Narrow Results

High-precision measurements of the proton-deuteron elastic and break-up reaction have been performed in the past at KVI and elsewhere with the aim to study three-nucleon force (3NF) effects. In the present work, we explored 3NF effects in the break-up scattering process by performing a measurement of vector analyzing powers and differential cross sections using a 135 MeV polarized-proton beam impinging on a liquid-deuterium target. For this study, we used a new experimental setup, Big Instrument for Nuclear-polarization Analysis, BINA, which covers almost the entire kinematical phase space of the break-up reaction. The results are interpreted with the help of state-of-the-art Faddeev calculations.

One of the experimental programs at the TOF spectrometer located at the COSY-accelerator (Forschungszentrum Jülich, Germany) is the study of ω-meson production in proton proton collisions (pp → ppω). Recently, a measurement was performed with a polarized beam at an excess energy of ∊ = 129 MeV, which offers the possibility to analyze polarization observables of this reaction channel for the first time. The analyzing power (A_y) of the pp → ppω-reaction was determined to be compatible with zero.

The proton analysing power in $\overrightarrow{p}p$ elastic scattering has been measured at small angles at COSY-ANKE at 796MeV and five other beam energies between 1.6 and 2.4GeV using a polarized proton beam. The asymmetries obtained by detecting the fast proton in the ANKE forward detector or the slow recoil proton in a silicon tracking telescope are completely consistent. The sources of the systematic uncertainties and the time stability issue were considered. The ANKE data at the higher energies lie well above the predictions of the most recent partial wave solution at small angles. An updated phase shift analysis that uses the ANKE results together with the World data leads to a better description of these new measurements.

The quasi-free np charge-exchange reaction $p\overrightarrow{d}\to {\{pp\}}_{s}n$ has to be employed to extend the investigations of np scattering at ANKE to the highest energy available at COSY. As the proof-of-principle experiment, the initial research has been conducted at proton energy $T_p=600$ MeV using a polarized Deuterium target. The vector and tensor analyzing powers $A_y$ and $A_{yy}$ were measured for momentum transfers $q⩾160$ MeV/c. These data connect smoothly with the previous measurements at $q⩽140$ MeV/c performed using a polarized deuteron beam. The reported data are well reproduced by the impulse approximation using the SAID np amplitudes. The results therefore proves that it is possible to continue the np programme at higher energies at ANKE.

Systems composed of a few nucleons are subject of experimental studies for many years with the aim to gain precise information on the interaction between nucleons. Intermediate energies, below the threshold for pion production, deserve special attention: it is a region where comparison with exact theoretical calculations is possible, while the sensitivity to various aspects of interaction, like subtle effects of the dynamics beyond the pairwise nucleon-nucleon force, is significant. In addition to differential cross section, the observables related to nuclear polarization are studied, like vector and tensor analyzing powers, spin-correlation coefficients or polarization transfer coefficients. A brief survey of results of recent studies in few-nucleon systems is given.

Spin-dependent asymmetry was measured for the elastic scattering at 71 MeV/nucleon making use of a solid polarized proton target specially designed for radioactive ion beam experiments. Absolute values of the analyzing power were deduced for the first time from the measured asymmetry and from the target polarization determined via the elastic scattering at 80 MeV/nucleon. Large discrepancy was found between obtained analyzing power data and predictions of g-matrix folding model.

The vector analyzing power has been measured for the elastic scattering of neutron-rich ⁶He from polarized protons at 71 MeV/A making use of a newly constructed solid polarized proton target operated in a low magnetic eld of 0.1 T and at a relatively high temperature of 100 K. An optical model analysis revealed that the spin-orbit potential for ⁶He is characterized by shallow and long-ranged shape compared with the global systematics of stable nuclei. Such a characteristics re ect a di used density distribution of the neutron-rich isotopes.