Submitted by l.capozza on Thu, 06/08/2020 - 14:04.
In recent decades, the quantum field theory of strong interaction (QCD) has been impressively demonstrated in the area of high energies and momentum transfers. Nowadays, novel experiments allow for challenging the methods for the calculation of QCD also in the non-perturbative regime by the continuous improvement of measurement accuracy. PANDA at the upcoming FAIR accelerator facility is one of such experiments. At PANDA, antiprotons with momenta of up to15 GeV/c will be annihilated at a fixed proton target under high luminosities. Among a variety of detector systems, PANDA stands out with its lead tungstate electromagnetic calorimeter (EMC), which is designed to have a wide dynamic range (10 MeVto14.6 GeV) and a relative energy resolution of better than 2.5 % at 1 GeV. The development of the backward part of the PANDA EMC is the first scientific goal of this thesis. Since the development of the backward EMC has progressed so far, it is foreseen for an experiment within the FAIRPhase-0 research programme. It is proposed to measure the double-virtual electromagnetic transition form factor (TFF) of the pion in the Primakoff π0 electroproduction at the Mainz Microtron facility (MAMI). The pion TFF is related via the hadronic light-by-light scattering to the g_μ−2 puzzle. Consequently, the second scientific goal of this thesis are preparatory studies for FAIR Phase-0. The developments of this work resulted in a fully functional prototype calorimeter, which operated stably in numerous tests at MAMI. However, the focus of this work is digital signal processing (DSP) for the PANDA EMC. A specially developed software framework allowed for testing and optimising signal filtering algorithms and parameter extraction methods on realistically simulated signals. Thus, the algorithms are well-adapted to the time structure of the ̄PANDA calorimeter preamplifier (APFEL) signals. Furthermore, the DSP methods were implemented on the Field Programmable Gate Arrays (FPGAs) of the PANDA digitisation board. The developed FPGA firmware provides a self-triggering readout for all calorimeter channels, an efficient implementation of a high order filter with a finite impulse response (FIR), noise hit suppression and pileup handling.Together with the calorimeter prototype, the digital signal processing was tested at MAMI. Thanks to the use of the DSP methods, an energy detection threshold (single-crystal) of less than 2.5 MeV was achieved. This allowed for a measured relative energy resolution of 2.190(2) % at 1 GeV. Moreover, the non-linearity of the calorimeter is in the order of a few per mill. Due to the self-triggering concept of the FPGA firmware,measurements under high detector rates were possible. Thus, a dead time of 464(13) ns and a pileup probability of 4.53(12) % at 100 kHz was determined. For the measurement of the pion TFF, a high flux of low energy electrons and photons is expected. Thus, test beams with the prototype were performed to determine the impact of the low energetic background on the measurement. By utilising both experiment data and simulations, an upper limit for the relative energy resolution (2.75(4) % to 6.57(2) % at 1 GeV) as a function of the luminosity (2.77μb−1/s to 55.34μb−1/s) was found. The study allows an estimation of the FAIR Phase-0 measuring time.
Understanding the excitation pattern of baryons is indispensable for the understanding of non-perturbative QCD. Up to now only the nucleon excitation spectrum has been subject to systematic experimental studies, in contrast very little is known on excited states of double or triple strange baryons. A better knowledge of the baryon spectrum in the double and triple strange sector is however important to scrutinize the models developed using data on N* and Δ states. In studies of antiproton-proton collisions, the P̅ANDA experiment is well-suited for a comprehensive baryon spectroscopy program in the multi-strange and charm sector.
For final states containing a Ξ‾ Ξ̅⁺ pair, cross sections of the order of μb are expected, corresponding to production rates of ~10⁶ /d at a luminosity L = 10³¹ cm‾² s‾¹. The present thesis focuses on excited Ξ states and investigates the possibility to reconstruct the reaction p̅p -> Ξ̅⁺Ξ*‾ and its charged conjugate channel with the P̅ANDA detector. Furthermore, first steps towards a partial wave analysis of the Ξ̅⁺Λ K‾ and Ξ‾Λ̅ K⁺ final states are presented.
The success of cluster-jet targets in hadron, lepton, and laser beam physics depends highlyon their performance. Therefore, a precise determination and optimisation of the targetproperties and understanding of the cluster formation process is essential.Within the work presented in this thesis, investigations and developments for andmeasurements using three different cluster-jet targets were performed: thePANDA cluster-jet target prototype for thePANDA experiment at FAIR, the MCT1S for CryoFlash atthe University of D ̈usseldorf and the jet target MCT-M for MAGIX at MESA.Laval nozzles, as key components of jet targets, originating from production processesdeveloped at the University of M ̈unster are reviewed with respect of their performance andbased upon that their developed processes were further improved yielding an optimisednozzle geometry, production processes, and a deeper insight into the complex clusterformation process.A new record hydrogen target thickness of(4.85±0.24)×10*15 atoms/cm*2 in a distanceof 2.1 m from the nozzle was achieved within this thesis work with thePANDA cluster-jettarget prototype.The high performance, state-of-the-art jet target for MAGIX at MESA was designed,built up, and set into operation. The suitability of a Mach-Zehnder interferometer toinvestigate the jet beam characteristics was shown and a well defined cluster beamwith a high range of constant target thickness of more than 30mmand a thickness of(2.1±0.2)×10*18 atoms/cm*2 directly behind the nozzle was recorded and the resultswere published [G+18]. Beam times at the MAinz MIcrotron results in elastic electron-proton cross sections and the feasibility to perform precise low energy physics like the determination of the proton radius using the jet target.The installation of a cluster-jet target at the high intensity ARCTURUS laser systemof the University of D ̈usseldorf resulted in accelerated protons with energies up to(88.0±14.5) keV, accelerated electrons, and X-rays within the framework of this thesis.Novel in this field is the stability and reproducibility of the accelerated particles. Moreover,a plasma temperature in the range of 1600 K to 4500 K by the cluster-laser interactionwith the U1 laser system was determined by the observation of Balmer spectral lines.Based on these successful results and the gained experience within this thesis, a newpowerful cluster-jet target was designed to perform extended measureme
In high energy particle experiments one is interested in observables that require a transverse target polarization. The particle physics experiment PANDA consists of a detector at the particle accelerator FAIR currently under construction at GSI Helmholtz Centre for Heavy Ion Research, Darmstadt (GSI). The detector requires a high magnetic field in longitudinal direction with respect to the antiproton beam to provide high momentum resolution of the electrically charged particles. For the feasibility of a transverse polarized target in PANDA, it is essential to shield the longitudinal magnetic field.
The ability to shield an intense magnetic flux with a high temperature superconductor BSCCO in form of a shielding tube was investigated experimentally.
A shielding factor was extracted. A measurement of the stability of the shielding in time and a measurement of the residual magnetic
flux density along the axis of the tube was performed. A numerical simulation of the induced current in the shielding tube and the residual magnetic flux density along its axis was developed. The experimental results were compared to the predictions based on the numerical simulation. For the measurements a dedicated apparatus consisting of a cryostat, filled with liquid helium, at a temperature of 4.2 K was developed and constructed at the Helmholtz-Institut Mainz (HIM). The shielding tube was equipped with a movable Hall probe, with a Zero-eld Magnet on top. The external magnetic eld was generated by a purpose-built superconducting solenoid, which can be mounted on top of the shielding tube. An external magnetic flux density of 1 T was applied and shielded with
a shielding factor of at least 3:2 105 with a 95 % confidence level. In a measurement over four days a penetration of it into the shielding tube could
not be observed. The measurement of the residual magnetic flux density along the axis of the tube showed a shielding of the the central region of 80 mm (from total 150 mm shielding tube) up to 1 T. BSCCO is a good shielding material and can be used to shield the high magnetic field within the PANDA spectrometer.
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.