arXiv subjects

I. V. Anikin

Publications and source records attributed to I. V. Anikin.

83 records · Page 5Linked to original sources

arXiv2004

Exotic hybrid mesons in hard electroproduction

We estimate the sizeable cross section for deep exclusive electroproduction of an exotic $J^{PC}=1^{-+}$ hybrid meson in the Bjorken regime. The production amplitude scales like the one for usual meson electroproduction, i.e. as $1/Q^2$. This is due to the non-vanishing leading twist distribution amplitude for the hybrid meson, which may be normalized thanks to its relation to the energy momentum tensor and to the QCD sum rules technique. The hard amplitude is considered up to next-to-leading order in $α_{S}$ and we explore the consequences of fixing the renormalization scale ambiguity through the BLM procedure. We study the particular case where the hybrid meson decays through a $πη$ meson pair. We discuss the $πη$ generalized distribution amplitude and then calculate the production amplitude for this process. We propose a forward-backward asymmetry in the production of $π$ and $η$ mesons as a signal for the hybrid meson production. We briefly comment on hybrid electroproduction at very high energy, in the diffractive limit where a QCD Odderon exchange mechanism should dominate. The conclusion of our study is that hard electroproduction is a promissing way to study exotic hybrid mesons, in particular at JLAB, HERA (HERMES) or CERN (Compass).

hep-ph↗

arXiv2004

Deep electroproduction of exotic hybrid mesons

We evaluate the leading order amplitude for the deep exclusive electroproduction of an exotic hybrid meson in the Bjorken regime. We show that, contrary to naive expectation, this amplitude factorizes at the twist 2 level and thus scales like usual meson electroproduction when the virtual photon and the hybrid meson are longitidinally polarized. Exotic hybrid mesons may thus be studied in electroproduction experiments at JLAB, HERA (HERMES) or CERN (COMPASS).

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arXiv2003

On $γγ^*$ production of two $ρ^0$ mesons

We present a theoretical estimation for the cross-section of exclusive two $ρ$-meson production in two photon collision when one of the initial photons is highly virtual. The compatibility of our analysis with recent experimental data obtained by the L3 Collaboration at LEP is discussed. We show that these data prove the scaling behavior of the exclusive production amplitude. They are thus consistent with a partonic description of the exclusive process $γγ^*\toρ^0ρ^0$ when $Q^2\sim 2 - 20 {\rm GeV^2}$.

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arXiv2003

Exclusive two $ρ^0$-mesons production in $γγ^*$ collision

We give a theoretical description of the L3 Collaboration data on the cross-section of the exclusive two $ρ$-mesons production in $γγ^*$ collision with large photon virtuality. These data prove the scaling behaviour of the leading twist generalized distribution amplitude of vector mesons. They thus prove the relevance of a partonic description of the exclusive process $γγ^*\toρ^0ρ^0$ at $Q^2\geq 1.2 {\rm GeV^2}$ and $W\leq 3.0 {\rm GeV}.$

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arXiv2002

Genuine twist 3 in exclusive electroproduction of transversely polarized vector mesons

We present the detailed analysis of genuine twist-3 contributions to the exclusive electroproduction amplitude of transversely polarized vector mesons. Using the formalism based on the QCD factorization in the momentum representation we calculated all the genuine twist-3 terms and found the total expression of this amplitude at 1/Q level. Generally speaking, these terms violate standard factorization owing to the existence of the infrared divergencies in the amplitude of hard sub-processes, although the strongest divergencies cancel due to the QCD equations of motion. We discuss the possible treatment of surviving divergencies.

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arXiv2002

Non-factorized genuine twist 3 in exclusive electro-production of vector mesons

We present an analysis of genuine twist-3 quark contributions to the amplitude of exclusive electro-production of transversely polarized vector mesons. Using the formalism based on the momentum representation we calculated all the genuine twist-3 terms of quark contributions to gamma_T^* --> rho_T amplitude. We found that these terms can not be factorized owing to the existence of the infrared divergencies in the amplitude of hard sub-processes.

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arXiv2001

Single Spin Asymmetry Parameter from Deeply Virtual Compton Scattering of Hadrons up to Twist-3 accuracy: I. Pion case

The study of deeply virtual Compton scattering has shown that electromagnetic gauge invariance requires, to leading order, not only twist two but additional twist three contributions. We apply this analysis and, using the Ellis-Furmanski-Petronzio factorization scheme, compute the single (electron) spin asymmetry arising in the collision of longitudinally polarized electrons with hadrons up to twist 3 accuracy. In order to simplify the kinematics we restrict the actual calculation to pions in the chiral limit. The process is described in terms of the generalized parton distribution functions which we obtain within a bag model framework.

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arXiv2001

Wandzura-Wilczek approximation from generalized rotational invariance

We present the alternative way of derivation of the Wandzura-Wilczek relations between the kinematical twist-3 and twist-2 functions, parameterizing hadronic matrix element in two-photon processes $γ^{\star}π\to γπ$ and $γ^{\star}γ\toππ$. The new equations, providing the independence of the physical cross-sections on the choice of the light-cone direction, are suggested and explored. The amplitude of $γ^{\star}γ\toππ$ up to genuine twist-3 accuracy is found.

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arXiv2000

Off-diagonal quark distribution functions of the pion within an effective single instanton approximation

We develop a relativistic quark model for pion structure, which incorporates the non-trivial structure of the vacuum of Quantum Chromodynamics as modelled by instantons. Pions are boundstates of quarks and the strong quark-pion vertex is determined from an instanton induced effective lagrangian. The interaction of the constituents of the pion with the external electromagnetic field is introduced in gauge invariant form. The parameters of the model, i.e., effective instanton radius and constituent quark masses, are obtained from the vacuum expectation values of the lowest dimensional quark and gluon operators and the low-energy observables of the pion. We apply the formalism to the calculation of the pion form factor by means of the isovector nonforward parton distributions and find agreement with the experimental data.

hep-ph↗

arXiv2000

On the gauge invariance of the DVCS amplitude

We analyze in detail the problem of gauge invariance of the deeply vitual Compton scattering (DVCS) amplitude. Using twist 3 one-gluon exchange diagram contributions and the QCD equations of motion, we derive the general gauge invariant expression of the DVCS amplitude on a (pseudo)scalar particle (pion, $He^4$). Similarly to the case of deep inelastic scattering, the amplitude does not depend on the twist-3 quark-gluon correlations at the Born level. The contribution of the derived amplitude to the single-spin asymmetry with longitudinally polarized lepton is calculated.

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arXiv1999

On high $Q^{2}$ behavior of the pion form factor for transitions $γ^{\ast} γ\to π^{0}$ and $γ^{\ast} γ^{\ast} \to π^{0}$ within the nonlocal quark-pion model

The behavior of the transition pion form factor for processes γ^*γ-> π^0 and γ^* γ^* -> π^0 at large values of space-like photon momenta is estimated within the nonlocal covariant quark-pion model. It is shown that, in general, the coefficient of the leading asymptotic term depends dynamically on the ratio of the constituent quark mass and the average virtuality of quarks in the vacuum and kinematically on the ratio of photon virtualities. The kinematic dependence of the transition form factor allows us to obtain the relation between the pion light-cone distribution amplitude and the quark-pion vertex function. The dynamic dependence indicates that the transition form factor γ^* γ-> π^0 at high momentum transfers is very sensitive to the nonlocality size of nonperturbative fluctuations in the QCD vacuum.

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