K. Ermisch

Systematic study of three-nucleon force effects in the cross section of the deuteron-proton breakup at 130 MeV

High-precision cross-section data of the deuteron-proton breakup reaction at 130 MeV are presented for 72 kinematically complete configurations. The data cover a large region of the available phase space, divided into a systematic grid of kinematical variables. They are compared with theoretical predictions, in which the full dynamics of the three-nucleon (3N) system is obtained in three different ways: realistic nucleon-nucleon (NN) potentials are combined with model 3N forces (3NFs) or with an effective 3NF resulting from explicit treatment of the Delta-isobar excitation. Alternatively, the chiral perturbation theory approach is used at the next-to-next-to-leading order with all relevant NN and 3N contributions taken into account. The generated dynamics is then applied to calculate cross-section values by rigorous solution of the 3N Faddeev equations. The comparison of the calculated cross sections with the experimental data shows a clear preference for the predictions in which the 3NFs are included. The majority of the experimental data points are well reproduced by the theoretical predictions. The remaining discrepancies are investigated by inspecting cross sections integrated over certain kinematical variables. The procedure of global comparisons leads to establishing regularities in disagreements between the experimental data and the theoretically predicted values of the cross sections. They indicate deficiencies still present in the assumed models of the 3N system dynamics.

Systematic investigation of the elastic proton-deuteron differential cross section at intermediate energies

To investigate the importance of three-nucleon forces (3NF) systematically over a broad range of intermediate energies, the differential cross sections of elastic proton-deuteron scattering have been measured at proton bombarding energies of 108, 120, 135, 150, 170, and 190 MeV at c.m. angles between 30degrees and 170degrees . Comparisons with Faddeev calculations show unambiguously the shortcomings of calculations employing only two-body forces and the necessity of including 3NF. They also show the limitations of the latest few-nucleon calculations at backward angles, especially at higher beam energies. Some of these discrepancies could be partially due to relativistic effects. Data at lowest energy are also compared with a recent calculation based on chiPT .

Performance of the KVI in-beam polarimeter

A beam polarimeter for medium-energy protons and deuterons has been constructed. Its operation is based on the elastic-scattering reactions (p) over right arrow + p or (d) over right arrow + p. The outgoing particles are detected in kinematical coincidence in four independent reaction planes, each equipped with two pairs of phoswich detectors

Three-nucleon force effects in the dp-breakup at 130 MeV

Indications for three nucleon force (3NF) effects in PJd elastic scattering and in specific kinematical configurations of the deuteron breakup reaction became motivation for complex studies of the three nucleon system dynamics in the dp breakup process over a broad region of phase-space. A dedicated experiment is aimed at precise determination of cross sections and both vector and tenser analyzing powers for the H-1((p) over right arrow pp)n breakup reaction at 130 MeV deuteron beam energy. The experiment, employs a position-sensitive detection system covering a large solid angle and allowing for excellent particle identification. The first data taking run has been completed and the accumulated data are being analyzed. The results will be compared with the rigorous calculations within the Faddeev formalism, including various nucleon-nucleon potentials and 3NF models.

Investigation of effects beyond two-body forces in three-nucleon systems

An experiment has been performed at KVI to measure vector analyzing powers and differential cross sections of the D((p) over right arrow pd) reaction as a function of incident beam energy. The measurements have been performed so far at several kinetic energies of the incoming particle between 108 MeV and 170 MeV. In this contribution, the preliminary results for the vector analyzing power A(y) will be presented.

Cross sections of the deuteron‐proton breakup at 130 MeV

Comparison of the cross sections measured over a large part of the phase space of the deuteron‐proton breakup at 130 MeV with the results of rigorous, Faddeev‐like calculations is presented. Global analysis, including nearly 1200 data points, reveals a better agreement for theoretical predictions which include three‐nucleon force (3NF) model over the results obtained with only nucleon‐nucleon realistic potentials. A possible way to probe details of the 3NF models via studying “non‐standard” projections of the multi‐dimensional phase space is envisaged.

Proton-proton bremsstrahlung towards the elastic limit

In oder to study proton‐proton bremsstrahlung moving towards the elastic limit, a detection system, consisting of Plastic‐ball and SALAD, was set up and an experiment at 190 MeV incident beam energy was performed. Here, the experimental setup and the data analysis procedure along with some results obtained in the measurement are discussed.

Dilepton and double-photon production in proton-proton scattering at 190 MeV

The first high-statistics measurement of dilepton and double-photon yields in proton—proton scattering below the pion threshold has been performed. The data obtained allow a detailed study of off-shell effects in the proton—proton interaction.

Three-Nucleon Dynamics Studied via 1 H ( d, pp) n Breakup at 130 MeV

An experiment to measure cross sections and both, vector and tensor analyzing powers, for the 1H(d,pp)n breakup reaction at 130 MeV deuteron beam energy is presented. Employing a position-sensitive detection system covering a large solid angle enables probing of a significant part of the whole phase space. First results are presented and compared with the rigorous Faddeev calculations using modern NN and 3NF potentials.

Virtual Bremsstrahlung in Proton-Proton Scattering

The virtual bremsstrahlung process, in addition to the real photon bremsstrahlung, provides an elaborate tool for studying the nucleon-nucleon interaction. The additional degree of freedom which exists in the virtual bremsstrahlung production, a longitudinal polarization of the virtual photon, allows transversal, longitudinal, and interference terms to be studied. The squared transition amplitude for p + p → p + p + e+ + e− can be written [1, 2]: