@phdthesis{Truestedt2016, author = {Tr{\"u}stedt, Jonas Elias}, title = {Long-wavelength radio observations of blazars with the Low-Frequency Array (LOFAR)}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-144406}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {Aktive Galaxienkerne (AGN) geh{\"o}ren zu den hellsten Objekten in unserem Universum. Diese Galaxien werden als aktiv bezeichnet, da ihre Zentralregion heller ist als alle Sterne in einer Galaxie zusammen beitragen k{\"o}nnten. Das Zentrum besteht aus einem supermassiven schwarzen Loch, das von einer Akkretionsscheibe und weiter außerhalb von einem Torus aus Staub umgeben ist. Diese AGN k{\"o}nnen {\"u}ber das ganze elektromagnetische Spektrum verteilt gefunden werden, von Radiowellen {\"u}ber Wellenl{\"a}ngen im optischen und R{\"o}ntgenbereich bis hin zur \$\gamma\$-Strahlung. Allerdings sind nicht alle Objekte bei jeder Wellenl{\"a}nge detektierbar. In dieser Arbeit werden {\"u}berwiegend Blazare bei niedrigen Radiofrequenzen untersucht. Blazare geh{\"o}ren zu den radio-lauten AGN, welche {\"u}blicherweise stark kollimierte Jets senkrecht zur Akkretionsscheibe aussenden. Bei Blazaren sind diese Jets in die Richtung des Beobachters gerichtet und ihre Emissionen sind stark variabel. \\ AGN werden anhand ihres Erscheinungsbildes verschiedenen Untergruppen zugeordnet. Diese Untergruppen werden in einem vereinheitlichen AGN Modell zusammengef{\"u}hrt, welches besagt, dass diese Objekte sich nur in ihrer Luminosit{\"a}t und ihrem Winkel zur Sichtlinie unterscheiden. Blazare sind diejenigen Objekte, deren Jets in unsere Sichtrichtung zeigen, w{\"a}hrend die Objekte deren Jets eher senkrecht zur Sichtlinie orientiert sind als Radiogalaxien bezeichnet werden. Daraus folgt, dass Blazare die Gegenst{\"u}cke zu Radiogalaxien mit einem anderen Winkel zur Sichtlinie sind. Diese Beziehung soll unter anderem in dieser Arbeit untersucht werden. \\ Nach ihrer Entdeckung in den 1940er Jahren wurden die aktiven Galaxien bei allen zug{\"a}nglichen Wellenl{\"a}ngen untersucht. Durch die Entwicklung von Interferometern aus Radioteleskopen, welche eine erh{\"o}hte Aufl{\"o}sung bieten, konnten die Beobachtungen stark verbessert werden. In den letzten 20 Jahren wurden viele AGN regelm{\"a}ßig beobachtet. Dies erfolgte unter anderem durch Programme wie dem MOJAVE Programm, welches 274 AGNs regelm{\"a}ßig mithilfe der Technik der ``Very Long Baseline Interferometry" (VLBI) beobachtet. Durch diese Beobachtungen konnten Informationen zur Struktur und Entwicklung der AGN und Jets gesammelt werden. Allerdings sind die Prozesse zur Bildung von Jets und deren Kollimation noch nicht vollst{\"a}ndig bekannt. Durch relativistische Effekte ist es schwierig die eigentlichen Gr{\"o}ßen der Jets anstelle der scheinbaren zu messen. Um die intrinsische Energie von Jets zu messen, sollen die ausgedehnten Emissionsregionen untersucht werden, in denen die Jets enden und mit dem Intergalaktischen Medium interagieren. Beobachtungen bei niedrigen Radiofrequenzen sind empfindlicher um solche ausgedehnte, diffuse Emissionsregionen zu detektieren. \\ Seit Dezember 2012 ist ein neues Radioteleskop f{\"u}r niedrige Frequenzen in Betrieb, dessen Stationen aus Dipolantennen besteht. Die meisten dieser Stationen sind in den Niederlanden verteilt (38 Stationen) und werden durch 12 internationale Stationen in Deutschland, Frankreich, Schweden, Polen und England erg{\"a}nzt. Dieses Instrument tr{\"a}gt den Namen ``Low Frequency Array'' (LOFAR). LOFAR bietet die M{\"o}glichkeit bei Frequenzen von 30--250 MHz bei einer h{\"o}heren Aufl{\"o}sung als bisherige Radioteleskope zu beobachten (Winkelaufl{\"o}sungen unter 1 arcsec f{\"u}r das gesamte Netzwerk aus Teleskopen). \\ Diese Arbeit behandelt die Ergebnisse von Blazaruntersuchungen mithilfe von LOFAR-Beobachtungen. Daf{\"u}r wurden AGNs aus dem MOJAVE Programm verwendet um von den bisherigen Multiwellenl{\"a}ngen-Beobachtungen und Untersuchungen der Kinematik zu profitieren. Das ``Multifrequency Snapshot Sky Survey'' (MSSS) Projekt hat den gesamten Nordhimmel mit kurzen Beobachtungen abgerastert. Aus dem daraus resultierenden vorl{\"a}ufigen Katalog wurden die Flussdichten und Spektralindizes f{\"u}r MOJAVE-Blazare untersucht. In den kurzen Beobachtungen von MSSS sind nur die Stationen in den Niederlanden verwendet worden, wodurch Aufl{\"o}sung und Sensitivit{\"a}t begrenzt sind. F{\"u}r die Erstellung des vorl{\"a}ufigen Kataloges wurde die Aufl{\"o}sung auf \$\sim\$120 arcsec beschr{\"a}nkt. Ein weiterer Vorteil der MOJAVE Objekte ist die regelm{\"a}ßige Beobachtung der AGN mit dem ``Owens Vally Radio Observatory'' zur Erstellung von Lichtkurven bei 15 GHz. Dadurch ist es m{\"o}glich nahezu zeitgleiche Flussdichtemessungen bei 15 GHz zu den entsprechenden MSSS-Beobachtungen zu bekommen. Da diese Beobachtungen zu {\"a}hnlichen Zeitpunkten durchgef{\"u}hrt wurden sind diese Flussdichten weniger von der Variabilit{\"a}t der Blazare beeinflusst. Die Spektralindizes berechnet aus den Flussdichten von MSSS und OVRO k{\"o}nnen verwendet werden um den Anteil an ausgedehnter Emission der AGNs abzusch{\"a}tzen. \\ Im Vergleich der Flussdichten aus dem MSSS Katalog mit den Beobachtungen von OVRO f{\"a}llt auf, dass die Flussdichten bei niedrigen Frequenzen tendenziell h{\"o}her sind, was durch den h{\"o}heren Anteil an ausgedehnter Struktur zu erwarten ist. Die Spektralindexverteilung zwischen MSSS und OVRO zeigt ihren h{\"o}chsten Wert bei \$\sim-0.2\$. In der Verteilung existieren Objekte mit steilerem Spektralindex durch den h{\"o}heren Anteil von ausgedehnter Emission in der Gesamtflussdichte, doch {\"u}ber die H{\"a}lfte der untersuchten Objekte besitzt flache Spektralindizes. Die flachen Spektralindizes bedeuten, dass die Emissionen dieser Objekte gr{\"o}ßtenteils von relativistischen Effekten beeinflusst sind, die schon aus Beobachtungen bei GHz-Frequenzen bekannt sind. \\ Durch neue Auswertung der MSSS Beobachtungsdaten konnten Bilder bei einer verbesserten Aufl{\"o}sung von \$\sim\$20--30 arcsec erstellt werden, wodurch bei einigen Blazaren ausgedehnte Struktur detektiert werden konnte. Diese h{\"o}her aufgel{\"o}sten Bilder sind allerdings nicht komplett kalibriert und k{\"o}nnen somit nur f{\"u}r strukturelle Informationen verwendet werden. Die {\"U}berarbeitung der Beobachtungsdaten konnte f{\"u}r 93 Objekte f{\"u}r ein Frequenzband durchgef{\"u}hrt werden. F{\"u}r 45 der 93 Objekte konnten sogar alle vorhandenen Frequenzb{\"a}nder {\"u}berarbeitet werden und dadurch gemittelte Bilder erstellt werden. Diese Bilder werden in dieser Arbeit vorgestellt. Die resultierenden Bilder mit verbesserter Aufl{\"o}sung wurden verwendet um Objekte auszuw{\"a}hlen, die mit allen LOFAR-Stationen beobachtet und auf ausgedehnte Struktur untersucht werden k{\"o}nnen. \\ Im zweiten Teil der Arbeit werden die Ergebnisse von internationalen LOFAR Beobachtungen von vier Blazaren pr{\"a}sentiert. Da sich die Auswertung und Kalibration von internationalen LOFAR Beobachtungen noch in der Entwicklung befindet, wurde ein Schwerpunkt auf die Kalibration und deren Beschreibung gelegt. Die Kalibration kann zwar noch verbessert werden, aber die Bilder aus der angewandten Kalibration erreichen eine Aufl{\"o}sung von unter 1 arcsec. Die Struktur der untersuchten vier Blazare entspricht den Erwartungen f{\"u}r Radiogalaxien unter einem anderen Sichtwinkel. Durch die gemessenen Flussdichten der ausgedehnten Struktur aus den Helligkeitsverteilungen konnte die Luminosit{\"a}t der ausgedehnten Emissionen berechnet werden. Im Vergleich mit den Luminosit{\"a}ten, die von Radiogalaxien bekannt sind, entsprechen auch diese Werte den Erwartungen des vereinheitlichten AGN Modells. \\ Durch die in dieser Arbeit vorgestellte Kalibration k{\"o}nnen noch mehr Blazare mit LOFAR inklusive den internationalen Stationen beobachtet werden und somit Bilder der Struktur bei {\"a}hnlicher Aufl{\"o}sung erstellt werden. Durch eine erh{\"o}hte Anzahl von untersuchten Blazaren k{\"o}nnten anschließend auch statistisch signifikante Ergebnisse erzielt werden.\\}, subject = {Blazar}, language = {en} } @phdthesis{BolanosRosales2016, author = {Bola{\~n}os-Rosales, Alejandro}, title = {Low Mach Number Simulations of Convective Boundary Mixing in Classical Novae}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-132863}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {Classical novae are thermonuclear explosions occurring on the surface of white dwarfs. When co-existing in a binary system with a main sequence or more evolved star, mass accretion from the companion star to the white dwarf can take place if the companion overflows its Roche lobe. The envelope of hydrogen-rich matter which builds on top of the white dwarf eventually ignites under degenerate conditions, leading to a thermonuclear runaway and an explosion in the order of 1046 erg, while leaving the white dwarf intact. Spectral analyses from the debris indicate an abundance of isotopes that are tracers of nuclear burning via the hot CNO cycle, which in turn reveal some sort of mixing between the envelope and the white dwarf underneath. The exact mechanism is still a matter of debate. The convection and deflagration in novae develop in the low Mach number regime. We used the Seven League Hydro code (SLH ), which employs numerical schemes designed to correctly simulate low Mach number flows, to perform two and three- dimensional simulations of classical novae. Based on a spherically-symmetric model created with aid of a stellar evolution code, we developed our own nova model and tested it on a variety of numerical grids and boundary conditions for validation. We focused on the evolution of temperature, density and nuclear energy generation rate at the layers between white dwarf and envelope, where most of the energy is generated, to understand the structure of the transition region, and its effect on the nuclear burning. We analyzed the resulting dredge-up efficiency stemming from the convective motions in the envelope. Our models yield similar results to the literature, but seem to depend very strongly on the numerical resolution. We followed the evolution of the nuclear species involved in the CNO cycle and concluded that the thermonuclear reactions primarily taking place are those of the cold and not the hot CNO cycle. The reason behind this could be that under the conditions generally assumed for multi-dimensional simulations, the envelope is in fact not degenerate. We performed initial tests for 3D simulations and realized that alternative boundary conditions are needed.}, subject = {Nova}, language = {en} } @article{BiedermannBilloniDenneretal.2016, author = {Biedermann, B. and Billoni, M. and Denner, A. and Dittmaier, S. and Hofer, L. and J{\"a}ger, B. and Salfelder, L.}, title = {Next-to-leading-order electroweak corrections to pp -> W\(^{+}\)W\(^{-}\) -> 4 leptons at the LHC}, series = {JOURNAL OF HIGH ENERGY PHYSICS}, volume = {06}, journal = {JOURNAL OF HIGH ENERGY PHYSICS}, number = {065}, doi = {10.1007/JHEP06(2016)065}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-167790}, year = {2016}, abstract = {We present results of the first calculation of next-to-leading-order electroweak corrections to W-boson pair production at the LHC that fully takes into account leptonic W-boson decays and off-shell effects. Employing realistic event selections, we discuss the corrections in situations that are typical for the study of W-boson pairs as a signal process or of Higgs-boson decays H → WW∗, to which W-boson pair production represents an irreducible background. In particular, we compare the full off-shell results, obtained treating the W-boson resonances in the complex-mass scheme, to previous results in the so-called double-pole approximation, which is based on an expansion of the loop amplitudes about the W resonance poles. At small and intermediate scales, i.e. in particular in angular and rapidity distributions, the two approaches show the expected agreement at the level of fractions of a percent, but larger differences appear in the TeV range. For transverse-momentum distributions, the differences can even exceed the 10\% level in the TeV range where "background diagrams" with one instead of two resonant W bosons gain in importance because of recoil effects.}, language = {en} } @article{DennerPellen2016, author = {Denner, Ansgar and Pellen, Mathieu}, title = {NLO electroweak corrections to off-shell top-antitop production with leptonic decays at the LHC}, series = {Journal of High Energy Phsyics}, volume = {08}, journal = {Journal of High Energy Phsyics}, number = {155}, doi = {10.1007/JHEP08(2016)155}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-166415}, year = {2016}, abstract = {For the first time the next-to-leading-order electroweak corrections to the full off-shell production of two top quarks that decay leptonically are presented. This calculation includes all off-shell, non-resonant, and interference effects for the 6-particle phase space. While the electroweak corrections are below one per cent for the integrated cross section, they reach up to 15\% in the high-transverse-momentum region of distributions. To support the results of the complete one-loop calculation, we have in addition evaluated the electroweak corrections in two different pole approximations, one requiring two on-shell top quarks and one featuring two on-shell W bosons. While the former deviates by up to 10\% from the full calculation for certain distributions, the latter provides a very good description for most observables. The increased centre-of-mass energy of the LHC makes the inclusion of electroweak corrections extremely relevant as they are particularly large in the Sudakov regime where new physics is expected to be probed.}, language = {en} } @article{DennerDittmaierHechtetal.2016, author = {Denner, Ansgar and Dittmaier, Stefan and Hecht, Markus and Pasold, Christian}, title = {NLO QCD and electroweak corrections to Z + γ production with leptonic Z-boson decays}, series = {JOURNAL OF HIGH ENERGY PHYSICS}, volume = {02}, journal = {JOURNAL OF HIGH ENERGY PHYSICS}, number = {057}, doi = {10.1007/JHEP02(2016)057}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-168766}, year = {2016}, abstract = {The next-to-leading-order electroweak corrections to pp→l\(^{+}\)l\(^{-}\)/ν¯¯¯ν+γ+X production, including all off-shell effects of intermediate Z bosons in the complex-mass scheme, are calculated for LHC energies, revealing the typically expected large corrections of tens of percent in the TeV range. Contributions from quark-photon and photon-photon initial states are taken into account as well, but their impact is found to be moderate or small. Moreover, the known next-to-leading-order QCD corrections are reproduced. In order to separate hard photons from jets, both a quark-to-photon fragmentation function {\´a} la Glover/Morgan and Frixione's cone isolation are employed. The calculation is available in the form of Monte Carlo programs allowing for the evaluation of arbitrary differential cross sections. Predictions for integrated cross sections are presented for the LHC at 7 TeV, 8 TeV, and 14 TeV, and differential distributions are discussed at 14 TeV for bare muons and dressed leptons. Finally, we consider the impact of anomalous ZZγ and Zγγ couplings.}, language = {en} } @article{RahmanKleinKlembtetal.2016, author = {Rahman, SK. Shaid-Ur and Klein, Thorsten and Klembt, Sebastian and Gutowski, J{\"u}rgen and Hommel, Detlef and Sebald, Kathrin}, title = {Observation of a hybrid state of Tamm plasmons and microcavity exciton polaritons}, series = {Scientific Reports}, volume = {6}, journal = {Scientific Reports}, number = {34392}, doi = {10.1038/srep34392}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-167617}, year = {2016}, abstract = {We present evidence for the existence of a hybrid state of Tamm plasmons and microcavity exciton polaritons in a II-VI material based microcavity sample covered with an Ag metal layer. The bare cavity mode shows a characteristic anticrossing with the Tamm-plasmon mode, when microreflectivity measurements are performed for different detunings between the Tamm plasmon and the cavity mode. When the Tamm-plasmon mode is in resonance with the cavity polariton four hybrid eigenstates are observed due to the coupling of the cavity-photon mode, the Tamm-plasmon mode, and the heavy- and light-hole excitons. If the bare Tamm-plasmon mode is tuned, these resonances will exhibit three anticrossings. Experimental results are in good agreement with calculations based on the transfer matrix method as well as on the coupled-oscillators model. The lowest hybrid eigenstate is observed to be red shifted by about 13 meV with respect to the lower cavity polariton state when the Tamm plasmon is resonantly coupled with the cavity polariton. This spectral shift which is caused by the metal layer can be used to create a trapping potential channel for the polaritons. Such channels can guide the polariton propagation similar to one-dimensional polariton wires.}, language = {en} } @phdthesis{Pasold2016, author = {Pasold, Christian}, title = {QCD and electroweak NLO corrections to W + Photon and Z + Photon production including leptonic decays}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-137456}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {At a hadron collider as the LHC or the Tevatron the production of a photon in association with a leptonically decaying vector boson represents an important class of processes. These processes stand out due to a very clean signal of a photon and two leptons. Furthermore they provide direct access to the photon-vector-boson couplings and thus an easy opportunity to test the gauge sector of the Standard Model. Within the scope of this work we present a full calculation of the next-to-leading-order corrections which include the O (αs) corrections of the strong interaction as well as the electroweak corrections of O (α) including all photon-induced contributions. For the creation of matrix elements we use methods based on Feynman diagrams. The IR singularities are treated with the dipole subtraction technique. In order to separate photons from jets, a quark-to-photon fragmentation function ´a la Glover / Morgan or Frixione's cone isolation is employed. Moreover, two different scenarios for charged leptons in the fi state were considered. The fi scenario for dressed leptons assumes that a charged lepton and a photon will be recombined if they are collinear. In the second scenario for bare muons it is assumed that leptons and photon can be separated in a detector also if they are collinear. For our calculation we implemented all corrections into a fl Monte Carlo program. Be- sides the computation of the total cross section this program is also able to generate diff tial distributions of several experimentally motivated observables. Apart from the expected large electroweak corrections in the high transverse-momentum regions and sizeable corrections in the resonance regions of the transverse or the invariant masses we found photon-induced corrections up to several 10\% for high transverse momenta. Within run I at the LHC for 7/8 TeV the experimental accuracy for Vγ production was roughly 10\%. Due to the higher luminosity at run II this accuracy will be reduced to the level of a few percent so that corrections of the same order within the theoretical predictions might become relevant. In this work we present results for the total cross section at the LHC for 7, 8 and 14 TeV and the corresponding distributions for 14 TeV.}, subject = {Quantenchromodynamik}, language = {en} } @phdthesis{Fuchs2016, author = {Fuchs, Moritz Jakob}, title = {Spin dynamics in the central spin model: Application to graphene quantum dots}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-136079}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {Due to their potential application for quantum computation, quantum dots have attracted a lot of interest in recent years. In these devices single electrons can be captured, whose spin can be used to define a quantum bit (qubit). However, the information stored in these quantum bits is fragile due to the interaction of the electron spin with its environment. While many of the resulting problems have already been solved, even on the experimental side, the hyperfine interaction between the nuclear spins of the host material and the electron spin in their center remains as one of the major obstacles. As a consequence, the reduction of the number of nuclear spins is a promising way to minimize this effect. However, most quantum dots have a fixed number of nuclear spins due to the presence of group III and V elements of the periodic table in the host material. In contrast, group IV elements such as carbon allow for a variable size of the nuclear spin environment through isotopic purification. Motivated by this possibility, we theoretically investigate the physics of the central spin model in carbon based quantum dots. In particular, we focus on the consequences of a variable number of nuclear spins on the decoherence of the electron spin in graphene quantum dots. Since our models are, in many aspects, based upon actual experimental setups, we provide an overview of the most important achievements of spin qubits in quantum dots in the first part of this Thesis. To this end, we discuss the spin interactions in semiconductors on a rather general ground. Subsequently, we elaborate on their effect in GaAs and graphene, which can be considered as prototype materials. Moreover, we also explain how the central spin model can be described in terms of open and closed quantum systems and which theoretical tools are suited to analyze such models. Based on these prerequisites, we then investigate the physics of the electron spin using analytical and numerical methods. We find an intriguing thermal flip of the electron spin using standard statistical physics. Subsequently, we analyze the dynamics of the electron spin under influence of a variable number of nuclear spins. The limit of a large nuclear spin environment is investigated using the Nakajima-Zwanzig quantum master equation, which reveals a decoherence of the electron spin with a power-law decay on short timescales. Interestingly, we find a dependence of the details of this decay on the orientation of an external magnetic field with respect to the graphene plane. By restricting to a small number of nuclear spins, we are able to analyze the dynamics of the electron spin by exact diagonalization, which provides us with more insight into the microscopic details of the decoherence. In particular, we find a fast initial decay of the electron spin, which asymptotically reaches a regime governed by small fluctuations around a finite long-time average value. Finally, we analytically predict upper bounds on the size of these fluctuations in the framework of quantum thermodynamics.}, subject = {Elektronenspin}, language = {en} } @article{Kuemmel2016, author = {K{\"u}mmel, Reiner}, title = {The Impact of Entropy Production and Emission Mitigation on Economic Growth}, series = {Entropy}, volume = {18}, journal = {Entropy}, number = {3}, doi = {10.3390/e18030075}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-163185}, pages = {75}, year = {2016}, abstract = {Entropy production in industrial economies involves heat currents, driven by gradients of temperature, and particle currents, driven by specific external forces and gradients of temperature and chemical potentials. Pollution functions are constructed for the associated emissions. They reduce the output elasticities of the production factors capital, labor, and energy in the growth equation of the capital-labor-energy-creativity model, when the emissions approach their critical limits. These are drawn by, e.g., health hazards or threats to ecological and climate stability. By definition, the limits oblige the economic actors to dedicate shares of the available production factors to emission mitigation, or to adjustments to the emission-induced changes in the biosphere. Since these shares are missing for the production of the quantity of goods and services that would be available to consumers and investors without emission mitigation, the "conventional" output of the economy shrinks. The resulting losses of conventional output are estimated for two classes of scenarios: (1) energy conservation; and (2) nuclear exit and subsidies to photovoltaics. The data of the scenarios refer to Germany in the 1980s and after 11 March 2011. For the energy-conservation scenarios, a method of computing the reduction of output elasticities by emission abatement is proposed.}, language = {en} } @article{OPUS4-16515, title = {The prototype detection unit of the KM3NeT detector}, series = {The European Physical Journal C}, volume = {76}, journal = {The European Physical Journal C}, number = {54}, organization = {KM3NeT Collaboration}, doi = {10.1140/epjc/s10052-015-3868-9}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-165159}, year = {2016}, abstract = {A prototype detection unit of the KM3NeT deep-sea neutrino telescope has been installed at 3500m depth 80 km offshore the Italian coast. KM3NeT in its final configuration will contain several hundreds of detection units. Each detection unit is a mechanical structure anchored to the sea floor, held vertical by a submerged buoy and supporting optical modules for the detection of Cherenkov light emitted by charged secondary particles emerging from neutrino interactions. This prototype string implements three optical modules with 31 photomultiplier tubes each. These optical modules were developed by the KM3NeT Collaboration to enhance the detection capability of neutrino interactions. The prototype detection unit was operated since its deployment in May 2014 until its decommissioning in July 2015. Reconstruction of the particle trajectories from the data requires a nanosecond accuracy in the time calibration. A procedure for relative time calibration of the photomultiplier tubes contained in each optical module is described. This procedure is based on the measured coincidences produced in the sea by the 40K background light and can easily be expanded to a detector with several thousands of optical modules. The time offsets between the different optical modules are obtained using LED nanobeacons mounted inside them. A set of data corresponding to 600 h of livetime was analysed. The results show good agreement with Monte Carlo simulations of the expected optical background and the signal from atmospheric muons. An almost background-free sample of muons was selected by filtering the time correlated signals on all the three optical modules. The zenith angle of the selected muons was reconstructed with a precision of about 3∘.}, language = {en} } @article{DreinerKraussO'Learyetal.2016, author = {Dreiner, Herbi K. and Krauss, Manuel E. and O'Leary, Ben and Opferkuch, Toby and Staub, Florian}, title = {Validity of the CMSSM interpretation of the diphoton excess}, series = {Physical Review D}, volume = {94}, journal = {Physical Review D}, number = {5}, doi = {10.1103/PhysRevD.94.055013}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-187429}, pages = {055013}, year = {2016}, abstract = {It has been proposed that the observed diphoton excess at 750 GeV could be explained within the constrained minimal supersymmetric standard model via resonantly produced stop bound states. We reanalyze this scenario critically and extend previous work to include the constraints from the stability of the electroweak vacuum and from the decays of the stoponium into a pair of Higgs bosons. It is shown that the interesting regions of parameter space with a light stop and Higgs of the desired mass are ruled out by these constraints. This conclusion is not affected by the presence of the bound states because the binding energy is usually very small in the regions of parameter space which can explain the Higgs mass. Thus, this also leads to strong constraints on the diphoton production cross section which is in general too small.}, language = {en} }