PhD ceremony Mr. D. Zhou: Partial-wave analysis and spin observables of antiproton-proton scattering

PhD ceremony: Mr. D. Zhou, 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Partial-wave analysis and spin observables of antiproton-proton scattering

Promotor(s): prof. R.G.E. Timmermans

Faculty: Mathematics and Natural Sciences

Motivated by renewed experimental interest in low-energy antiproton-proton scattering, we developed a new partial-wave analysis of all antiproton-proton elastic and charge- exchange scattering data below 925 MeV/ c antiproton laboratory momentum.

The theoretical input was improved by using for the long-range interaction, next to the electromagnetic potential, the charge-conjugated one- and two-pion exchange potential derived from the effective chiral Lagrangian of QCD. The short-range interactions, including the coupling to annihilation channels, are parametrized by a complex boundary condition at a radius of 1 . 2 fm. The database contains 3749 data points; the minimum X ² per degree of freedom is X ² _min /N _df = 1 . 048. The description of the experimental data is excellent.

The polarization of a circulating antiproton beam scattered by a polarized proton target was studied. In a reasonable time, the maximal transverse polarization reaches between − 20% and 5%, while the longitudinal polarization is between − 3% and 6%. Predictions for unmeasured spin observables up to rank-two were given. In the charge- exchange case, the values of the polarization-transfer parameters R ^′ _t and A _t are large for the very forward angles at low energies. This characteristic may be exploited to produce polarized antineutrons.

Additional spin data can further improve the analysis, provided they are precise enough. It will be interesting to generalize the methods developed here to higher energies, to search for quark-gluon states predicted by nonperturbative QCD.