arXiv subjects
Publications and source records attributed to S. Wycech.
The optical potential for the $η$-meson is calculated. This is based on a new determination of a large $η$-N scattering length and recent experiments of $η$ production in two nucleon collisions. These determine the $η$ - nuclear potential well to be about 45 MeV deep and able to support S, P, D and F quasibound states. Some of the higher angular momentum states are fairly narrow and offer a chance of experimental detection.
We extract pole positions for the N(1535) and N(1650) resonances using two different models. The positions are determined from fits to different subsets of the existing $πN\toπN$, $πN\toηN$ and $γp\toηp$ data and found to be 1515(10)--i85(15)MeV and 1660(10)--i65(10)MeV, when the data is described in terms of two poles. Sensitivity to the choice of fitted data is explored. The corresponding $ππ$ and $ηη$ residues of these poles are also extracted.
The coupled eta N, pi N system is described by a K-matrix method. The parameters in this model are adjusted to get an optimal fit to pi N -> pi N, pi N -> eta N and gamma N -> eta N data in an energy range of about 100MeV each side of the eta threshold. In the notation T^(-1)+iq_(eta) = 1/a + (r_0)/2 q^2_(eta) + s q^4_(eta), q_(eta) being the momentum in the eta N center-of-mass, the resulting effective range parameters for eta N scattering are found to be a(fm) = 0.75(4)-i0.27(3), r_0(fm) = -1.50(13)-i0.24(4) and s(fm^3) = -0.10(2)-i0.01(1)
Eta-deuteron scattering lengths are calculated. A summation of the multiple scattering series is carried out and the result is checked against more involved calculations. The necessity to go beyond the fixed nucleon approximation is emphasized. It is shown that a quasibound or virtual state in the $η$-deuteron system may occur within the range of $η$-nucleon scattering lengths suggested by other experiments.
Nuclear capture of antiprotons from atomic states is studied. Partial widths for single nucleon capture events leading to cold residual nuclei are calculated. Recent CERN experiments that compare the neutron and proton captures are analysed. Nuclear density distributions at extreme nuclear surface are calculated and tested against the experimental results.
Nuclear interactions of antiprotons in atomic states are discussed. The total as well as partial widths for single nucleon capture events are calculated. These are compared to the X-ray and recent single nucleon capture data. The rates of the neutron or proton captures test nuclear density distributions at the extreme nuclear surface. Recently found cases of neutron and proton haloes are analysed.
Using multiple scattering theory the scattering lengths of $η$ mesons on helium nuclei are calculated and checked against final state $η$ interactions from the $pd \rightarrow η^3$He and $dd \rightarrow η^4$He reactions. The existence of an $η^4$He quasibound state is indicated.
Estimates are made of the signals to be expected in the production of the exotic atoms Pionium ($π^+π^-$), Kaonium ($K^+K^-$) and also $K^+π^-$ in pp, pd and $e^+e^-$ reactions. Such experiments are now being undertaken or contemplated at CELSIUS, COSY, Indiana and SATURNE.