Searcharxiv⌕ Search

arXiv subjects

S. Wycech

Publications and source records attributed to S. Wycech.

At least 19 recordsLinked to original sources
arXiv2020

Extraction of baryonia from the lightest anti-protonic atoms

Anti-protonic hydrogen and helium atoms are analyzed. Level shifts and width are expressed in terms of $\bar{p}$-nucleon sub-threshold scattering lengths and volumes. Experimental data are compared to results obtained from the 2009 version of the Paris $N\bar{N}$ interaction potential. Comparison with 1999 version is also made. Effects of $N\bar{N}$ quasi-bound states are discussed. Atomic 2P hyperfine structure is calculated for antiprotonic deuterium and the significance of new measurements is indicated.

nucl-th↗
arXiv2019

K$^-$ multi-nucleon absorption cross sections and branching ratios in $Λ$p and $Σ^0$p final states

The determination of low-energy cross sections and branching ratios of the K$^-$ multi-nucleon absorption processes in $Λ$p and $Σ^0$p final states performed by the AMADEUS collaboration is presented. Low momentum K$^-$ ($p_\mathrm{K} \simeq$ 127 MeV/c) produced at the DA$Φ$NE collider are impinged on a Carbon target within the KLOE detector and the two and three nucleon absorption processes are disentangled by comparing the experimental data to phenomenological calculations. The $Λ$p spectra are interpreted in terms of K$^-$ multi-nucleon absorption processes; the possible contribution of a K$^-$pp bound state is demonstrated to overlap with the two nucleon capture process, its absolute yield thus resulting indistinguishable.

nucl-ex↗
arXiv2018

Photon or meson formation in $J/ψ$ decays into $p {\overline{p}}$

The measurements of the $J/ψ\rightarrow γp \overline{p}$ decays by the BES Collaboration indicate an enhancement at the $p \overline{p}$ threshold which, however, is not present in the J/$ψ$ decays into $ωp \overline{p}$ and into $πp \overline{p}$. Here, two processes for describing the decays $J/ψ\rightarrow \mathcal{B} p \overline{p}$ where $\mathcal{B} = γ, ω$ are presented in some detail and the cases $\mathcal{B} =ϕ, π$ are briefly touched on. The first one, applied not only to the radiative decay to reproduce the threshold peak but also to the $ωp \overline{p}$ decay channel to improve the description of the spectrum, postulates a direct emission of the boson before the baryon pair is formed. The second process assumes that the boson $\mathcal{B}$ is emitted from the baryon pair following the $J/ψ$ decay and includes for the decays into $γp \overline{p}$ a final state nucleon-antinucleon interaction based on the Paris $N \overline{N}$ potential. The reproduction of the $p \overline{p}$ distribution in the $J/ψ\rightarrow ωp \overline{p}$ decays needs a final state interaction involving a $N(2050)\ 3/2^-$ resonance. The photon- and meson-emission rates are reproduced in a semi-quantitative way.

hep-ph↗
arXiv2017

Antikaon Interactions with Nucleons and Nuclei - AMADEUS At Da$Φ$ne

The aim of AMADEUS is to provide unprecedented experimental information on K$^-$ absorption in light nuclear targets, to face major open problems in hadron nuclear physics in the strangeness sector, namely the nature of the $Λ$(1405), strongly related to the possible existence of kaonic nuclear clusters, kaons and hyperon scattering cross sections on nucleons and nuclei. These issues are fundamental for a better understanding of the non-perturbative QCD in the strangeness sector. AMADEUS step 0 deals with the analysis of the 2004-2005 KLOE collected data. The interactions of the negative kaons produced by the DA$Φ$NE collider (a unique source of monochromatic low-momentum kaons) with the materials of the KLOE detector, used as active targets, provide samples of K$^-$ absorptions on H, ${}^4$He, ${}^{9}$Be and ${}^{12}$C, both at-rest and in-flight. A second step deals with the data from the implementation in the central region of the KLOE detector of a pure graphite target, providing a high statistic sample of K$^- \, {}^{12}$C nuclear captures at rest. For the future a new setup, with various dedicated gaseous and solid targets, is under preparation.

nucl-ex↗
arXiv2015

K$^-$ absorption on two nucleons and ppK$^-$ bound state search in the $Σ^0$p final state

We report the measurement of K$^-$ absorption processes in the $Σ^0$p final state and the first exclusive measurement of the two nucleon absorption (2NA) with the KLOE detector. The 2NA process without further interactions is found to be 12\% of the sum of all other contributing processes, including absorption on three and more nucleons or 2NA followed by final state interactions with the residual nucleons. We also determine the possible contribution of the ppK$^-$ bound state to the $Σ^0$p final state. A yield of ppK$^- /\mathrm{K^-_{stop}}$ is found to be $(0.044 \pm 0.009\, stat ^{+ 0.004} _{- 0.005} \,syst) \cdot 10^{-2}$ but its statistical significance based on an F-test is only 1$σ$.

nucl-ex↗
arXiv2015

Antinucleon-nucleus interaction near threshold from the Paris $\bar NN$ potential

A general algorithm for handling the energy dependence of hadron-nucleon amplitudes in the nuclear medium, consistently with their density dependence, has been recently applied to antikaons, eta mesons and pions interacting with nuclei. Here we apply this approach to antiprotons below threshold, analyzing experimental results for antiprotonic atoms across the periodic table. It is also applied to antiproton and antineutron interaction with nuclei up to 400 MeV/c, comparing with elastic scattering and annihilation cross sections. The underlying $\bar pN$ scattering amplitudes are derived from the Paris $\bar NN$ potential, including modifications in the medium. Emphasis is placed on the role of the $P$-wave amplitudes with respect to the repulsive $S$-wave amplitudes.

nucl-th↗
arXiv2015

Baryonium, a common ground for atomic and high energy physics

Indications of the existence of quasi-bound states in the N-Nbar system are presented. Measurements by BES discovered a broad enhancement close to the p-pbar threshold in the S wave, isospin 0 state formed in radiative decays of J/psi. Another enhancement located about 50 MeV below the threshold was found in mesonic decays of J/psi. In terms of the Paris potential model it was shown that these are likely to represent the same state. Antiprotonic atomic data provide some support for this interpretation and indicate the existence of another fairly narrow quasi-bound state in a P wave.

nucl-th↗
arXiv2011

Probing the nuclide 180W for neutrinoless double-electron capture exploration

The mass difference of the nuclides 180W and 180Hf has been measured with the Penning-trap mass spectrometer SHIPTRAP to investigate 180W as a possible candidate for the search for neutrinoless doubleelectron capture. The Q-value was measured to 143.20(27)keV. This value in combination with the calculations of the atomic electron wave functions and other parameters results in a half-life of the 0+ \rightarrow 0+ ground-state to ground-state double-electron capture transition of approximately 5\cdot10E27 years/ ^2.

nucl-ex↗
arXiv2010

K-Mesic Nuclei Versus eta -Mesic Nuclei

The nuclear states of \bar K and ηare bound by a similar mechanism - the excitations of nucleons to Λ(1405) and N*(1535) resonant states. The observed large differences in binding energies are understood in terms of separation of the involved energies and the resonance positions. The other experimental findings: broad \bar K-mesic and narrow η-mesic states are more difficult to understand. A phenomenological model for η-N interactions is used to explain the suppression of the ηabsorption in light nuclei.

nucl-th↗
arXiv2009

On the structure of the X(1835) baryonium

The measurement by the BES collaboration of J/psi -> gamma p pbar decays indicates an enhancement at the p-pbar threshold. In another experiment BES finds a peak in the invariant mass of pi-mesons produced in the possibly related decay J/psi -> gamma pi+ pi- eta'. Using a semi-phenomenological potential model which describes all the N-Nbar scattering data, we show that the explanation of both effects may be given by a broad quasi-bound state in the spin and isospin singlet S wave. The structure of the observed peak is due to an interference of this quasi-bound state with a background amplitude and depends on the annihilation mechanism.

nucl-th↗
arXiv2009

Paris nucleon-antinucleon potential constrained by recent antiprotonic-atom data and antineutron-proton total cross sections

We report on an updated Paris nucleon-antinucleon optical potential. The long- and intermediate-range real parts are obtained by G-parity transformation of the Paris nucleon-nucleon potential based on a theoretical dispersion-relation treatment of the correlated and uncorrelated two-pion exchange. The short-range imaginary potential parametrization results from the calculation of the nucleon-antinucleon annihilation box diagram into two mesons with a nucleon-antinucleon intermediate state in the crossed channel. The parametrized real and imaginary short range parts are determined by fitting not only the existing experimental data included in the 1999 version of the Paris nucleon-antinucleon potential, but also the recent antiprotonic-hydrogen data and antineutron-proton total cross sections. The description of these new observables is improved. Only this readjusted potential generates an isospin zero 1S0, 52 MeV broad quasibound state at 4.8 MeV below the threshold. Recent BES data on J/psi decays could support the existence of such a state.

nucl-th↗
arXiv2008

Variational calculations for K-few-nucleon systems

Deeply bound KNN, KNNN and KNNNN states are discussed. The effective force exerted by the K meson on the nucleons is calculated with static nucleons. Next the binding energies are obtained by solving the Schrodinger equation or by variational calculations. The dominant attraction comes from the S-wave Lambda(1405) and an additional contribution is due to Sigma(1385). The latter state is formed at the nuclear peripheries and absorbs a sizable piece of the binding energy. It also generates new branches of quasi-bound states. The lowest binding energies based on a phenomenological KN input fall into the 40-80 MeV range for KNN, 90-150 MeV for KNNN and 120-220 MeV for K-alpha systems. The uncertainties are due to unknown KN interactions in the distant subthreshold energy region.

nucl-th↗
arXiv2007

Neutron density distributions from antiprotonic 208Pb and 209Bi atoms

The X-ray cascade from antiprotonic atoms was studied for 208Pb and 209Bi. Widths and shifts of the levels due to the strong interaction were determined. Using modern antiproton-nucleus optical potentials the neutron densities in the nuclear periphery were deduced. Assuming two parameter Fermi distributions (2pF) describing the proton and neutron densities the neutron rms radii were deduced for both nuclei. The difference of neutron and proton rms radii /\r_np equal to 0.16 +-(0.02)_{stat} +- (0.04)_{syst} fm for 208Pb and 0.14 +- (0.04)_{stat} +- (0.04)_{syst} fm for 209Bi were determined and the assigned systematic errors are discussed. The /\r_np values and the deduced shapes of the neutron distributions are compared with mean field model calculations.

nucl-ex↗
arXiv2007

Nuclear surface studies with antiprotonic atom X-rays

The recent and older level shifts and widths in pbar atoms are analyzed. The results are fitted by an antiproton-nucleus optical potential with two basic complex strength parameters. These parameters are related to average S and P wave scattering parameters in the subthreshold energy region. A fair consistency of the X-ray data for all Z values, stopping pbar data and the Nbar-N scattering data has been achieved. The determination of neutron density profiles at the nuclear surface is undertaken, and the determination of the neutron R_{rms} radii is attempted. Uncertainties due to the input data and the procedure are discussed.

nucl-th↗
arXiv2005

Antiproton-Proton Channels in J/psi Decays

The recent measurements by the BES Collaboration of J/psi decays into a photon and a proton-antiproton pair indicate a strong enhancement at the proton-antiproton threshold not observed in the decays into a neutral pion and a proton-antiproton pair. Is this enhancement due to a proton-antiproton quasi-bound state or a baryonium? A natural explanation follows from a traditional model of proton-antiproton interactions based on G-parity transformation. The observed proton-antiproton structure is due to a strong attraction in the 1S0 state, and possibly to a near-threshold quasi-bound state in the 11S0 wave.

hep-ph↗
arXiv2005

The antinucleon-nucleon quasi-bound states: J/psi and atomic evidence

The measurements of J/psi decays into photon, proton and antiproton show a strong enhancement at the proton-antiproton threshold not seen in the decays into neutral pion, proton and antiproton. What is the nature of this enhancement? A natural interpretation can be performed in terms of a classical model of nucleon-antinucleon interactions based on G-parity transformation. The observed proton-antiproton structure is the consequence of the strong attraction in the singlet S-wave state related predominantly to pion exchanges. Similar attractions generate near threshold: an isospin-zero virtual (or quasi-bound) state in singlet S-wave, an isospin-one quasi-bound state in triplet P-wave with total angular momentum one and an isospin-zero resonance in triplet P-wave with total angular momentum zero. These P-wave structures find support in the antiproton-atomic data.

hep-ph↗
arXiv2005

The physical interest in kaonic- and antiprotonic-deuterium atoms

Exotic deuterium and helium are discussed. The S, P and D levels of antiprotonic and kaonic atoms are calculated. Absorptive, subthreshold antiproton-nucleon amplitudes are extracted from experimental data and compared to model calculations. The existence of a quasi-bound state in the antiproton-nucleon system is indicated. In the kaonic atoms some effects of the Sigma(1385) resonance are evaluated.

nucl-th↗