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Ziel der Simulationsstudien in dieser Arbeit war es, die Leistungsfähigkeit des Transition Radiation Detectors zur Identifikation von leichten Kernen und Hyperkernen im CBM-Experiment zu untersuchen. Die Trennung von Helium und Deuterium
mithilfe ihres spezifischen Energieverlustes im TRD ist zentral, um eine Rekonstruktion des seltenen Hyperkerns 6 ΛΛHe mit einem hohen Signal-zu-Untergrund-Verhältnisse zu leisten. Zur Erfüllung der Anforderungen, die sich aus dem CBM-Forschungsprogramm ergeben, wird eine Auflösung des Energieverlustes dEdx von Helium von höchstens 30 % verlangt...
The Compressed Baryonic Matter experiment (CBM) at FAIR and the NA61/SHINE experiment at CERN SPS aim to study the area of the QCD phase diagram at high net baryon densities and moderate temperatures using heavy-ion collisions. The FAIR and SPS accelerators cover energy ranges 2-11 and 13-150 GeV per nucleon respectively in laboratory frame for heavy ions up to Au and Pb. One of the key observables to study the properties of a matter created in such collisions is an anisotropic transverse flow of particles.
In this work, the performance of the CBM experiment for anisotropic flow measurements is studied with Monte-Carlo simulations using gold ions at SIS-100 energies employing different heavy-ion event generators. Also, procedures for centrality estimation and charged hadron identification are described and corresponding frameworks are developed.
The measurement of the reaction plane angle is performed with Projectile Spectator Detector (PSD), which is a hadron calorimeter located at a very forward angle. To prevent radiation damage by the high-intensity ion beam, the PSD has a hole in the center to let the beam pass through. Various combinations of CBM detector subsystems are used to investigate the possible systematic biases in flow and centrality measurements. Effects of detector azimuthal non uniformity and the PSD beam hole size on physics performance are studied. The resulting performance of CBM for flow measurements is demonstrated for identified charged hadron anisotropic flow as a function of rapidity and transverse momentum in different centrality classes.
The measurement techniques developed for CBM were also validated with the experimental data recently collected by the NA61/SHINE experiment at CERN SPS for Pb+Pb collisions at the beam momenta 30A GeV/c. Compared to the existing data from the NA49 experiment at the CERN SPS, the new data allows for a more precise measurement of anisotropic flow harmonics. The fixed target setup of NA61/SHINE also allows extending flow measurements available from the STAR at the RHIC beam energy scan (BES) program to a wide rapidity range up to the forward region where the projectile nucleon spectators appear. In this thesis, an analysis of the anisotropic flow harmonics in Pb+Pb collisions at beam momenta 30A GeV/c collected by the NA61/SHINE experiment in the year 2016 is presented. Flow coefficients are measured relative to the spectator plane estimated with the Projectile Spectators Detector (PSD). The flow coefficients are obtained as a function of rapidity and transverse momentum in different classes of collision centrality. The results are compared with the corresponding NA49 data and the measurements from the RHIC BES program.
The last decades have brought tremendous progress in understanding the phase structure of the strongly interacting matter. This has been driven by studying heavy-ion collisions on the experimental side and Lattice QCD, functional approaches to QCD, perturbation theory and effective theories on the theoretical side. Of particular interest is the transition from hadrons to partonic degrees of freedom which is expected to occur at high temperatures or high baryon densities. These phases play an important role in the early universe and the core of neutron stars. Nowadays, the existence of a deconfined phase, i.e. Quark Gluon Plasma (QGP) and its phase transition at vanishing and small net-baryon densities, are well established. However, the situation at larger densities is less clear.
Complementary to the studies of matter at high temperatures and low net-baryon densities performed at RHIC and LHC, the proposed Compressed Baryonic Matter (CBM) experiment at the future FAIR facility, aims to explore the QCD phase diagram at very high baryon-net densities and moderate temperatures. The CBM research program includes the search for the deconfinement phase transition, the study of chiral symmetry restoration in super dense baryonic matter, the search for the critical endpoint, and the study of the nuclear equation of state at high densities. While other experiments (STAR-BES at BNL, BM@N at NICA) are suited to measure bulk observables, CBM is explicitly designed to access rare observables, such as multi-strange hadrons, dileptons, hypernuclei and charmonium. Therefore, a key feature of CBM is the very high interaction rate, exceeding those of contemporary and proposed nuclear collision experiments by several orders of magnitude. However, some of the rare probes have a complex signature, hidden in a background of several hundreds of charged tracks. This forbids a conventional, hardware-triggered readout; instead, the experiment combines self-triggered front-end electronics, fast and free-streaming data transport, online event reconstruction and online event selection.
The central detector for tracking and momentum determination of charged particles in the CBM experiment is the Silicon Tracking System (STS). It is designed to measure up to 700 charged particles in nucleus-nucleus collisions between 0.1 and 10 MHz interaction rate, to achieve a momentum resolution in 1 Tm dipole magnetic field better than 2%, and to be capable of identifying complex particle decays topologies, e.g., such with strangeness content. The STS comprises 8 tracking stations equipped with double-sided silicon microstrip sensors. Two million channels are read out with self-triggering electronics, matching the data streaming and on-line event analysis concept applied throughout the experiment. The detector’s functional building block consists of a silicon sensor, aluminum-kapton microcables and two front-end electronics boards integrated in a module. The custom-designed ASIC (STS-XYTER) implements the analog front-end, the digitizer and the generation of individual hit data for each signal.
Design of the front-end chip requires finding an optimal solution for time and input charge measurements with tight constraints: small area (58 μm channel pitch), low noise levels (below 1500 ENC(e− )), low power consumption (610 mW/channel), radiation hard architecture and speed requirements. Being a part of the first processing stage in the full readout and data acquisition chain, the characterization of the chip and its integration with the detector components is a crucial task. In this work, various methods and tools are established for testing and qualifying the ASIC analog front-end. A procedure for amplitude and timing calibration is developed using different functionalities of the chip. The procedure is optimized for our prototype system in order to achieve the best accuracy in the shortest amount of time. Results were verified using a gamma source and an external pulse generator, showing discrepancies below 5%.
Among the multiple operation requirements of the ASIC, the noise performance is of essential importance. The characterization of the chip noise is carried out as a function of a large number of parameters such as: low-voltage power regulators, input capacitance, shaping time, temperature and bond’s protective glue (glob-top). These studies allowed to optimize the ASIC configuration settings, to identify possible malfunctions in the low voltage powering scheme and to select possible glob-top materials to be used in the module assembly. Moreover, important differences are found among odd and even channels, which main cause was related to the bias scheme of the amplifiers of the two groups of channels. This effect has been corrected in the new version (v2.1) of the ASIC.
Despite the STS front-end electronics being located outside of the physics acceptance, they will be exposed to high fluxes of charged particles. Considering the SIS100 possible running scenario, the lifetime dose at the location of the electronics is expected not to exceed 800 krad. Consequently, the STS-XYTERv2 ASIC implements a radiation hard design based on dual-interlocked cells (DICE), and triple modular redundancy (TMR).
Multiple dedicated beam campaigns were carried out to evaluate the ASIC’s design in terms of immunity to single event upsets (SEU) errors and overall performance after a lifetime doses. The DICE cell SEU cross section was measured in a high-intensity proton beam. Result show a significant improvement of the SEU immunity in the STS-XYTERv2 compared to its predecessor, and allows to estimate the upset rate in the CBM running scenario, resulting in less than one SEU/ASIC/day.
The studies on the total ionizing dose (TID) show that the overall noise levels for the ASIC, at the end of the experiment lifetime, are expected to increase by approximately 40 – 60%. Moreover, they demonstrated that short periods of annealing at room temperature can favorably influence the noise performance of the chip.
The assembly and test of the STS modules, a complex process with multiple stages and a long learning curve, is illustrated in different parts of this work. The first prototype modules were built with the front-end board type B (FEBs-B), capable of reading out 128 channels for p and n side respectively. The studies were conducted with a relativistic proton beam of 1.7 GeV/c momentum at the COSY accelerator facility, Research Center Juelich, in March 2018. The campaign brought valuable insights to the development of an effective grounding and powering scheme for reading out the detectors. The signal-to-noise was measured for one of the prototype modules, resulting in values larger than 15 for both polarities. A deeper analysis into the collected data allowed the identification of a logic error in the ASIC that affected the readout rate and the quality of the data. This issue was corrected in the new version of the chip.
A precursor of the STS detector, named mini-STS (mSTS), has been built within the mCBM project carried out in FAIR Phase0. mSTS was built from 4 fully assembled detector modules. To ensure the proper operation of the ASICs that were used in the module assembly, it was required to develop a rigorous quality assurance procedure. A dedicated setup was built based on a custom designed pogo-pin station and a total of 339 chips were tested. More than 90% of good-quality and operational ASICs were obtained. In the mCBM beam campaign of March 2019, four detector modules were successfully operated in a close-to-final readout chain and valuable data were collected. The mSTS detector was exposed to the products of Ag+Au collisions at energies above 1.58 AGeV and overall interaction rates up to 106 , which resembles the real conditions of the CBM experiment.
Along this work, significant progress for the development of the STS detector modules was achieved. Techniques for characterization of the front-end electronics and the complete detector system were developed and worked out. They will be applied for QA of the components during the series production.
HADES (High Acceptance DiElectron Spectrometer), located at GSI, is a versatile detector for precise spectroscopy of e+ e- pairs and charged hadrons produced on a fixed target in a 1 to 3.5 AGeV kinetic beam energy region. The main experimental goal is to investigate properties of dense nuclear matter created in heavy ion collisions and learn about in-medium hadron properties.
In the HADES set-up 24 Mini Drift Chambers (MDC) allow for track reconstruction and determining the particle momentum by exploiting charged particle deflection in a magnetic field. In addition, the drift chambers contribute to particle identification by measuring the energy loss. The read-out concept foresees each sensing wire to be equipped with a preamplifier, analog pulse shaper and discriminator. In the current front-end electronics, the ASD-8 ASIC comprises the above modules. Due to limitations of the current on-board time to digital converters (TDC), especially regarding higher reaction rates expected at the future FAIR facility (HADES at SIS-100), the electronics need to be replaced by new board featuring multi-hit TDCs. Whereas ASD-8 chips cannot be procured anymore, a promising replacement candidate is the PASTTREC ASIC, developed by JU Krakow, which was tested w.r.t. suitability for MDC read-out in a variety of set-ups and, where possible, in direct comparison to ASD-8.
The timing precision, being the most crucial performance parameter of the joint system of detector and read-out electronics, was assessed in two different set-ups, i.e. a cosmic muon tracking set-up and a beam test at the COSY accelerator at Juelich using a minimum ionizing proton beam.
The beam test results were reproduced and can thus be quantitatively explained in a three dimensional GARFIELD simulation of a HADES MDC drift cell. In particular, the simulation is able to describe the characteristic dependence of the time precision on the track position within the cell.
A circuit simulation (SPICE) was used to closely model the time development of a raw drift chamber pulse, measured as a response to X-rays from a 55 Fe source. The insights gained from this model were used for attributing realistic charge values to the time over threshold values measured with the read-out ASICs in a charge calibration set-up. Furthermore, a high-level circuit simulation of the PASTTREC shaper is implemented to serve as a demonstration of the effect of the individual shaping and tail cancellation stages which are present in both ASICs.