PhD ceremony: M. Eslamikalantari, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen
Thesis: Three-nucleon force effects in proton-deuteron studied with BINA at 135 MeV
Promotor(s): prof. N. Kalantar-Nayestanaki
Faculty: Mathematics and Natural Sciences
In the past two decades, several high-quality models were developed describing the force between two nucleons. To a large extent, their force can be understood as the exchange of light particles known as mesons. These phenomenologically driven models describe the phenomena involving two nucleons very well. However, exact calculations for systems with more than two nucleons fail to describe the experimental data. The most pronounced discrepancy has been observed in the binding energy of light nuclei, which existing models clearly underestimate. The missing ingredient is often called the three-nucleon force. Its existence is supported by meson-exchange and quantum-field theoretical models. In 1998 a program started at KVI to systematically study the three-nucleon force effects in three-nucleon scattering processes. In 2004, a new generation of breakup measurements were carried out using a new detection system with the name Big Instrument for Nuclear-polarization Analysis, BINA. It enabled us to perform experiments at intermediate energies of up to 200 MeV/nucleon. The first experiment with BINA was performed in 2005 with a polarized proton beam of 190 MeV. The results of that experiment will soon be published and showed that in some parts of the phase space, the deficiency increases even further when the three-nucleon force was added. In 2006, the p + d -> p + p + n reaction was studied using BINA at an energy of 135 MeV. Comparison between the experimental polarization observables and the theoretical calculations show a systematic deficiency when the scattered protons move relatively close to each other, which corresponds to small relative energies. Since the polarization observables are, in general, not sensitive to three-nucleon force effects, we suspect that this discrepancy stems from effects that are not included in the present models. This thesis shows that there is room for more developments based on theoretical considerations in the construction of the three-nucleon force.
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