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Abstract: The electron-ion collider (EIC) will be built at the Brookhaven National Laboratory over the next ten years, with the purpose of giving insight into nucleon structure, origins of nucleon mass and spin, and quark and gluon confinement. This thesis pertains to the silicon vertex tracker for an EIC experiment; the detector closest to the interaction point. The purpose of a silicon vertex tracker is to locate the origin vertex position of charged particles and measure the particle momentum, and the EIC physics goals require detector resolutions beyond current state-of-the-art silicon vertex trackers. The aim of this thesis is to find a suitable silicon sensor technology for further developments by tests performed in a lab and at a testbeam, and to find a silicon vertex tracker geometry with performance matching the EIC physics requirements using simulations. The baseline sensor for the studies comes from the ALICE inner tracker upgrade, and is called the ALPIDE sensor. A new monolithic silicon sensor development designed to increase depletion is tested and compared to the performance of an ALPIDE-like sensor, and found to improve charge collection performance while keeping the sensor capacitance low. This aids tracking performance, and the new development is thus considered a possible path for development of an EIC-specific sensor. Simulations of different silicon vertex tracker geometries and parameters are performed using GEANT4, and a high-performing layout consisting of inner and outer silicon sensor layers surrounded by a gaseous detector and silicon disks is developed. It is also found that if a more compact tracker is desired, an all-silicon concept outperforms a combination of silicon and gaseous detectors. Further simulations of the best-performing layouts with current projections of possible silicon sensor material thickness and pixel size show that they meet the requirements of the EIC physics goals in terms of momentum resolution if a 3 T solenoidal magnetic field is used, and pointing resolution regardless of magnetic field strength. The silicon vertex tracker developed in this work is one of two baseline tracker concepts used in the ongoing development of an EIC reference detector. The performance of different detector concepts is also studied using realistic electron-proton collision events generated using PYTHIA and propagated through the detector simulation, with a focus on charmed meson reconstruction. It is found that a compact all-silicon tracker can perform as well as an all-silicon concept with a larger radius in these studies, but a large-radius combination of silicon and gaseous detectors is always better than all-silicon concepts in the studied open charm case.

Open Access

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Abstract: Modules for the ATLAS Inner Tracker (ITk) strip tracker include a DC-DC converter circuit glued directly to the silicon sensor which converts the 11 V supplied to the module to the 1.5 V required for the operation of the readout chips. The DC-DC converter unit, consisting of a copper solenoid and custom ASIC, is located directly above the silicon strip sensor and therefore needs to be shielded to protect the sensor from EMI noise created during the operation of the circuit. Despite dedicated shielding, consisting of an aluminium shield box with continuous solder seams encompassing the surface components and a copper layer in the PCB beneath it, module channels connected to sensor strips located beneath the converter circuit were found to show a noise increase. While the DC-DC converter unit causing the underlying EMI noise operates at a frequency of 2 MHz, module characterisation measurements for ITk strip tracker modules are typically performed asynchronously to the DC-DC switching and are therefore averaged over the full range of time bins with respect to the converter frequency. In order to investigate the time dependence of the noise injection relative to the DC-DC switching frequency, a dedicated setup to understand the time-resolved performance change in modules was developed. By using a magnetic field probe to measure the field leaking through the shield box and triggering on its rising edge, data taking could be synchronised with the DC-DC switching. This paper illustrates the concept and setup of such time-resolved performance measurements using magnetic triggering and presents results for the observed effects on signal and noise for ATLAS ITk strip modules from both laboratory and beam tests.

Open Access

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Abstract: Multiple coincidence events from charge-sharing and fluorescent cross-talk are typical drawbacks in room-temperature semiconductor pixel detectors. The mitigation of these distortions in the measured energy spectra, using charge-sharing discrimination (CSD) and charge-sharing addition (CSA) techniques, is always a trade-off between counting efficiency and energy resolution. The energy recovery of multiple coincidence events is still challenging due to the presence of charge losses after CSA. In this work, we will present original techniques able to correct charge losses after CSA even when multiple pixels are involved. Sub-millimeter cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors were investigated with both uncollimated radiation sources and collimated synchrotron X rays, at energies below and above the K-shell absorption energy of the CZT material. These activities are in the framework of an international collaboration on the development of energy-resolved photon counting (ERPC) systems for spectroscopic X-ray imaging up to 150 keV.

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Abstract: A newly supplied 80 × 80 chromium compensated GaAs sensor with a matrix of 80 × 80 pixels on a 250 m pixel pitch has been characterised utilising microbeam mapping techniques at the Diamond Light Source. The GaAs:Cr sensor was mounted to a HEXITEC DAQ system before raster scanning an x-ray beam with area 25 × 25 m in steps of 25 m, providing sub-pixel resolution spectroscopic imaging. Scans were performed with incident x-ray energies ranging from 12 to 45 keV. Following processing of the data in MatLab 2019b an analysis of defects previously observed in etched GaAs wafers occured. Findings indicate the presence of regions with reduced charge collection efficiency where up to 88 % of incident events show significant charge loss, and changing charge carrier lifetimes across the sensor.

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Abstract: Thanks to the development of high-quality X-ray focusing optics during the past decades, synchrotron-based X-ray transmission microscopy techniques enable to study specimens with extremely high spatial resolution. However, on one hand at the expense of the field of view (100 μm x 100 μm) and on the other hand to the detriment of the photon energies range (below 20 keV), which significantly limits the specimens' scope to be investigated, particular- ly in material science. In this work, the so-called pixel super-resolution scanning transmission hard X-ray microscopy technique was developed, allowing to enlarge the field of view and drastically reduce the scanning time thanks to sub-pixel specimen scanning through a large number of X-ray probes created by biconcave para- bolic shaped refractive multi-lenses. High-resolution images with a spatial resolution corresponding to the X-ray (micro-) nanoprobe size are achieved, even if the pixel size of an imaging detector employed for data acquisition is much larger than that. Since the technique's key element is X-ray optics, the development and fabri- cation of one (two)-dimensional X-ray refractive multi-lenses (RMLs) for focusing high energy X-rays (17-35 keV) fabricated by deep X-ray lithogra- phy and electroplating technique are presented. The X-ray characterization of these optics and microscopy experiments performed at KARA (Germany), Diamond Light Source (England), and SPring-8 (Japan) synchrotron facilities are provided. Since the height of existing refractive multi-lenses still restricts the field of view (maximum in the mm range), the staircase array of RMLs inclined to the substrate was developed, allowing pixel super-resolution scanning transmission hard X-ray microscopy with a 1.64 cm × 1.64 cm field of view while keeping a 780 ± 40 nm resolution using 35 keV X-rays. The scanning time was only about four minutes. The unique capability of the pixel super-resolution scanning transmission hard X-ray microscopy has been demonstrated by imaging biomedical implant abutments fabricated via selective laser melting using Ti-6Al-4V. Accordingly, the investigation of extend- ed and thick specimens for material science has been demonstrated.