Experiments we are involved
Overall
Our group is focused on a specific branch of particle physics, namely hadron physics. Its main purpose is the study of the strong interaction among quarks and gluons, which is described by quantum chromodynamics (QCD). According to current scientific knowledge, these particles are the fundamental building blocks of mesons and baryons. One method to study the strong interaction is via so-called formation experiments. In such processes, one (or more) of the constituent quarks are excited. The excited meson/baryon may form an intermediate resonant state with unique properties such as mass, width and quantum numbers J
P.
Hardware
In order to analyse those resonant states, the remnants of the reaction have to be detected. For this purpose we are involved in the development/improvement of particle detectors for baryon spectroscopy. This embraces the development and upgrade of readout and trigger electronics, slowcontrol as well as the data acquisition.
Analysis
The collected data is first of all calibrated in order to assign each detected particle an energy and time information (along with the flight direction). This enables us e.g. to reconstruct the four momentum of the photons that are detected in the electromagnetic calorimeters. A look at the two photon invariant mass spectrum shows the π0, η, (ω) and η' mesons. During the task of analyzing the data, the desired reaction is selected and signal and background contributions are studied using Monte Carlo simulations. For this purpose, it is important to simulate the geometry of all detector components as accurate as possible. After the selection process, unpolarized and polarized cross sections, asymmetries are extracted from the data.
Interpretation
In order to study the quantum mechanical interaction of initial and final state, and thus learn more about the strong interaction, partial wave analysis (PWA) has to be employed. Its aim is the reconstruction of all complex scattering amplitudes, and thus the matrix element M, from experimental data. However, a full PWA is highly complex, time consuming and model-dependent. Within our group an alternative approach is studied, the so-called truncated partial wave analysis (TPWA). Here, the infinite partial wave expansion is truncated at some appropriate finite angular momentum l
max where all higher partial waves vanish to a good approximation. Compared to a full PWA the TPWA is a straightforward analysis. Furthermore, due to the truncation of the partial wave expansion, the TPWA is completely model-independent.
