arXiv subjects

A. Sibirtsev

Publications and source records attributed to A. Sibirtsev.

At least 73 records · Page 4Linked to original sources

arXiv2003

Charmonium photoproduction

The available data on $J/Ψ$ photoproduction are analyzed in terms of pomeron exchange, two gluon exchange and photon-gluon fusion models. Allowing the pomeron-quark interaction to be flavour dependent and introducing the soft and hard pomerons it is possible to reproduce the data at $\sqrt{s}{>}$10 GeV and small $|t|$. The two gluon exchange calculations indicate strong sensitivity to the gluon distribution function. The results obtained with the most modern MRST2001 and DL PDF reproduce the forward $J/Ψ$ photoproduction cross section at $\sqrt{s}{>}$10 GeV. The calculations with the photon-gluon fusion model and with MRST2001 and DL PDF are also in reasonable agreement with the data on the total $J/Ψ$ photoproduction cross section. We allocate the $J/Ψ$ photoproduction at low energies and large $|t|$ to the mechanism different from pomeron or two gluon exchanges. We consider that this might be axial vector trajectory exchange that couples to the axial form factor of the nucleon.

nucl-th↗

arXiv2003

Systematic Regge theory analysis of omega photoproduction

Systematic analysis of available data for $ω$-meson photoproduction is given in frame of Regge theory. At photon energies above 20 GeV the $γ{+}p{\to}ω{+}p$ reaction is entirely dominated by Pomeron exchange. However, it was found that Pomeron exchange model can not reproduce the $γ{+}p{\to}ρ{+}p$ and $γ{+}p{\to}ω{+}p$ data at high energies simultaneously with the same set of parameters. The comparison between $ρ$ and $ω$ data indicates a large room for meson exchange contribution to $ω$-meson photoproduction at low energies. It was found that at low energies the dominant contribution comes from $π$ and $f_2$-meson exchanges. There is smooth transition between the meson exchange model at low energies and Regge theory at high energies.

nucl-th↗

arXiv2002

Hadrons with charmed quarks in matter

We investigate the $D{\bar D}$ decay width of excited charmonium states at finite nuclear density with simultaneous modification of both $D$ and ${\bar D}$ mesons in nuclear matter. The strongest effect is found for the $Ψ^{\prime}$ meson. The medium modification can be detected by dilepton spectroscopy as substantial $Ψ^{\prime}$ broadening and anomalous $Ψ^{\prime}$ absorption.

nucl-th↗

arXiv2002

Omega photoproduction

Photoproduction of omega-meson is analyzed within meson exchange model and Regge model and compared to rho-meson photoproduction. An interplay between two models and uncertainties in data reproduction are discussed.

nucl-th↗

arXiv2002

Photoproduction of the Eta Meson from the Deuteron Near Threshold

Very recent data for the reaction gamma{d} --> eta{np} are analyzed within a model that includes contributions from the impulse approximation and next order corrections due to the np and eta{N} interactions in the final state. Comparison between the calculations and data indicate sizable contributions from the np and eta{N} final state interactions close to threshold.

nucl-th↗

arXiv2002

Pseudovector vs. pseudoscalar coupling in one-boson exchange NN potentials

We examine the effects of pseudoscalar and pseudovector coupling of the pi and eta mesons in one-boson exchange models of the NN interaction using two approaches: time-ordered perturbation theory unitarized with the relativistic Lippmann-Schwinger equation, and a reduced Bethe-Salpeter equation approach using the Thompson equation. Contact terms in the one-boson exchange amplitudes in time-ordered perturbation theory lead naturally to the introduction of s-channel nucleonic cutoffs for the interaction, which strongly suppresses the far off-shell behavior of the amplitudes in both approaches. Differences between the resulting NN predictions of the various models are found to be small, and particularly so when coupling constants of the other mesons are readjusted within reasonable limits.

nucl-th↗

arXiv2002

Coherent $ω$ photoproduction from nuclei and $ω$ properties in nuclear matter

The coherent $ω$-meson photoproduction from nuclei is proposed as a phenomenological method to evaluate the momentum dependence of $ω$-meson mass shift and width in nuclear matter. We analyze available data on un-separated coherent and incoherent $ω$-meson photoproduction from nuclei and extract the imaginary part of the the complex forward $ω{N}$ scattering amplitude, which is proportional to the in-medium $ω$-meson width. The accuracy of the currently available data is not sufficient to evaluate the real part of forward $ω{N}$ scattering amplitude and reconstruct the momentum dependence of the mass shift of the $ω$-meson.

nucl-th↗

arXiv2002

Incoherent Eta Photoproduction from the Deuteron near Threshold

Very recent data for the reaction gamma+d ->eta np, namely total cross sections, angular and momentum spectra, are analyzed within a model that includes contributions from the impulse approximation and next order corrections due to the np and eta-N interactions in the final state. Comparison between the calculations and the new data indicate sizable contributions from the np and eta-N final state interactions. Some systematic discrepancies between the calculations and the data are also found.

nucl-th↗

arXiv2002

Omega photoproduction beyond the resonance region at small u

Within the meson exchange model we study $ω$ meson photoproduction at energies above the s channel resonance region. Different model prescriptions for the $ω{NN}$ vertex function are investigated imposing gauge invariance as well as crossing symmetry. The calculations reproduce the energy dependence of the differential $ω$ photoproduction cross sections at moderate $|u|$ for $E_γ{\le}4.7$ GeV, which previously were discussed as an indication of the hard interaction between the photon and quarks of the nucleon.

nucl-th↗

arXiv2001

Eta-N Final State Interaction in incoherent Photoproduction of Eta-mesons from the Deuteron near Threshold

An analysis of incoherent photoproduction of $η$ mesons off the deuteron for photon energies from threshold to 800 MeV is presented. The dominant contribution, the $γ$N-$η$N amplitude, is described within an isobar model. Effects of the final state interactions in the $NN$ as well as the $ηN$ systems are included employing models derived within the meson-exchange approach. It is found that their consideration is important. Specifically, due to an interference effect the influence of the $ηN$ final state interaction is enhanced in the reaction $γd \to np η$ close to threshold.

nucl-th↗

arXiv2001

The reaction $πN{\to}ωN$ revisited: the $ω{-}N$ scattering length

We reinvestigate the experimental data on $ω$--meson production in pion-nucleon collisions based on both an analytical approach and a Monte Carlo simulation. Our analysis allows us to study the kinematical peculiarities of the $π^-p{\to}ω{n}$ reaction at energies close to threshold. Based on the hypothesis, that the formalism derived in ref. [1] was applied improperly, the unusually strong energy dependence claimed for the near--threshold cross section is identified as a purely kinematical effect. Based on this hypothesis, we deduce an effective ${π^-}p{\to}ωn$ cross section that is larger by an order of magnitude compared to the one commonly used. In addition we extract a lower limit for the imaginary part $\Im a_{ωN}$ of the $ωN$ scattering length. We find a value of $\Im a_{ωN}{=}0.24{\pm}0.05$ fm, which is significantly larger than that presently found in the literature.

hep-ph↗

arXiv2001

Phenomenological analysis of K+ meson production in proton-nucleus collisions

Total and differential cross sections from literature, on the production of K+ mesons in pA interactions at projectile energies between T=0.8 and 2.9 GeV, covering the transition across the free nucleon-nucleon threshold at 1.58 GeV, have been investigated. From the target-mass dependence of the production cross sections no evidence for the expected change of the dominant reaction mechanism from two-step to direct kaon production was found. At T=1.0 GeV the A dependences of the total cross sections and of the most recent data from COSY-Juelich, differential cross sections measured under forward angles, are strongly different. The invariant K+ production cross sections show an overall exponential scaling behavior with the squared four-momentum transfer between the beam proton and the produced K+ meson for t< -0.05 GeV^2 independent of the beam energy and emission angle. The data from COSY-Juelich reveal a strongly different t dependence in the region of t>0 GeV^2. Further data at forward angles and different beam energies should be taken in order to explore this region of kinematically extreme conditions.

nucl-ex↗

arXiv2001

Studying the $ω$-mass in-medium in $γ+ A\to π^0γ+X$ reactions

Simulations based on a coupled-channel transport model have been performed to analyze the feasibility to study the in-medium $ω$ mass exploiting the process $γ+A\toπ^0γ+X$ for C, Ca and Nb nuclei. The distortions due to final-state interactions of the $π^0$ and background contributions from the reaction $γ+A\toπ^0π^0+X$ are found to be small in the mass range of interest ($0.6<M_{π^0γ}<0.8$ GeV). Furthermore, the effect of the detector resolution on the $π^0γ$-mass determination is discussed.

hep-ex↗

arXiv2001

Incoherent Photoproduction of $η$-mesons from the Deuteron near Threshold

Incoherent photoproduction of the $η$-meson on the deuteron is studied for photon energies from threshold to 800 MeV. The dominant contribution, the $γ$N-$η$N amplitude, is described within an isobar model. The final state interaction derived from the CD-Bonn potential is included and found to be important for the description of the production cross section close to threshold. Possible effects from the $ηN$ final state interaction are discussed.

nucl-th↗

arXiv2001

Charmonium absorption by nucleons

$J/Ψ$ dissociation in collisions with nucleons is studied within a boson exchange model and the energy dependence of the dissociation cross section is calculated from the threshold for $Λ_c{\bar D}$ production to high energies. We illustrate the agreement of our results with calculations based on short distance QCD and Regge theory. The compatibility between our calculations and the data on $J/Ψ$ photoproduction on a nucleon is discussed. We evaluate the elastic $J/Ψ{+}N$ cross section using a forward dispersion relation and demonstrate the overall agreement with the predictions from QCD sum rules. Our results are compatible with the phenomenological dissociation cross section evaluated from the experimental data on $J/Ψ$ production from $γ{+}A$, $p{+}A$ and $A{+}A$ collisions.

nucl-th↗

arXiv2001

Open charm production in relativistic nucleus-nucleus collisions

We calculate excitation functions for open charm mesons in $Au+Au$ reactions from AGS to RHIC energies within the HSD transport approach which is based on string, quark, diquark ($q, \bar{q}, qq, \bar{q}\bar{q}$) and hadronic degrees of freedom. The open charm cross sections from $pN$ and $πN$ reactions are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. From our dynamical calculations we find an approximate $m_T$-scaling for pions, kaons, $D$-mesons and $J/Ψ$ -- when discarding final state elastic scattering of kaons and $ϕ$-mesons with pions -- in central collisions of $Au + Au$ at 160 A$\cdot$GeV (with an apparent slope of 176 MeV) without employing the assumption of a Quark-Gluon Plasma (QGP). We demonstrate that this result is essentially due to a relative $m_T$-scaling in $pp$ collisions at $\sqrt{s} \approx$ 17.3 GeV. At lower bombarding energies of 25 A$\cdot$GeV a suppression of $D$-mesons by a factor of $\sim$ 10 relative to a global $m_T$-scaling with slope 143 MeV is expected. However, when incorporating attractive $D$-meson self energies as suggested by QCD sum rules, an approximate $m_T$-scaling is regained even at 25 A$\cdot$GeV. The effects of $D$-meson rescattering and charmonium absorption are discussed, furthermore, with respect to rapidity and transverse mass distributions in central collisions of $Au + Au$ at 25, 160 A$\cdot$GeV and 21.3 A$\cdot$TeV.

nucl-th↗

arXiv2000

Kaon properties and cross sections in nuclear medium

Results for the $π+ N \to Λ, Σ+ K$ reactions in nuclear matter of Ref. nucl-th/0004011 are presented. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states in the resonance model. These vector and scalar potentials were calculated using the quark meson coupling model. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production at SIS energies are consistent with a repulsive $K^+$-nucleus potential.

nucl-th↗

arXiv2000

Strangeness production from $πN$ collisions in nuclear matter

Kaon production in pion-nucleon collisions in nuclear matter is studied in the resonance model. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states. These vector and scalar potentials were calculated using the quark-meson coupling (QMC) model. The in-medium kaon production cross sections in pion-nucleon interactions for reaction channels with $Λ$ and $Σ$ hyperons in the final state were calculated at the baryonic densities appropriate to relativistic heavy ion collisions. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production are consistent with a repulsive $K^+$-nucleus potential.

nucl-th↗