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A. Sibirtsev

Publications and source records attributed to A. Sibirtsev.

At least 19 recordsLinked to original sources
arXiv2015

Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K- momentum dependence of the differential cross section has been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K- -nucleus potential of about -60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K- momenta.

nucl-ex↗
arXiv2013

Final-State Interactions in the Process pp -> pKLambda

The possibility to determine the pLambda scattering length from the final-state interaction in the reaction pp->pKLambda is investigated experimentally. From a transversely polarized measurement, the K analyzing power (A_N) which, in principle, allows one to extract the spin triplet scattering length is studied. An unexpected energy dependence of the forward/backward symmetric part of A_N is found. The influence of N*-resonances on the pLambda invariant mass spectrum is investigated by exploiting the large acceptance for the process pp->pKLambda->pKppi and is found to be the main source of uncertainty for determining the pLambda scattering length.

nucl-ex↗
arXiv2013

Q^2-evolution of the electric and magnetic polarizabilities of the proton

The generalized Baldin sum rule at finite four-momentum transfer Q^2 is evaluated utilizing a structure function parameterization fit to recent experimental data. The most recent measurements on F_1 from Hall C at Jlab, as well as the F_2 structure function data from Hall B at Jlab and SLAC, were used in constructing our parameterization. We find that at Q^2 below 1 GeV^2 the dominant contribution to the electric and magnetic polarizabilities of the nucleon comes from the resonance region.

nucl-th↗
arXiv2012

Momentum dependence of the phi-meson nuclear transparency

The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb.

nucl-ex↗
arXiv2011

Upper limits for a narrow resonance in the reaction p + p -> K^+ + (Lambda p)

The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and Θ= 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. Narrow S = -1 resonances predicted by bag model calculations are not visible in the missing mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV/c^2.

hep-ex↗
arXiv2011

Analysis of the new Crystal Ball data on $K^-p\toπ^0Λ$ reaction with beam momenta of $514\sim 750$ MeV/$c$

The Crystal Ball Collaboration has recently reported the differential cross sections and $Λ$ polarization for the reaction $K^-p\rightarrow π^0Λ$ using an incident $K^-$ beam with momenta between 514 and 750 MeV/$c$. We make a partial wave analysis for this process with an effective Lagrangian approach and study the properties of some $Σ$ resonances around this energy range. With the inclusion of the 4-star resonances $Σ(1189)$, $Σ^*(1385)$, $Σ(1670){3\over 2}^-$, $Σ(1775){5\over 2}^-$, as well as a $Σ(1635){1\over 2}^+$, which is compatible with the 3-star $Σ(1660){1\over 2}^+$ in PDG, our results can well reproduce the experimental data. The parameters on the $Σ$ resonances and related couplings are studied.

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arXiv2010

Analysis of recent eta photoproduction data

Recent data on eta-meson photoproduction off a proton target in the energy range 2 < sqrt{s} < 3 GeV are analyzed with regard to their overall consistency. Results from the ELSA and CLAS measurements are compared with predictions of a Regge model whose reaction amplitude was fixed via a global fit to pre-2000 measurements of differential cross sections and polarization observables for gamma p -> eta p at higher energies. We find that all recent experimental results on differential cross sections for eta-meson photoproduction are in good agreement with each other, except for the CLAS data from 2009. However, the latter can be made consistent with the other data at the expense of introducing an energy-dependent renormalization factor. We point out that there indications in the data for a possible excitation of baryon resonances with masses around 2.1 and 2.4 GeV.

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arXiv2010

Measurement of the in-medium phi-meson width in proton-nucleus collisions

The production of phi mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the phi -> K+K- decay using the COSY-ANKE magnetic spectrometer. The phi meson production cross section follows a target mass dependence of A^0.56+/-0.02 in the momentum region of 0.6-1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium phi width is about an order of magnitude larger than its free value.

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arXiv2010

Proton-proton scattering above 3 GeV/c

A large set of data on proton-proton differential cross sections, analyzing powers and the double polarization parameter A_NN is analyzed employing the Regge formalism. We find that the data available at proton beam momenta from 3 GeV/c to 50 GeV/c exhibit features that are very well in line with the general characteristics of Regge phenomenology and can be described with a model that includes the rho, omega, f_2, and a_2 trajectories and single Pomeron exchange. Additional data, specifically for spin-dependent observables at forward angles, would be very helpful for testing and refining our Regge model.

hep-ph↗
arXiv2010

Cross section of the $pp\to K^+Σ^+n$ reaction close to threshold

We have measured inclusive data on $K^+$-meson production in $pp$ collisions at COSY Jülich close to the hyperon production threshold and determined the hyperon-nucleon invariant mass spectra. The spectra were decomposed into three parts: $Λp$, $Σ^0p$ and $Σ^+n$. The cross section for the $Σ^+n$ channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence.

hep-ex↗
arXiv2010

gamma-Z corrections to forward-angle parity-violating e-p scattering

We use dispersion relations to evaluate the gamma-Z box contribution to parity-violating electron scattering in the forward limit arising from the axial-vector coupling at the electron vertex. The calculation makes full use of the critical constraints from recent JLab data on electroproduction in the resonance region as well as high energy data from HERA. At the kinematics of the Qweak experiment, this gives a correction of 0.0047{+0.0011}{-0.0004}$ to the Standard Model value 0.0713(8) of the proton weak charge. While the magnitude of the correction is highly significant, the uncertainty is within the anticipated experimental uncertainty of +- 0.003.

hep-ph↗
arXiv2010

Primakoff effect in eta-photoproduction off protons

We analyse data on forward eta-meson photoproduction off a proton target and extract the eta to gamma gamma decay width utilizing the Primakoff effect. The hadronic amplitude that enters into our analysis is strongly constrained because it is fixed from a global fit to available gamma p to p eta data for differential cross sections and polarizations. We compare our results with present information on the two-photon eta-decay from the literature. We provide predictions for future PrimEx experiments at Jefferson Laboratory in order to motivate further studies.

hep-ph↗
arXiv2010

High resolution study of the Lambda p final state interaction in the reaction p + p -> K+ + (Lambda p)

The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. The large final state enhancement near the Lambda p threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering.

nucl-ex↗
arXiv2009

Backward pion-nucleon scattering

A global analysis of the world data on differential cross sections and polarization asymmetries of backward pion-nucleon scattering for invariant collision energies above 3 GeV is performed in a Regge model. Including the $N_α$, $N_γ$, $Δ_δ$ and $Δ_β$ trajectories, we reproduce both angular distributions and polarization data for small values of the Mandelstam variable $u$, in contrast to previous analyses. The model amplitude is used to obtain evidence for baryon resonances with mass below 3 GeV. Our analysis suggests a $G_{39}$ resonance with a mass of 2.83 GeV as member of the $Δ_β$ trajectory from the corresponding Chew-Frautschi plot.

nucl-th↗
arXiv2009

Charmed Exotics

These are the mini-proceedings of the CHARMEX workshop. The meeting focused on recent developments in charm spectroscopy, especially on the possible role of the states that do not fit into the quark model classification, the so-called exotic states. The goal of this write-up is to provide the community with a short summary of the individual talks as well as a comprehensive, up-to-date list of relevant references.

hep-ph↗
arXiv2009

Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics.

nucl-ex↗
arXiv2009

Neutral pion photoproduction at high energies

A Regge model with absorptive corrections is employed in a global analysis of the world data on the reactions gamma p -> pi0 p and gamma n -> pi0 n for photon energies from 3 to 18 GeV. In this region resonance contributions are expected to be negligible so that the available experimental information on differential cross sections and single- and double polarization observables at -t < 2 GeV^2 allows us to determine the non-resonant part of the reaction amplitude reliably. The model amplitude is then used to predict observables for photon energies below 3 GeV. A detailed comparison with recent data from the CLAS and CB-ELSA Collaborations in that energy region is presented. Furthermore, the prospects for determining the pi0 radiative decay width via the Primakoff effect from the reaction gamma p -> pi0 p are explored.

hep-ph↗