Phd (PHD)

The hadron spectroscopy and structure are currently very active fields of research to study the non-perturbative regime of quantum chronodynamics. The first one studies the complex structure of excited hadrons by looking at their decay products, while the latter uses lepton scattering on nucleons. Both methods require reconstruction algorithms with great efficiency and good particle identification and background rejection rates. This work aims to provide these by either improving the existing methods or developing new ones.

The first part of this document presents a feasibility study of a predicted hybrid charmonium state for the $\mathrm{\overline{P}}$ANDA experiment. Lattice QCD calculations predict the ground state hybrid charmonium to be a spin exotic with quantum numbers of $J^{PC}=1^{-+}$ at a mass of around 4.3 GeV with a width to be around 20 MeV. A machine learning based data analysis scheme is proposed to further improve the signal efficiency and the background reduction, alongside with improvements of the analysis software (PandaRoot), that are vital for this study. These improvements include a reworked clustering algorithm for the electromagnetic calorimeter (EMC) and an optimized monte carlo matching for neutral particles.

The second part of this document is about studying the proton structure. A multidimensional study of the structure function ratio $\mathrm{F_{LU}^{sin(\phi)}/F_{UU}}$ has been performed for K$^\mathrm{\pm}$, based on the measurement of beam-spin asymmetries. It uses the high statistics data recorded with the CLAS12 spectrometer at Jefferson Laboratory. $\mathrm{F_{LU}^{sin(\phi)}}$ is a twist-3 quantity that provides information about the quark gluon correlations in the proton. This document will present for the first time a simultaneous analysis of two kaon channels over a large kinematic range of $z$, $x_B$, $P_T$ and $Q^2$ with virtualities $Q^2$ ranging from 1 GeV$^2$ up to 8 GeV$^2$ using machine learning techniques for improved particle identification.

The PANDA (anti-Proton ANnihilation at DArmstadt) experiment at FAIR (Facility for Anti-proton and Ion Research) aims to study strong interactions in the confinement domain. In PANDA, a continuous beam of anti-protons will impinge on a fixed hydrogen target inside the High Energy Storage Ring (HESR), a feature intended to attain high interaction rates for various physics studies e.g. hyperon production.

This thesis addresses the challenges of running PANDA under realistic conditions. The focus is two-fold: developing deep learning methods to reconstruct particle trajectories and reconstruct hyperons using realistic target profiles. Two approaches are used: (i) standard deep learning model such as dense network, and (ii) geometric deep leaning model such as interaction graph neural networks. The deep learning methods have given promising results, especially when it comes to (i) reconstruction of low-momentum particles that frequently occur in hadron physics experiments and (ii) reconstruction of tracks originating far from the interaction point. Both points are critical in many hyperon studies. However, further studies are needed to mitigate e.g. high clone rate. For the realistic target profiles, these pioneering simulations address the effect of residual gas on hyperon reconstruction. The results have shown that the signal-to-background ratio becomes worse by about a factor of 2 compared to the ideal target, however, the background level is still sufficiently low for these studies to be feasible. Further improvements can be made on the target side to achieve a better vacuum in the beam pipe and on the analysis side to improve the event selection.

Finally, solutions are suggested to improve results, especially for the geometric deep learning method in handling low-momentum particles contributing to the high clone rate. In addition, a better way to build ground truth can improve the performance of our approach.

The PANDA experiment at FAIR offers unique possibilities for performing hyperon physics.
The detector will enable the reconstruction of both hyperon and antihyperon, which will
be created together in proton-antiproton collisions. This enables investigations of the strong
interaction in the non-perturbative regime. Due to their relatively long-lived nature, the hyperons
impose a particular challenge on the track reconstruction and event building. In order to
exploit the large expected reaction rates to the fullest, PANDA will utilize a fully software-based
event filtering. Therefore, reconstructing hyperons for such a filter requires online track
reconstruction that can handle particles created a measurable distance away from the interaction
point and, at the same time, operate on free streaming data is needed. Until antiprotons are
available at PANDA, a part of the hyperon program can be carried out with the predecessor,
PANDA@HADES using a proton beam.
In this thesis, investigations of the detector signatures from the decay channels Λ → pπ-, Ξ- →
Λπ- and Ω- → Λ K- produced in YbarY reactions are presented. The detector signatures guide
the subsequent track reconstruction algorithms. A candidate for online track reconstruction
algorithms on free streaming data based on a 4D Cellular Automaton has been developed and is
benchmarked. It utilizes information from the PANDA straw tube tracker and is agnostic to the
point of origin of the particle. The track reconstruction quality assurance procedure and results
from the tracking at different event rates are also presented. Finally, extrapolation algorithms
for including hit information from additional detectors in the tracks are outlined.
In order to maximize the potential of the predecessor experiment PANDA@HADES, a
kinematic fitting procedure has been developed for HADES that combines geometric the decay
vertex information of neutral particles and track parameters such as momentum. Benchmark
studies on simulated data from the channel p(3.5 GeV)p → ΛK+p are presented as well as tests
of the kinematic fit on experimental data from 2007.

This thesis presents work focused on three topics related to hyperon physics.
The first part presents a track finding algorithm for the future PANDA experiment forward tracker using the state-of-art graph neural networks. The detection of forward emitted particles plays a significant role in the reconstruction and analysis of the ground state and excited hyperons (e.g., $\Sigma^{0}$ , $\Sigma(1385)$, $\Lambda(1405)$ and $\Lambda(1520)$). The network accepts an image of the forward tracker as an input, where the detector hits are the graph vertices, and all possible connections between two hits in adjacent layers are the graph edges. It was trained as a binary classifier to classify the graph edges.
The second part of the thesis presents a study of the production mechanism of the $\Sigma^{0}$ hyperon via the exclusive reaction $pp \rightarrow pK^{+}#Sigma^{0}$ at beam energy 3.5 GeV with the HADES detector setup. In total, 2613 events were reconstructed 58\% are within the main HADES acceptance and 42\% within the forward wall acceptance. Furthermore, the dynamics of the reaction \Ssignal were investigated by studying the angular distributions in the CMS, Gottfried-Jackson and helicity frames. The total production cross section of the \Szero hyperon was obtained by integrating the yield for the different angular distributions and found to be $\sigma = 18.74 \pm 1.01 (stat) \pm 1.71 (syst)$ $\mu b$.
The last part of the thesis presents a feasibility study to investigate excited hyperons radiative decays using the upgraded HADES setup and the new forward detector as part of the FAIR Phase-0 physics program.

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.