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A. I. Titov

Publications and source records attributed to A. I. Titov.

At least 37 records · Page 2Linked to original sources
arXiv2008

Exclusive charm production in pbar p collisions at s^1/2 <15 GeV

We discuss the open charm production in peripheral reactions $\bar pp\to \bar Y_cY_c$ and $\bar pp\to M_c\bar M_c$, where $Y_c$ and $M_c$ stand for $Λ_c^+,Σ_c^+$ and $D,D^*$, respectively, at $\sqrt{s}\lesssim 15$ GeV, which corresponds to the energy range of FAIR. Our consideration is based on the topological decomposition of the planar quark and diquark diagrams which allows to estimate consistently meson and baryon exchange trajectories and energy scale parameters as well. The spin dependence is determined by the effective interaction of lowest exchanged resonance. Unknown parameters are fixed by an independent analysis of open strangeness production in $\bar pp\to \bar YY$ and $\bar pp\to \bar KK$ reactions and of SU(4) symmetry. We present the corresponding cross sections and longitudinal double-spin asymmetries for exclusive binary reactions with open charm mesons and baryons in the final state. The polarization observables have a non-trivial $t$ and $s$ dependence which is sensitive to details of the open charm production mechanism.

hep-ph↗
arXiv2008

Selected vector-meson decay-distributions in reactions of polarized photons with protons

We develop a formalism for studying vector meson ($V$) photo-production at the proton ($p$) with polarized photons, $\vecγp \to V p $, through an analysis of the decay distribution in the channel $V\toπ^0γ$. We show that this decay distribution differs noticeably from the distributions of purely hadronic decays, like $ϕ\to K^+K^-$, $ω\to π^0π^+π^-$. Formulas for the decay distributions are presented which are suitable for data analysis and interpretation.

nucl-th↗
arXiv2007

Photoproduction of phi meson off deuteron near threshold

We discuss coherent and incoherent $ϕ$ meson photoproduction off the deuteron at low energy and small momentum transfer with the aim to check whether the recent experimental data need for their interpretation the inclusion of exotic channels. Our analysis of the differential cross section and spin-density matrix elements shows that the existing data may be understood on the base of conventional dynamics. For a firm conclusion about a possible manifestation of exotic channels one has to improve the resolution of the data with providing additional information on channels with spin- and double-spin flip transitions being sensitive to the properties of the photoproduction amplitude in $γp$ and $γD$ reactions.

nucl-th↗
arXiv2006

Theta+ formation in inclusive gamma D -> pK- X

We analyze the possibility to produce an intermediate Theta^+ via a KN->Θ+ formation process in gamma D-> pK^- X (X=nK^+,pK^0) reactions at some specific kinematical conditions, in which a pK^- pair is knocked out in the forward direction and its invariant mass is close to the mass of Lambda(1520). The Θ^+ signal may appear in the [γD,pK^-] missing mass distribution. The ratio of the signal (cross section at the Θ^+ peak position) to the smooth background processes varies from 0.7 to 2.5 depending on the spin and parity of Theta+, and it decreases correspondingly if the pK^- invariant mass is outside of the Lambda(1520)-resonance region. We analyze the recent CLAS search for the Theta+ in the gamma D ->pK^-nK^+ reaction and show that the conditions of this experiment greatly reduce the Theta+ formation process making it difficult to extract a Theta+ peak from the data.

nucl-th↗
arXiv2006

Parity non-conservation in nuclear excitation by circularly polarized photon beam

We show that the asymmetries in the nuclear resonance fluorescence processes with a circular polarized photon beam may be used as a tool for studying the parity non-conservation (PNC) in nuclei. The PNC asymmetry measurements both in exciting the parity doublet states and in exciting the discrete states near the ground states with parity mixing are discussed. We derived the formulae needed for measuring the PNC asymmetries.

nucl-th↗
arXiv2005

Diffractive $ϕ$-meson photoproduction on proton near threshold

Photoproduction of $ϕ$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_γ$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_γ$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $ϕ$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.

nucl-ex↗
arXiv2005

Coherent Theta^+ and Lambda(1520) photoproduction off the deuteron

We analyze an effect of the coherent $Θ^+Λ(1520)$ photoproduction in $γD$ interaction near the threshold. We demonstrate that the coherence effect becomes manifest in a comparison of the $nK^+$ invariant mass distribution when the $pK^-$ invariant equals the $Λ(1520)$ mass. Our model calculations indicate a sizeable contribution of resonant and non-resonant background processes in the $γD\to np K^+K^-$ reaction which generally exceed the contribution of the coherent resonant channel. However, we find that the coherent $Θ^+Λ(1520)$ photoproduction is enhanced relative to the background processes in the forward hemisphere of the $pK^-$ pair photoproduction. Moreover, the coherence effect does not depend on the $Θ^+$ photoproduction amplitude and is defined by the probabilities of the $Λ(1520)$ photoproduction and the $Θ^+\to NK$ transition. Therefore, this coherence effect may be used as an independent method for studying the mechanism of $Θ^+$ production and $Θ^+$ properties.

nucl-th↗
arXiv2004

Some aspects of $Θ^+$ parity determination in the reaction $γN\to Θ^+ \bar{K}\to N K \bar{K}$

We analyze the problem of how to determine the parity of the $Θ^+$ pentaquark in the reaction $γN\to KΘ\to NK\bar{K}$, where $N=n,p$. Our model calculations indicate that the contribution of the non-resonant background of the reaction $γN\to NK\bar{K}$ cannot be neglected, and that suggestions to determine the parity based solely on the initial-stage process $γN\to KΘ$ cannot be implemented cleanly. We discuss the various mechanisms that contribute to the background, and we identify some spin observables which are sensitive.

nucl-th↗
arXiv2004

Comment on the $Θ^+$-production at high energy

We show that the cross sections of the $Θ^+$-pentaquark production in different processes decrease with energy faster than the cross sections of production of the conventional three-quark hyperons. Therefore, the threshold region with the initial energy of a few GeV or less seemsto be more favorable for the production and experimental study of $Θ^+$-pentaquark.

nucl-th↗
arXiv2004

Parity violation in deuteron photo-disintegration

We analyze the energy dependence for two types of parity-non-conserving (PNC) asymmetries in the reaction $γD\to np$ in the near-threshold region. The first one is the asymmetry in reaction with circularly polarized photon beam and unpolarized deuteron target. The second one corresponds to those with an unpolarized photon beam and polarized target. We find that the two asymmetries have quite different energy dependence, and their shapes are sensitive to the PNC-meson exchange coupling constants. The predictions for the future possible experiments to provide definite constraints for the PNC-coupling constants are discussed.

nucl-th↗
arXiv2003

Spin effects and baryon resonance dynamics in phi-meson photoproduction at few GeV

The diffractive $ϕ$-meson photoproduction amplitude is dominated by the Pomeron exchange process and contains the terms that govern the spin-spin and spin-orbital interactions. We show that these terms are responsible for the spin-flip transitions at forward photoproduction angles and appear in the angular distributions of $ϕ\to K^+K^-$ -decay in reactions with unpolarized and polarized photon beams. At large momentum transfers, the main contribution to the $ϕ$-meson photoproduction is found to be due to the excitation of nucleon resonances. Combined analysis of $ω$ and $ϕ$ photoproduction indicates strong OZI-rule violation in $ϕNN^*$ - couplings. We also show that the spin observables are sensitive to the dynamics of $ϕ$-meson photoproduction at large angles and could help distinguish different theoretical models of nucleon resonances. Predictions for spin effects in $ϕ$-meson photoproduction are presented for future experimental tests.

nucl-th↗
arXiv2002

Baryon Resonance Dynamics in pi N \to N V Reactions Near Threshold

The rho - omega interference in the exclusive reaction pi N \to N' e+ e- is studied within a schematic model including the established baryon resonances up to 1720 MeV. Near threshold the interference can be used to separate the isoscalar part of the electromagnetic current. The role of various baryon resonances is highlighted.

nucl-th↗
arXiv2002

Coherent phi and omega meson photoproduction from deuteron and non-diffractive channels

For coherent photoproduction of phi and omega mesons from deuteron at forward angles, the isovector pi-exchange amplitude is strongly suppressed. We show a possibility to study the non-diffractive channels associated with the unnatural parity exchange in phi-photoproduction and with the baryon resonance excitations in omega-photoproduction by measuring the spin observables.

nucl-th↗
arXiv2002

Effective Lagrangian approach to the omega meson photoproduction near threshold

We apply the effective Lagrangian approach to investigate the role of the nucleon resonances in $ω$ meson photoproduction at energies near the threshold. The resonant amplitudes are calculated from effective Lagrangians with the gamma NN* and omega NN* coupling constants fixed by the empirical helicity amplitudes and the vector meson dominance model. The contributions from the nucleon resonances are found to be significant in changing the differential cross sections in a wide interval of t and various spin observables.

nucl-th↗
arXiv2001

Isoscalar-Isovector Interferences in $πN \to N e^+ e^-$ Reactions as a Probe of Baryon Resonance Dynamics

The isoscalar-isovector ($ρ-ω$) interferences in the exclusive reactions $π^- p \to n e^+ e^-$ and $π^+ n \to p e^+ e^-$ near the $ω$ threshold leads to a distinct difference of the dielectron invariant mass distributions depending on beam energy. The strength of this effect is determined by the coupling of resonances to the nucleon vector-meson channels and other resonance properties. Therefore, a combined analysis of these reactions can be used as a tool for determining the baryon resonance dynamics.

nucl-th↗
arXiv2001

Production of $ω$ and $ϕ$ Mesons in Near-Threshold $πN$ Reactions: Baryon Resonances and Validity of the OZI Rule

Results of a combined analysis are presented for the production of $ω$ and $ϕ$ mesons in $πN$ reactions in the near-threshold region using throughoutly a conventional ''non-strange'' dynamics based on such processes which are allowed by the non-ideal $ω-ϕ$ mixing. We show that strong interferences of the $t$ (meson exchange) and $s$ and $u$ (nucleon and nucleon resonance) channels differ significantly in $ω$ and $ϕ$ production amplitudes. This leads to a decrease of the relative yields in comparison with expectations based on one-channel models with standard $ω- ϕ$ mixing. We find a strong and non-trivial difference between observables in $ω$ and $ϕ$ production reactions caused by the different role of the nucleon and nucleon resonance amplitudes. A series of predictions for the experimental study of this effect is presented.

nucl-th↗