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Matteo Giomi
PHD student | DESY
Gamma Rays
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Currently, my research activity is focused on gamma-ray variability. Variability provides precious information on the physical processes at the basis of a source's emission; however, especially at the highest energies, represent a challenge for the observations. As a part of my master thesis, I have studied how variable sources such as active galactic nuclei can be efficiently observed with small field of view instruments such as Imaging Atmospheric Cherenkov Telescopes. Now, for my PhD, I am approaching variable sources from a less technical point of view, working for an updated catalogue of variable sources detected with the Large Area Telescope (LAT) on board of the Fermi satellite. This catalogue use the Fermi All Sky Variability Analysis (FAVA). This analysis technique is simple and robust, and provide an unbiased and model independent way to spot transients in the gamma-ray sky. The catalogue will improve on the first FAVA catalogue in many aspects, and, together with the associated on-line tool and automatic analysis pipeline, will provide real time information on the variable gamma-ray sky to the community. Another field I am working on is polarization. Polarization is an intrinsic property of the light, and as such carries information on the properties and geometry of the sources. However, as of today, polarization has not been measured for astrophysical gamma rays. Although not designed for this, the Fermi LAT could have the possibility of measuring polarization for some of the brightest sources, if one could isolate the right sample of events. My work in this field is focused on event selection and systematic estimates.
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Thorsten Glüsenkamp
PHD student | DESY
High-Energy Neutrinos
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Blazars are active galactic nuclei with relativistic plasma jets whose symmetry axis is pointing towards Earth. They are a prime source candidate for the production of high-energy neutrinos. My thesis work describes the search for a cumulative neutrino flux from all 862 Fermi-LAT 2LAC blazars and four spectrally defined sub-populations. I have analyzed selected muon-track events from three years of IceCube data with an unbinned likelihood stacking approach. Two different weighting schemes were used to account for the unknown relative flux contributions of each source. Nine of ten tests show slight overfluctuations, none of which are statistically significant. An upper flux limit is calculated constraining the maximal contribution of the 2LAC blazars to the recently discovered diffuse TeV-PeV neutrino flux to be around 25% or less assuming the currently favored spectral index for the astrophysical flux of around −2.5 and an equal composition of neutrino flavors arriving at Earth. The results do not require a purely hadronic production of the observed gamma rays and remain valid for moderately harder spectra or smaller sub-populations, e.g. the TeVCat sub-sample, up to a factor of around 2. Additionally, I calculated upper limits for generic power-law spectra and for concrete spectral models of the diffuse neutrino emission of blazar populations. The upper limits for 12 out of 14 tested diffuse neutrino flux models are constraining. If I interpret the largest overfluctuation as a physics effect, I find a soft flux in the 5-10 TeV region that is compatible with gamma-ray observations. Further years of data are already available which makes this scenario testable in the near future. If confirmed, blazars might become the first known extragalactic hadronic acceleration site.
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Timo Karg
Post-Doc | DESY
High-Energy Neutrinos
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TAXI: A Transportable Array for eXtremely large area Instrumentation studies A common challenge in many experiments in high-energy astroparticle physics is the need for sparse instrumentation in areas of 100 km2 and above, often in remote and harsh environments. All these arrays have similar requirements for read-out and communication, power generation and distribution, and synchronization. Within the TAXI project, we are developing a transportable, modular four-station test-array that allows us to study different approaches to solve the aforementioned problems in the laboratory and in the field. Well-defined interfaces will provide easy interchange of the components to be tested and easy transport and setup will allow in-situ testing at different sites. Every station consists of three well-understood 1 m2 scintillation detectors with nanosecond time resolution, which provide an air shower trigger. An additional sensor, currently a radio antenna for air shower detection in the 100 MHz band, is connected for testing and calibration purposes.
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Samridha Kunwar
Post-Doc | DESY
Advanced Technologies
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The goal of the project I am working on is to address the common challenges faced by several high-energy astroparticle detectors in that they require numerous detectors in typically harsh environmental conditions. With TAXI (Transportable Array for eXtremely large area Instrumentation studies), we are working on developing an array of stations, each comprising of three well understood 1 m2 scintillation detectors with nanosecond resolution that subsequently provides an air shower trigger. This modular station provides a means by which we can address typical astroparticle detector requirements namely read-out, communication, power generation and distribution. We have currently deployed the first of what will eventually be an array of 4 stations at the DESY-Zeuthen site. My role within the project has been all encompassing, ranging from testing the electronics, developing firmware for the fpga embedded system at the heart of detector and will involve analysing data which we have recently begun taking.
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Alexander Stasik
PHD student | DESY
High-Energy Neutrinos
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I am working on neutrino astronomy with IceCube. My technical work is to develop a framework to transmit and analyse neutrino events in real time allowing IceCube to trigger follow up observatories like optical, X- or gamma- ray telescopes. Goal is minimal delay (tenth of seconds up to few minutes) in a fully automated analysis pipeline 24/7 without a human in the loop. Main challenges are limited computational power and bandwidth at South Pole as well as high stability of the systems for years. My analysis is a stacked point source search for type IIn and Ib/c supernovae. Supernovae in densed circumstellar media are expected to be efficient accelerators of hadrons and also neutrinos. While the mechanism can be compared to standard supernova remnants, in the presence of circumstellar media the full evolution is compressed from several thousand years to just a few years resulting in much higher expected neutrino fluxes. While current models are consistent with the IceCube diffuse neutrino flux, the goal for my analysis is to resolve individual sources and thus identify neutrino point sources for the first time.
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Oleg Kalekin
Post-Doc | FAU Erlangen
High-Energy Neutrinos
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In 2014, a prototype of the KM3NeT detection unit consisting of a string with three digital optical modules (DOMs) has been deployed at a depth of 3500 metres, 100 kilometres off the coast of Portopalo di Capo Passero, Italy. Such novel optical module consists of a 17" glass sphere, equipped with 31 ultra-fast sensors that can detect light at the quantum level, electronics for the digitization of the signals a fibre optics to transmit the data to shore. One of these fully operated DOMs has been integrated at ECAP with a use of R12199-02 Hamamatsu PMTs. This PMT type was developed by Hamamatsu in a close contact with KM3NeT in a few iterations with characterization of each new version by KM3NeT. ECAP was the leading group in such tests characterizing a few hundred PMTs to the end of development. Currently, ECAP participates in the DOM production for the KM3NeT Phase-1. Up to 70 DOMs will be built at ECAP in 2015-2016. Based on experience in the PMT characterization and optical module design for KM3NeT, such activities started for Pingu-IceCube and FlashCam-CTA projects. New multi-PMT DOM is being designed for Pingu and characterization of the new Hamamatsu R11920 and R12992 PMTs has started at ECAP.
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Post-Doc | HU Berlin
Dark Matter
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One of my primary focusses has been DaOne of my primary focusses has been Dark Matter (DM) research. I have carried out Dark matter (DM) sensitivity studies for the Galactic Centre region for the Cherenkov Telescope Array (CTA). I used simulations to compare the expected sensitivity of DM searches with CTA at different altitudes and for different telescope array layouts, as input for the decision on the location of the CTA sites. For the HAP DM workshop in Adlershof in 2014 I set up and helped to run tutorials using the DarkSUSY simulation package. I have taken observation shifts at the H.E.S.S. experiment in Namibia and worked on H.E.S.S. data analysis including Galactic Centre studies, PWN and DM clump analyses. Additionally, I have worked on the development of a pointing model for the CTA Medium Sized Telescope (MST) prototype in Adlershof, Berlin, as well as studying the performance of the telescope structure, such as bending of the telescope frame due to the weight of the (dummy) Cherenkov camera. An accurate bending model of the telescope and pointing calibration is essential for future data analysis with the CTA array including DM searches. The development of this model is ongoing, and current work includes the calibration of the CCD cameras used to take pointing images using OpenCV libraries, analysis of sky images to find the true pointing direction of the telescope with Astrometry.net software and the identification of the telescope camera position (via LEDs) using CCD images, as well as estimation of the systematic errors on the pointing accuracy of the telescope. Through multiple measurements of the sagging of the MST prototype at different elevations, the bending and hysteresis effects that we initially observed have been better understood and significantly reduced.
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Francesca Bisconti
PhD student | KIT
Ultra-High Energy Cosmic Rays
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My working topic is to make simulations of the EUSO-TA detector response. EUSO-TA is a fluorescence detector developed by the JEM-EUSO Collaboration and installed in the Telescope Array site in Utah (USA). Its purpose is the validation of the JEM-EUSO prototype (lenses, PDM, electronics) via calibration with Electron Light Source and the Central Laser Facility. Inter-calibration with TA fluorescence detectors is possible, through comparison of noise and signal, as well as observation of cosmic ray air showers triggered by TA. The detector is active since March 2015 and I have participated to the May campaign and planned to go to Utah for the November campaign. Using the EUSO-Offline software, I simulate the laser and cosmic ray shower events and compare the results with data. The software development is still ongoing and I contribute to this.
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Jorge Diaz
Post-Doc | KIT
Astroparticle Theory
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Astroparticle physics has opened new window for studying the most violent events in the Universe. Moreover, the high energies of cosmic rays and gamma rays can be used as tools for testing some of the most fundamental assumptions upon which our current theories for describing Nature are based. My topic of research is the study of Lorentz invariance, the symmetry that underlies special relativity, which makes Lorentz invariance a cornerstone of modern physics being one of the basic ingredients in the construction the two most successful theories to date: general relativity and the standard model of particle physics. My research involves theoretical studies of Lorentz invariance by elaborating techniques to search for signals of possible violations of Lorentz symmetry in astroparticle physics. More precisely, during my research funded by the Helmholtz Alliance for Astroparticle Physics I performed the calculation of a nonstandard decay process to be tested using high-energy cosmic rays. The observation of energetic cosmic rays at the Pierre Auger Observatory allows the determination of unprecedented limits on possible violations of Lorentz invariance in the form of modifications of conventional electrodynamics.
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Stefanie Falk
PhD student | KIT
Ultra-High Energy Cosmic Rays
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I have been working in the field of cosmic rays (CR). At the most extreme energies, exceeding 60 EeV, the Extreme Universe Space Observatory (EUSO) is planned to investigate the CR flux from a low earth orbit. The measurement technique involves the detection of the UV light emission by extensive air showers (EAS), mainly nitrogen fluorescence and Cherenkov radiation. For the purpose of this future experiment, I conducted simulation studies on different aspects of the atmospheric influence on the UV light detection from space. I studied the influence of varying global atmospheric conditions on light emission and transmission for selected locations in different climate zones and seasons. In detail, I studied the significance of UV absorption by ozone with respect to UV light emitted by EAS. I also performed a simulation study on the change in UV reflection on ground assuming varying UV albedo from literature. In the course of my work. I developed and implemented algorithms and modules for the simulation framework.
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Florian Fraenkle
Post-Doc | KIT
Neutrino Mass
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I am working at the Karlsruhe Tritium Neutrino (KATRIN) experiment. KATRIN is a large-scale experiment for the model independent determination of the mass of electron anti-neutrinos with a sensitivity of 200 meV/c2. It investigates the kinematics of electrons from tritium beta decay close to the endpoint of the energy spectrum with a high-resolution electrostatic spectrometer. Within the experiment, I am involved in the spectrometer commissioning measurements, with a focus on spectrometer background processes. |
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PhD student | KIT
Dark Matter
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The topic of my PhD thesis is about dark matter search with a multidimensional maximum likelihood model. For this, I analyse data of the EDELWEISS-III experiment. For a period of 8 months between 2014 and 2015 the experiment took WIMP search data with 24 FID Ge-bolometers of 800 g mass each. To look specifically for low mass WIMPs in the GeV-range, 8 detectors with particularly good performance and high efficiency at low energies were selected. For each of these detectors, the different backgrounds event populations have been extracted from sidebands of the data and are described with models. With these background models and an additional PDF describing a possible WIMP signal, the data can be fitted. In case of a result compatible with zero, exclusion limits can be derived statistically. The results of this likelihood fit can be directly compared to a BDT analysis of the same data. With the effective subtraction of backgrounds and the higher signal yield due to a lack of cuts, the likelihood method can achieve higher sensitivity for WIMP signals.
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Markus Hoetzel
Post-Doc | KIT
Neutrino Mass
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The Karlsruhe Tritium Neutrino Experiment KATRIN aims to determine the mass of the electron antineutrino. A sensitivity of 200 meV requires a precise measurement of the endpoint region of the tritium beta-spectrum and dedicated analyses. For that purpose, detailed simulations of the windowless gaseous tritium source of KATRIN have been developed to include effects of density and temperature inhomogeneities. Measurements at a source test experiment revealed the thermal behaviour of the source and allowed to include directly the temperature profiles into the simulations. In combination with precise simulations of the beta-electron spectrum, expected KATRIN measurement spectra were simulated. Newly developed analysis routines then allowed studying statistical and systematical effects of the source: The sensitivity of KATRIN was calculated using various statistical approaches. The influence of background electrons in the spectrometers on the sensitivity was investigated. Systematic uncertainties arising from source inhomogeneities or tritium impurities were studied.
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Olga Kambeitz
PhD student | KIT
Ultra-High Energy Cosmic Rays
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Radio Detection of Horizontal Extensive Air Showers with AERA: AERA, the Auger Engineering Radio Array, is located at the Pierre Auger Observatory in Malargüe, Argentina. AERA is measuring the radio emission of extensive air showers, which is coherent at MHz frequencies. AERA is consisting of 124 antenna station of which 24 are low periodic dipole antennas (LPDAs) and 100 are so called butterfly antennas. Both antenna types are optimized for the detection of more vertical air showers. Together with the Auger surface detector, the fluorescence detector and the muon detector, AERA is able to measure cosmic rays in the energy range of 1017 to 1019 eV by a hybrid detection mode. My work focused on the analysis of the horizontal air showers at AERA. My analysis lead to a better understanding of the emission mechanisms and the angular dependence of the radio signals of cosmic air showers. It also achieved a higher statistics in the detection of high-energetic cosmic particles. Then, I studied less vertical air showers, as for inclined air showers the atmosphere is thick enough to distinguish neutrino-induced air showers from those generated by charged nuclei. To investigate and improve the sensitivity of AERA to these inclined showers, I was involved in the installation of prototype stations including antennas for vertical polarization and lower frequencies on the AERA site in November 2013.
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Michael Karus
PhD student | KIT
Ultra-High Energy Cosmic Rays
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For the detection of extensive air showers that are induced by cosmic rays, the detection of Cherenkov and/or fluorescence light is one essential detection method. The JEM-EUSO mission for example strives for the detection of UHECR from space via fluorescence light, using Earth's atmosphere as a calorimeter. In order to reliably estimate the energy of the primary particle, the amount of light emitted by the air shower must be measured, and for that the performance of the used photo detectors must be very well known. Designing and building a calibration stand for various photo sensors, like PMTs and SiPMs, of different sizes, was my topic. For this, a single-photon light source and a photon shielding were built and readout electronics were implemented. Test measurements in single-photon mode with different PMTs and SPMs were done. In addition, several improvements of the light source were implemented, e.g. different levels of light output or a spectral light source for ten different wavelengths.
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Valentin Kozlov
Post-Doc | KIT
Dark Matter
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The ongoing work is being done within HAP research topic 3 "The Dark Universe", work package "Key technologies for next generation Dark Matter experiments". It overlaps with and profits from close relation to research topic 4 "Advanced Technologies". In particular, I am working on defining requirements and the design of a readout system for the next generation experiment, EURECA. The design process is based on the accumulated experience within running EDELWEISS, CRESST and SuperCDMS dark matter experiments. It is therefore performed in close collaboration with other HAP members: University of Tübingen and Technical University of Munich, and also includes non-HAP international partners from Europe, U.S., and Canada.
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Chuan Miao
Post-Doc | KIT
Advanced Technologies
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Advanced technologies for data acquisition and data processing New experiments rely on latest detector technology with an increasing temporal and/or spatial resolution. These devices are demanding for the data acquisition and data processing systems. New concepts need to be developed to cope with this new magnitude of data states. We research on using massive parallel computing architectures for online monitoring and trigger systems. We proved that high-performance graphic processors are a solution and can be integrated in DAQ systems. To support system development, we developed a parallel computing framework that allows to configure and to extend data processing workflows in a modular manner. In order to manage complexity we analyse advanced monitoring concepts aiming for data quality and system performance. The location of physics experiments aim for reliable remote analytics. Web-based technologies are investigated to visualize complex data structures and DAQ systems.
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Susanne Mertens
Post-Doc | KIT
Neutrino Mass
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At present, I am working as a fellow of the Helmholtz Postdoc Program at the Lawrence Berkeley National Laboratory (LBNL) and the Karlsruhe Institute of Technology (KIT). In the years 2013 and 2014, the Feodor Lynen Research Fellowship of the Alexander von Humboldt foundation additionally funded my research. My work is focused on the Majorana Demonstrator and the Karlsruhe Tritium Neutrino (KATRIN) experiments. A unique way to explore the nature of neutrinos is the search for a rare decay process, the neutrinoless double beta decay (0nbb). The Majorana Demonstrator will perform a search for 0nbb in detectors enriched in 76Ge. Here, I lead the characterization of the integrated detector system at Sanford Underground Research Facility (SURF), South Dakota, where the experiment is currently being commissioned. The KATRIN experiment is the world-leading experiment to measure directly the effective electron anti-neutrino mass from the kinematics of tritium beta decay with a sensitivity of 200 meV (90% CL). Here, my main focus is the investigation and mitigation of spectrometer-related background sources. Beyond that, my research is focused on the investigation of the sensitivity of next-generation tritium β-decay experiments to search for a new elementary particle, a so-called sterile neutrino, which is a prime candidate for dark matter. To this end, I started the development of a novel detector technology, supported by the Research Seed Capital funding (RiSC) by the Ministerium für Wissenschaft, Forschung und Kunst (WMK) Baden-Württemberg, with the goal to enable the KATRIN experiment to search for this new species of neutrinos.
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Felix Riehn
PhD student | KIT
Ultra-High Energy Cosmic Rays
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Particle astrophysics is a field of research focused on high energetic processes in the universe. These processes are studied through the detection of messenger particles, like photons, neutrinos and protons or nuclei. Everything from the production at the source, the propagation through space and the arrival at earth is influenced by the interactions of these particles with matter. My work within HAP is focused on modelling of hadron interactions at all energies. The model I work on is developed and tuned to describe the largest possible set of laboratory measurements and then gives a prediction for interactions at energies up to PeV centre-of-mass. It is mainly used for the simulation of air showers but would be applicable for any hadron interaction, be it at the source or in the interstellar medium. With the inclusion of the production of charmed hadrons, the model is one of the first to allow a full inclusive prediction of the atmospheric backgrounds for the measurement of neutrinos at high energy.
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Post-Doc | KIT
Ultra-High Energy Cosmic Rays
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I was involved in the JEM-EUSO mission. The JEM-EUSO experiment is a next-generation international project to study the ultra-high energy universe with cosmic rays above 5x1019 eV from the International Space Station. In the project, I worked on simulation study to evaluate the performance of JEM-EUSO. I also worked on the design and the evaluation of expected performance of the on-board calibration system for JEM-EUSO.
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Sven Schoo
PhD student | KIT
Ultra-High Energy Cosmic Rays
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I am working on two different projects. One is the development of a web platform that is used to publish the data measured with KASCADE (KASCADE Cosmic ray Data Centre (KCDC)). Making the data available to the broad public presents several challenges. The two major concerns are to enable the user to retrieve the data in a customizable (selecting only those events that are of interest etc.) yet intuitive way and to make the data actually usable, i.e. to provide detailed documentation on the detector setup and on the reconstruction procedures used having in mind two main audiences, colleagues as well as pupils/students (mainly for outreach). The second project is a combined reconstruction of KASCADE and KASCADE-Grande measurements. The goal is to retrieve the energy spectrum and mass composition of cosmic rays in the energy range from 1 PeV to 1 EeV treating KASCADE and KASCADE-Grande as one detector. The advantage over the stand-alone analyses is a more accurate reconstruction of the shower observables as well as a larger fiducial area while avoiding differences in possible systematics depending on slightly different details in the reconstruction of the shower observables and quite different procedures used to reconstruct the energy and mass of the primary particle. The influence of the hadronic interaction models on the energy and mass reconstruction are studied and astrophysical models on acceleration and propagation of cosmic rays are confronted with the results.
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Bernhard Siebenborn
PhD student | KIT
Dark Matter
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Installing a new hardware on the EDELWEISS experiment with an internal FPGA based trigger algorithm that is used to identify events on two ionization channels. After one event is identified, an event-based readout of the same event with a higher sample rate of 40 MHz instead of 0.1 MHz is started. These time resolved ionization channel data is analysed within my PhD project. A new processing chain for the time resolved raw data had to be programmed which reduces several hundreds of GB raw data to the most important information like pulse rise time and amplitude. Based on the reduced data, a statistical analyse can be done. I have shown that a difference between surface and fiducial events can be seen in the rise time.
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Nikolaus Trost
PhD student | KIT
Neutrino Mass
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I worked on the development of a full background model for the KATRIN Experiment. The goal of my thesis is to understand all sources of background electrons and, if possible, to eliminate or reduce them. These sources of background include radioactive decays from Radon 219, 220 and Lead 210, field emission, secondary electrons from cosmic rays and possible ionisation of Rydberg atoms. For the study, I conducted extensive measurements at the KATRIN main spectrometer and also performed numeric simulations.
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Lenka Tomankova
PhD student | KIT
Ultra-High Energy Cosmic Rays
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During my PhD research, I have focused on the optical properties of the Pierre Auger fluorescence telescopes, in particular on describing the telescope point spread function and its effects on the reconstruction of cosmic-ray air showers. A large part of my work has revolved around a novel method for probing the telescope response – a remotely controlled flying platform equipped with an absolutely calibrated light source that mimics a snapshot of an extensive air shower traversing the atmosphere, providing unprecedented understanding of our telescopes.
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Richard Walker
Post-Doc | KIT
Dark Matter
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I was working on R&D projects in support of future tonne-scale direct dark matter detection experiments. As part of the next generation of dark matter detectors, EURECA was planned as a collaboration between the cryogenic dark matter searches of CRESST and EDELWEISS. My topics of research revolved around the conceptual design of EURECA, in particular contributing to the infrastructure and cooling facilities of the experiment. I assembled and commissioned a test facility for PMTs viewing a water-based Cherenkov detector designed as a prototype active muon veto, taking and analysing data with routines that I had written. Measurements taken with this prototype were further used to optimise a simulation package developed to aid the EURECA veto design. Plans were made, and initial designs constructed, to allow an easy exchange of detector modules with other cryogenic dark matter search experiments, and I was involved in the initial design work for European-produced detectors to be mounted in a setup that would allow these detectors to be used at a host facility in the US.
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Martin Bissok
PhD student | RWTH Aachen
High-Energy Neutrinos
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I searched for neutrinos originating in dark matter annihilations in the Galactic centre, using data taken by IceCube in the 79-string configuration. Since the Galactic centre is about 30° above the horizon, the major challenge for this analysis was the overwhelming background of atmospheric muons and neutrinos. The strategy of choice was to use parts of IceCube as veto, and accept only muons which seem to start inside the detector and are more likely to originate in neutrino interactions. Thus, the first step was to develop and implement pre-selection algorithms (filters) to run at Pole and reduce the large amount of data to a manageable size. The second step was offline data selection and processing making use of more sophisticated event reconstruction techniques. The third step consisted of a likelihood-ratio based veto making use of the timing and location of even the faintest detected light in IceCube. Finally, a shape-likelihood analysis was performed exploiting the difference in the expected arrival directions of the remaining atmospheric background and the halo-centric signal was performed. No excess flux was found, and the result is compatible with the background hypothesis. Thus, exclusion limits on the self-annihilation cross-section are presented, reaching down to 1e-23 cm3/s, assuming the NFW halo profile.
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Christian Haack
PhD student | RWTH Aachen
High-Energy Neutrinos
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Search for the origin of the astrophysical neutrino flux measured by the IceCube Neutrino Observatory. The IceCube neutrino observatory has measured a diffuse flux of astrophysical neutrinos with high significance (>6sigma). But still the sources of this flux remain elusive. Dedicated analyses performed by the IceCube Collaboration searching for spatial clustering of neutrino arrival directions or temporal clustering of neutrino events have thus far been inconclusive. In my work, I search for a neutrino flux contribution from the galactic plane originating from cosmic rays interacting with interstellar matter. The analysis utilizes a multi-component forward-folding likelihood fit, taking into account multiple background components. The method can also be used for other spatial profiles e.g. a galactic halo for dark matter searches.
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Raphael Krause
PhD student | RWTH Aachen
Ultra-High Energy Cosmic Rays
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The working topic is to measure the electric field strength of radio emission from cosmic ray induced air showers using the Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory. To get maximal information about the electric field strength a new 3D-Antenna were designed and set up at AERA. In addition to the north-south and east-west polarization, this antenna measures the vertical signal polarization as well. Therefore, it firstly improves the electric field measurements and secondly extend the radio station field of view towards the horizon. The measurements are only possible with very well understood radio stations. To measure the antenna response pattern a calibration setup was developed using an octocopter. During a measurement campaign, several measurements of the antenna response pattern as well as of the soil conditions were performed and compared with the simulations. Further simulations have been performed to get an idea about how the antenna response pattern of different types of radio stations at AERA looks like. With such simulations several influences on the antenna response pattern has been investigated, e.g. uncertainties caused by the antenna alignment, influences of the antenna structure itself or the influence of soil conditions.
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Mathieu Pellen
PhD student | RWTH Aachen
Astroparticle Theory
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The AMS-02 experiment is providing extremely precise measurements on the flux of electrons and positrons.
As the annihilation of dark matter would give rise to such a flux, it is then possible to exclude the existence of such process for certain parameters.
I have thus set model independent limits on the annihilation cross section.
In addition, I have also explore the correlation between the fluxes of antiparticles by making a prediction for the maximum flux of anti-proton produce by a dark matter annihilation.
But dark matter could be detected at direct detection and collider experiments.
It is thus important to explore this complementarity to set constraints on dark matter models.
I have thus derived LHC, IceCube and relic density limits on a particular model.
This simple model is supposed to catch most of the characteristic of other dark matter model and make thus its study important.
Finally, the search for dark matter at the LHC is one of the main task of the experimental collaboration.
In order to set limits or to find a sign of dark matter, one needs appropriate and precise predictions for the dark matter signal.
To that end, I have computed NLO QCD corrections for s-channel simplified models for arbitrary processes in fully automatised way.
This tool is now public and can be used by experimental collaboration.
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Christine Peters
PhD student | RWTH Aachen
Ultra-High Energy Cosmic Rays
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I am working on a detector prototype optimized for the measurement of the muon content of extensive air showers. The determination of the muon content is essential for the identification of the chemical composition of UHECRs. The most important innovation and characteristic of our prototype is that our detector is read out by semiconductor photo sensors, silicon photomultipliers, which outperform current photomultiplier tubes. Besides putting the prototype into operation, a dedicated detector simulation is needed to study the improvements on the investigation of ultra-high-energy cosmic ray air showers by an implementation of our detector in current detector arrays. The simulation framework can then be cross-checked by measurements with the prototype. I have been working on these simulation studies.
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Leif Rädel
PhD student | RWTH Aachen
High-Energy Neutrinos
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My PhD focuses on the measurement of the astrophysical muon neutrino flux. Since IceCube dominantly measures atmospheric muons it is necessary to filter out neutrino events. I implemented an event selection using boosted decision trees for five years of IceCube data which selects about 70,000 neutrinos per year which are dominantly of atmospheric origin. The background of atmospheric muons in negligibly small. In order to extract the astrophysical flux from these data an maximum likelihood fit in reconstructed muon energy and zenith direction was implemented which determines the best combination of atmospheric and astrophysical neutrinos compatible with the data. Detector and atmospheric neutrino flux uncertainties are taken into account as nuisance parameters. An atmospheric-only origin of the neutrino flux can be excluded by 6 sigma. Additionally I found the highest energy neutrino event observed to date. It has deposited an energy of about 2.6 PeV in the detector and the most likely neutrino energy is around 10 PeV. Using dedicated simulations I validated the directional and energy reconstruction of this event and tried to correlate it with potential neutrino sources.
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Maurice Stephan
PhD student | RWTH Aachen
Advanced Technologies
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I studied the feasibility of instrumenting fluorescence telescopes with silicon photomultipliers. Together with my colleagues I designed, constructed and commissioned the seven pixel version of FAMOUS (First Auger Multi-pixel-photon counter camera for the Observation of Ultra-high-energy air Showers), a small fluorescence telescope prototype. In parallel, I constructed a photometer, which makes use of a single silicon photomultiplier and used it to measure the diffuse night-sky brightness and starlight. In this context, I developed an analysis method to determine the absolute light flux originating from continuous light sources and detected with silicon photomultipliers. The measurement results have been compared to data from models of star light emission.
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Björn Eichmann
PhD student | TU Dortmund
Astroparticle Theory
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In order to distinguish the leptonic from the hadronic origin of the non-thermal emission of a flaring blazar I developed a semi-analytical model that describes the temporal development of the emergent particles (i.e. photons and neutrinos) based on their leptonic and hadronic origins, respectively. The emission is supposed to be generated by relativistic particles that are picked up by a spherically symmetric knot consisting of a dense thermal plasma that leaves the central engine of the active galactic nucleus. My approach started with the transport equation of the injected relativistic particles and takes spatial diffusion and continuous energy losses into account. I determined a general solution of these primary particles and subsequently specified them by different constraints on the cosmic environment. On the one hand, a pickup of relativistic electron is considered, that leads to synchrotron, as well as external Compton radiation. On the other hand, also relativistic protons are picked up, which are able to generate high-energy photons and neutrinos by inelastic proton-proton collisions. Subsequently, I investigated the temporal development of the emergent photon and neutrino intensities of blazar flares in hadronic and leptonic interaction scenarios are calculated, given useful predictions of flare durations and time lags between photons of different wavelength and high energy neutrinos. Finally, I showed that a combination of hadronic and leptonic emission models give an accurate description of the flaring from optical to gamma-ray energies of PKS 2155-304 on 2006 July 29-30.
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Thomas Wester
PhD student | TU Dresden
Double Beta Decay
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My work concentrates on data analysis and Monte Carlo simulations, largely in the field of double beta decay and dark matter research. The focus lies on alternative decay modes that lead to emission of gamma/x-rays, like double beta decays into excited states of the daughter nucleus or double beta+ decays and double electron capture. The research in the framework of the GERDA experiment allows searching for several double beta decay modes of Ge-76. Furthermore, as GERDA employs its detectors in a large liquid argon cryostat, it allows studying background related to liquid argon and search for the double electron capture of Ar-36. This can then be transferred to future large scale dark matter experiments in an attempt to expand the physics program of those experiments, as several of them utilize large masses of liquid noble gases like argon or xenon. Sensitivity studies using proposed designs like the DARWIN project will test the feasibility of double beta decay searches of Xe and Ar isotopes within those experiments. In addition, the potential background that double beta decays pose to dark matter processes can be estimated. For this purpose, more realistic Monte Carlo simulations considering additional double beta decay modes and further background (e.g. from solar neutrinos) are being developed.
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Andrea Münster
PhD student | TU München
Dark Matter
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The direct dark matter search experiment CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) uses scintillating CaWO4 single crystals as targets for possible recoils of dark matter particles. My work deals with the production of these CaWO4 crystals, which happens to be produced on site at the Technische Universität München (TUM) for several years. The production process includes the CaWO4 powder production from the raw materials CaCO3 and WO3, the CaWO4 crystal growth via the Czochralski method as well as the after-growth treatment of the crystals. Here good optical properties and a radiopurity as good as possible are crucial for the performance of the experiment. The aim of my work is to improve further the quality of the CaWO4 crystals, especially their radio purity. One way to achieve an improvement is a chemical purification of the raw materials. First promising tests have been performed and the crystal successfully produced from these raw materials is now being investigated.
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Sabine Roth
Post-Doc | TU München
Dark Matter
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I was working in the CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) and EURECA (European Underground Rare Event Calorimeter Array) group at TUM. The CRESST experiment aims at the detection of dark matter particles by measuring phonons and light generated in a CaWO4 crystal at mK temperatures. For particle identification, light detectors with excellent resolution and the knowledge of the Quenching Factors (QFs: relative amount of light detected for interacting particles) are required. I developed improved light-detectors by employment of the Neganov-Luke amplification. An understanding of the experimentally demonstrated improvement as well as of still outstanding problems was achieved. In addition, I developed a comprehensive microscopic model for the light generation and quenching in CaWO4 crystals. With the help of measurements at room temperature and ~20 K, employing ion-beam excitation with the tandem accelerator at the Maier Leibnitz Laboratorium as well as two-photon excitation with a N2-gas laser, I could successfully validated this model also experimentally.
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Marc Tippmann
PhD student | TU München
Low Energy Neutrinos
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My thesis focused on the development of an Optical Module (OM) for the LENA detector. This OM consists of a large, fast photomultiplier (PMT), a non-imaging light concentrator (LC) enhancing the PMT's collection area and the homogeneity in the detector, a Mu-metal magnetic shielding and a voltage divider, all housed within a lightweight pressure encapsulation with a transparent front window, allowing the use of the PMTs even at 12bar pressure at the tank bottom. I developed a PMT testing setup with a fast ps-diode laser to characterize the candidate PMT series, which are available currently or soon. As a side-product, I discovered a novel disturbing effect in PMTs - fast after-pulses emerging after only a few tenths of ns after the original photon pulse - and traced back to photon emission from the PMT via bremsstrahlung in the dynodes and fluorescence of the amorphous ruby dynode mount. In addition, light concentrator shapes of various types were calculated and their influence on the detector homogeneity and light yield was studied in a broad MC simulation campaign to find the optimum shape. Finally, I developed a pressure encapsulation based on LC and PMT shape through FEM simulations. Most of these results are generic and can be applied to any large volume neutrino detector or help improve PMT behaviour (e.g. medical imaging). For example, the code developed to analyse the LC transmission behaviour as a crosscheck for the MC simulations is now used for the JUNO project aiming to discover the neutrino mass hierarchy.
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Arindam Chatterjee
PhD student | Uni Bonn
Astroparticle Theory
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The existence of Dark Matter is now well established and its contribution to the energy budget of our Universe has been measured with an accuracy of less than 2% by PLANCK collaboration. Within the Minimal Supersymmetric [extension of the] Standard Model (MSSM) with conserved R-parity, the lightest neutralino is a good candidate for Dark Matter. To compute its relic abundance in the standard thermal production scenario and to meet the desired precision, quantum corrections to various (co-)annihilation processes involving the lightest neutralino have to be considered. In the frame of my PhD I have developed a variation of the on-shell renormalization scheme for the chargino-neutralino sector of the MSSM, which I have used to estimate a class of electro-weak corrections to the relevant (co-)annihilation processes using the "effective coupling" approach. I have then modified the publicly available code "micrOMEGAS" to include these radiative corrections and compute the relic abundance of the lightest neutralino with an enhanced precision. In a different work, I have also shown that the Higgs bosons in the MSSM can be a good inflation candidate in the context of "inflection-point inflation" models.
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Raghuveer Garani
PhD student | Uni Bonn
Astroparticle Theory
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I am currently working on Indirect detection of WIMP dark matter, and more specifically, using low energy (tens of MeV) neutrinos to search for WIMPs captured in the Sun. Recently, it was proposed that neutrinos of tens of MeV coming from stopped pions and muons in the Sun could be used to detect/constrain captured WIMPs annihilating in the Sun. The agenda of the project is to explore in detail whether existing/upcoming supernova neutrino detectors can use this signal to probe light WIMPs. The flux of neutrinos from WIMP annihilation in the Sun is determined by the capture rate of WIMPs in the Sun. This is proportional to the WIMP–nucleus scattering cross section, which is the quantity determined (constrained) by direct WIMP detection experiments. The connection between these two signals is mostly model–independent and there could be potential interplay between these experiments. The aim is to set better bounds on spin dependent WIMP-nucleus cross section using this technique.
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Natacha Leite
PhD student | Uni Hamburg
Astroparticle Theory
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The main projects I am involved in connect magnetic field generation and amplification with the chiral magnetic effect. This comprises the possible role of chiral magnetic instability in amplifying seed fields in neutron stars and magnetars, contributing to the understanding of the origin of the strong magnetic fields of compact objects. I also studied the implications that the chiral magnetic effect has in modifying the magnetohydrodynamics of the early universe. I focused especially on its impact around phase transitions, namely the electroweak transition, as a way to reveal details of the evolution of cosmological magnetic fields. Additionally I am constraining dark matter indirect detection by studying the radio signal originated as synchrotron radiation expected from dark matter annihilations. Privileged locations for this studies are recently discovered dark matter dwarf spheroidal galaxies and objects such as the Smith cloud, where we predict the signal expected from these sources that should be detected by upcoming experiments. I am also interested in the often disregarded contribution that cosmological cosmic rays had on heating up the intergalactic medium before the reionization epoch. Observations of the 21 cm signal will be able to confirm our predictions of the impact that cosmic rays had on reheating the early universe.
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Rayk Nachtigall
PhD student | Uni Hamburg
Gamma Rays
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The topic I am working at deals with the setup of the HiSCORE detector (non-imaging air Cherenkov observations) at Pierre Auger Observatory. This consists of two general parts - the development of the HiSCORE stations to a level where they can run nearly autonomously, requiring only 230V and an ethernet connection, - and air shower simulations, focusing on their radio and Cherenkov parts. For the first part, I deployed two stations in Hamburg, one on the roof of a building exposed to the environment and a clone in a laboratory. Both are used to optimise the stations mechanics (shielding to the environment, remote controlled lid, light collectors, etc.) and electronics (complete DAQ). Aiming at an automatized remote controlled detector. Furthermore the rooftop station is used to observe Cherenkov events in the Hamburgian sky. Since a small HiSCORE array is planned to be deployed in the Infill array of the Pierre Auger Observatory, preferably close to AERA stations, CORSIKA-simulations on hybrid radio and Cherenkov detection of air showers are done in the second part of my work.
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Andrey Saveliev
PhD student | Uni Hamburg
Astroparticle Theory
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Magnetic Fields are a fundamental observable, which has crucial influence on most of the astrophysical phenomena. The main topic of the work carried out during the HAP-funded period have been Intergalactic Magnetic Fields (IGMF), i.e. the fields in the voids outside Galaxies and Galaxy Clusters. Due to several difficulties observing them their exact magnitude, origin and structure are little known. Under the assumption of a magnetogenesis in the early Universe, an analysis of their time dependence has been done by using a novel semi-analytical approach to derive a set of differential equations which directly describe the evolution of the magnetic energy spectrum. Furthermore, also the influence of magnetic helicity was investigated by taking into account the corresponding terms. With this semi-analytical method good results have been achieved, also in comparison with numerical simulations, such that it is a powerful tool for further analysis. A different investigated aspect of IGMF has been their influence on the propagation of particles, in particular on gamma-ray induced electromagnetic cascades. Assuming that their charged component is deflected by the resulting Lorentz Force, it is possible to deduce information on IGMF parameters like magnitude, correlation length and morphology. This scenario, however, is still under debate, since various authors claim that also the interaction of the particles with the intergalactic medium has to be taken into account. Both of these aspects have been thoroughly investigated by running thorough numerical simulations.
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Bastian Beskers
PhD student | Uni Mainz
Advanced Technologies
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My PhD thesis focused on the development of a dual-phase Xenon time-projection chamber. After setting up the time-projection chamber, a second part of my work was to measure and analyse the xenon scintillation pulse-shape.
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Jan Lünemann
PhD student | Uni Mainz
Dark Matter
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During my PhD in Mainz, I worked on a dark matter search with the IceCube neutrino telescope. I developed and unblinded the first IceCube analysis searching for a neutrino signal that could be produced by self-annihilating dark matter in dwarf galaxies, the Andromeda galaxy and the Virgo and Coma galaxy clusters. No signal could be detected in the analysed data, which was taken during ~340 days of livetime with the IceCube detector in the 59-string configuration. Strong limits on the annihilation cross-section have been derived, that - depending on the amount of sub-clusters in dark matter halos - can challenge the WIMP interpretation of a positron excess seen by PAMELA and FERMI. For the analysis a new method for the angular resolution estimator based on the Cramér-Rao inequality was developed. Due to its analytical nature, it is a fast alternative to the conventional method, which evaluates the likelihood function in the environment of the reconstructed direction. The Cramér-Rao estimator was implemented in the IceCube analysis framework and is part of the standard processing. Due to its low computational costs allows providing a resolution estimator already at low levels of the standardized collaboration wide event selection.
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Klaus Wiebe
PhD student | Uni Mainz
Dark Matter
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I have worked on solar dark matter searches with the IceCube Neutrino Observatory, using neutrinos of all flavors. The dark matter candidate is assumed to be of supersymmetric nature (the lightest neutralino) and limits are thus presented in the frame of the pMSSM. I have investigated this supersymmetric scenario for valid models and exclusion complementarities between direct, indirect and accelerator searches. In addition, I have developed a new and efficient resolution estimator algorithm which significantly improved the reconstruction of cascade-shaped signatures. I have employed an unbinned likelihood approach, using directional and energy information to obtain limits on signal events and as such also on the spin-dependent neutralino-proton scattering cross section.
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Moritz Meinecke
PhD student | Uni Münster
Astroparticle Theory
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In a first project, I worked on the calculation of the full SUSY-QCD corrections at NLO for gaugino annihilation and co-annihilation into light and heavy quarks in the Minimal Supersymmetric Standard Model (MSSM). We demonstrated that these channels can become phenomenologically relevant within the so-called phenomenological MSSM. We discussed selected technical details such as the dipole subtraction method in the case of light quarks and the treatment of the bottom quark mass and Yukawa coupling and presented numerical results for the (co-)annihilation cross sections and the predicted neutralino relic density. In a second project, I have calculated the full supersymmetric QCD corrections at NLO for stop-antistop annihilation into electroweak final states within the MSSM. Moreover, I have incorporated Coulomb corrections due to gluon exchange between the incoming stops and presented numerical results for the annihilation cross sections and the predicted neutralino relic density. Both projects revealed that the impact of higher order corrections on the cosmologically preferred region of the parameter space can be larger than the current experimental uncertainty from Planck data.
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Stephan Rosendahl
PhD student | Uni Münster
Dark Matter
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Title of the Thesis: Gas purification of the XENON dark matter search. In the context of my PHD thesis, I designed the gas purification for the XENON1T experiment, based on adsorption and distillation. Especial the removal of the radioactive Kr-85 from xenon using cryogenic distillation has been the main part of my work. A novel cryogenic package column has been designed and successfully been commissioned, producing ultra-clean xenon for the next generation dark matter experiment XENON1T. In this context also a novel tracer method using radioactive Kr-83m has been developed, which allows investigating the distillation process for very tiny concentrations of krypton in xenon on the sub-ppt scale.
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Robert Brose
PhD student | Uni Potsdam
Astroparticle Theory
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I am working on the acceleration of cosmic rays (CR) in supernova remnants (SNR). As there is a lack of a model explaining the gamma-ray emissions from supernova remnants as well as the spectrum of the CR up to the knee, we try to develop a fully time-dependent model. Therefore, we developed a numerical model that accounts for the resonant amplification of Alfven-waves that scatter CRs and allow Fermi-acceleration to take place. Further several processes as cascading, damping a convection of the turbulence are considered to cover the most dominant. This requires solving a system of coupled partial differential equations while accounting for a very fine numerical resolution close to the shock. The simulation results allow the calculation of emission spectra that can be compared with experimental data to check the quality of the model or constrain simulation parameters and decide whether e.g. Gamma-ray emission are of leptonic or hadronic origin. In addition, the escape process can be studied which is essential to understand how CRs self-confined in a SNR become free galactic CRs that can be measured at the earth after their propagation. Currently also the possibility to extend the model beyond the current test-particle regime is explored, which would allow to account for the back-reaction of the CRs on the shock-structure. This would make it necessary to solve also the hydrodynamic-equations on the fly, which makes the whole simulation much more difficult and numerical expensive. The result would be the first fully time-dependent simulation of non-linear Fermi-acceleration.
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Xuhui Chen
Post-Doc | Uni Potsdam
Astroparticle Theory
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My work focuses on the developments and applications of a numerical model that describes the multiwavelength variability of AGN jets. This model employs the Monte Carlo method for the photons, and the Fokker-Planck equation for the electrons. This way the model can track the evolutions of both the radiative transfer and the particle acceleration. In addition, we also calculate the time-dependent polarization from the jets. The model is mostly applied to Blazars, which usually show strong variability in both gamma ray and X-ray, as well as optical wavelength. In recent developments of the model, we also consider the diffusion of particles in the jets. This allows us to study the inhomogeneity in the jets. All these efforts help to understand the particle acceleration and radiative mechanism in AGN jets. This is important in determining the composition of AGN jets, i.e. whether they are primarily leptons or hadrons. The answer to this question has profound implication on whether AGNs are viable sources of ultra-high-energy cosmic rays.
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Alina Wilhelm
PhD student | Uni Potsdam
Astroparticle Theory
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My scientific work is concentrated on particle acceleration in Supernova remnants (SNRs) that are most probably the sources of Cosmic rays (CR). Using a very detailed code ”PATRON” from Telezhinsky et al. (2012) solving the time-dependent transport equation for CR and combining it with hydrodynamical simulations, I model broad spectrum from particular SNRs. During my PhD, we found that standard acceleration model, so-called Diffusive Shock Acceleration (DSA) fails to explain radio spectrum from various SNRs. Therefore, the above-mentioned code was extended by an additional acceleration mechanism in the vicinity of the SNR shock: the Stochastic Acceleration (SA). First of all, we studied the generic impact of SA and found a significant difference to the standard DSA results, especially in the low energy range. Next, we applied the extended "PATRON" code (containing two independent mechanism SA & DSA) to the young type Ia SNR Tycho. Studying Tycho, we worked out several self-consistent models which reproduce its multiwavelength spectrum extremely well. Moreover, for the observed data we found explanations alternative to the widely accepted models. Recently I started to work on my next project: Cas A, which is assumed to be a Ib type SNR (to wit it resulted of a core-collapse of a Wolf-Rayet star). Its hydrodynamical structure differs from Tycho’s SNR significantly, and also in this case the impact of SA is of the great scientific interest.
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Nils Hakansson
PhD student | Uni Potsdam
Dark Matter
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I am doing a dark matter lines search in the energy regime. The data comes from VERITAS, which is an array of four Cherenkov telescopes. The method of acquiring the energy of the particle generating the Cherenkov radiation is done by fitting a 3D-gausian to said shower. From the fit 3D-model parameters are gotten which are den used to search a look-up table for the energy. The energy range that I am analyzing goes from about 100 GeV too 10 TeV. The line search is done via the so called sliding window approach, fitting the background and signal region with a pure power-law and a power-law plus gaussian. The significance of a line is then calculated via the log likelihood ratio between the two fits.
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Piotr Homola
Post-Doc | Uni Siegen
Ultra-High Energy Cosmic Rays
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My research activity concerns the studies on photons as ultra-high energy cosmic rays. During my stay at the Siegen University I was working on the development of a method to calibrate the absolute energy scale of air showers with ultra-high energy photons. Calibrating the absolute energy scale of air showers initiated by ultra-high energy cosmic rays is an important experimental issue. Currently, the corresponding systematic uncertainty amounts to 14-21% using the fluorescence technique. We developed a new, independent method which can be applied if ultra-high energy photons are observed. While such photon-initiated showers have not yet been identified, the capabilities of present and future cosmic-ray detectors may allow their discovery. The method makes use of the geomagnetic conversion of UHE photons (preshower effect), which significantly affects the subsequent longitudinal shower development. The conversion probability depends on photon energy and can be calculated accurately by QED. The comparison of the observed fraction of converted photon events to the expected one allows the determination of the absolute energy scale of the observed photon air showers and, thus, an energy calibration of the air shower experiment. We showed that already a very small number of UHE photons may help to test and fix the absolute energy scale.
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Mariangela Settimo
Post-Doc | Uni Siegen
Ultra-High Energy Cosmic Rays
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My research activity is focused on the study of ultra high-energy cosmic rays, hitting the Earth with energies up to about 30 Joules. Their origin and nature is still unknown, although they are most probably produced in extragalactic astrophysical sources. During my post-doc at the University of Siegen and with HAP, I was primarily involved in the search for ultra-high energy photons with the Pierre Auger Observatory, the largest experiment ever built for the detection of such particles. These photons are expected to be extremely rare. No photons have been identified so far but they are privileged messengers of the sources and the propagation of the most energetic particles in the Universe which makes this research compelling. As result of my activity, I have derived the most stringent limits currently available at energies above 1018 eV and I developed a Monte Carlo code (EleCa) for the propagation of high-energy photons in the extragalactic space. I was coordinator of the analysis task for the search of ultra-high energy photons within the Auger Collaboration and member of the multi-messenger working group in collaboration with IceCube and Telescope Array colleagues.
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Alexey Yushkov
Post-Doc | Uni Siegen
Ultra-High Energy Cosmic Rays
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I have studied the mass composition of the ultra high-energy cosmic rays using the data of the Pierre Auger Observatory with methods having reduced sensitivity to details of the hadronic interactions. These methods are: 1. the analysis of the correlation between depth of the shower maximum Xmax and signal in ground stations S1000 for establishing if the primary beam near the "ankle" (lg(E/eV)~18.7) consists of a single or several components; 2. The analysis of the distributions of the depth of the shower maximum for estimation of proton to helium ratio in the primary beam; 3. the analysis of the Xmax elongation rate (Xmax evolution with the energy) for all events, and separately for deeper and shallower events, i.e. for events originating from lighter and heavier primary nuclei, for understanding of the origin of the features observed in the elongation rate (in particular for distinguishing changes in mass composition from possible changes in hadronic interactions); 3. The development of the method for proving the presence of protons in the primary radiation at the highest energies (for testing of astrophysical scenarios or possible Lorentz invariance violation). In additional work, I was the coordinator of the task regarding mass-composition analysis of the Pierre Auger Collaboration and of the joint work with the Telescope Array members on comparison of results of Xmax measurements of the two experiments.
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Shinozaki Kenji
Post-Doc | Uni Tübingen
Ultra-High Energy Cosmic Rays
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My main research fields are ultra-high energy cosmic ray physics and air shower simulation, participating in the JEM-EUSO mission. With HAP support, it has been fruitful in promoting our institute's contribution to the mission and extending the international collaboration, particularly with European partners. The key result that I have been devoted to is the simulation study for evaluation and maximisation of scientific performance. As they act as reduction factor of the performance, the atmospheric phenomena such as airglow and cloud proprieties have been studied in collaborating with scientists in these fields. In parallel, I also join data analysis of a pathfinder mission "EUSO-Balloon", in particular on the UV background measurements. As a result, we successfully demonstrated for the first time that EUSO-type telescope is capability of imaging the light structure on the earth in UV band from the stratosphere. The clear correlation of V background flux was found with the presence of clouds. These results will help improve the background models assumed in the present simulation studies. We also investigated the possibility of EUSO-type wide FOV telescope using for very high energy comic ray physics in lower energies. The key result have been accepted in series of journals, mainly and also represented in the last two International Cosmic Ray Conference.
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Post-Doc | Uni Tübingen
Advanced Technologies
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My work in the University of Tübingen concentrates on the development of the perspective measuring technique for the next phase of the upgraded CRESST dark matter experiment. It focuses on the testing of the cryogenic detectors at very low temperatures. I particularly worked on the development of the SQUID multiplexing system for the simultaneous measurements of many readout channels. In collaboration with KIT Karlsruhe and TU Munich, we are working on the design for such readout system for the next generation dark matter experiment - EURECA. The aim of this work is the construction of a prototype of the multi-channels SQUID system to read you a large number of superconducting transition edge sensors. It should fulfil the requirements of CRESST and EURECA experiments and its future perspectives.
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Daniel Bindig
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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IceTop is the surface array of the IceCube detector located at the Amundsen-Scott-Station at the geographical South Pole. While IceCube mainly searches for cosmic neutrinos, IceTop can be used as a stand-alone detector to address questions related to different Cosmic Ray topics. One of the most important problems is the exact mass composition of Cosmic Rays that reach the Earth after traveling long distances from their sources. Cosmic Ray particles striking the Earth’s atmosphere cause a cascade of particles traveling to ground. Measurements of these particles with experiments such as IceTop help to conclude on properties of the incident primary. Several observables, such as the number of muons at ground, are known to vary for different mass compositions of the primaries. I am working on a measurement of the muon number density using data from IceTop, which is located at an atmospheric depth of 680 g/cm2. For this purpose, only detector signals far away from the shower core are used in order to suppress the otherwise dominant electromagnetic background. Using simulations it can be shown that the number of IceTop sensors recording a signal is a reliable estimator for the true muon number per area. After a few cuts, that reduce systematic uncertainties, the final result can be calculated providing a useful contribution to determine the mass composition of Cosmic Rays.
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Daniel Fuhrmann
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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In the subsequent years, various insights about the shape of the energy spectrum of cosmic rays have been attained. The flux of cosmic rays follows a power law over many orders of magnitude in energy, overall appearing rather featureless. However, there are a few structures observable. There is a distinct steepening at some PeV, the so-called "knee" of the cosmic ray spectrum. It is attributed to a magnetic rigidity dependent cut-off in the particle fluxes of lighter cosmic ray mass groups. It was expected that also the spectra of heavier cosmic ray primaries ought to exhibit such knee structures successively – the so-called "second knee". The KASCADE-Grande experiment aimed at the investigation of the cosmic rays spectra and composition at energies well beyond the first "knee", where the "second knee" was expected. My work was to perform an unfolding analysis disentangling the manifold convoluted energy spectra of five mass groups from the measured two-dimensional shower size distribution of electrons and muons at observation level. The results have confirmed that also the heavier cosmic-ray mass groups exhibit knee like structures, and that the spectrum beyond the first knee is dominated by cosmic rays heavier than protons or helium.
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Ingolf Jandt
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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HEAT (High Elevation Auger Telescopes), as the low energy extension of the Fluorescence Detector, measure showers’ light traces created by nitrogen excitation (fluorescence) and Cherenkov emission. Low Energy showers have weaker light yield, and emerge higher in the atmosphere. HEAT can be tilted upwards, and then measure showers with a smaller angle to the axis, receiving higher fractions of Cherenkov radiation, which is concentrated around the axis. At lower viewing angles only short signal traces come about, which makes geometry reconstruction difficult. The Profile Constrained Geometry Fit (PCGF) incorporates the longitudinal shower development into the geometry reconstruction. This allows reconstruction of Cherenkov-rich, monocular events with accuracy similar to hybrid or binocular measurements. I have implemented the PCGF into the software framework used to reconstruct events measured by the Pierre Auger Observatory. For very low energy events, I have shown that it reconstructs the shower geometry more accurately than the method used up to now. Another part of my work was implementing a model of how asymmetry of the Cherenkov radiation, induced by the geomagnetic field, affects the light yield measured by the fluorescence detector. Studies are ongoing on how much the enhanced reconstruction accuracy and higher statistics can help to improve our knowledge of the distribution of shower maxima and energies, leading to a better understanding of the mass composition of the galactic component of high-energy cosmic rays, and of the transition region to the extragalactic component.
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Sebastian Mathys
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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Cosmic rays interact with the Earth's atmosphere developing extensive air showers (EAS) which can be measured not only using particle detectors on the ground, but also using radio antennas detecting the radio emission in a wide frequency range. The Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory measures the radio emission from air showers in the MHz range using 153 autonomous detector stations. My contribution was the development of a flexible, ROOT based input/output library (AERAROOTIOLib). This improved the efficiency in data handling and analysis of the AERA data. The design with a write functionality is especially necessary for a low-level event extraction and merging procedure. With the new AERAROOTIOLib, the data volume could be reduced by 20% and the read-in part of the analysis could be speed up by a factor of 5. The library also enables the production of important subsets of data for different purposes, e.g. monitoring. An additional AERAConverter tool acting as the interface for the data handling including lots of different converter modes, has been integrated.
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Philipp Papenbreer
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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Photons at energies above 10 EeV are predicted by the Greisen-Zatsepin-Kuzmin effect as well as by several exotic models for the origin of ultra-high-energy cosmic rays, but could not yet be detected experimentally. A proof of these particles as well as a strong limit on their flux is of great importance for models of creation and propagation of cosmic rays. The Pierre Auger Observatory is the largest ultra-high-energy cosmic ray detector in the world and provides a very good sensitivity on primary photons. An ongoing major upgrade of this experiment includes a higher sampling rate for the surface detector electronics. The crucial algorithms which are used to decide for each individual detector station which data are processed for further analyses have to be tuned for the new electronics. For my PhD thesis, I performed studies for those data selection algorithms to enhance the efficiency on photon primary particles. The enhanced relative fluctuations in the data are a challenge for these analyses. Furthermore I used simulations in order to enhance the efficiency of photons as much as possible without an increase in the noise rate.
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Anna Pollmann
PhD student | Uni Wuppertal
High-Energy Neutrinos
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Various extensions of the Standard Model motivate the existence of stable magnetic monopoles that could have been created during an early high-energy epoch of the Universe. These primordial magnetic monopoles would be gradually accelerated by cosmic magnetic fields and could reach high velocities that make them visible in Cherenkov detectors such as IceCube. Equivalently to electrically charged particles, magnetic monopoles produce direct and indirect Cherenkov light while traversing through matter at relativistic velocities. I searched for mildly relativistic (0.5<v<0.85) magnetic monopoles using one year of data taken in the 2011/2012 season by IceCube. IceCubes policy is to prepare analysis just on simulated data in a blind way. During HAP support, I was preparing unblinding. My analysis was reviewed by the IceCube collaboration. Finally, it was applied on the data. No monopole candidate was detected. However the upper flux limit of monopoles was constrained down to a level of 1.55·10-18 cm-2 s-1 sr-1. This is an improvement of almost two orders of magnitudes over previous limits.
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Sven Querchfeld
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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Fluorescence telescopes are an important technique to measure extensive air showers initiated by ultra-high energetic cosmic rays. They detect the longitudinal profile of the energy deposited in the atmosphere by the de-excitation of nitrogen molecules in the UV-range. In the past years the development of photomultiplier tubes (PMT) has led to an increase by more than 30% in photon detection sensitivity, by using new super-bialkali (SBA) photocathodes. Thus, the telescopes can detect even fainter signals over a farther area with a significant increase in aperture. I have worked on developing a telescope for a next generation cosmic ray observatory. This includes a camera, which needs to have a maximal sensitive area of the focal plane. Winston-cones can efficiently cover the dead area between the photocathode of the PMTs. I have worked on developing such a highly efficient system composed of a SBA PMT and Winston cone based on the design of the fluorescence telescopes of the Pierre Auger Observatory and I have performed first measurements of a prototype on site in Argentina.
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Biswajit Sarkar
PhD student | Uni Wuppertal
Ultra-High Energy Cosmic Rays
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Unveiling the mystery of the sources of ultra high-energetic cosmic rays (UHECR) that possess energies above 1018 eV is one of the most urgent questions in contemporary astroparticle physics. Up to now, no final identification of the sources is achieved even after more than one century of research has passed since Victor Hess discovered cosmic rays in the year 1912. In my work predictions for UHECR observables are made and a comparison with the data mainly from the Pierre Auger Observatory is carried out to constrain the properties of source candidates in this energy range. A number of different observables that measure a variety of properties of cosmic rays as the energy spectrum, the mass composition, the direction and the existence of UHE photons and neutrinos are used to ensure a holistic view on UHECR. The theoretical predictions of these observables from astrophysical scenarios including assumptions on sources and on the properties of the intergalactic space are employed to explain the observed data and consequently lead to new insights of the sources itself and the properties of the universe. The predictions are executed with the sophisticated Monte Carlo code CRPropa 2.0 that enable simulation of the UHECR propagation from putative sources to Earth by taking into account all relevant processes. With this procedure, the discrimination of the mass composition, the energy spectrum and the maximum energy of the cosmic rays at the sources was possible. Additionally, also the distributions of the sources and the magnetic field are studied.
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Dennnis Soldin
PhD student | Uni Wuppertal
High-Energy Neutrinos
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Cosmic ray air showers with primary energies above 1 TeV can produce muons with high transverse momentum (pT). These isolated muons can have large transverse separations from the shower core, up to several hundred meters where the lateral separation is a measure of the transverse momentum of the muon's parent particle. Together with the muon bundle, these muons form a double track signature in large neutrino telescopes such as IceCube. I have shown using dedicated simulation methods that the muon lateral distribution depends on the composition of the incident nuclei. Hence, I have determined the composition of high-energy cosmic rays using muon separation measurements from large neutrino telescopes. Moreover, based on these simulations I have studied the contributions from various hadrons to the high pT muon flux. I have shown that these muons may contribute to test pQCD predictions of high energy interactions involving intermediate nuclei.
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Daniela Dorner
Post-Doc | Uni Würzburg
Gamma Rays
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My main research topic is AGN physics with a focus on variability studies of blazars. For the investigations, I use multi-wavelength data with a focus on the very high energies. I am involved in the projects FACT, M@TE, MAGIC and CTA. Using SiPMs, FACT is an ideal instrument for long-term monitoring of bright TeV blazars and provides an unprecedented data set. With the M@TE project, we will close more gaps extending the continuous observation window for the sources to 10 hours per night. Based on this data set and including a large multi-wavelength data sample, I am investigating the variability of bright TeV blazars in the multi-wavelength context. The unbiased and continuous TeV data sample provided allows for periodicity studies on a wide range of time scales searching for binary black holes. Short time variability allows for constraining the emission region and possibly quantum gravity effects. Studying the duty cycle, flare statistics, flare shapes with this large statistics allows characterizing the variability behaviour of blazars. Based on this, conclusion on the underlying physics can be drawn and models can be constrained.
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