Online dynamic flat-field correction for MHz Microscopy data at European XFEL

The X-ray microscopy technique at the European X-ray free-electron laser (EuXFEL), operating at a MHz repetition rate, provides superior contrast and spatial-temporal resolution compared to typical microscopy techniques at other X-ray sources. In both online visualization and offline data analysis for microscopy experiments, baseline normalization is essential for further processing steps such as phase retrieval and modal decomposition. In addition, access to normalized projections during data acquisition can play an important role in decision-making and improve the quality of the data. However, the stochastic nature of XFEL sources hinders the use of existing flat-flied normalization methods during MHz X-ray microscopy experiments. Here, we present an online dynamic flat-field correction method based on principal component analysis of dynamically evolving flat-field images. The method is used for the normalization of individual X-ray projections and has been implemented as an online analysis tool at the Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX) instrument of EuXFEL.Comment: 14 pages, 7 figure

Ultrasound cavitation and exfoliation dynamics of 2D materials re-vealed in operando by X-ray free electron laser megahertz imaging

Ultrasonic liquid phase exfoliation is a promising method for the production of two-dimensional (2D) layered materials. A large number of studies have been made in investigating the underlying ultrasound exfoliation mechanisms. However, due to the experimental challenges for capturing the highly transient and dynamic phenomena in real-time at sub-microsecond time and micrometer length scales simultaneously, most theories reported to date still remain elusive. Here, using the ultra-short X-ray Free Electron Laser pulses (~25ps) with a unique pulse train structure, we applied MHz X-ray Microscopy and machine-learning technique to reveal unambiguously the full cycles of the ultrasound cavitation and graphite layer exfoliation dynamics with sub-microsecond and micrometer resolution. Cyclic fatigue shock wave impacts produced by ultrasound cloud implosion were identified as the dominant mechanism to deflect and exfoliate graphite layers mechanically. For the graphite flakes, exfoliation rate as high as ~5 angstroms per shock wave impact was observed. For the HOPG graphite, the highest exfoliation rate was ~0.15 angstroms per impact. These new findings are scientifically and technologically important for developing industrial upscaling strategies for ultrasonic exfoliation of 2D materials

Development of crystal optics for Multi-Projection X-ray Imaging for synchrotron and XFEL sources

X-ray Multi-Projection Imaging (XMPI) is an emerging technology that allows for the acquisition of millions of 3D images per second in samples opaque to visible light. This breakthrough capability enables volumetric observation of fast stochastic phenomena, which were inaccessible due to the lack of a volumetric X-ray imaging probe with kHz to MHz repetition rate. These include phenomena of industrial and societal relevance such as fractures in solids, propagation of shock waves, laser-based 3D printing, or even fast processes in the biological domain. Indeed, the speed of traditional tomography is limited by the shear forces caused by rotation, to a maximum of 1000 Hz in state-of-the-art tomography. Moreover, the shear forces can disturb the phenomena in observation, in particular with soft samples or sensitive phenomena such as fluid dynamics. XMPI is based on splitting an X-ray beam to generate multiple simultaneous views of the sample, therefore eliminating the need for rotation. The achievable performances depend on the characteristics of the X-ray source, the detection system, and the X-ray optics used to generate the multiple views. The increase in power density of the X-ray sources around the world now enables 3D imaging with sampling speeds in the kilohertz range at synchrotrons and megahertz range at X-ray Free-Electron Lasers (XFELs). Fast detection systems are already available, and 2D MHz imaging was already demonstrated at synchrotron and XFEL. In this work, we explore the properties of X-ray splitter optics and XMPI schemes that are compatible with synchrotron insertion devices and XFEL X-ray beams. We describe two possible schemes designed to permit large samples and complex sample environments. Then, we present experimental proof of the feasibility of MHz-rate XMPI at the European XFEL.Comment: 47 pages, 17 figure

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

cptnHook - Summer Student Project Report

The present is a report of the work that was conducted during my 8-week summer school internship at CERN. The project was centered on the development of an instrumentation tool for the usage of mathematical functions in a scientific application. More specifically, $\textbf{cptnHook}$ addresses a current issue that arises from the the extensive use of very time-consuming mathematical functions (such as transcendental functions) that results in them accounting for a big portion of their run-time. It is believed that the problem can be addressed with ad-hoc approximations of mathematical functions, for which a clear overview of the usage of the functions in the program is required. $\textbf{cptnHook}$ approaches this problem by providing a measurement of the use of mathematical functions in a program by hooking into the machine code and probing the arguments of the functions, without modifying the application's source code. The outputs of the tool are provided in ROOT format for further on analysis

Search for charged Higgs bosons with tau-lepton signatures at the ATLAS experiment of the Large Hadron Collider and development of novel semiconductor particle detectors

Experimental High Energy Physics (HEP) studies are discussed in the context of exotic particle searches and data analysis techniques and the development and production of suitable detectors. The main covered topics span the aforementioned areas and are primarily related to the ATLAS experiment at the Large Hadron Collider (LHC). The Higgs boson discovery by the ATLAS and CMS experiments in 2012, solidified the Standard Model (SM), but at the same type provided a suitable probe for searches of new physics, beyond the SM (BSM). This thesis covers a study for a new particle, the charged Higgs boson, which is predicted by several BSM theories and its discovery would be a clear sign for new physics. The study was focused on the predicted τν final state using a 36.1fb−1 dataset of pp collisions collected at √s = 13TeV with the ATLAS detector. No discovery was made, but new limits on relevant parameters were set. Studies that involve hadronically decaying τ leptons, such as the aforementioned charged Higgs boson search, are affected by background processes where quark- and gluon-initiated jets as misidentified as τs. A universal method for determining the impact of this background, and the associated systematic uncertainties, is being developed in ATLAS and is introduced in this thesis. The Large Hadron Collider (LHC) is presently preparing for the High-Luminosity upgrade that is designed to meet the current physics goals. The upgrade will result in more demanding conditions for the LHC experiments, in terms of higher particle fluences and larger collected data volumes, necessitating changes in their detector systems. The ATLAS inner tracker upgrade is discussed, focusing on the workflow and the quality assurance and quality control procedures necessary for the production of the strip modules that will be part of its new end-cap system in collaboration with industry. Neutron detection is essential for a wide range of neutron science applications and research. The evaluation of a novel boron-coated semiconductor with respect to its suitability of neutron detection is discussed

Search for charged Higgs bosons with tau-lepton signatures at the ATLAS experiment of the Large Hadron Collider and development of novel semiconductor particle detectors

Experimental High Energy Physics (HEP) studies are discussed in the context of exotic particle searches and data analysis techniques and the development and production of suitable detectors. The main covered topics span the aforementioned areas and are primarily related to the ATLAS experiment at the Large Hadron Collider (LHC). The Higgs boson discovery by the ATLAS and CMS experiments in 2012, solidified the Standard Model (SM), but at the same type provided a suitable probe for searches of new physics, beyond the SM (BSM). This thesis covers a study for a new particle, the charged Higgs boson, which is predicted by several BSM theories and its discovery would be a clear sign for new physics. The study was focused on the predicted τν final state using a 36.1fb−1 dataset of pp collisions collected at √s = 13TeV with the ATLAS detector. No discovery was made, but new limits on relevant parameters were set. Studies that involve hadronically decaying τ leptons, such as the aforementioned charged Higgs boson search, are affected by background processes where quark- and gluon-initiated jets as misidentified as τs. A universal method for determining the impact of this background, and the associated systematic uncertainties, is being developed in ATLAS and is introduced in this thesis. The Large Hadron Collider (LHC) is presently preparing for the High-Luminosity upgrade that is designed to meet the current physics goals. The upgrade will result in more demanding conditions for the LHC experiments, in terms of higher particle fluences and larger collected data volumes, necessitating changes in their detector systems. The ATLAS inner tracker upgrade is discussed, focusing on the workflow and the quality assurance and quality control procedures necessary for the production of the strip modules that will be part of its new end-cap system in collaboration with industry. Neutron detection is essential for a wide range of neutron science applications and research. The evaluation of a novel boron-coated semiconductor with respect to its suitability of neutron detection is discussed

Video of the radioscopic sequence of images that was collected with the X-ray Multi-projection Imaging (XMPI) technique during the foaming of an aluminum alloy at 1 kHz.

Study of foaming of an aluminum alloy, using the X-ray Multi-projection Imaging (XMPI) technique. The foaming was produced by a fast and self-triggering pressure release method. The video shows the radioscopic sequence of images that was collected with XMPI during the process, with 1 kHz acquisition speed. Details can be found in the main body of the article

Performance of the ATLAS tau-lepton trigger at the LHC in Run 2

The ATLAS experiment has a rich physics program of Standard Model measurements and searches for physics Beyond the Standard Model involving tau leptons. Most of these analyses depend on an efficient tau-lepton trigger that can cope with the overwhelming background from multi-jet events produced in proton-proton collisions at the Large Hadron Collider. The ATLAS trigger system is composed of two stages. At Level-1, tau leptons are reconstructed as energy deposits in neighbouring towers of calorimeter cells. The High Level Trigger (HLT) exploits the full calorimeter granularity as well as inner-detector tracks, and runs reconstruction and identification algorithms similar to those used in the offline reconstruction. The performance of the tau-lepton trigger in ATLAS Run-2 data will be discussed, and trigger efficiencies measured with a tag-and-probe method will be presented. An emphasis will be made on the improved HLT algorithms deployed in 2018 and mentioned below. The association of tracks to the energy deposit in the calorimeter was tightened to reduce the contamination from fake tracks at high pileup. An energy calibration based on a Boosted Regression Tree with improved energy resolution has replaced the simpler calibration based on pileup subtraction and calorimeter response correction. An identification algorithm based on a Recurrent Neural Network was also deployed, which provides increased jet rejection compared to the previously-used Boosted Decision Tree identification algorithm