Detector software

PANDA Collaboration Meeting 20/3 Minutes

PANDA Management Quarterly Report 20Q3

This document describes the technical layout and the expected performance of the Data Acquisition system for the PANDA experiment (Phase 1). This is the latest version approved by FAIR on August 25, 2021 after the review by FAIR ECE in spring 2021.

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.

PANDA Management Quarterly Report 20Q1Q2

PANDA Management Quarterly Report 20Q1Q2

PANDA Collaboration Meeting 20/2 Minutes

$\overline{\text{P}}$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}.