Analysis of J/ψ→φηη at BESIII and Calibration of the Temperature Monitoring System for the PANDA Electromagnetic Calorimeter
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Monday, 13 May, 2019
The present thesis comprises two parts, in the first part a data sample of 1.31 billion J/ψ events recorded by the BESIII experiment has been used to analyze the hadronic decay J/ψ → φηη and in the second part calibration measurements of the temperature monitoring system for the electormagnetic calorimeter of the PANDA target spectrometer are evaluated. Events of this decay pattern J/ψ → φηη with a final state consisting of a pair of charged kaons and four photons have been selected with an efficiency of about 12.5%. A partial wave analysis was performed with the PAWIAN softwarte and the information criteria BIC and AIC were used in an iterative approach to determine the hypotheses which optimally describe the data. The dynamics of scalar contributions are parameterized by a K-matrix with fixed pole positions and coupling strengths according to previous measurements. Utilizing Breit-Wigner functions to parameterize the dynamics of all other resonances, the hypothesis consisting of a (ππ) S-wave contribution as well as f2'(1525), f2(1810), ω2(1975), φ(1690), and h1(2215) resonances yields the best results. Additionally, hypotheses which use a K-matrix with released pole positions and coupling strengths to parameterize the dynamics of tensor contributions are tested. Scattering data from different measurements are used to constrain the K-matrix to reasonable parameter values. The best result is obtained for the hypothesis consisting of a K-matrix with three poles, (ππ) S-wave, ω2(1975), φ(1680), and h1(1965) contributions. Product branching fractions are determined for all contributions, most of them for the first time. For the f2'(1525) resonance, the branching fraction B(J/ψ → φ f2'(1525)) = (10.5 ± 0.6 stat ± 2.3 sys ) · 10^−4 is obtained, which is compatible with the result obtained by DM2 but not with the only other published value obtained by MARKII. The electromagnetic calorimeter of the PANDA detector, which is currently under construction and will start data taking in 2025, is based on lead tungstate crystal scintillators. The operating temperature is chosen to be −25 °C in order to increase the light yield. To ensure the envisaged energy resolution, the temperature must be regulated precisely and monitored with a relative accuracy of 0.02 °C. Customized sensors and dedicated readout electronics have been developed to fulfill the strong requirements and are produced at Ruhr-Universität Bochum. Within the scope of this thesis numerous instances of both sensors and electronics have been calibrated to obtain an accurate readout chain. The hysteresis effect of the temperature sensors is taken into account by fitting the corresponding subsamples separately. The RMS of the differences between these fits and the data typically yields 0.01 °C. The typical hysteresis at −25 °C amounts to 0.03 °C. Several dedicated measurements have been performed to characterize the hysteresis effect. Furthermore, measures are taken to increase the production rate of accurate and reliable sensors and to obtain a high calibration throughput. The readout electronics, called THMP, is designed modularly so that it can read out several kinds of sensors, in particular resistance temperature sensors. Evaluating the calibrations of 10 devices with 64 readout channels each, a typical resistance uncertainty of 4 mΩ is determined, which is by a factor of two better than the design requirement. The reproducibility of the THMP calibrations is in the order of the requirement.