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The Compressed Baryonic Matter (CBM) is one of the core experiments at the future Facility for Anti-proton and Ion Research (FAIR), Darmstadt, Germany. Its goal is to investigate nuclear matter characteristics at high net-baryon densities and moderate temperatures. The Silicon Tracking System (STS) is a central detector system of CBM.
It is placed inside a 1Tm magnet and operated at a temperature of about −10 °C to keep radiation-induced bulk current in the 300μm double-sided microstrip silicon sensors low. The design of the STS aims to minimize the material budget in the detector acceptance (2.5° < θ < 25°). In order to do so, the readout electronics is placed outside the active area, and the analog signals are transported via ultra-thin micro-cables. The STS comprises eight tracking stations with 876 modules. Each module is assembled on a carbon fiber ladder, which is subsequently mounted in the C-shaped aluminum frame.
The scope of the thesis focused on developing a modular control system framework that can be implemented for different sizes of experimental setups. The developed framework was used for setups that required a remote operation, like the irradiation of the powering modules for the front-end electronics (FEE), but also in laboratory-based setups where the automation and archiving were needed (thermal cycling of the STS electronics).
The low voltage powering modules will be placed in the vicinity of the experiment, therefore they will experience a total dose of up to 40mGy over the 10 years of STS lifetime.
To estimate the effects of the radiation on the low-voltage module performance, a dedicated irradiation campaign took place. It aimed at estimating the rate of radiation induced soft errors, that lead to the switch off of the FEE.
Regular power cycles of multiple front-end boards (FEBs) pose a risk to the experiment operation. Firstly, such behavior could negatively influence the physics performance but also have deteriorating effects on the hardware. It was further assessed what are the limitations of the FEBs with respect to the thermal cycling and the mechanical stress. The results served as an indication of possible failure modes of the FEB at the end of STS lifetime. Failure modes after repeated cycles and potential reasons were determined (e.g., Coefficient of Thermal Expansion (CTE) difference between the materials).
Due to the conditions inside the STS efficient temperature and humidity monitoring and control are required to avoid icing or water condensation on the electronics or silicon sensors. The most important properties of a suitable sensor candidate are resilience to the magnetic field, ionizing radiation tolerance, and fairly small size.
A general strategy for ambient parameters monitoring inside the STS was developed, and potential sensor candidates were chosen. To characterize the chosen relative humidity sensors the developed control framework was introduced. A sampling system with a ceramic sensor and Fiber Optic Sensors (FOS) were identified as reliable solutions for the distributed sensing system. Additionally, the industrial capacitive sensors will be used as a reference during the commissioning.
Two different designs of FOS were tested: a hygrometer and 5 sensors multiplexed in an array. The FOS hygrometer turned out to be a more reliable solution. One of the possible reasons for a worse performance is a relatively low distance between the subsequent sensors (15 cm) and a thicker coating. The results obtained from the time response study pointed out that the thinner coating of about 15μm should be a good compromise between the humidity sensitivity and the time response.
The implementation of the containerized-based control system framework for the mSTS is described in detail. The deployed EPICS-based framework proved to be a reliable solution and ensured the safety of the detector for almost 1.5 years. Moreover, the data related to the performance of the detector modules were analyzed and significant progress in the quality of modules was noted. Obtained data was also used to estimate the total fluence, which was based on the leakage current changes.
The developed framework provided a unique opportunity to automate and control different experimental setups which provided crucial data for the STS. Furthermore, the work underlines the importance of such a system and outlines the next steps toward the realization of a reliable Detector Control System for STS.
This work focuses on the investigation of K+, K- and ϕ-meson production in Ag(1.58 A GeV)+Ag collisions. The energetically cheapest channel for direct K+ production in binary NN-collisions NN→NΛK+ lies at exactly this energy. For the remaining K- and ϕ-mesons, an excess energy of 0.31 GeV and 0.34 GeV in the centre of mass system has to be provided by the system. This makes these particles an excellent probe for effects inside the medium.
K+ and K- mesons can be reconstructed directly as they possess a cτ of approximately 3.7 m. Using the approximately 3 billion recorded Ag(1.58 A GeV)+Ag 0-30% most central collision events, all reconstructed K+ and K- within the detector acceptance are investigated for their kinematic properties and their particle production rates compared to a selection of existing models.
Sensors for high rate charge particle tracking have to withstand the harsh radiation doses deposited by the particles to be sensed. This holds particularly for the novel CMOS Monolithic Active Pixel Sensors, which are considered a promising sensor technology for future vertex detectors due to their very light material budget and excellent spatial resolution. To resist the radiation doses expected close to the interaction regions of heavy-ion experiments, the sensors have to be hardened against radiation doses, which exceed the native tolerance of CMOS technology significantly. In this thesis, the results of non-ionizing radiation hardness studies at the IKF on sensor prototypes developed at the IPHC in Strasbourg are presented. Our results demonstrate that the CMOS sensors evaluated in the context of this thesis can withstand non-ionizing radiation of up to 5×10^14 neq/cm^2. This hardness qualifies them as promising candidates for use in future vertex detectors.
In this thesis, the emission of protons as well as the production of Λ hyperons, Κ0S mesons and 3ΛH hypernuclei are analyzed multi-differentially as a function of transverse momentum, rapidity and centrality. Therefore, the 3.03 billion 30 % most central Ag(1.58A GeV)+Ag events recorded by HADES are used. Furthermore, the lifetimes of Λ hyperons, Κ0S mesons and 3ΛH hypernuclei are measured. The obtained 3ΛH lifetime of (253 ± 24 ± 42) ps is compatible with the lifetime of free Λ hyperons, as predicted by theoretic calculations due to its low binding energy. Finally, also the double strange Ξ– hyperons are reconstructed. Unfortunately, the fully optimized signals lie below the confidence threshold of 5σ, which is why both an production rate and an upper production limit are estimated using averaged acceptance and efficiency corrections. Never before, 3ΛH or Ξ– were successfully reconstructed and analyzed in heavy-ion collisions at such low energies. The obtained results are compared to previous measurements and put in context with world data form different energies and collision systems.
In this thesis, the flow coefficients vn of the orders n = 1 − 6 are studied for protons and light nuclei in Au+Au collisions at Ebeam = 1.23 AGeV, equivalent to a center-of-mass energy in the nucleon-nucleon system of √sNN = 2.4 GeV. The detailed multi-differential measurement is performed with the HADES experiment at SIS18/GSI. HADES, with its large acceptance, covering almost full azimuth angle, combined with its high mass-resolution and good particle-identification capability, is well equipped to study the azimuthal flow pattern not only for protons, deuterons, and tritons but also for charged pions, kaons, the φ-mesons, electrons/positrons, as well as light nuclei like helions and alphas. The high statistics of more than seven billion Au-Au collisions recorded in April/May 2012 with HADES enables for the first time the measurement of higher order flow coefficients up to the 6th harmonic. Since the Fourier coefficient of 7th and 8th order are beyond the statistical significance only an upper bound is given. The Au+Au collision system is the largest reaction system with the highest particle multiplicities, which was measured so far with HADES. A dedicated correction method for the flow measurement had to be developed to cope with the reconstruction in-efficiencies due to occupancies of the detector system. The systematical bias of the flow measurement is studied and several sources of uncertainties identified, which mainly arise from the quality selection criteria applied to the analyzed tracks, the correction procedure for reconstruction inefficiencies, the procedures for particle identification (PID) and the effects of an azimuthally non-uniform detector acceptance. The systematic point-to-point uncertainties are determined separately for each particle type (proton, deuteron and triton), the order of the flow harmonics vn, and the centrality class. Further, the validity of the results is inspected in the range of their evaluated systematic uncertainties with several consistency checks. In order to enable meaningful comparisons between experimental observations and predictions of theoretical models, the classification of events should be well defined and in sufficiently narrow intervals of impact parameter. Part of this work included the implementation of the procedure to determine the centrality and orientation of the reaction.
In the conclusion the experimental results are discussed, including various scaling properties of the flow harmonics. It is found that the ratio v4/v2 for protons and light nuclei (deuterons and tritons) at midrapidity for all centrality classes approaches values close to 0.5 at high transverse momenta, which was suggested to be indicative for an ideal hydrodynamic behaviour. A remarkable scaling is observed in the pt dependence of v2 (v4) at mid-rapidity of the three hydrogen isotopes, when dividing by their nuclear mass number A (A^2) and pt by A. This is consistent with naive expectations from nucleon coalescence, butraises the question whether this mass ordering can also be explained by a hydrodynamical-inspired approach, like the blast-wave model. The relation of v2 and v4 to the shape of the initial eccentricity of the collision system is studied. It is found that v2 is independent of centrality for all three particle species after dividing it by the averaged second order participant eccentricity v2/⟨ε2⟩. A similar scaling is shown for v4 after division by ⟨ε2⟩^2.
The Compressed Baryonic Matter (CBM) Experiment will investigate heavy ion collisions and reactions at interaction rates of 100 kHz in a targeted energy range of up to 11 AGeV for systems such as gold-gold or lead-lead. It will be one of the major scientific experiments of the Facility for Antiproton and Ion Research in Europe (FAIR) currently under construction at the site of the GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany. CBM is going to be a fixed target experiment consisting of a superconducting magnet, multiple detectors of various types, and high-performance computing for online event reconstruction and selection. The detector closest to the interaction point of the experiment will be the Micro Vertex Detector (MVD). Consisting of four planar stations equipped with custom CMOS pixel sensors, it will allow to reconstruct the primary vertex with high precision and will help to reconstruct secondary vertices and identify particles originating from conversion in the detector material.
Due to the high interaction rates foreseen for CBM, understanding and minimizing systematic errors due to the detectors’ operating conditions will become all the more important to obtain significant measurement results, as statistical errors in the measurements of many observables are diminishing due to the enormous amount of data available.
Furthermore, the MVD will be the first detector based on CMOS pixel sensors used in a large physics experiment, that will be operated in vacuum. As a result, many aspects of the mechanical and electrical integration of the detector require careful testing and validation.
This thesis addresses both those challenges specifically for the Micro Vertex Detector with the development of a control system for the operation and validation of the MVD prototype “PRESTO” in vacuum. The prototype was selected as device under test as the final MVD is not yet built.
The developed control system helps a) to operate the prototype safely and keep it at the desired working point and b) to record important time-series data of the state of the detector prototype. Those two aspects allow the control system (which might later serve as a ‘blueprint’ for the final detector) to minimize the mentioned systematic errors as much as possible and to contribute to the understanding of remaining systematic errors using correlations with the time-series data. The controlled operation of the prototype in vacuum allowed to validate the integration concepts from a wide range of mechanical and electrical aspects in an endurance test for more than a year with 24/7 operation.
The prototype for this study itself was named “PRESTO” (standing for ‘PREcursor of the Second sTatiOn of the CBM-MVD’). It represents one quadrant of an MVD detector plane, equipped with a total of 15 MIMOSA-26 sensors on the front and back side of a carrier plate. Within this thesis, major parts of the prototype itself were designed. Custom ultra-thin flat flexible cables for data and power were designed and validated. Furthermore, the CNC-machined Aluminium heatsink to mount and cool the prototype design was refined to increase thermal performance. A custom vacuum feedthrough for a total of 21 flat ribbon cables was designed and fabricated. The read-out chain for MIMOSIS-26 was extended to cover a total of 8 sensors with a single and newer TRB-3 FPGA board and was set-up with the prototype. Vacuum equipment including chambers, hoses, pumps, valves and gauges were integrated to form a large vacuum testing system. A cooling circuit for the prototype was assembled comprising an external chiller, hoses, vacuum feedthroughs, as well as temperature, flow and pressure sensors.
The control system was developed to serve the needs of the prototype, while taking the requirements of the final MVD already into account. The main design goals of the control system are:
• compatibility with the other detectors and the overall CBM experiment,
• access to real-time measurements of all necessary parameters (‘process values’),
• reliable, fail-safe operation of the detector,
• recording of all time-series data (‘archiving’),
• cost efficiency and acceptance within the physics community,
• good usability for the users (‘operators’),
• long-term maintainability.
The recorded time-series data of the process variables (i.e. sensor readings) allow a post-measurement analysis of variations in the detector performance. The longterm archiving of all relevant system parameters is therefore of outstanding importance, which is why the software intended for this purpose – called “archiver” – was given special attention in this thesis.
For this reason in particular, it is necessary to implement a comprehensive control system that allows the detector to be operated safely under these conditions and cooled effectively. Before the start of this doctoral thesis, vigilant and extensively trained operators were always necessary for this. The control system that has been developed makes it possible that, after basic training, the detector can also be operated by a less specialised shift supervisor during measurement campaigns.
...
Understanding the hadron spectrum is one of the primary goals of non-perturbative QCD. Many predictions have experimentally been confirmed, others still remain under experimental investigation. Of particular interest is how gluonic excitations give rise to states with constituent glue. One class of such states are hybrid mesons that are predicted by theoretical models and Lattice QCD calculations. Searching for and understanding the nature of these states is a primary physics goal of the GlueX experiment at the CEBAF accelerator at Jefferson Lab. A search for a JPC = 1−− hybrid meson candidate, the Y(2175), in φ(1020)π+π+ and φ(1020)f0(980) channels in photoproduction on a proton target has been conducted. A first measurement of non-resonant φ(1020)π+π+ and φ(1020)f0(980) total cross sections in photoproduction has been performed. An upper limit on the resonance production cross section for the Y (2175) → φ(1020)π+π+ and Y (2175) → φ(1020)f0(980) channels are estimated. Since the analysis essentially depends on the quality of the charged kaon identification, also an optimization of particle identification through an improvement of the energy loss estimation in the central drift chamber by a truncated mean method has been investigated.
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.
High-energetic heavy-ion collisions offer the unique opportunity to produce and to study dense nuclear matter in the laboratory. The future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, will provide beams of heavy nuclei up to kinetic energies of 11 GeV/nucleon. At these energies, the nuclear matter in the collision zone of two nuclei will be compressed to densities of up to 5 − 10 times the saturation density of atomic nuclei, similar to matter densities existing in the core of massive neutron stars. Under those conditions, nucleons are expected to melt and form a new state of matter, which consists of quarks and gluons, the so called Quark-Gluon Plasma (QGP). The search for such a phase transition from hadronic to partonic matter, and the exploration of the nuclear matter equation-of-state at high densities are the major goals of heavy ion experiments worldwide.
The observables, which are proposed to probe the properties of dense nuclear matter and possible phase transitions, include multi-strange hyperons, antibaryons, lepton pairs, collective flow of identified particles, fluctuations and correlations of various particles, particles containing charm quarks, and hypernuclei. These observables have to be measured in multi-dimensions, i.e. as function of collision centrality, rapidity, transverse momentum, energy, emission angle, etc., which requires extremely high statistics. Moreover, some of these particles are produced very rarely.
Therefore, the Compressed Baryonic Matter (CBM) experiment at FAIR is designed to run at collision rates of up to 10 MHz, in order to perform measurements with unprecedented precision. Due to the complicated decay topology of many observables, no hardware trigger can be applied, and the data have to be analysed online in order to filter out the interesting events.
This strategy requires free-streaming read-out electronics, which provides time stamps to all detector signals, a high performance computer center, and high-speed reconstruction algorithms, which provide an online track and event reconstruction based on time and position information of the detector hits (”4-D“ reconstruction).
The core detector of the CBM experiment is the Silicon Tracking System (STS). The main task of the STS is to provide track reconstruction and momentum de- termination of charged particles originating from beam-target interactions. To fulfil the whole tasks the STS is located in the large gap of a superconducting dipole magnet with a bending power of 1 Tm providing momentum measurements for charged particles. The STS comprises 8 detector stations, which are positioned from 30 cm to 100 cm downstream the target. The corresponding active area of the stations grows up from 40×50 cm 2 up to 100×100 cm 2 with a totalarea of 4 m2. The silicon double-sided sensors exhibit 1024 strips on each side with a stereo angle at p-side of 7.5 ◦ and a strip pitch of 58 μm. The strip length ranges from 2 cm for sensors located in a close vicinity to the beam axis, up to 12 cm for other sensors where the flux of the reaction products drops down substantially. In total, the STS consist of 896 sensors mounted on 106 detector ladders. The detector readout electronics dissipates 40 kW and will be equipped with a CO 2 bi-phase cooling system. The detector including electronics will be mounted in a thermal enclosure to allow for sensor operation at below −5 ◦ C which minimizes radiation induced leakage currents.
The task of the STS is to measure the trajectories of up to 800 charged particles per collision with an efficiency of more than 95% and a momentum resolution of 1 − 2%. In order to guarantee the required performance over the full lifetime of the CBM experiment, the detector system has to have a low material budget, a high granularity, a high signal-to-noise (SNR) ratio, and a high radiation tolerance. As a result of optimisation studies, the STS consists of double-sided silicon microstrip sensors, about 300 μm thick, which have to provide a SNR ratio of more than 10, even after radiation with the expected equivalent lifetime fluence of 10 14 1 MeV n eq cm −2.
This thesis is devoted to the characterization of double-sided silicon microstrip sensors with an emphasis on investigation of their radiation hardness. Different prototypes of double sided silicon sensors produced by two vendors have been irradiated by 23 MeV protons up to the double life time fluence for the CBM experiment (2 × 10 14 1 MeV n eq cm −2 ).
The sensor properties have been characterised before and after irradiation. It was found, that after irradiation with a double lifetime fluence the leakage current increased 1000 times, which results in an increased shot noise. Moreover, the relative charge collection efficiency of irradiated with respect to non-irradiated sensors drops down to 85% for the lifetime equivalent fluence, and down to 73% for the double lifetime fluence, both for the p-side and n-side. For non-irradiated sensors the SNR was found to be in the range of 20 − 25, whereas for irradiated sensors it dropped down to 12 − 17.
In addition to the sensor characterization, a part of this thesis was devoted to the optimisation of the sensor readout scheme. In order to investigate the possible increase of SNR, and to reduce the number of readout channels in the outer aperture of STS, three versions of routing lines have been realized for the p-side readout of the sensor prototype, and have been tested in the laboratory and under beam conditions.
The tests have been performed with different inclination angles between beam direction and sensor surface, corresponding to the polar angle acceptance of the CBM experiment, which is from 2.5 ◦ to 25 ◦.
As a result of the studies carried out in this thesis work, the radiation hardness of the double-sided silicon microstrip sensors developed for the CBM STS detector was confirmed. Also the advantage of individual read-out of sensor channels in the lateral regions of the detector was verified. This allowed to start the tendering process for sensor series production in industry, an important step towards the construction of the detector in the coming years.
The mission of the Compressed Baryonic Matter (CBM) experiment is to investigate the phase diagram of strongly interacting matter in the region of high net-baryon densities and moderate temperatures. According to various transport models, matter densities of more than 5 times saturation density can be reached in collisions between gold nuclei at beam energies between 5 and 11 GeV per nucleon, which will be available at FAIR. The core detector of the CBM experiment is the Silicon Tracking System (STS), which is used to measure the tracks of up to 700 particles per collision with high efficiency (>95%) and good momentum resolution (<1.5%). The technological and experimental challenge is to realize a detector system with very low material budget, in order to reduce multiple scattering of the particles, and a free-streaming data readout chain, in order to achieve reaction rates up to 10 MHz together with an online event reconstruction and selection.
The STS comprises 8 tracking stations positioned between 30 cm and 100 cm downstream the target inside a magnetic field, covering polar emission angles up to 25 degrees. A station consists of vertical structures with increasing number (between 8 and 16, depending on station number), each structure carrying between 2 and 10 double-sided microstrip silicon sensors, which are connected through low-mass microcables to the readout electronics placed at the detector periphery outside the active detector area.
The work presented in this thesis focuses on the detector performance simulation and local hit pattern reconstruction in the STS. For efficient detector design and reconstruction performance, a reliable detector response model is of utmost importance. Within this work, a realistic detector response model was designed and implemented in the CBM software framework. The model includes non-uniform energy loss of an incident particle within a sensor, electric field of a planar p-n junction, Lorentz shift of the charge carriers, their diffusion, and the influence of parasitic capacitances. The developed model has been verified with experimental data from detector tests in a relativistic proton beam. Cluster size distributions at different beam incident angles are sensitive to charge sharing effects and were chosen as an observable for the verification. Taking into account parasitic capacitances further improves the agreement with measured data.
Using the developed detector response model, the cluster position finding algorithm was improved. For two-strip clusters, a new, unbiased algorithm has been developed, which gives smaller residuals than the Centre-Of-Gravity algorithm. For larger clusters, the head-tail algorithm is used as the default one. For an estimate of the track parameters, the Kalman Filter based track fit requires not only hit positions but their uncertainties as an input. A new analytic method to estimate the hit position errors has been designed in this work. It requires as input neither measured spatial resolution nor information about an incident particle track. The method includes all the sources of uncertainties independently, namely: the cluster position finding algorithm itself, the non-uniform energy loss of incident particles, the electronics noise, and the discretisation of charge in the readout chip.
The verification with simulations shows improvements in hit and track pull distributions as well as x²-distributions in comparison to the previous simple approach. The analytic method improves the track parameters reconstruction by 5-10%.
Several STS module prototypes have been tested in a relativistic proton beam. A signal to-noise ratio was obtained at the level of 10-15 for modules made of 30 cm long microcable and of either one or two 6.2 x 6.2 cm² CiS sensors.
First simulations have shown that this signal-to-noise ratio is sufficient to reach the required efficiency and momentum resolution. The high-radiation environment of CBM operation will deteriorate the sensor performance. Radiation hardness of sensors has been studied in the beam with sensors irradiated to 2 x 10[hoch 14] 1MeV [neq/cm²], twice the lifetime dose expected for CBM operation. Charge collection efficiency drops by 17-25%, and simultaneously noise levels increase 1.5-1.75 times. The simulations show that if all sensors in the STS setup are exposed to such a fluence uniformly, the track reconstruction efficiency drops from 95.5% to 93.2% and the momentum resolution degrades from 1.6% to 1.7%.