Despite recent advances leading to unprecedented performance in organic photovoltaic devices, the underlying processes of charge generation in these semiconductors are still unclear. Furthermore, the operational stability of organic solar cells - a key requirement for successful application outside the laboratory - is often neglected. This thesis addresses these urgent and complex challenges by investigating the photophysics and degradation mechanisms of two high-efficiency material systems by employing ultrafast transient spectroscopy. The first part is devoted to the understanding of charge generation in PffBT4T-2OD:PC70BM which acts as a model system for a new class of organic photovoltaic materials. It is unambiguously shown that the separation of electron-hole pairs is field-dependent, with significant implications for the research of novel combinations of materials with low energy offsets. Based on these results, the second part of this thesis focuses on the environmental stability of the aforementioned system which is shown to be exceptionally sensitive to the influence of oxygen. The observed results can be comprehended by oxygen-induced p-doping of the active layer, resulting in rapid deterioration of the device properties. Finally, the photophysics and degradation of solar cells based on the small molecule donor DRCN5T, representative of a new trend in solar cell design, are addressed. These devices display remarkable stability which is accredited to an ultrafast energy transfer from the unstable to the stable components. This insight can potentially influence design rules for future research on organic solar cells. Therefore, this work contributes substantially to the understanding of the photophysics at short timescales and the stability of organic solar cells with high relevance for the field.
Diffusion is the major short-range transport mechanism in living cells. Within individual compartments of a eukaryotic cell, such as the nucleus, mitochondria or the cytosol, biological macromolecules find their targets mostly by thermally driven random motion. For instance, specific access of DNA-binding proteins to their target sequences in the genome occurs through a sequence of three-dimensional diffusion, DNA-binding and one-dimensional search events on the DNA. The DNA/chromatin network in the cell nucleus thus has two effects on protein diffusion: obstruction due to crowding and accelerated association to specific sequences through guided diffusion along the DNA chain. The problem of target finding of proteins in the cell nucleus is only one example of diffusion-controlled reactions in a dense polymer network. Outside the direct relevance for molecular and cellular biology, the study of diffusing particles in viscoelastic media has important applications in many fields of physics. By recording fast image series of two-dimensional sections of live cells, we monitor these diffusion processes in real time and gain better understanding of the underlying physics. The method used is light sheet fluorescence microscopy followed by auto (-cross) correlation analysis. We particularly studied the random motion of chromatin and its interconnection with nucleoplasmic A-type lamins. Utilizing this method, we find that 1. Nucleoplasmic lamin As and chromatin show significant co-mobility, indicating that their motions are interconnected in the nucleus. 2. The random motion of histones H2A within the chromatin network is subdiffusive, i.e. the effective diffusion coefficient decreases for slow timescales. Knocking out lamin A changes the diffusion back to normal. Thus, lamin A influences the dynamics of the entire chromatin network. 3. A-type lamins affect the spatial organisation of chromatin inside the cellular interior. We have also attempted to develop a modelling framework that describes chromatin dynamics within the cell nucleus in the presence and absence of nucleoplasmic A-type lamins. Our conclusion is that lamin A plays a central role in determining the viscoelasticity of the chromatin network and helping to maintain local ordering of interphase chromosomes. These findings enabled us to derive a qualitative description of diffusion based on the viscoelasticity of the cellular environment.
Detecting repeating firing motifs of neuron groups (so-called neuronal assemblies) and cell segmentation in calcium imaging, a microscopy technique enabling the observation of neuronal activity, are two fundamental and challenging tasks in neurophysiological data analysis. In this thesis, three novel approaches are presented, which use machine learning to tackle both problems from different perspectives. First, SCC is presented for the detection of motifs in neuronal spike matrices, which are gained from calcium imaging data by cell segmentation. SCC uses sparse convolutional coding and outperforms established motif detection methods by leveraging sparsity constraints specifically designed for this data type combined with a method to avoid false-positive detections. Second, LeMoNADe is the first method ever to detect spatio-temporal motifs directly in calcium imaging videos, eliminating the cumbersome extraction of individual cells. It is a variational autoencoder framework tailored for the extraction of neuronal assemblies from videos and matches the performance of state-of-the-art detection methods requiring cell extraction. Although LeMoNADe enables the detection of neuronal assemblies without previous cell extraction, this step is still essential for a wide range of downstream analyses. Therefore, the third method, DISCo, combines a deep learning model with an instance segmentation algorithm to address this task from a new perspective and thereby outperforms similarly trained existing models.
Exclusive photoproduction of ρ 0 vector mesons is studied with the H1 detector at HERA. A sample of over 900 000 π + π − photoproduction events was collected in the years 2006-2007 using the H1 Fast Track Trigger. It corresponds to an integrated luminosity of 1.3 pb −1 . The dataset is used to study single-, double-, and triple-differential π + π − photoproduction cross-sections as a function of the invariant mass of the pions m ππ , the photon-proton collision energy W γp , and the squared momentum transfer at the proton vertex t. The phasespace is restricted to 0.5 GeV < m ππ < 2.2 GeV, 20 GeV < W γp < 80 GeV, −t < 1.5 GeV 2 , and a photon virtuality Q 2 < 0.1 GeV 2 . Reactions in which the scattered proton stays intact are statistically separated from those where it dissociates to a low-mass hadronic system in the range m p < m Y < 10 GeV. The m ππ distributions are parametrized by a Söding model to extract the ρ 0 contribution to π + π − production. Single- and double-differential ρ 0 cross-sections are measured as a function of W γp and t. The observed kinematic cross-section dependencies are parametrized using őts and are compared to expectations from phenomenological models as well as results from previous measurements. From the double-differential ρ 0 cross-section, the effective intercept and slope of the leading Regge trajectory in the measurement phasespace are extracted:
α(t = 0) = 1.0659 ± 0.0033 (stat.) +0.0099/−0.0059 (syst.) α (t = 0) = 0.243 ± 0.050 (stat.) +0.030/−0.042 (syst.) GeV −2 .
In 2011, stereotactic body radiotherapy was introduced for the treatment of hepatocellular carcinoma at the Heidelberg Ion-Beam Therapy Center (HIT). Initially, thirteen patients were treated, including the first patient treated using respiratory beam gating. This thesis presents the work flow and data acquisition for the treatment of moving organs. Based on the acquired patient data, simulated and reconstructed 4D dose distributions are now available.
Simulations of 4D dose distributions require precise knowledge of the organ motion and accelerator timing. To improve the prediction, the properties of the HIT synchrotron cycle were investigated, revealing energy-dependent and stochastic aspects and day-to-day beam intensity fluctuations. A simulation was implemented based on a realistic model of the accelerator. The accuracy of calculated irradiation sequences was verified using treatment records. Experimental verification using a patient treatment plan was performed in a moving water phantom, where a total dose deviation of (1.0±7.3)% was determined.
Since 2012, the HIT heavy-ion gantry offers new treatment options. In a treatment planning study, optimal plan geometries for the treatment of esophageal carcinoma were determined. Effects of intrafractional organ motion were accounted for in a quasi-static dose calculation. Results can potentially be used for margin and gating window definition.
This thesis reports the amplitude analysis of Lambda_b^0 --> Lambda_c^+ D^0 K^− decays using data collected by the LHCb experiment from proton-proton collisions, corresponding to an integrated luminosity of 9.1 fb −1 . A new amplitude fitter has been developed in the context of this analysis, which exploits novel computing concepts and software frameworks. Numerous models predict large couplings of the pentaquark candidates observed by LHCb to the Lambda_c^+ D^0 system. This makes the Lambda_b^0 → Lambda_c^+ D^0 K^− channel meaningful to discriminate between models which attempt to describe the internal structure of the pentaquark states. Amplitude fits are performed to measure the contributions of intermediate resonances to Lambda_b^0 → Lambda_c^+ D^0 K^− decays and upper limits are set for the observation of pentaquark states in this channel. The results obtained are in contrast with the expectations from the most popular theory models which describe the pentaquark states as Σ D^∗ -Σ^∗ D molecules.
THe-Trap ist ein Penningfallen Experiment zur Präzisionsmassenbestimmung am Max-Planck- Institut für Kernphysik in Heidelberg, Deutschland. Für das Datenerfassungssystem wurden ein neues Python-Program und eine neue PHP-Website entwickelt. Unter Verwendung eines Lock-In Amplifiers wurde ein neues Locksystem implementiert. Ein Gaseintrittssystem wurde entwickelt und verwendet, um die hochgeladenen Neon-Isotope 20Ne8+ und 22Ne7+ Neon zu erzeugen und in der Penningfalle einzufangen. Ihre Masse wurde gegen ein 12C Referenzion gemessen. Die 20Ne-Masse wurde mit einer relativen Messunsicherheit von 5.8 ⋅ 10-10 bestimmt. Diese befindet sich innerhalb einer Standardabweichung mit dem Literaturwert mit einer Unsicherheit von 8.4 ⋅ 10-11 im Einklang. Die 22Ne Masse wurde mit einer relative Messunsicherheit von 7.7 ⋅ 10-10 gemessen. Diese befindet sich innerhalb fünf Standardabweichungen im Vergleich zur Messunsicherheit des Literaturwerts, 8.2 ⋅ 10-10. Aufgrund der langen Messdauer ist die Messunsicherheit jeweils von zeitlichen Variationen des Magnetfelds limitiert. Das leichte Edelgas Neon gehört zum “Backbone of the Atomic Mass Evaluation”, weshalb es als Bezugsmasse nützlich ist. Die Verbesserung der relativen Neonmessunsicherheit kann also die relative Messunsicherheit von Messungen verbessern, die Neon als Bezugsmasse verwenden.
This work connects the three domains of experimental nuclear physics, computational physics and environmental physics centered around the neutron. The CASCADE thermal neutron detector is based on a combination of solid 10B coatings in several layers, GEMs as gas amplification stages, a microstructured readout, multichannel ASICs and FPGA hardware triggered data acquisition. The detailed analysis to improve the system in terms of time-of-flight resolution for Neutron Resonance Spin Echo Spectroscopy required for a simulation model of the detector. The limitations of existing codes led to the development of the Monte Carlo transport code URANOS, which fully integrates the detector components and features a voxel-based geometry definition. The simulation could then successfully be applied to precisely understand neutron transport within the frame of Cosmic-Ray Neutron Sensing. This novel and interdisciplinary method offers the possibility to non-invasively measure soil moisture on the hectare scale using neutrons of the environmental radiation. The endeavor of this work led to the development of the footprint weighting function, which describes the neutron density change by different hydrogen pools in the air-ground interface. Significant influences of the near-field topology around the sensor were predicted by this work, experimentally verified and correction methods were successfully tested.
This dissertation investigates hadronic multi-body decays of beauty and charm mesons providing insights into both the CKM sector of the Standard Model and strong interaction dynamics at the hadronic energy scale. First, the resonant substructure of the decay D0->4pi is studied. Quantum-entangled D0 bar_D0 pairs produced in electron-positron collisions are used. The data sample corresponds to an integrated luminosity of 818 pb^−1 recorded by the CLEO-c detector. An amplitude analysis exploiting the full information provided by the five-dimensional phase space is performed to disentangle the various intermediate state components and measure their relative phases. The global decay-rate asymmetry between D0 and bar_D0 decays is measured and a search for CP asymmetries in the amplitude components is conducted; no evidence for CP violation is found. The fractional CP-even content and related hadronic parameters are derived from the amplitude model and found to be consistent with model independent measurements. These hadronic parameters are crucial input for a future measurement of the CP-violating phase gamma in B^±->(D->4pi)K^± decays, where D represents a superposition of D0 and bar_D0 mesons. With currently existing proton-proton collision data collected by the LHCb experiment, a precision of around sigma_gamma = 12 degrees can be achieved, competitive with the most precise single measurement of the CKM angle to date. Second, hadronic multi-body decays of Bs mesons are studied using proton-proton collision data corresponding to 7 fb^−1 recorded by the LHCb detector. The Bs−bar_Bs oscillation frequency is measured from flavor-specific Bs->Ds3pi decays to be delta_ms = (17.7651 ± 0.0084 (stat) ± 0.0058 (syst)) ps^−1, consistent with and significantly more precise than the current world-average value. Mixing-induced CP violation in Bs->DsKpipi decays is explored by means of a time-dependent amplitude analysis. The weak phase difference between Bs->Ds^−K^+pi^+pi^− and bar_Bs->Ds^−K^+pi^+pi^− decays is determined to be gamma = (60 ± 17(stat+syst)) degrees; the most precise measurement of this quantity in the Bs meson system.
This thesis presents a study of the decay $B^0_s\rightarrow J/\psi\phi$ with the LHCb experiment. Due to the mixing between $B^0_s$ and $\bar{B}^0_s$ mesons and a final state that is accessible for both species, this decay is sensitive to CP violation originating from the interference between the mixing and the decay process. The CP violating is parametrized by the weak phase difference $\phi_s$, which can be precisely constrained within the Standard Model of particle physics based on other measurements. Thus, the measurement of this phase difference constitutes an interesting test for possible contributions of physics phenomena from beyond the Standard Model. A flavour-tagged analysis of the time-dependent decay rates of $B^0_s$ and $\bar{B}^0_s$ mesons is performed. In addition, an angular analysis is needed to disentangle the different CP components of the final state. The analysis is based on a proton-proton collision data set collected in 2015 and 2016 by the LHCb experiment, corresponding to an integrated luminosity of $1.9\,$fb$^{-1}$. The obtained value for the CP violating phase difference is $\phi_s=(−0.083 \pm 0.041_{\rm stat} \pm 0.006_{\rm syst})\,$rad, which, combined with a previous analysis of this channel by the LHCb experiment, constitutes the most precise single channel and single experiment measurement of this quantity. No significant deviation from the Standard Model expectation is observed.
Besides the measurement of $\phi_s$, the main other determined parameters are the decay width and decay-width splitting of the $B^0_s$ meson system. In contrast to previous analyses of this channel, the decay width is directly measured with respect to decay width of the $B^0$ meson.
Exciton-polaritons are quasiparticles with hybrid light-matter character, offering a unique combination of photonic properties, such as a light mass, with those of excitons, for example strong nonlinearities and fast relaxation. Strong light-matter coupling enables a rich set of polaritonic quantum phenomena as well as applications. While originally observed in inorganic materials, organic semiconductors have recently attracted tremendous attention since their large oscillator strength facilitates particularly strong light-matter coupling and enabled polariton formation at room temperature. In particular, electrical excitation is pursued to apply these quantum-mechanical effects in practical polariton devices. However, a lack of organic materials with sufficiently high charge-carrier mobility and suitable device architectures impede their full utilization. Nanomaterials, in particular low-dimensional materials, present a novel material class that combines the excitonic properties of organic and electric characteristics of inorganic materials. In this thesis, single-walled carbon nanotubes (SWCNTs) were employed to demonstrate, for the first time, exciton-polariton formation in the near infrared (nIR) at room temperature. SWCNTs are identified as an ideal material facilitating strong light-matter coupling due to their high oscillator strength. Moreover, by implementing a strongly coupled microcavity into a light-emitting field effect transistor (LEFET), electrically pumped polariton emission at high current density was observed. These practical polariton devices emit in ranges relevant for telecommunication and support high currents due to the excellent optoelectronic properties of SWCNTs. Pumping polaritons at high rates presents a major step towards electrical lasing with carbon-based materials. For the realization of these experiments it was crucial to overcome current limitations in post-growth sorting of SWCNTs, which are intrinsically restricted to low-volume and damage the nanotubes. For this purpose, selective polymer wrapping by high-speed shear-force mixing, which can be easily scaled up, was developed. By using shear forces, the SWCNT-yield was drastically increased while, at the same time, the SWCNT-quality could be improved. In addition to strong light-matter coupling and polariton emission, the selected SWCNTs were employed in organic light-emitting diodes. These devices showed pure nIR emission with narrow linewidth at efficient electrical performance. This work paves the way for fundamental investigations as well as advanced applications of SWCNT-based optoelectronic devices.
Penning traps are currently the most precise mass measurement devices resulting from a long development, which started around 1900. With a relative precision of up to E−12 , Penning traps allow testing of various physical theories by means of mass measurements, such as quantum electrodynamics (QED), the CPT (charge, parity and time) theorem and theory of special relativity. In order to achieve this precision, many devices have to be coordinated and measurements have to be performed repeatedly. This work presents the basic structure of a newly-developed Python based control system for the THe-Trap experiment at the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. During the development the focus was placed on enabling the user to recognize the state of the experiment at just one glance. It is also possible to control and automate the experiment with external scripts based on Python as well. High-precision Penning trap experiments worldwide with the above-mentioned precision are limited among other things by the so-called image charge effect. This effect is caused by the image charges induced by the ion in the surrounding electrodes of the Penning trap. These image charges generate an additional electric field, which systematically shifts the frequency of the ion and thus the measurement result. This thesis presents a numerical calculation of the image charge effect for various experiments using the finite element method in COMSOL multiphysicsTM. The results of the simulation have an uncertainty of 1 % and agree with the measurement results, which have an uncertainty of about 5 %. Time-of-flight measurements show their strength in determining the mass of short-lived nuclides with a half-life of less than 100 ms. Ions are reflected several times to extend the flight distance, which has given the instruments the name multi-reflection time-of-flight mass spectrometer (MR-ToF MS). They also serve as fast mass separators. However, MR-Tof MS require ion pulses with a temporal width of about 100 ns or shorter. In this work, an ion buncher using SIMION was developed, built, and tested for the IGISOL experiment in Jyväskylä, Finland. During the test a pulse width of 107 ns could be achieved.
This thesis describes studies on a Rydberg-dressed ultracold atom system as a versatile platform for non-equilibrium physics research, atom-light interactions analysis and atomic sensing applications. This work includes a description of the experimental system, an ultracold potassium atom setup where we can prepare a gas of atoms in an optical dipole trap and precisely control their ground state properties. To excite the atoms to strongly-interacting Rydberg states, we set up and characterize a high-power and widely tunable excitation laser system, for driving both single and two-photon Rydberg excitations. Together this establishes a unique system for studying the effects of driving, long-range interactions and dissipation (due to the relatively short lifetime of excited states) on many-body dynamics. Using this setup we study the phase structure of a driven-dissipative system out of equilibrium , where exploiting the atom loss rate as an observable,we discover different power-laws depending on the system parameters (i.e driving,dissipation and interaction). We study further in detail a regime which shows loss rates much larger than those for single particles, and discover that due to the Rydberg population decay the system evolves to a self-organized critical state.Our key observations can be well described by effectively classical models for the many-body dynamics, which we understand as a consequence of rapid dephasing of atomic coherences. To quantify the coherence of the atom-light interactions, we realize a Rydberg dressed interferometer. This technique combines the precision of atomic clock transitions with the exaggerated properties of Rydberg atoms such as their long-range interactions and extreme response to electric fields. Using the interferometer, we are able to characterize the Rydberg-dressed ensemble, including the effects of population decay and dephasing both of which affect the coherence time. This enables us to identify power fluctuations in the excitation laser as the dominant effects limiting the coherence in the system, which will be used in the experiment for future improvements of the coherence time. As an additional application, we demonstrate that the Rydberg dressed interferometer can be used to precisely measure static electric fields down to 17 mV/cm which is comparable to state-of-the-art electrometers. These results together highlight the versatility of the Rydberg platform and pave the way towards a better understanding of long-range interacting systems out-of-equilibrium. This work paves the way to new studies of non-equilibrium phenomena and applications of many-body quantum systems which make use of both quantum coherent and dissipative interactions.
ALICE is one of the four major experiments at the Large Hadron Collider (LHC). It is the dedicated heavy-ion experiment and therefore primarily examines the Quark–Gluon Plasma. In order to prepare for the running conditions of 50 kHz lead-lead interactions at the LHC after the Long Shutdown 2 (2018–2021), an extensive upgrade program is carried out. The goal of the upgrade is a continuous readout of the TPC without the need of a trigger. It is essential to reduce the enormous data rate of 3.7 TB/s, generated by the upgraded detector, already during the data taking by a factor of about 60. Otherwise the data volume would exceed the expected available bandwidth and storage capabilities. In this thesis, an online Cluster Finder (CF) was developed and implemented for FPGAs which processes the whole data volume in real-time during the read out. This is the first step in the data reduction sequence which achieves already a factor of about 5 by keeping only physically relevant information and making use of a better suited data format. In addition to the CF, also the whole data preparation chain was designed and implemented to decode the input data stream, to resort the individual channels to allow for cluster finding and to correct the detector effects in the input signals. All modules which were implemented were extensively simulated to verify their proper functionality. With this, the complete processing chain within the FPGAs was prepared and validated.
The measurement of time-dependent CP violation in Bs->DsKpipi decays and the determination of the CKM angle gamma is performed using a dataset collected by the LHCb experiment in proton-proton collisions during Run I (2011-2012) and Run II (2015-2017) of the LHC operation, corresponding to an integrated luminosity of 6.7 fb^-1. The results are presented in terms of the CP-violating parameters C, D_f ans S_f, which are found to be
C = 0.68 +/- 0.12 +/- 0.02, D_f = 0.01 +/- 0.32 +/- 0.08, D_fbar = 0.38 +/- 0.30 +/- 0.08, S_f = -0.14 +/- 0.17 +/- 0.04, S_fbar = -0.54 +/- 0.17 +/- 0.04,
where the uncertainties are statistical and systematic, respectively. The measured parameters correspond to 3.4 sigma evidence for CP violation in the interference between decay and decay after mixing. These parameters are used together with the value of the Bs mixing phase beta_s to determine the CKM angle gamma using Bs->DsKpipi decays, yielding
gamma = (65^+27_-20)°,
where statistical and systematic uncertainties are combined. The obtained value of gamma agrees with the world average within its uncertainties. This analysis represents the first determination of CP violation in this decay channel and the second result on the CKM phase gamma from a time-dependent measurement. In addition, an amplitude analysis of Bs->DsKpipi decays is presented and the sensitivity of a time-dependent amplitude model to gamma in this decay channel is discussed.
The measurement of J/ψ production in heavy-ion collisions is seen as a key measurement in the hunt for the Quark-Gluon Plasma. At high collision energies as reached at the LHC it was predicted that a significant fraction of the J/ψ yield is formed by (re)combination of deconfined charm and anticharm quarks in the medium or at the phase boundary. This mechanism is expected to be most important at very low transverse momentum. In this thesis the production of J/ψ mesons is studied at mid-rapidity (|y| < 0.9) in pp and Pb–Pb collisions at a collision energy of √s_NN = 5.02 TeV with ALICE. The J/ψ mesons are reconstructed in the e+e− decay channel down to vanishing transverse momentum (pT = 0). The electrons and positrons are identified using the specific energy loss dE/dx in the TPC. The J/ψ spectrum and the nuclear modification factor R_AA in most central collisions are consistent with models which include (re)combination as a dominant source of J/ψ production. The measurement of the first two moments of the pT distribution as a function of centrality shows that this mechanism becomes more important for more central collisions.
Intensity modulated proton therapy (IMPT) plans precisely balance thousands of proton beamlets, giving high dose to the tumor while trying to spare healthy tissues. However, plan quality is affected by factors including: 1) dose calculation inaccuracies, 2) underestimation of the biological effect of the dose in sensitive areas and geometrical changes like 3) patient movement or 4) changes in posture and anatomy. All these factors are addressed in the projects here presented.
Project 1, in collaboration, introduces an upgraded version of a Monte Carlo package for graphics processing units (GPU-MC) to provide fast and accurate dose calculations. This package is extended to serve as the unique dose calculation engine in the following projects. Project 2, in collaboration, presents a prioritized optimization method to reduce the potential biological effect of the radiation in organs at risk near the tumor.
Project 3 compares computationally efficient strategies to take into account the patient respiratory motion by defining planning target volumes based on a 4DCT of the patient. Density overwrites considering water-equivalent-path-length to voxels across the 4DCT targets works best.
Project 4 demonstrates an online algorithm that maintains IMPT plan quality through treatment, adapting it to the daily patient posture and anatomy using GPU-MC calculations.
In this work we present a quantum theoretical account of hard x-ray time-domain interferometry, which is an experimental technique to probe the correlations in time between particles in a condensed matter system via their interaction with hard x-radiation. This technique has so far been successfully applied to classical systems. The recent proposal of using the same technique on systems for which quantum effects play a major role requires a detailed analysis due to the dramatic effect that the measurement act can have on the dynamics of a quantum system. In particular, trying to access the correlations in a quantum system via direct measurements would give only incomplete information about them. Treating both the probed matter system and the probing radiation as quantum systems which interact weakly, we show that in time-domain interferometry the radiation does not affect the system in the above sense, such that it can access the particles correlations in time fully. Furthermore, in view of some recent advancements in x-ray control, it is proposed that time-domain interferometry can be used for the reconstruction of particles correlations and for detecting the presence of quantum effects in the probed system.
Neugierde gilt nicht gerade als die feinste Charakter-Eigenschaft. Aber ohne hartnäckige menschliche Neugierde hätten wir weder Radio, noch Smartphone und auch keine Krebs-Therapie. Neugierde ist für die Wissenschaft unverzichtbar. Wer Leidenschaft für Neues hat, für den ist Forscher ein Traumjob. Campus Reporter Nils Birschmann fragt in loser Folge Heidelberger Forscher, was „ihr Ding“ ist und sprach diesmal mit der Physikerin Johanna Stachel.
Der Beitrag erschien in der Sendereihe "Campus-Report" – einer Beitragsreihe, in der über aktuelle Themen aus Forschung und Wissenschaft der Universitäten Heidelberg, Mannheim, Karlsruhe und Freiburg berichtet wird. Zu hören ist "Campus-Report" montags bis freitags jeweils um ca. 19.10h im Programm von Radio Regenbogen (Empfang in Nordbaden: UKW 102,8. In Mittelbaden: 100,4 und in Südbaden: 101,1).
This dissertation presents a search for physics beyond the Standard Model in D0->π+π-μ+μ−und D0->K+K−μ+μ− decays at the LHCb experiment. These rare four-body decays of neutral charm mesons receive contributions from electroweak flavour-changing neutral current c->ul+l− transitions and are unique probes for potential new heavy degrees of freedom and for additional sources of CP violation in the up-type quark sector. Using a sample of proton-proton collisions corresponding to an integrated luminosity of 2 fb−1 recorded at a center-of-mass energy of 8TeV in 2012, the first observation of D0->π+π-μ+μ−und D0->K+K−μ+μ− decays is reported. Furthermore, their branching fractions are measured. With an increased data set, corresponding to an integrated luminosity of 5 fb−1 and recorded at center-of-mass energies of 7, 8 and 13TeV in the years 2011-2016, the first measurement of the CP asymmetry ACP , the forward-backward asymmetry in the lepton system AFB and the triple-product asymmetry A2ϕ in these decays is presented. All observables are also investigated as functions of the dimuon mass. The results are consistent with Standard Model predictions.
New experiments, designed to test the Standard Model of particle physics with unprecedented precision and to search for physics beyond, push detector technologies to their limits. The Mu3e experiment searches for the charged lepton flavor violating decay μ+ → e+e−e+ with a branching ratio sensitivity of better than 1 ·10−16. This decay is suppressed in the StandardModel to unobservable levels but can be sizable in models beyond the Standard Model. The Mu3e detector consists of a thin pixel spectrometer combined with scintillating detectors to measure the vertex, momentum and time of the decay particles. Requirements on rate and material budget cannot be fulfilled by classical pixel sensors and demand the development of a novel pixel technology: high-voltage monolithic active pixel sensors (HV-MAPS). Two important steps towards a final pixel detector are discussed within the scope of this thesis: the characterization of two HV-MAPS prototypes from the MUPIX family and the development of a tracking telescope based on HV-MAPS with online monitoring, tracking and efficiency calculation for particle rates above 10 MHz. Using the telescope it is shown that the transition from the small-scale MUPIX7 to the full-scale MUPIX8 has been successful. Sensor characterization studies of the MUPIX8 show efficiencies above 99% at noise rates below 0.4 Hz/pixel over a large threshold range as well as a time resolution of 6.5 ns after time-walk corrections, thus fulfilling allMu3e sensor requirements. Additionally, the radiation tolerance of the MUPIX7 has been demonstrated up to a fluence of 1.5 ·10+15 24 GeV p/cm2.
Silicon tracking detectors play a key role in many current high energy physics experiments. To enhance experimental sensitivities for searches for new physics, beam energies and event rates are constantly being increased, which leads to growing volumes of detector data that have to be processed. This thesis covers high-speed data acquisition for silicon tracking detectors in the context of the Mu3e experiment and future hadron collider experiments. For the Mu3e experiment, a vertical slice of the trigger-less readout system is realized as a beam telescope consisting of 8 layers of pixel sensors that are read out using a prototype of the Mu3e front-end board. The performance of the full readout system is studied during beam tests. Sensor hit rates of up to 5 MHz can be handled without significant losses. Hence, the system fulfils the requirements for the first phase of the experiment. To fully exploit the potential of silicon tracking detectors at future hadron collider experiments, the implementation of high-speed data links is mandatory. Wireless links operating at frequencies of 60 GHz and above present an attractive alternative to electrical and optical links, as they offer high bandwidth, small form factor and low power consumption. This thesis describes readout concepts for tracking detectors applying wireless data transfer and presents studies of wireless data transmission.