Furthermore, we study the dependence of the production cross section on the energy and momentum transfer t due to variations of the finite longitudinal interaction length. Kinematic regions are determined where the production cross section is most sensitive to the final state interaction of the initially produced hadronic wave packet. For unpolarized deuteron targets this double scattering contribution can be investigated mainly at large values of the momentum transfer t. For polarized targets kinematic windows sensitive to double scattering are available also at moderate t. We suggest several methods for an investigation of color coherence effects at intermediate energies.

hep-ph↗
arXiv1996

Nuclear beams in HERA

A study has been made of the physics interest and feasibility of experiments with nuclear beams in HERA. It is shown that such experiments widen considerably the horizon for probing QCD compared to that from free nucleon targets. In addition there is some sensitivity to physics beyond the standard model. Hence the option to include circulating nuclear beams in HERA allows a wide range of physics processes to be studied and understood.

hep-ph↗
arXiv1996

Interaction of small size wave packet with hadron target

We calculate in QCD the cross section for the scattering of an energetic small-size wave packet off a hadron target. We use our results to study the small-$σ$ behaviour of $P_π(σ)$, the distribution over cross section for the pion, in the leading $α_{s}$-order.

hep-ph↗
arXiv1996

Coherent $ρ$ Production from Polarized Deuterium

We discuss the coherent leptoproduction of vector mesons from polarized deuterium as a tool to investigate the evolution of small size quark-gluon configurations. Kinematic regions are determined where the final state interaction of the initially produced quark-gluon wave packet contributes dominantly to the production cross section. Two methods for an investigation of color coherence effects, which are appropriate for future experiments at HERMES, are suggested.

hep-ph↗
arXiv1996

Nearthreshold Large $Q^2$ Electroproduction off Polarized Deuteron

The exclusive and inclusive electroproduction off the polarized deuteron is considered at large $Q^2$ and $x \ge 0.5$. It is shown that the use of a polarized target will allow to emphasize smaller than average internucleon distances in the deuteron. As a result, we expect amplification of all the effects (color transparency, relativistic dynamics, etc.) sensitive to small internucleon distances. Numerical estimates are given for the processes $e+ \vec d \rightarrow e +p+n$ and $e+ \vec d \rightarrow e +X$.

nucl-th↗
arXiv1996

Color Transparency and Color Opacity in Coherent Production of Vector Mesons off Light Nuclei at small x

Coherent electroproduction of vector mesons off $^2$H and $^4$He is considered in the kinematics of deep inelastic scattering. Special emphasis is given to the $-t\sim 0.8-1$ GeV$^2$ region where the cross section is dominated by the interaction of the $q\bar q$ configuration in the $γ^*$ with two nucleons. These kinematics provide the unique possibilities to study quantitatively in vector meson production the onset of Color Transparency with increasing $Q^2$ as well as its gradual disappearance at very small $x$, i.e., perturbative Color Opacity.

hep-ph↗
arXiv1996

Chiral Transparency

Color transparency is the vanishing of initial and final state interactions, predicted by QCD to occur in high momentum transfer quasielastic nuclear reactions. For specific reactions involving nucleons, the initial and final state interactions are expected to be dominated by exchanges of pions. We argue that these interactions are also suppressed in high momentum transfer nuclear quasielastic reactions; this is ``chiral transparency". We show that studies of the $e ^3He \to e'Δ^{++} nn$ reaction could reveal the influence of chiral transparency.

nucl-th↗
arXiv1996

Hard diffractive electroproduction of vector mesons in QCD

Hard diffractive electroproduction of longitudinally polarized vector mesons is calculated within the leading $α_s\ln{Q^2\overΛ_{QCD}^2}$ approximation of QCD using the leading order parton densities within the nucleon. Novel QCD features of the production of excited states and of the restoration of flavor symmetry are analyzed. At the onset of the asymptotic regime, our analysis finds an important role of quark Fermi motion within the diffractively produced vector mesons, and we suggest to use this effect to measure the high momentum tail of the wave function of the vector mesons. We deduce a kinematical boundary for the region of applicability of the decomposition of the hard amplitudes over powers of $Q^2$ and/or a limit on the increase of the cross sections of hard processes at small $x$, and briefly analyze its consequences. We also estimate the nuclear attenuation of the diffractive electroproduction of vector mesons and compare with estimates of the shadowing of the longitudinal structure function.

hep-ph↗
arXiv1996

The nuclear effects in $g_{1^3\rm{He}}$ and the Bjorken sum rule for A=3

The Bjorken sum rules for the $A=3$ and $A=1$ are used as a guide to estimate nuclear effects in extracting $g_{1n}(x,Q^{2})$ from the $\vec{e}\,\vec{^3\rm{He}}$ data. We estimate that the combination of the spin depolarization, the nonnucleonic degrees of freedom in the $A=3$ system and nuclear shadowing is likely to reduce $g_{1^3\rm{He}}(x\le 0.05)$ by $\sim 15 \%$ while a significant enhancement of the structure functions $g_{1^3\rm{He}}, g_{1^3\rm{H}}$ at $x \sim 0.1$ is predicted.

hep-ph↗
arXiv1995

The Nucleon's Antiquark Sea: A Virtual Meson Cloud or Gluons?

We study the possible contribution of the nucleon's virtual meson cloud to the sea quark distribution as observed in deep inelastic lepton scattering. We adjust the meson-nucleon cut-offs to the large-x tails of the antiquark distributions, find qualitatively different behavior in the flavor singlet and non-singlet channels and study the scale dependence of our results. We demonstrate that, within convolution models, to reproduce the sea quark distribution the relevant pion momenta should be around 0.8 GeV.

hep-ph↗