Single top-quark production with the Matrix Element Method in next-to-leading order accuracy

Single top-quark production offers a unique laboratory for precision tests of the Standard Model and searches of possible extensions. Furthermore, assuming the Standard Model, single top-quark production can be used to determine top-quark related couplings. For precise determinations of parameters like the electroweak gauge couplings or the mass of the top quark, efficient, unbiased, and theoretically unambiguous analysis methods are needed. Within this context, the Matrix Element Method (MEM) has been established in hadron collider analyses due to its possibility to top out at utilising the information available in experimental data. However, so far it has mostly been applied in Born approximation only. We discuss the extension to next-to-leading order (NLO) accuracy. As a necessary prerequisite we introduce an efficient method to calculate NLO QCD weights for jet events. As proof of concept and representative example we use the MEM at NLO to reproduce the top-quark mass in a toy experiment where we treat single top-quark events generated at NLO accuracy as pseudo-data. This is the first application of the MEM at NLO accuracy to the hadronic production of jets originating from coloured final state partons. We observe that analysing NLO events with Born likelihoods can introduce a pronounced bias in the extracted mass which would require significant calibration with associated uncertainties. Although we focus on parameter determinations, the methods presented here can also be used to search for new physics using likelihood ratios.Comment: 5 pages with 4 figures; proccedings to XXV International Workshop on Deep-Inelastic Scattering and Related Subjects, 3-7 April 2017, University of Birmingham, U

Extending the Matrix Element Method beyond the Born approximation: Calculating event weights at next-to-leading order accuracy

In this article we illustrate how event weights for jet events can be calculated efficiently at next-to-leading order (NLO) accuracy in QCD. This is a crucial prerequisite for the application of the Matrix Element Method in NLO. We modify the recombination procedure used in jet algorithms, to allow a factorisation of the phase space for the real corrections into resolved and unresolved regions. Using an appropriate infrared regulator the latter can be integrated numerically. As illustration, we reproduce differential distributions at NLO for two sample processes. As further application and proof of concept, we apply the Matrix Element Method in NLO accuracy to the mass determination of top quarks produced in e+e- annihilation. This analysis is relevant for a future Linear Collider. We observe a significant shift in the extracted mass depending on whether the Matrix Element Method is used in leading or next-to-leading order.Comment: 35 pages, 12 figures, references & acknowledgments added, typos corrected, matches published versio

Deglaciation stages of the Laurentide Ice Sheet in Canada and related glaciomarine and glaciolacustrine deposits. Review of selected features

Durante la deglaciación de los mantos de hielo se genera una gran cantidad de agua de fusión, una gran parte de la cual queda retenida en grandes lagos en los bordes de los glaciares. Un ejemplo es el Manto de Hielo Laurentido que cubrió una gran extensión de Norteamérica y dio lugar a vastos lagos en las distintas etapas de su deglaciación. Restos de estos ambientes son los Grandes Lagos de Norteamérica así como otros lagos en el centro y noroeste de Canadá. También se formaron mares glaciales poco profundos, desecados en parte a causa del levantamiento isostático postglacial. El legado de estos ambientes son vastas planicies, actualmente fértiles áreas agrícolas en su mayor parte, situadas sobre arenas y arcillas glaciolacustres y glaciomarinas. Los sedimentos depositados en los lagos y mares glaciales adquieren características específicas que son fácilmente preservadas en el registro geológico. Los emplazamientos glaciolacustres y glaciomarinos se caracterizan por su reletivamente amplia distribución y por la complejidad de los depósitos deltaicos, costeros y de aguas profundas. Las ritmitas son facies formadas por decantación diferencial en verano (fusión) e invierno (bajo cobertura de hielo), o por flujos turbios procedentes de los rios glaciales. Igualmente típicos son los depósitos de sedimentos gruesos de origen fluvial depositados en aguas profundas, generalmente en el frente sumergido de los glaciares, en los puntos de descarga de corrientes glaciales canalizadas. Otros depósitos de material grueso de aguas profundas son los generados por materiales transportados por bloques de hielo estacional o icebergs. El tipo de sedimentos y los paisajes a que han dado lugar tienen importantes implicaciones para los usos del suelo. Los ambientes deltaicos y costeros constituyen valiosas fuentes de áridos, mientras las areas predominantemente limo-arcillosas son generalmente excelentes áreas agrícolas. Sin embargo, los depósitos de arcillas marinas son muy inestables y pueden dar lugar a deslizamientos, como ocurre con las arcillas de la formación Leda en el sureste de Canadá. Además algunas llanuras de ortigen lacustre, topográficamente bajas, en el centro de Canadá suelen inundarse durante la primavera

America\u27s Melting Pot

The American public, in its increasing attention to foods, is demonstrating a desire for greater variety in restaurant service and foods. The author assesses recent restaurant food trends, including the emphasis on light food, entertainment in dining, and a broader range of ethnic foods

The Scope of the IBGP Routing Anomaly Problem

Correctness problems in the iBGP routing, the de-facto standard to spread global routing information in Autonomous Systems, are a well-known issue. Configurations may route cost-suboptimal, inconsistent, or even behave non-convergent and -deterministic. However, even if a lot of studies have shown many exemplary problematic configurations, the exact scope of the problem is largely unknown: Up to now, it is not clear which problems may appear under which iBGP architectures. The exact scope of the iBGP correctness problem is of high theoretical and practical interest. Knowledge on the resistance of specific architecture schemes against certain anomaly classes and the reasons may help to improve other iBGP schemes. Knowledge on the specific problems of the different schemes helps to identify the right scheme for an AS and develop workarounds

Determination of the top-quark mass from top-quark pair events with the matrix element method at next-to-leading order: Potential and prospects

In 2004 the matrix element method was used in a pioneering work by the Tevatron experiment D0 to determine the top-quark mass from a handful of events. Since then the method has been matured into a powerful analysis tool. While the first applications were restricted to leading-order accuracy, in the meantime also the extension to next-to-leading order (NLO) accuracy has been studied. In this article we explore the potential of the matrix element method at NLO to determine the top-quark mass using events with pair-produced top quarks. We simulate a toy experiment by generating unweighted events with a fixed input mass and apply the matrix element method to construct an estimator for the top-quark mass. Two different setups are investigated: unweighted events obtained from the fixed-order cross section at NLO accuracy as well as events obtained using POWHEG matched to a parton shower. The latter lead to a more realistic simulation and allow to study the impact of higher-order corrections as well as the robustness of the approach. We find that the matrix element method in NLO accuracy leads to a significant reduction of the theoretical uncertainties compared to leading order. In view of the high luminosity phase of the LHC, this observation is especially relevant in analyses which are no longer dominated by statistical uncertainties.Comment: Two references added, particle labels adjusted to improve readability, error bars added in ratio plots, minor changes to the tex

Evolution and architecture of a West Mediterranean Upper Pleistocene to Holocene coastal apron-fan system

The Quaternary deposits of tectonically stable areas are a powerful tool to investigate high-frequency climate variations (<10 ka) and to distinguish allogenic and autogenic factors controlling deposition. Therefore, an Upper Pleistocene—Holocene coastal apron-fan system in north—western Sardinia (Porto Palmas, Italy) was studied to investigate the relations between climate changes, sea-level fluctuations and sediment source-supply that controlled its development. The sedimentary sequence records the strong influence of local (wet/dry) and worldwide (sea-level) environmental variations in the sedimentation and preservation of the deposits. A multi-disciplinary approach allowed subdivision of the succession into four major, unconformity-bounded stratigraphic units: U1 U2, U3 and U4. Unit U1, tentatively dated to the warm and humid Marine Isotopic Stage (MIS) 5, consists of sandy, gravelly coastal/beach deposits developed during high sea-level in low-lying areas. Unit U2 consists of debris-flow dominated fan-deposits (ca 74 ka; MIS 4), preserved as partial fills of small valleys and coves. Unit U2 is mainly composed of reddish silty conglomerate to pebbly siltstones sourced from the Palaeozoic metamorphic inland hills (bedrock), superficially disintegrated during the preceding warm, vegetation-rich MIS 5. The cold and semi-arid climate strongly reduced vegetation cover along the valley flanks. Therefore, sediment gravity-flow processes, possibly activated by rainstorms, led to deposition of debris-flow dominated fans. Unit U3 consists of water-flow dominated alluvial-fan deposits (ca 47 to 23 ka; MIS 3), developed on a slightly inclined coastal plain. Unit U3 is composed of sandstone and sandy conglomerate fed from two main sediment sources: metamorphic inland bedrock and Quaternary bioclastic-rich shelf-derived sands. During this cold phase, sea-level dropped sufficiently to expose bioclastic sands accumulated on the shelf. Frequent climate fluctuations favoured inland aeolian transport of sand during dry phases, followed by reworking of the aeolian bodies by flash floods during wet phases. Bedrock-derived fragments mixed with water-reworked, wind-blown sands led to the development of water-flow dominated fans. The Dansgaard—Oeschger events possibly associated with sand landward deflation and main fan formations are Dansgaard—Oeschger 13 (ca 47 ka), Dansgaard—Oeschger 8 (ca 39 ka) and Dansgaard—Oeschger 2 (ca 23 ka). No record of sedimentation during MIS 2 was observed. Finally, bioclastic-rich aeolianites (Unit U4, ca 10 to 5 ka; MIS 1), preserved on a coastal slope, were developed during the Holocene transgression (ca 10 to 5 ka; MIS 1). The studied sequence shows strong similarities with those of other Mediterranean sites; it is, however, one of the few where the main MIS 4 and MIS 3 climatic fluctuations are registered in the sedimentary record