Precision Meson Spectroscopy: Diffractive Production at COMPASS and Development of a GEM-based TPC for PANDA

Meson spectroscopy is a unique way to access Quantum Chromo Dynamics (QCD) and learn about its properties. Due to the non-Abelian structure, QCD predicts new states of matter with gluonic degrees of freedom. In particular q ¯ qg hybrids, which can have spin-exotic quantum numbers forbidden for conventional q ¯ q mesons, are expected to exist. Such states were searched for in the past, mostly in the light-quark sector. However, the experimental situation is still ambiguous and needs to be clarified. Further insights will certainly also come from the heavy-quark spectroscopy. Several new charmonium-like resonances were for example discovered during the last years, which have to be studied in more detail by future experiments to reveal their nature. Diffractive dissociation reactions at COMPASS provide clean access to meson resonances with masses below 2.5 GeV/c2. During a pilot run in 2004 using pion beams on lead targets, a competitive number of −−+ final state events were recorded within a few days of data taking. A full partial wave analysis (PWA) of these data has been performed for this dissertation, concentrating on the kinematic domain of large momentum transfer (t0 2 [0.1, 1.0] GeV2/c2). While well-known mesons are resolved with high quality, also a strong signal consistent with the much disputed hybrid candidate 1(1600) is observed in the spin-exotic JPC = 1−+ partial wave. A Breit-Wigner parameterization yields a mass and width of 1.660+0.010 −0.074 and 0.269+0.063 −0.085 GeV/c2, respectively. In addition, a first PWA of events with small momentum transfer (t0 2 10−3, 10−2 GeV2/c2) has been carried out, yielding several high-mass radial-excitation states. In the future, the PANDA experiment at the FAIR facility will perform highprecision spectroscopy in the charm-sector employing ¯ pp annihilations. Due to its excellent tracking capabilities for charged particles, a time projection chamber (TPC) has been proposed for the central tracker of PANDA. A continuous operation without ion gate is foreseen, which constitutes a novel development in high-rate particle physics experiments. Gas Electron Multiplier (GEM) foils offer an intrinsic ion back-flow suppression combined with high gains, and will therefore be used for gas amplification. A small-size GEM-TPC test chamber has been constructed during this thesis and commissioned using both X-rays and muons from cosmic-ray air-showers. From the latter data, a spatial resolution down to 140 μm has been achieved. The detector has been operated stably for many months with Ar/CO2 (70/30) and at typical gas amplification factors of (5-10)·103