<p>This diploma thesis presents a preliminary study of the ratio of branching ratio r = BR(η → 3π⁰) / BR(η → π⁺ π^-π⁰). The experimental data used is collected by WASA-at-COSY which is a 4π sr detector optimised to detect light mesons and their decay products and is situated in Jülich, Germany.The focus of the work is to see how different reconstruction methods for the detected particles can alter both the measured values of the  branching ratios and the luminosity dependence of these branching ratios. The results show that for some of the methods, the measured branching ratios have a clear luminosity dependence. Depending on method, the extracted branching ratios vary differently. A few different methods have been studied, so the results provides a qualitative understanding of the behaviour of the measured branching ratios for different luminosities.</p>

We used recent phenomenological form factors to calculate the effect of on-shell two-pion exchange in nucleon-nucleon scattering below the two-pion production threshold. As expected, the contributions of partial wave amplitudes are all negligible. We also noticed that the relativistic spin-operator decomposition of the scattering amplitude is not unique at certain momenta and angles. / Graduation date: 2000

This diploma thesis presents a preliminary study of the ratio of branching ratio r = BR(η → 3π0) / BR(η → π+ π- π0). The experimental data used is collected by WASA-at-COSY which is a 4π sr detector optimised to detect light mesons and their decay products and is situated in Jülich, Germany.The focus of the work is to see how different reconstruction methods for the detected particles can alter both the measured values of the  branching ratios and the luminosity dependence of these branching ratios. The results show that for some of the methods, the measured branching ratios have a clear luminosity dependence. Depending on method, the extracted branching ratios vary differently. A few different methods have been studied, so the results provides a qualitative understanding of the behaviour of the measured branching ratios for different luminosities.

The present study combines modern jet reconstruction algorithms and particle identification (PID) techniques in order to study the enhancement of proton/pion ratio at mid transverse momentum ([mathematical symbols] 1.5 - 4.0 GeV/c) observed in central Au + Au collisions at [mathematical symbols] = 200 GeV. The ratio enhancement is thought to be caused by recombination processes and/or parton fragmentation modification of jets in relativistic heavy ion collisions. The fragmentation modification hypothesis is tested in this analysis by reconstructing and selecting energetic jets presumably biased to fragment outside of the medium created in Au + Au collisions and comparing their particle composition to the recoiling (medium-traversing) jets. The bias assumption is confirmed by comparing jets in central collisions, where the effect of proton/pion enhancement is present, with peripheral ones where no medium effects are expected. The selected jets are reconstructed by using the anti-k[subscript T] algorithm from the modern FASTJET package. The PID in the p[subscript T] region of interest is possible by combining measurements of the particles' energy deposition and velocity from the Time Projection Chamber and the recently installed (2009-2010) Time of Flight detectors at STAR. The acceptance of these detectors, [eta] < 1.0 and full azimuth, make them extraordinary tools for correlation studies. These features allow for the measurement of relative azimuth ([phi] [subscript jet] - [phi] [subscript pion,proton]) distributions by using the selected jet axis in order to disentangle the uncorrelated background present in the high multiplicity heavy ion collisions. The proton/pion ratios in two different centrality bins and p[subscript T] = 1.2 - 3.0 GeV/c are presented for biased (vacuum fragmenting) jets and their recoiling counterparts / text

Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991. / Includes bibliographical references (leaves 135-146).

Thesis (Doctoral)--Justus-Liebig-Universität Giessen, 1981.

Thesis (Ph.D.)--University of California, Berkeley, 1962. / "UC-34 Physics" -t.p. "TID-4500 (17th Ed.)" -t.p. Includes bibliographical references (p. 81-83).

Universiẗat, Diss., 2003--Tübingen.

University, Diss., 2000--Mainz. / Zeichendarstellung im Hauptsacht. teilw. nicht vorlagegemäß wiedergegeben.

Techn. Universiẗat, Diss., 2004--Dresden.