arXiv subjects

A. Sibirtsev

Publications and source records attributed to A. Sibirtsev.

At least 55 records · Page 3Linked to original sources

arXiv2005

Resonances and final state interactions in the reaction pp->pK^+Lambda

A study of the strangeness production reaction pp->pK^+Lambda for excess energies of epsilon \le 150 MeV, accessible at high-luminosity accelerator facilities like COSY, is presented. Methods to analyze the Dalitz plot distribution and angular spectra in the Jackson and helicity frames are worked out and suitable observables for extracting information on low lying resonances that couple to the K-Lambda system and for determining the Lambda-p effective-range parameters from the final state interaction are identified and discussed. Furthermore, the chances for identifying the reaction mechanism of strangeness production are investigated.

nucl-th↗

arXiv2005

Aspects of phi-meson production in proton-proton collisions

We analyze near-threshold cross section data for the reaction pp->pp phi published by the DISTO collaboration and recent, still preliminary results presented by the ANKE Collaboration. We formulate a procedure to evaluate the OZI ratio at low energies by taking into account corrections from the kinematics and the final-state interaction. Combining the new data with the few measurements available at higher energies we give a limit for the OZI rule violation and estimate the possible contribution from a five-quark baryonic resonance coupled to the phi-p system.

nucl-th↗

arXiv2005

Okubo-Zweig-Iizuka rule violation in photoproduction

We investigate OZI rule violation in omega and phi-meson photoproduction off nucleons. Data on the total cross sections indicate a large phi/omega ratio of about 0.8 at the maximal available photon energy that is in good agreement with expectations from QCD. On the other hand, data at large four momentum transfer exhibit a ratio of about 0.07, showing that the perturbative QCD regime is not approached at |t| > 2 GeV^2 and photon energies E_γ< 4 GeV. The anomanously large phi/omega ratio at low energies, that is close to the reaction threshold, remains to be explained within nonperturbative QCD.

hep-ph↗

arXiv2005

The K^- αscattering length and the reaction dd \to αK^+ K^-

We present predictions for the the K^- αscattering length obtained within the framework of the multiple scattering approach. Evaluating the pole position of the K^- αscattering amplitude within the zero range approximation, we find a loosely bound K^- αstate with a binding energy of E_R = -2 ... -7 MeV and a width Γ_R = 11 ... 18 MeV. We propose to measure the K^- αscattering length through the final state interaction between the αand K^- meson produced in the reaction dd \to αK^+ K^-. It is found that the K^-αinvariant mass distribution from this reaction at energies near the threshold provides a new tool to determine the s-wave K^- αscattering length.

nucl-th↗

arXiv2005

The interaction of slow J/psi and psi' with nucleons

The interaction of the charmonium resonances J/psi and psi' with nucleons at low energies is considered using the multipole expansion and low-energy theorems in QCD. A lower bound is established for the relevant gluonic operator average over the nucleon. As a result we find the discussed interaction to be significantly stronger than previously estimated in the literature. In particular we conclude that the cross section of the J/psi - nucleon elastic scattering at the threshold is very likely to exceed 17 millibarn and that existence of bound states of the J/psi in light nuclei is possible. For the psi' resonance we estimate even larger elastic scattering cross section and also a very large cross section of the process psi'+N -> psi+N giving rise to the decay width of tens of MeV for the psi' resonance in heavy nuclei.

hep-ph↗

arXiv2004

Near threshold enhancement of the ppbar mass spectrum in J/Psi decay

We investigate the nature of the near-threshold enhancement in the ppbar invariant mass spectrum of the reaction J/Psi -> gamma ppbar reported recently by the BES Collaboration. Using the Juelich NNbar model we show that the mass dependence of the ppbar spectrum close to the threshold can be reproduced by the S-wave ppbar final state interaction in the isospin I=1 state within the Watson-Migdal approach. However, because of our poor knowledge of the NNbar interaction near threshold and of the J/Psi -> gamma ppbar reaction mechanism and in view of the controversal situation in the decay J/Psi -> pi0 ppbar, where no obvious signs of a ppbar final state interaction are seen, explanations other than final state interactions cannot be ruled out at the present stage.

hep-ph↗

arXiv2004

New results on the limit for the width of the exotic Theta^+ resonance

We investigate the impact of the Θ^+(1540) resonance on differential and integrated cross sections for the reaction K^+d{\to}K^0pp, where experimental information is available at kaon momenta below 640 MeV/c. The calculation utilizes the Jülich KN model and extensions of it that include contributions from a Θ^+(1540) state with different widths. The evaluation of the reaction K^+d{\to}K^0pp takes into account effects due to the Fermi motion of the nucleons within the deuteron and the final three-body kinematics. We conclude that the available data constrain the width of the Θ^+(1540) to be less than 1 MeV.

hep-ph↗

arXiv2004

Bounds on the bound η^3He system

We investigate the relation between the η^3He binding energy and width and the (complex) η^3He scattering length. Following our systematic analysis of the eta 3He scattering length we set limits on the η^3He binding. If bound states exist the binding energy (width) should not exceed 5 MeV (10 MeV). In addition, we comment on a recently claimed observation of an η-mesic ^3He quasi-bound state by the TAPS collaboration based on ηphotoproduction data. Although our limits are in reasonable agreement with the values reported by this collaboration, our analysis of these data does not lead to a solid conclusion concerning the existence of an η-mesic bound state. More dedicated experiments are necessary for further clarification.

nucl-th↗

arXiv2004

Analysis of Theta^+ production in K^+Xe collisions

The reaction K^+Xe->K^0pX is investigated in a meson-exchange model including rescattering of the secondary protons with the aim to analyze the evidence for the Theta^+(1540) resonance reported by the DIANA collaboration. We confirm that the kinematical cuts introduced by the DIANA collaboration efficiently suppress the background to the K^+n->K^0p reaction which may contribute to the Theta^+(1540) production. We find that these kinematical cuts do not produce a narrow structure in the K^0p effective mass spectra near 1540 MeV. We study the effect of a narrow Theta^+ resonance of both positive and negative parity in comparison with the DIANA data. We show that the K^+Xe->K^0pX calculations without Theta^+ contribution as well as the results obtained with a Theta^+ width of 1 MeV are in comparably good agreement with the DIANA results. More dedicated experiments are called for to establish this exotic baryon resonance.

nucl-th↗

arXiv2004

The $η{-}^3$He scattering length revisited

The possible existence of $η$-mesic nuclei poses an interesting and still open issue of research. Since the occurence of such $η$-nucleus bound states is reflected in the corresponding $η$-nucleus scattering length, we critically review the present knowledge for the $η$$^3$He system. Specifically, we scrutinize the available experimental information for the reaction $p{+}d \to η{+} ^3{\rm He}$ which is commonly used to extract the $η$$^3$He scattering length. We point out several striking discrepancies between the various measurements. Subject to those inconsistencies we deduce a value of $a{=}|4.3{\pm}0.3|{+}i(0.5{\pm}0.5)$ fm.

nucl-th↗

arXiv2004

Determination of the \bar K^0 d scattering length from the reaction pp \to d \bar K^0 K^+

The real and imaginary parts of the \bar K^0 d scattering length are extracted from the \bar K^0 d mass spectrum obtained from the reaction pp \to d \bar K^0 K^+ measured recently at the Cooler Synchrotron COSY at Jülich. We extract a new limit on the K^- d scattering length, namely Im a \le 1.3 fm and |Re a| \le 1.3 fm. The limit for the imaginary part of the K^- d scattering length is supported by data on the total K^- d cross sections.

nucl-th↗

arXiv2004

Subthreshold antiproton production in proton-carbon reactions

Data from KEK on subthreshold antiproton as well as on pi(+-) and K(+-) production in proton-nucleus reactions are described at projectile energies between 3.5 and 12.0 GeV. We use a model which considers a hadron-nucleus reaction as an incoherent sum over collisions of the projectile with a varying number of target nucleons. It samples complete events and allows thus for the simultaneous consideration of all particle species measured. The overall reproduction of the data is quite satisfactory. It is shown that the contributions from the interaction of the projectile with groups of several target nucleons are decisive for the description of subthreshold production. Since the collective features of subthreshold production become especially significant far below the threshold, the results are extrapolated down to COSY energies. It is concluded that an antiproton measurement at ANKE-COSY should be feasible, if the high background of other particles can be efficiently suppressed.

nucl-th↗

arXiv2004

Analysis of the Lambda p Final State Interaction in the Reaction p+p->K^+(Lambda p)

The missing mass spectrum measured in high resolution studies of the reaction pp -> K^+X is analyzed with respect to the strong final state interaction near the Lambda p production threshold. The observed spectrum can be described by factorizing the reaction amplitude in terms of a production amplitude and a final state scattering amplitude. Parametrizing the Lambda p final state interaction in terms of the inverse Jost function allows a direct extraction of the low-energy phase-equivalent potential parameters. Constraints on the singlet and triplet scattering lengths and effective ranges are deduced in a simultaneous fit of the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering using the effective range approximation.

nucl-ex↗

arXiv2004

How to measure the parity of the $Θ^+$ in $\vec p\vec p$ collisions

Triggered by a recent paper by Thomas, Hicks and Hosaka, we investigate which observables can be used to determine the parity of the $Θ^+$ from the reaction $\vec p\vec p \to Σ^+Θ^+$ near its production threshold. In particular, we show that the sign of the spin correlation coefficient $A_{xx}$ for small excess energies yields the negative of the parity of the $Θ^+$. The argument relies solely on the Pauli principle and parity conservation and is therefore model--independent.

hep-ph↗

arXiv2003

Hadron Physics at COSY

The workshop 'Hadron Physics at COSY' held from July 7th to July 10th 2003 in Bad Honnef brought together experimentalists and theoreticians from various fields of hadron physics to identify the key physics questions, which can be addressed with (un-) polarized proton and deuteron induced reactions at COSY. Topics discussed include charge symmetry breaking, elastic and inelastic nucleon-nucleon and nucleon-deuteron interactions, hadrons in the medium, mesonic bound states, meson and baryon resonances, and the hyperon-nucleon system. In addition prospects of the planned GSI facility were discussed. These Miniproceedings contain besides short summaries of the presentations the most relevant references for the field.

hep-ph↗

arXiv2003

Indication of anomalous exchange in exclusive charmonium photoproduction

We find that available data on $J/Ψ$ photoproduction at $|t|{\ge}$1 GeV are energy independent over the range $22{\le}\sqrt{s}{\le}170$ GeV and show a very soft $t$ dependence. Through a systematic analysis of the data we detect a new trajectory, which manifests itself at threshold and is energy independent. The trajectory couples to the axial form factor of the nucleon and can reproduce the $J/Ψ$ exclusive photoproduction data at large -$t$.

nucl-th↗

arXiv2003

a0+(980)-resonance production in pp->dK+Kbar0 reactions close to threshold

The reaction pp->d K+ Kbar0 has been investigated at an excess energy of Q=46 MeV above the (K+ Kbar0) threshold with ANKE at COSY-Juelich. From the detected coincident dK+ pairs about 1000 events with a missing Kbar0 were identified, corresponding to a total cross section of sigma(pp->d K+ Kbar0)=(38 +/- 2(stat) +/- 14(syst)) nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p-wave between the deuteron and the kaon system. This is interpreted in terms of a0+(980)-resonance production.

nucl-ex↗

arXiv2003

Photoproduction of eta-prime-mesons from the Proton

The presently available data for the reaction $γp{\to}η^\prime{p}$ are analyzed in terms of a model in which the dominant production mechanism is the exchange of the vector mesons $ω$ and $ρ$. To describe the data at photon energies close to the production threshold we introduce a resonance contribution due to the well established $S_{11}(1535)$ resonance. Finally we study the contributions due to nucleon exchange to the $η^\prime$ photoproduction and find, that those contributions can be seen at large angles in the differential cross section.

nucl-th↗