91 research outputs found

    Measurement of s-channel single top-quark production with the ATLAS detector using total event likelihoods

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    Es wird eine Messung der s-Kanal Einzel Top-Quark Produktion in Proton-Proton Kollisionen bei einer Schwerpunktsenergie von 8 TeV vorgestellt. Der verwendete Datensatz wurde mit dem ATLAS Detektor am LHC aufgenommen und entspricht einer integrierten Luminosität von 20.3 inversen Femtobarn. Kollisionsereignisse werden selektiert, sodass der resultierende Anteil der Signalereignisse relativ hoch ist. Selektierte Ereignisse enthalten ein isoliertes Elektron oder Myon, fehlenden Transversalimpuls und zwei Jets, die durch b-Quarks induziert wurden. Alle Objekte haben hohe transversalimpulse. Auch nach dieser Selektion überwiegen Untergrundprozesse, insbesondere die Paarproduktion von Top-Quarks und die Produktion von W-Bosonen begleitet von Jets. Um den Signalprozess weiter von den Untergründen zu trennen, werden mehrere Wahrscheinlichkeitsdichten näherungsweise berechnet. Sie unterscheiden sich hinsichtlich der Annahme des zugrundeliegenden Streuprozesses. Zusammen ergeben sie eine Funktion der gemessenen Impulse, mit deren Hilfe das Signal weiter von den Untergründen getrennt werden kann. Ein statistisches Modell der entsprechenden Verteilung wird an die Messdaten angepasst. Diese Messung ergibt eine Signifikanz des Signalprozesses von 3.4 Standardabweichungen und einen totalen Wirkungsquerschnitt von 5.3^+1.8_-1.6 Pikobarn. Dies ist die erste signifikante Messung der s-Kanal Einzel Top-Quark Produktion in Proton-Proton Kollisionen. Die Ergebnisse stimmen mit der Vorhersage des Standardmodells überein.A measurement of s-channel single top-quark production in proton-proton collisions at a centre-of-mass energy of 8 TeV is presented. The data set has been recorded with the ATLAS detector at the LHC and corresponds to an integrated luminosity of 20.3 inverse femtobarn. Collision events are selected so that a subset of the data is obtained where the signal fraction is relatively high. Selected events contain one isolated electron or muon, missing transverse momentum and 2 jets, both of which are induced by b-quarks. All of these objects have large transverse momenta. The resulting set of events is still dominated by background processes, most notably top-quark pair production and the production of W bosons in association with jets. In order to further separate the signal from the backgrounds, several approximate event likelihoods are computed. They are based on different hypotheses regarding the scattering process at hand. Together they result in a function of the measured momenta which allows for the desired separation of the signal process. A statistical model of the corresponding distribution is used in a fit to the measured data. The fit results in a signal significance of 3.4 standard deviations and a total cross section of 5.3^+1.8_-1.6 picobarn. This is the first evidence for s-channel single top-quark production in proton-proton collisions. The results agree with the standard model prediction

    Up-scaling lessons from the EU-Sida-GTZ Ecosan promotion project in Kenya

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    This paper analyses the requirements for up-scaling of sustainable sanitation systems based on the lessons learnt from the EU-Sida-GTZ EcoSan Promotion Project (EPP) in Kenya. The EPP reached 50,000 users with reuse oriented sanitation systems (ecosan). The project areas for urine diversion dehydration toilets (UDDTs) were villages in rural and peri-urban areas of Kenya where farming is practiced and cholera is common during the rainy season. The total number of installed UDDTs in households and schools was 984 with an estimated 20,000 users. The UDDTs were implemented either directly through Community Based Organisations (CBOs), or via the pro-poor basket fund called Water Services Trust Fund (WSTF) together with the regional Water Services Boards (WSBs) and CBOs. Future strategies for up-scaling must provide a comprehensive strategy to bundle resources and create synergies of the sanitation related sectors in Kenya with a focus on behaviour change and sanitation market development that can provide sustained demand and trigger community investment in sanitation

    Recommendations for the Transition to Open Access in Austria

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    Based on 16 recommendations, efforts should be made to achieve the following goal: By 2025, a large part of all scholarly publication activity in Austria should be Open Access. In other words, the final versions of most scholarly publications (in particular all refereed journal articles and conference proceedings) resulting from the support of public resources must be freely accessible on the Internet without delay (Gold Open Access). This goal should be pursued by taking into account the different disciplinary practices and under consideration of the different disciplinary priorisations of Open Access. The resources required to meet this obligation shall be provided to the authors, or the cost of the publication venues shall be borne directly by the research organisations. The necessary funding must be brought in line with the overall funding priorities for research

    Efficient Search for New Physics Using Active Learning in the ATLAS Experiment

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    Searches for new physics set exclusion limits in parameter spaces of typically up to 2 dimensions. However, the relevant theory parameter space is usually of a higher dimension but only a subspace is covered due to the computing time requirements of signal process simulations. An Active Learning approach is presented to address this limitation. Compared to the usual grid sampling, it reduces the number of parameter space points for which exclusion limits need to be determined. Hence it allows to extend interpretations of searches to higher dimensional parameter spaces and therefore to raise their value, e.g. via the identification of barely excluded subspaces which motivate dedicated new searches. In an iterative procedure, a Gaussian Process is fit to excluded signal cross-sections. Within the region close to the exclusion contour predicted by the Gaussian Process, Poisson disc sampling is used to determine further parameter space points for which the cross-section limits are determined. The procedure is aided by a warm-start phase based on computationally inexpensive, approximate limit estimates such as total signal cross-sections. The procedure is applied to a dark matter search on data collected by the ATLAS detector at the LHC, extending its interpretation from a 2 to a 4-dimensional parameter space while keeping the computational effort at a low level. The result is published in two formats: on one hand there is a publication of the Gaussian Process model. On the other hand, a visualization of the full 4-dimensional contour is presented as a collection of 2-dimensional exclusion contours where the 2 remaining parameters are chosen by the user

    Empfehlungen für eine nationale Open Science Strategie in Österreich / Recommendations for a National Open Science Strategy in Austria

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    A look at international activities on Open Science reveals a broad spectrum from individual institutional policies to national action plans. The present Recommendations for a National Open Science Strategy in Austria are based on these international initiatives and present practical considerations for their coordinated implementation with regard to strategic developments in research, technology and innovation (RTI) in Austria until 2030. They are addressed to all relevant actors in the RTI system, in particular to Research Performing Organisations, Research Funding Organisations, Research Policy, memory institutions such as Libraries and Researchers. The recommendation paper was developed from 2018 to 2020 by the OANA working group "Open Science Strategy" and published for the first time in spring 2020 for a public consultation. The now available final version of the recommendation document, which contains feedback and comments from the consultation, is intended to provide an impetus for further discussion and implementation of Open Science in Austria and serves as a contribution and basis for a potential national Open Science Strategy in Austria. The document builds on the diverse expertise of the authors (academia, administration, library and archive, information technology, science policy, funding system, etc.) and reflects their personal experiences and opinions.Der Blick auf internationale Aktivitäten zu Open Science zeigt ein breites Spektrum von einzelnen institutionellen Policies bis hin zu nationalen Aktionsplänen. Die vorliegenden Empfehlungen für eine nationale Open Science Strategie in Österreich orientieren sich an diesen internationalen Initiativen und stellen praktische Überlegungen für ihre koordinierte Implementierung im Hinblick auf strategische Entwicklungen in Forschung, Technologie und Innovation (FTI) bis 2030 in Österreich dar. Dabei richten sie sich an alle relevanten Akteur*innen im FTI System, im Besonderen an Forschungsstätten, Forschungsförderer, Forschungspolitik, Gedächtnisinstitutionen wie Bibliotheken und Wissenschafter*innen. Das Empfehlungspapier wurde von 2018 bis 2020 von der OANA-Arbeitsgruppe "Open Science Strategie" entwickelt und im Frühling 2020 das erste Mal für eine öffentliche Konsultation veröffentlicht. Die nun vorliegende finale Version des Empfehlungsdokuments, die Feedback und Kommentare aus der Konsultation enthält, soll ein Anstoß für die weitere Diskussion und Umsetzung von Open Science in Österreich sein und als Beitrag und Grundlage einer potentiellen nationalen Open Science Strategie in Österreich dienen. Das Dokument baut auf der vielfältigen Expertise der Autor*innen auf (Wissenschaft, Administration, Bibliothek und Archiv, Informationstechnologie, Wissenschaftspolitik, Förderwesen etc.) und spiegelt deren persönliche Erfahrungen und Meinung wider

    Flashlights: More than A Dozen High-Significance Microlensing Events of Extremely Magnified Stars in Galaxies at Redshifts z=0.7-1.5

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    Once only accessible in nearby galaxies, we can now study individual stars across much of the observable universe aided by galaxy-cluster gravitational lenses. When a star, compact object, or multiple such objects in the foreground galaxy-cluster lens become aligned, they can magnify a background individual star, and the timescale of a magnification peak can limit its size to tens of AU. The number and frequency of microlensing events therefore opens a window into the population of stars and compact objects, as well as high-redshift stars. To assemble the first statistical sample of stars in order to constrain the initial mass function (IMF) of massive stars at redshift z=0.7-1.5, the abundance of primordial black holes in galaxy-cluster dark matter, and the IMF of the stars making up the intracluster light, we are carrying out a 192-orbit program with the Hubble Space Telescope called "Flashlights," which is now two-thirds complete owing to scheduling challenges. We use the ultrawide F200LP and F350LP long-pass WFC3 UVIS filters and conduct two 16-orbit visits separated by one year. Having an identical roll angle during both visits, while difficult to schedule, yields extremely clean subtraction. Here we report the discovery of more than a dozen bright microlensing events, including multiple examples in the famous "Dragon Arc" discovered in the 1980s, as well as the "Spocks" and "Warhol" arcs that have hosted already known supergiants. The ultradeep observer-frame ultraviolet-through-optical imaging is sensitive to hot stars, which will complement deep James Webb Space Telescope infrared imaging. We are also acquiring Large Binocular Telescope LUCI and Keck-I MOSFIRE near-infrared spectra of the highly magnified arcs to constrain their recent star-formation histories

    Empfehlungen für die Umsetzung von Open Access in Österreich

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    Based on 16 recommendations, efforts should be made to achieve the following goal: By 2025, all scholarly publication activity in Austria should be Open Access. In other words, the final versions of all scholarly publications resulting from the support of public resources must be freely accessible on the Internet without delay (Gold Open Access). The resources required to meet this obligation shall be provided to the authors, or the cost of the publication venues shall be borne directly by the research organisations

    A shot in the Dark (Ages): a faint galaxy at z=9.76z=9.76 confirmed with JWST

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    The appearance of galaxies over the first billion years after the Big Bang is believed to be responsible for the last dramatic change in the state of the Universe. Ultraviolet photons from galaxies within this time period - the Epoch of Reionization - ionized intergalactic Hydrogen, rendering the Universe transparent to UV radiation and ending the so-called cosmic Dark Ages, sometime after redshift z8z\sim8. The majority of ionizing photons in the first few hundred Myrs of cosmic history are thought to derive from galaxies significantly fainter than the characteristic luminosity LL^{*}. These faint galaxies are thought to be surrounded by sufficient neutral gas to prevent the escape of the Lyman-α\alpha photons that would allow confirmation with current observatories. Here we demonstrate the power of the recently commissioned James Webb Space Telescope to transform our understanding of the sources of reionization, by reporting the first spectroscopic confirmation of a very low luminosity (0.05L\sim0.05 L^{*}) galaxy at z=9.76z=9.76, observed 480 Myr after the Big Bang, via the detection of the Lyman-break and redward continuum with the NIRSpec and NIRCam instruments. The galaxy JD1 is gravitationally magnified by a factor of μ13\mu\sim13 by the foreground cluster A2744. The power of JWST and lensing allows us to peer deeper than ever before into the cosmic Dark Ages, revealing the compact (\sim150 pc) and complex morphology and physical properties of an ultrafaint galaxy (MUV=17.45M_{\rm UV}=-17.45).Comment: Submitted to Nature. 34 pages, 4 main figures, 1 supplementary figure, 2 supplementary tables. Comments are welcom

    Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

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    A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

    ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider