\panda is a planned experiment at FAIR (Darmstadt) with a cooled antiproton beam in a range [1.5; 15] GeV/$c$, allowing a wide physics program in nuclear and particle physics. It is the only experiment worldwide, which combines a solenoid field (B=2T) and a dipole field (B=2Tm) in a spectrometer with a fixed target topology, in that energy regime. The tracking system of \panda involves the presence of a high performance silicon vertex detector, a GEM detector, a Straw- Tubes central tracker, a forward tracking system, and a luminosity monitor. The offline tracking algorithm is developed within the PandaRoot framework, which is a part of the FairRoot project. The tool here presented is based on algorithms containing the Kalman Filter equations and a deterministic annealing filter. This general fitting tool (GENFIT2) offers to users also a Runge-Kutta track representation, and interfaces with Millepede II (useful for alignment) and RAVE (vertex finder). It is independent on the detector geometry and the B field map, and written in C++ o.o. modular code. Several fitting algorithms are available with GENFIT2, with user-adjustable parameters; therefore the tool is of friendly usage. A check on the fit convergence is done by GENFIT2 as well. The Kalman-Filter-based algorithms have a wide range of applications; among those in particle physics they can perform extrapolations of track parameters and covariance matrices. The impact of GENFIT2 on physics simulations performed for the \panda experiment is shown, with the PandaRoot framework: significant improvement is reported for those channels where a good low momentum tracking is required ($\rm{p_T} <$ 400 MeV/$c$

The non-perturbative nature of the strong interaction leads to spectacular phenomena, such as the formation of hadronic matter, color confinement, and the generation of the mass of visible matter. To get deeper insight into the underlying mechanisms remains one of the most challenging tasks within the field of subatomic physics. The antiProton ANnihilations at DArmstadt (${\bar{\rm P}}$ANDA) collaboration has the ambition to address key questions in this field by exploiting a cooled beam of antiprotons at the High-Energy Storage Ring (HESR) at the future Facility for Antiproton and Ion Research (FAIR) combined with a state-of-the-art and versatile detector. In this contribution, I will address some of the unique features of ${\bar{\rm P}}$ANDA that give rise to a promising physics program together with state-of-the-art technological developments.

The present thesis comprises two parts, the first of which deals with the analysis of data recorded by the BESIII experiment at the symmetric electron-positron collider BEPCII located in Beijing, China. A data set of 1.31 · 10^9 recorded J/ψ events has been analyzed to study the radiative decay J/ψ → γωω. Both ω mesons were reconstructed via their decay into π^+ π^− π^0 . A clean sample of 75245 ± 274 events was retained after the application of an event-based back- ground subtraction method. Prominent enhancements located at the ωω mass threshold and at the mass of the η_c (1S) are observed in the invariant mass spectrum of the ωω system; no resonant structures are observed in the γω system. The selected data set was subjected to a full partial wave analysis, for which two strategies were employed: A model independent partial wave analysis in slices of the invariant ωω mass revealed that the ωω system is dominated by pseudoscalar (0^−+ ) contributions. This assignment also holds for both enhancements discussed above. Additionally, significant scalar (0^++ ) and tensor (2^++ ) contributions in the region below 2.3 GeV/c^2 were found. Based on these results, three main contributions were considered in a model dependent analysis, where the K- matrix formalism was employed for the description of the decay dynamics. As the result of an iterative approach, a good description of the data was achieved using parameteriza- tions containing five poles for the pseudoscalar (η(1760), X(1835), η(2225), X(2500), η c ), and two poles for each of the scalar (f_0 (1710), f_0 (2020)) and tensor (f_2 (1640), f_2 (1950)) contributions, respectively. The branching fraction for the decay J/ψ → γωω was deter- mined to be B(J/ψ → γωω) = (2.50 ± 0.01 stat ± 0.16 syst ) · 10^−3 . In a dedicated analysis step, the branching fraction of the decay η_c → ωω was measured for the first time as a part of this thesis and amounts to B(η_c → ωω) = (1.88±0.09 stat. ±0.17 syst. ±0.44 ext. )·10^−3 . In the second part, studies to facilitate the construction of the electromagnetic calorimeter of the PANDA detector at the antiproton storage ring HESR are presented. The PANDA experiment is to be built as a part of the future FAIR facility near Darmstadt, Germany. The production of close-to-final sub-modules for the forward endcap of the calorimeter is presented and the assembly of photodetector-preamplifier units is discussed. These units are equipped with a Vacuum Photo Tetrode or two Avalanche Photo Diodes, each, to detect scintillation light from lead tungstate crystals. The calorimeter modules were tested during various test beam times with a prototype setup, utilizing electron and tagged photon beams in the energy range between 23 and 15000 MeV. The energy resolution of symmetric crystal matrices was determined to be σ_E/E = (2.41±0.02)%⊕ (0.86 ± 0.02)% / sqrt(E[GeV ]) the analysis of the test beam data.