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Michail P. Rekalo

Publications and source records attributed to Michail P. Rekalo.

At least 19 recordsLinked to original sources
arXiv2008

New possibility for further measurements of nucleon form factors at large momentum transfer in time-like region: $\bar{p}+{p}\to \ell^+ +\ell^-$, $\ell=e$ or $μ$

We briefly summarize the status with electromagnetic nucleon form factors, and give in this framework, arguments to study the angular dependence of the differential cross section and single-spin polarization phenomena (polarized target or polarized beam) in $\bar{p}+{p}\to \ell^++\ell^-$, in view of the availability of future antiproton beams.

hep-ph↗
arXiv2008

Estimation of charm particles elementary cross sections relevant to GSI-CBM project

This note collects formulas relative to the energy dependence of the cross sections for open charm and $J/ψ$ production for $NN$-collisions at threshold. It is a basis for the best input to MonteCarlo calculations, for associative charm particle production in nucleon-nucleon, nucleon-nucleus, ion-ion and proton-antiproton collisions.

hep-ph↗
arXiv2004

$P$-parity of charm and strange particles in electroproduction processes, in collinear regime

We show that definite polarization observables for the simplest electroproduction processes, $\ell+N\to \ell+B(1/2^\pm)+M(0^\pm)$, $B=Y(Λ, Σ$ or $Y_c$-hyperon, $Θ^+$-pentaquark) and $M=K$, $\bar{K}$ or $D$, are sensitive to the relative P-parity $π(B)$ of the NBM-system. The interference of the longitudinal and transversal amplitudes for the collinear regime of the processes $γ^*+N\to B+M $($γ^*$ is the virtual photon) - at any value of momentum transfer squared and excitation energy of the $BM$-system - generates model independent relations between analyzing powers (in unpolarized lepton scattering by polarized target), from one side, and the components of the produced baryon $B$ polarization. It is important to stress that these relations depend on the above mentioned P-parity, and constitute a model independent method for the determination of unknown parities of strange and charm particles.

hep-ph↗
arXiv2004

Model-independent methods to measure the $P$-parity of the $Θ^+$-pentaquark in photoproduction experiments

We discuss model independent methods to measure the $P$-parity of the $Θ^+$-pentaquark, in the simplest processes of photoproduction, $γ+N\to \bar{K}+Θ^+$, using definite relations between T-even polarization observables, which depend on the $P$-parity of the $Θ^+$ baryon (with respect to the $NK$ system). One method, which holds for any photon energy and any $K$ meson production angle, is based on the relation between the $Σ_B$ asymmetry (induced by a linearly polarized photon beam, with unpolarized target) and the $D_{nn}$ component of the depolarization tensor (for unpolarized photon beam). Another method, which applies in collinear kinematics (or in threshold conditions), is related to the sign of the $D_{nn}$ component, with linearly polarized photon beam.

hep-ph↗
arXiv2004

Polarization observables in the processes $p+p\to Θ^+ +Σ^+$ and $n+p\to Θ^+ +Λ^0$, for any spin and parity of the $Θ^+$-hyperon in the threshold region

Using the symmetry properties of the strong interaction, such as the Pauli principle, the P-invariance, the conservation of the total angular momentum and isotopic invariance, we establish the spin structure of the threshold matrix elements for the processes $p+p\to Θ^+ +Σ^+$ and $n+p\to Θ^+ +Λ^0$, in a model independent way, which applies to any spin and parity of the $Θ^+$-hyperon in the near threshold region. We predict the double spin observables for these processes, such as the dependence of the differential cross section on the polarizations of the colliding nucleons, and the coefficients of polarization transfer from a nucleon beam or target to the produced $Σ^+$ or $Λ^0$ hyperon. We prove that these observables are sensitive to the P-parity of the $Θ^+$ baryon, for any value of its spin. As an example of dynamical considerations, we analyzed these reactions in the framework of K-meson exchange.

hep-ph↗
arXiv2004

Possible methods for the determination of the $P$-parity of the $Θ^+$-pentaquark in NN-collisions

We present two possibilities to determine the P-parity of the pentaquark $Θ^+$, in a model independent way, via the measurement of polarization observables in $p+p\to Θ^+ +Σ^+$, or $n+p\to Θ^+ +Λ^0$, in the near threshold region. Besides the measurement of the spin correlation coefficient, $A_{xx}=A_{yy}$, (in collisions of transversally polarized nucleons), the coefficient $D_{xx}$ of polarization transfer from the initial proton to the final $ Σ^+(Λ^0)$ hyperon is also unambiguously related to the $Θ^+$ parity.

hep-ph↗
arXiv2004

Exclusive photoproduction of charmed $D^*$ vector mesons, $γ+N\to Y_c+ \bar{D}^*$, $Y_c=Λ_c^+$ or $Σ_c$

The spin structure of the matrix element for the reactions $γ+ N\to Y_c +{D}^*$, where $Y_c=Λ_c^+(2285)$, $Σ_c(2455)$ are charmed baryons with spin 1/2, and $D^*(2010)$ is the vector charmed meson, can be parametrized, in collinear regime, in terms of three independent scalar amplitudes, which are functions of the photon energy $E_γ$, only. In framework of an effective Lagrangian approach generalized to charm photoproduction, we calculate the energy dependence of the differential cross section, the density matrix element of $\bar{D}^*$, $ρ_{11}$, the asymmetry $A_z$ in the collision of circularly polarized photons with polarized nucleons, and the polarization of the produced $Y_c$-hyperon, $P_z$, in the collision of circularly polarized photons with unpolarized target. All these polarization observables either vanish or are large, in absolute value, with a smooth $E_γ$-dependence, and differ for $Λ_c^+$ and $Σ_c$ --production.

hep-ph↗
arXiv2003

Polarization phenomena in open charm photoproduction processes

We analyze polarization effects in associative photoproduction of pseudoscalar ($\bar{D}$) charmed mesons in exclusive processes $γ+ N\to Y_c +\bar{D}$, $Y_c=Λ_c^+$, $Σ_c$. Circularly polarized photons induce nonzero polarization of the $Y_c$-hyperon with $x$- and $z$-components (in the reaction plane) and non vanishing asymmetries ${\cal A}_x$ and ${\cal A}_z$ for polarized nucleon target. These polarization observables can be predicted in model-independent way for exclusive $\bar{D}$-production processes in collinear kinematics. The T-even $Y_c$-polarization and asymmetries for non-collinear kinematics can be calculated in framework of an effective Lagrangian approach. The depolarization coefficients $D_{ab}$, characterizing the dependence of the $Y_c$-polarization on the nucleon polarization are also calculated.

hep-ph↗
arXiv2003

QCD-view on hadron form factors in space-like and time-like momentum transfer regions

QCD gives definite predictions for hadron electromagnetic form factors in space-like and time-like momentum transfer regions, such as the quark counting rules, the hypothesis of hadron helicity conservation, and the relations between nucleon and deuteron form factors in the formalism of reduced nuclear matrix elements. Recent precise data about these form factors, obtained in polarization experiments at the Jefferson Laboratory, have essentially changed our view on this subject. QCD-predictions do not apply to these data up to $Q^2$=5-6 GeV$^2$ for deuteron and for the electric form factor of proton. An analysis of these data suggests that the asymptotic region will more probably start at $Q^2$=20-25 GeV$^2$. We show that the separation of magnetic and electric proton form factors in the time-like region represents the most stringent test of the asymptotic regime and QCD-predictions.

nucl-th↗
arXiv2003

The $g_{Vσγ}$-coupling constants in hadron electrodynamic

Recent measurements of the branching ratios for the decays $ω\toπ^0π^0γ$ and $ρ^0\toπ^0π^0γ$ lead to coupling constants of the $Vσγ$-interaction ($V$ is a vector meson) one order of magnitude smaller than previously assumed to describe the threshold cross section of $γ+p\to p+ρ^0$ and the HERMES effect. The new $g^2_{Vσγ}$ couplings are in contradiction with the predictions of the QCD sum rules, but are in good agreement with VDM-estimation of the $σ\to γγ$-width.

nucl-th↗
arXiv2002

Sensitivity of pQCD deuteron structure to the nucleon form factors

We discuss the applicability of pQCD to the elastic scattering of electrons on protons and deuterons. We analyze the $Q^2$-dependence of the reduced deuteron form factor, taking into account the recent data on the electric proton form factor and we find that the value of the QCD-scale parameter $Λ$ differs essentially from the value $Λ=0.1$ GeV, previously found using the dipole parametrization of the electromagnetic nucleon form factors $G_E$ and $G_M$. Moreover the predicted scaling behavior of the reduced deuteron form factor can not be recovered in the Dirac and Pauli representations for the nucleon electromagnetic form factors.

hep-ph↗
arXiv2002

Scalar meson production in nucleon-nucleon collisions near threshold

We establish the model-independent spin structure of the matrix elements for the near-threshold scalar meson production in $pp-$ and $np$-collisions, when the final particles are emitted in S-state. Polarization phenomena are derived in a general form. The properties of the $t-$channel dynamics, which is based on different meson exchanges, are studied in terms of the $s-$channel parametrization of the matrix element. The prediction of a 'realistic' model, based on $π+σ$-exchanges are also presented.

nucl-th↗
arXiv2002

Polarization phenomena for heavy meson production in NN-collisions near threshold

Polarization phenomena are essential for the understanding of elementary processes, and are typically large in the threshold region. The selection rules with respect to P-parity, angular momentum, isotopic spin and the Pauli principle allow to parametrize in a model independent way, the spin structure of the matrix elements for the near-threshold heavy meson production in NN-collisions in terms of a small number of partial amplitudes. Such parametrization is very powerful for the analysis of polarization phenomena and possible $t-$exchange mechanisms.

nucl-th↗
arXiv2002

Determination of the $g_{ρσγ}$ coupling constant through the process $γ+N\to N+V$ with circularly polarized photons

We suggest a method to determine the product of the coupling constants $g_{ρσγ}g_ {σNN}$, in absolute value and relative sign, through the $t$-dependence of the two possible T-even asymmetries for the photoproduction of vector mesons, $γ+p\to p+V^0$, $V^0=ρ$ or $ω$, in the collision of circularly polarized photons with a polarized proton target. In the framework of a $π+σ$-model, these asymmetries are very sensitive to the relative role of $π$- and $σ$-exchanges, in the near threshold region.

hep-ph↗
arXiv2002

P-parity of charmed particles from associative photoproduction of D and D^*-mesons

We suggest to measure the triple polarization correlations in the exclusive associative charm particle photoproduction, vector gamma + vector p --> vector Lambda_c^{++} bar{D^0} with linearly polarized photons, as a method to determine the P-parity of the charmed D-meson. The dependence of these correlations on the parity P(N Lambda_c D) can be predicted in model independent way. The t-dependence of the differential cross section for vector meson photoproduction, gamma + p --> Lambda_c^{++} bar{D^{*0}}, in a model based on D-exchange, is also sensitive to P(N Lambda_c D).

hep-ph↗
arXiv2002

Associative charm photoproduction with circularly polarized photons

We calculate the asymmetries for the processes $\vecγ+\vec p\to Λ_c^+ (Σ_c^+)+\bar{D^0}$ and $\vecγ+\vec p\to Λ_c^+ (Σ_c^+)+\bar{D^*}$, induced by circularly polarized photons on a polarized proton target in the framework of an effective Lagrangian model. We found large and positive values for the asymmetry induced by the $z-$component of the proton polarization, in a wide energy region, from threshold up to $E_γ=70$ GeV. In the case of pseudoscalar meson photoproduction, the predictions are qualitatively model-independent. For $D^*$-photoproduction, there is a strong dependence of the asymmetries on $NΛ_c D(D^*)$-coupling constants.

hep-ph↗
arXiv2002

Considerations on rescattering effects for threshold photo- and electro-production of $π^0$ on deuteron

We show that for the S-state $π^0$-production in processes $γ+d\to d+π^0$ and $e^-+d\to e^-+d+π^0$ the rescattering effects due to the transition: $ γ+d\to p+p+π^-$ (or $n+n+π^+)\to d+π^0$ are cancelled out due to the Pauli principle. The large values for these effects predicted in the past may result from the fact that the spin structure of the corresponding matrix element and the necessary antisymmetrization induced by the presence of identical protons (or neutrons) in the intermediate state was not taken into account accurately. One of the important consequences of these considerations is that $π^0$ photo- and electro-production on deuteron near threshold can bring direct information about elementary neutron amplitudes.

nucl-th↗