arXiv subjects

L. A. Kondratyuk

Publications and source records attributed to L. A. Kondratyuk.

36 records · Page 2Linked to original sources

arXiv2001

Open charm enhancement by secondary interactions in relativistic nucleus-nucleus collisions?

We calculate open charm production in $Pb+Pb$ reactions at SPS 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 - including the production of open charm pairs from secondary 'meson'-'baryon' (or quark-diquark and antiquark-diquark) collisions. It is argued that at collision energies close to the $c\bar{c}$ pair threshold the dominant production mechanism is related to the two body (or quasi two body) reactions $πN \to \bar{D} (\bar{D^*}) Λ_c, (Σ_c)$. Estimates within the framework of the Quark-Gluon String model suggest cross sections of a few $μb$ for $πN \to \bar{D} Λ_c$ in the region of 1 GeV above threshold. The dynamical transport calculations for $Pb + Pb$ at 160 A$\cdot$GeV indicate that the open charm enhancement reported by the NA50 Collaboration might be due to such secondary reaction mechanisms.

hep-ph↗

arXiv2001

Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories

We investigate deuteron two-body photodisintegration within the framework of the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special attention is paid to the use of QCD motivated Regge trajectories of the logarithmic and square-root form which have been suggested recently by Brisudová, Burakovsky and Goldman. We find that the recent experimental data from TJNAF in the few GeV region can reasonably be described by the model. Angular distributions at different $γ$-energies are presented and the effect of a forward-backward asymmetry is discussed. Predictions for the energy dependence of $dσ/dt$ at higher energies and different $Θ_{cm}$ are presented, too.

hep-ph↗

arXiv2000

Production of $a_0$-mesons in the reactions $πN \to a_0 N$ and $p p \to d a_0^+$ at GeV energies

We investigate the reactions $πN \to a_0 N$ and $p p \to d a_0^+$ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross section of the reaction $πN \to a_0 N$. These results are used to calculate the differential and total cross sections of the reaction $p p \to d a_0^+$ within the framework of the two-step model in which two nucleons produce an $a_0$-meson via $π$ -meson exchange and fuse to a deuteron. The necessity of new measurements on $a_0$ production and branching fractions (of its decay to the $K\bar K$ and $πη$ channels) is emphasized for clarifying the $a_0$ structure. Detailed predictions for the reaction $pp \to d a_0^+$ are presented for the energy regime of the proton synchrotron COSY-Jülich.

nucl-th↗

arXiv2000

Electromagnetic Pion and Nucleon Form Factors at Positive and Negative $q^2$ Within the Framework of Quark-Gluon Strings Model

The electromagnetic form factors of pion and nucleon are considered within the framework of the Quark-Gluon Strings Model, where the dependence of the form factors on $q^2$ is determined by the intercept of a dominant Regge trajectory and Sudakov form factor. The analytical expressions for the form factors found in the time-like region can be directly continued to the space-like region. Good agreement with available experimental data on the pion and magnetic nucleon form factor is obtained at positive as well as negative $q^2$. It is shown that the difference in $F_π$ and $G_m$ at positive and negative values of $q^2$ is mainly related to the behavior of the double logarithmic term in the exponent of Sudakov form factor. The model describes also existing data on the Pauli nucleon form factor $F_2$ and the ratio $G_e/G_m$.

hep-ph↗

arXiv1999

Interactions of charmed mesons with nucleons in the $\bar p d$ reaction

We study the possibility to measure the elastic $ΦN$ ($Φ\equiv J/ψ, ψ(2S), ψ(3770),χ_{2c}$) scattering cross section in the reaction $\bar p{+}d{\to}Φ{+}n_{sp}$ and the elastic $D(\bar D) N$ scattering cross section in the reaction $\bar p{+}d \to D^- D^0 p_{sp}$. Our studies indicate that the elastic scattering cross sections can be determined for $Φ$ momenta about 4-6 GeV/c and $D/ \bar D$ momenta 2 -- 5 GeV/c by selecting events with $p_t \geq 0.4$ GeV/c for $Φ$'s and $p_t(p_{sp})\geq$ 0.5 GeV/c for $D/\bar D$-meson production.

nucl-th↗

arXiv1999

Studying the $ωN$ elastic and inelastic cross section with nucleons

We explore the possibility to measure the elastic and inelastic $ωN$ cross section in $p{+}d{\to}d{+}ω{+}p_{sp}$ and $p{+}A$ reactions. Our studies indicate that the elastic scattering cross sections can be determined for $ω$ momenta above 1 GeV/c in $p{+}d$ reactions by gating on high proton spectator momenta whereas the $ωN$ absorption cross section down to low relative $ω$ momenta is most effectively studied in $p{+}A$ reactions at beam energies 2.0--2.7 GeV

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arXiv1999

Omega- and phi-meson production in p n -> d M reactions near threshold and OZI-rule violation

We investigate the reactions p n -> d omega and p n -> d phi close to the corresponding thresholds. The S-wave amplitudes are calculated within the framework of the two-step model which is described by a triangle graph with pi, rho and omega mesons in the intermediate state. The cross sections of the reactions p n -> d omega and p n -> d phi are predicted to be significantly larger than the cross sections of the corresponding reactions p p -> p p omega and p p -> p p phi at the same values of the c.m. excess energy Q. The ratio of the yields of phi to omega is found to be (30 +/- 7) x 10^-3.

nucl-th↗

arXiv1999

Eta and eta-prime meson production in the reaction pn -> dM near threshold

The two-step model with pi-, rho- and omega- exchanges taken into account is applied to investigate the reactions pn -> d eta and pn -> d eta-prime. The existing experimental data on the reaction pn -> d eta are analysed and predictions for the cross section of the reaction pn -> d eta-prime are presented. It is found that pi- as well as rho exchange yield significant contributions in both reactions. The effect of the final state interaction is also studied.

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arXiv1998

On the possibility of $f_0$ observation in low energy $pp$ collisions

Within the meson-exchange model we calculate $f_0$-meson production cross section in $\piN$ and $NN$ reactions and investigate the possibility for $f_0$ observation via the $K\bar{K}$ decay mode in $pp$ collisions. Our studies indicate that an extraction of the $f_0$ signal is unlikely due to the large background from other reaction channels.

nucl-th↗

arXiv1998

Omega- and Phi-meson production in pn -> dV reactions and OZI-rule violation

We investigate the reactions p n -> d omega and p n -> d phi close to threshold and at higher energies. Near threshold we calculate the S-wave amplitudes within the framework of the two-step model which is described by a triangle graph with pi-mesons in the intermediate state and find a ratio of the S-wave amplitudes squared of R =|A(phi)|^2/|A(omega)|^2 = (4-8) x 10^{-3}. Any significant enhancement of the experimental value of R(phi/omega) over this prediction can be interpreted as a possible contribution of the intrinsic s - anti s component in the nucleon-wave function. We present arguments that there is a strong resonance effect in the omega N channel close to threshold. At higher energies we calculate the differential cross sections of the reactions p n -> d omega, p n -> d phi and the ratio of the phi/omega yields within the framework of the quark-gluon string model. An irregular behavior of the phi/omega-ratio is found at s <= 12 GeV^2 due to the interference of the t- and u-channel contributions.

nucl-th↗

arXiv1998

$ρ$-meson properties at finite nuclear density

We calculate the momentum dependence of the $ρ$-meson selfenergy based on the dispersion relation for the $ρN$ scattering amplitude $f(ω$) at low nuclear density. The imaginary part of $f(ω)$ is determined from the optical theorem, while the total $ρN$ cross section is obtained within the VDM at high energy and within the resonance model at low energy. Our numerical results indicate a sizeable broadening of the $ρ$-meson width in the medium especially for low relative momenta $p$ while the real part of the $ρ$ selfenergy is found to change its sign and becomes repulsive already at momenta above 100 MeV/c. Extrapolating to nuclear saturation density $ρ_0$ we find a dropping of the $ρ$-mass for $p \approx$ 0 in line with the QCD sumrule analysis of Hatsuda while at high energy an increase of the $ρ$-mass in line with the prediction by Eletsky and Joffe is obtained. However, when including a broadening of the baryonic resonances in the medium, the $ρ$-meson mass shift at $p \approx$ 0 becomes slightly repulsive whereas the width increases substantially.

nucl-th↗

arXiv1997

Nuclear transparency in quasielastic A(e,e'p): intranuclear cascade versus eikonal approximation

The problem of nuclear propagation through the nuclear medium in quasielastic A(e,e'p) reactions is discussed in the kinematic range 1<Q^2<7 (GeV/c)^2. The coefficient of nuclear transparency is calculated for each Q^2 in the framework of the intranuclear cascade model (INC) and of the eikonal approximation (EA). The predictions of both models are in good agreement with each other and with experimental data recently obtained at SLAC, BATES and TJNAF. The EA gives an explanation of the Q^2 behaviour of the transparency coefficient as a kinematic effect related to the superposition of contributions from each target shell.

nucl-th↗

arXiv1997

Medium effects in the production and decay of vector mesons in pion-nucleus reactions

The $ω$-, $ρ$- and $ϕ$-resonance production and their dileptonic decay in $π^- A$ reactions at 1.1 - 1.7 GeV/c are calculated within the intranuclear cascade (INC) approach. The invariant mass distribution of the dilepton pair for each resonance can be decomposed in two components which correspond to their decay 'inside' the target nucleus and in the vacuum, respectively. The first components are strongly distorted by the nuclear medium due to resonance-nucleon scattering and a possible mass shift at finite baryon density. These medium modifications are compared to background sources in the dilepton spectrum from $πN$ bremsstrahlung as well as the Dalitz decays of $ω$ and $η$ mesons produced in the reaction. Detailed predictions for $π^- Pb$ reactions at 1.3 and 1.7 GeV/c are made within several momentum bins for the lepton pair.

nucl-th↗

arXiv1997

Resonance Production on Nuclei at High Energies: Nuclear-Medium Effects and Space-Time Picture

The influence of nuclear matter on the properties of coherently produced resonances is discussed. It is shown that, in general, the mass distribution of resonance decay products has a two-component structure corresponding to decay outside and inside the nucleus. The first (narrow) component of the amplitude has a Breit-Wigner form determined by the vacuum values of mass and width of the resonance. The second (broad) component corresponds to interactions of the resonance with the nuclear medium. It can be also described by a Breit-Wigner shape with parameters depending e.g. on the nuclear density and on the cross section of the resonance-nucleon interaction. The resonance production is examined both at intermediate energies, where interactions with the nucleus can be considered as a series of successive local rescatterings, and at high energies, $E>E_{crit}$, where a change of interaction picture occurs. This change of mechanisms of the interactions with the nucleus is typical for the description within the Regge theory approach and is connected with the nonlocal nature of the reggeon interaction.

nucl-th↗

arXiv1996

Medium effects in the production and decay of $ω$- and $ρ$-resonances in pion-nucleus interactions

The $ω$- and $ρ$-resonance production and their dileptonic decay in $π^- A$ reactions at GSI energies are calculated within the intranuclear cascade (INC) approach. The invariant mass distribution of the dilepton pair for each resonance is found to have two components which correspond to the decay of the resonances outside and inside the target nucleus. The latter components are strongly distorted by the nuclear medium due to resonance-nucleon scattering and a possible mass shift at finite baryon density. These medium modifications are compared to background sources in the dilepton spectrum from $πN$ bremsstrahlung and the Dalitz decays of $Δ$'s and $η$ mesons produced in the reaction.

nucl-th↗

arXiv1996

Density dependence of resonance broadening and shadowing effects in nuclear photoabsorption

Medium effects as a function of the mass number $A$ are studied in the total photonuclear cross section from the $Δ$-resonance region up to the region where shadowing effects are known to exist. A consistent picture is obtained by simply assuming a density dependence of the different mechanisms of resonance broadening and shadowing. The $Δ$-mass shift is found to increase with $A$.

nucl-th↗

arXiv1995

Two step mechanism of $η, η', ω, ϕ$ meson prodction in $pD \to ^3He $ reaction$

The differential cross sections of $pD\to ^3He X$ reactions, where $X=η, \ η'\ ,ω, \ ϕ$, are calculated on the basis of a two-step mechanism involving the subprocesses $pp\to dπ^+$ and $π^+n\to Xp $. It is shown that this model describes well the form of energy dependence of available experimental cross sections at the final c.m.s. momentum $p^*$=0.4-1$ GeV/c$ for the $η$ and at $p^*=0-0.5$ GeV/c for the $ω$ meson as well as the ratios $R(η'/η) $ and $R(ϕ/ω)$. The absolute value of the cross section is underestimated by an overall normalization factor of about 3 for $η, \ η'$ and by nearly one order of magnitude for $ω$ and $ϕ$. The spin-spin correlations are predicted for the reaction ${\vec D}{\vec p}\to ^3He X$ in the forward-backward approximations for the elementary amplitudes.

nucl-th↗

arXiv1994

Relativistic Three-Dimensional Two- and Three-Body Equations on a Null Plane and Applications to Meson and Baryon Regge Trtajectories

We start from a field-theoretical model of zero range approximation to derive three-dimensional relativistic two- and three-body equations on a null plane. We generalize those equations to finite range interactions. We propose a three-body null-plane equation whose form is different from the one presented earlier in the framework of light-cone dynamics. We discuss the choices of the kernels in two- and three-body cases and apply our model to the description of meson and baryon Regge trajectories. Our approach overcomes some theoretical and phenomenological difficulties met in preceding relativized treatments of the three-body problem.

hep-ph↗