Thesis

Next-generation DIRC detectors, like the PANDA Barrel DIRC, with improved optical designs and better spatial and timing resolution, require correspondingly advanced reconstruction and PID methods. The investigation of the PID performance of two DIRC counters and the evaluation of the reconstruction and PID algorithms form the core of this thesis. Several reconstruction and PID approaches were developed, optimized, and tested using hadronic beam particles, experimental physics events, and Geant simulations. The near-final design of the PANDA Barrel DIRC was evaluated with a prototype in the T9 beamline at CERN in 2018. The analysis finds excellent agreement between the experimental data and the Geant simulations for all reconstruction algorithms. The best PID performance of up to $5.2 \pm 0.2$ s.d. $\pi$/K separation at 3.5 GeV/c, was obtained with a time imaging PID method. The PANDA Barrel DIRC simulation, as well as the reconstruction and PID algorithms, were evaluated using experimental data from the GlueX DIRC as part of the FAIR Phase-0 program. The performance validation was carried out using physics events of the GlueX experiment and simulations. The initial analysis results of the commissioning dataset show a $\pi$/K separation power of up to 3 s.d. at a momentum of 3.0-3.5 GeV/c, obtained using a geometric reconstruction algorithm.

The Barrel Time-of-Flight Detector (B-ToF) is a timing detector for the Panda
experiment which is currently under construction at the Facility for Antiproton and
Ion Research (FAIR) in Darmstadt, Germany. In fixed target p̄p collisions, with
antiprotons accelerated up to a momentum of 15 GeV/c producing a center of mass
energy of up to 5.5 GeV, open questions of hadron physics will be studied. This
effort includes charmonium spectroscopy and the search for exotics and hybrids
as well as the study of hypernuclei and of hadrons in matter. In this context the
B-ToF complements the particle identification information of the DIRC detectors
and provides valuable information for particles in the lower momentum range up
to about 1 GeV/c via relative time-of-flight measurements.
A >1800 mm long transmission line PCB connects the SiPMs on the scintillators
to the front-end electronics and provides mechanical support to the scintillator tiles
acts as the backbone of the detector. In order to determine the best performing
layout three prototype iterations are examined and tested for the crosstalk level and
signal attenuation effects. While the crosstalk is negligible in all design iterations
an amplitude reduction of (11.7 ± 0.5) % is observed for the newest board prototype
using low loss materials. This is well above the attenuation of a standard coaxial
cable. The employed connections lead to a doubling of the signal rise time. The
effect of this on the time resolution is yet to be determined.
To achieve intended functionality a highly granular and efficient detector design
is necessary providing a time resolution of below 100 ps. The detector is made up
of 16 identical sections each carrying 120 scintillating tiles, which are read out by
an array of four SiPMs connected in series.
This work presents time resolution scans using a 90 Sr source over the entire
scintillator surface in order to evaluate the detector performance and determine the
optimal scintillator tile thickness. Comparing four 3 mm to 6 mm thick scintillator
tiles, the measurements show that a 5 mm thick scintillator providing a mean
time resolution of 52.3 ps with a spread of ±5.9 ps over the entire surface, is the
optimal choice for the detector. In addition the performance was verified in test
beam measurements at the T9 beamline at CERN under conditions closer to the
expected conditions in Panda using mixed particle beam mainly containing pions
and kaons. Time resolutions of (55.8 ± 4.3) ps to (80.1 ± 1.5) ps were measured for
detector modules utilizing SiPMs by different manufacturers.

The topic of the following thesis is the investigation of Microchannel-Plate Photomultiplier Tubes (MCP-PMTs) and their suitability for the P̄ANDA experiment. After an introduction to the physical goals of P̄ANDA the setup of the detector will be described. The Cherenkov detectors for particle identification, for which the MCP-PMTs are used, will be discussed in more detail. After this the general functionality and new improvements of the MCP-PMTs will be illustrated. The different measurement methods for the performance parameters will be explained in detail. The results obtained in this thesis show that at least two MCP-PMTs that have been optimized in a long R&D process, the Hamamatsu R13266-07-M64M and the PHOTONIS XP85112/A1-Q-HA, are well suited for the usage in P̄ANDA.

The main focus of this thesis is the investigation of the aging and the measurement of the lifetime of newly developed MCP-PMTs. A critical value for the lifetime is the quantum efficiency, which is measured as a function of the integrated anode charge. An existing lifetime measurement setup has been modified during this work to fit the measurement requirements of the new MCP-PMTs. The lifetime increases significantly when a so-called ALD coating is applied to the MCP pores. This caused the lifetime measurements to get lengthy. With the results of this thesis it can be concluded that this new treatment method leads to an increased lifetime by a factor of 50 − 100 compared to not treated devices. The obtained results are also in agreement with the few measurements obtained at other institutions. Furthermore, it could be shown, that the aging of the photocathode is caused by feedback ions. These ions get accelerated by the electrical field of the PMT and damage the photocathode irreversibly on impact. The ALD coating reduces this flux of feedback ions considerably. Meanwhile, MCP-PMTs are the favored sensors for high energy experiments, which expect a high radiation environment and need a very fast single photon detection that is located in a high magnetic field.

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.

The strong interaction between quarks and gluons is one of the fundamental interactions described by the standard model of particle physics. Systems of quarks bound together by the strong interaction are known as hadrons, of which the proton and the neutron are the most common examples. The theoretical framework of quantum chromodynamics (QCD) is used to describe the strong interaction, but becomes increasingly difficult to use as the distance between the interacting particles increases. On the length scales relevant for hadrons, for instance, non-perturbative approaches to QCD have to be used. Experimental data are needed to verify these approaches. PANDA is one of the four experimental pillars of the upcoming FAIR facility in Darmstadt, Germany. In PANDA, an antiproton beam with a momentum between 1.5 and 15 GeV/c will interact in a hydrogen or nuclear target, allowing studies of various aspects of non-perturbative QCD. Motivated by the high interaction rates and the diverse physics goals of the experiment, a triggerless readout approach will be employed. In this approach, each detector subsystem will be equipped with intelligent front-end electronics that independently identify signals of interest in real time. In the electromagnetic calorimeter, FPGA-based digitiser modules will be used for this task. The high-radiation environment in PANDA will pose a challenge to these modules, due to both potential radiation damage and high signal rates from the calorimeter. In this thesis, these issues are addressed. First, the results from experimental measurements and Monte Carlo modelling of radiation-induced single event upsets in the FPGA are described. These studies have allowed predictions of the rate of single event upsets during operation of PANDA. Secondly, a newly developed algorithm for real-time processing of calorimeter signals in an FPGA at high pile-up rates is described. This algorithm provides a significant improvement in the time resolution of the calorimeter and allows reconstruction of the pulse height and timing of piled-up detector signals.

Binary hyperon production in antiproton-proton annihilations will be carried out with the PANDA experiment at FAIR, and probes the strong interaction in the non-perturbative regime where the relevant degrees of freedom are unclear. The self-analyzing decays of hyperons provide a straightforward way to study reaction dynamics via the measurement of spin observables. However, since weakly decaying hyperons can travel several centimeters before decaying, they are challenging to reconstruct. Conventional track reconstruction algorithms assume that charge particles originate in the experiment interaction point.

In this thesis, software tools are developed for the reconstruction and fitting of charged particles in the collaboration-wide software package PandaRoot. Pattern recognition algorithms are developed for the reconstruction of charged particle tracks with displaced vertices. Three algorithms that reconstruct the longitudinal momentum in the Straw Tube Tracker (STT) of PANDA are developed. They are based on a combinatorial approach, a Hough Transform, and a recursive annealing fit. The implementation and performance of these algorithms are presented. The track fitting scheme of PandaRoot is overhauled to treat the five particle species that PANDA is expected to measure, namely electrons, muons, pions, kaons and protons. The new track fitting scheme is outlined and discussed.

When the PANDA experiment is taken into operation, beam time will be allocated to many different measurements. For this reason, feasibility studies are performed in this thesis. The pbar p -> Lambdabar Lambda reaction is simulated at 1.642 GeV/c and the pbar p -> Xibar+ Xi- reaction is simulated at 7.0 and 4.6 GeV/c beam momenta. The simulation and analysis chain of the studies are explained. Expected reconstruction rates are presented. Furthermore, the feasibility of reconstructing spin observables in the reactions is discussed.

$\overline{\text{P}}$ANDA is a new experiment in hadron physics at the upcoming FAIR facility in Darmstadt, Germany. The combination of $\overline{\text{P}}$ANDA and
the antiproton beam, provided by the antiproton storage ring HESR, yields high production rates of
strange hyperon-antihyperon pairs. This enables multiple experiments in strangeness nuclear physics which allow to study the interaction of hyperons and
antihyperons within nuclear matter. This is essential to understand the composition of neutron star matter and solve the ``hyperon puzzle''.

The modularity of $\overline{\text{P}}$ANDA allows to
design and integrate a dedicated setup for the high resolution X-ray and $\gamma$ spectroscopy of heavy $\Xi^-$ hyperatoms and
double $\Lambda$ hypernuclei. The germanium detector array PANGEA (PANda GErmanium Array) is mandatory for these experiments.
Its optimization and integration into the $\overline{\text{P}}$ANDA target spectrometer is discussed in this thesis.
During the experiments at $\overline{\text{P}}$ANDA, the HPGe (High Purity Germanium) crystals of PANGEA will suffer from
inevitable hadronic background. %during the experiments.
Especially fast neutrons will damage the lattice structure of the crystal and deteriorate its resolution. This effect has
been experimentally studied in irradiation tests at the COSY accelerator in J\"ulich, Germany, with up to
\SI{5.6e9}{neutrons\per\centi\meter\squared}.
A large fraction of the performance loss of the detector could be corrected by analyzing the pulse shape of the detector response.
The initial crystal performance could be restored by annealing of the crystal in the laboratory after the irradiation.

The effects of the irradiation had to be kept in mind when the feasibility of the hyperatom experiment was studied. $\overline{\text{P}}$ANDA is unique
in its ability to study the $\Xi^-$ nucleon interaction in the neutron-rich periphery of $\Xi^-$-\ce{^{208}Pb} hyperatoms. Full simulations of the experiment show that multiple experimental observables will allow to measure the real and imaginary part of the $\Xi^-$ optical potential with a
precision of \SI{\pm 1}{\mega\eV}.

The P̄ANDA experiment represents the central part of the hadron physics program at the
FAIR facility that is under construction at GSI in Darmstadt. In the early stages of the
experiment, during the commissioning phase, a proton beam instead of an antiproton
beam will be provided by the accelerator and the reduced Day-1 setup will be available.
One of the first experiments that could be performed already during the commissioning
phase are cross section measurements of π 0 and η production in proton proton reactions.
The reconstruction efficiency for photons, π⁰, η and protons of the Day-1 setup has
been studied using PandaRoot simulations. In addition the full meson production chain
including baryonic resonances has been simulated and efficiencies for complete final
state reconstruction have been determined. There are some losses due to the incomplete
Day-1 setup but the relevant phase space for those reactions is covered sufficiently well.
P̄ANDA will be able to contribute to the measurement of total as well as differential meson
production cross sections with high precision. Moreover a first study on the channel
p̄p → φφπ⁰ has been performed. P̄ANDA could play an important role in confirming the
existence of the predicted 2 ++ glueball resonance in φφ and measure its properties.