Searching for Dark Matter at the LHC with a Mono-Z

We investigate a mono-Z process as a potential dark matter search strategy at the LHC. In this channel a single Z boson recoils against missing transverse momentum, attributed to dark matter particles, $\chi$, which escape the detector. This search strategy is related, and complementary to, monojet and monophoton searches. For illustrative purposes we consider the process $q\bar{q} -> \chi\chi Z$ in a toy dark matter model, where the Z boson is emitted from either the initial state quarks, or from the internal propagator. Among the signatures of this process will be a pair of muons with high pT that reconstruct to the invariant mass of the Z, and large amounts of missing transverse energy. Being a purely electroweak signal, QCD and other Standard Model backgrounds are relatively easily removed with modest selection cuts. We compare the signal to Standard Model backgrounds and demonstrate that, even for conservative cuts, there exist regions of parameter space where the signal may be clearly visible above background in future LHC data, allowing either new discovery potential or the possibility of supplementing information about the dark sector beyond that available from other observable channels.Comment: 11 pages, 13 figure

Von Baumdiagrammen über Doppelbäume zu Häufigkeitsnetzen – kognitive Überlastung oder didaktische Unterstützung?

In stochastischen Situationen mit zwei dichotomen Merkmalen erlauben weder die schulüblichen Baumdiagramme noch Vierfeldertafeln die simultane Darstellung sämtlicher in der Situation möglicher Wahrscheinlichkeiten. Das im vorliegenden Beitrag vorgestellte Netz hat die Kapazität, alle vier möglichen Randwahrscheinlichkeiten, alle vier Schnittwahrscheinlichkeiten sowie alle acht bedingten Wahrscheinlichkeiten gleichzeitig darzustellen. Darüber hinaus ist – aufgrund der Knoten-Ast-Struktur des Netzes – die simultane Darstellung von Wahrscheinlichkeiten und absoluten Häufigkeiten mit dieser Visualisierung ebenfalls möglich. Bei der sukzessiven Erweiterung des typischen Baumdiagramms zunächst zum Doppelbaum und schließlich zum Netz sinkt der Inferenzgrad (d. h. weniger kognitive Schritte sind erforderlich) z. B. für Fragen nach bedingten Wahrscheinlichkeiten, aber gleichzeitig steigt die Komplexität der Darstellung und somit die extrinsische kognitive Belastung. Im vorliegenden Artikel erfolgt zunächst ein theoretischer Vergleich dieser Knoten-Ast-Strukturen. Eine anschließende Studie illustriert, dass sich die sukzessive Erweiterung bereits vollständig ausgefüllter Diagramme positiv auf die Performanz von N = 269 Schülerinnen und Schülern auswirkt. Obwohl Häufigkeitsdoppelbäume und Häufigkeitsnetze den Schülerinnen und Schülern gänzlich unbekannt waren, unterstützten diese Visualisierungen die Schülerinnen und Schüler bei der Bearbeitung der Aufgaben am meisten. In stochastic situations with two dichotomous events, neither typical tree diagrams nor 2 × 2 tables allow the simultaneous representation of all possible probabilities in the situation. The net diagram presented in this paper has the capacity to represent all four possible marginal probabilities, all four joint probabilities, and all eight conditional probabilities simultaneously. Furthermore, due to the node-branch structure of the frequency net, the simultaneous representation of probabilities and absolute frequencies is also possible with this visualization. With the successive extension of the typical tree diagram to the double tree and finally to the net diagram, the inference degree, e.g., for questions about conditional probabilities, decreases (i.e., less mental steps are required), however, at the same time the complexity of the representation increases and thus the extrinsic cognitive load. In the present article, a theoretical comparison of these node-branch-structures is made. Furthermore, we demonstrate with an empirical study that the successive extension of these node-branch structures, which were already completely worked out, positively affects the performance of N = 269 students. Although frequency double trees and frequency nets were entirely unfamiliar to the students, these visualizations provided the best support to the students in completing the tasks

Mehr Äste – mehr Panik? Extrinsische kognitive Belastung bei Baumdiagrammen, Doppelbäumen und Häufigkeitsnetzen

Für den Stochastikunterricht stehen eine Reihe von Visualisierungen zur Verfügung, um Situationen mit zwei dichotomen Merkmalen (z. B. Merkmal 1: Gesundheitsstatus mit den Ausprägungen krank vs. gesund; Merkmal 2: Testergebnis mit den Ausprägungen Test positiv vs. Test negativ) zu illustrieren: Baumdiagramme, Vierfeldertafeln, Einheitsquadrate, Doppelbäume, Netzdiagramme und viele mehr. Schulisch werden vor allem Vierfeldertafeln mit absoluten oder relativen Häufigkeiten (bzw. Wahrscheinlichkeiten) und Baumdiagramme mit relativen Häufigkeiten an den Ästen eingesetzt. Da Knoten-Ast-Strukturen wie Baumdiagramme das Potential besitzen, sowohl absolute Häufigkeiten in den Knoten (vgl. Abb. 1) als auch relative Häufigkeiten an den entsprechenden Ästen darzustellen, stehen Baumdiagramme sowie die erweiterten Knoten-Ast-Strukturen Doppelbaum (Wassner, 2004) und Netzdiagramm (Binder et al., 2020; Binder et al., in review) im Fokus des vorliegenden Beitrags. Diese Verbindungsmöglichkeit der beiden Repräsentationen ist entscheidend, weil es einerseits die Aufgabe von Mathematiklehrkräften ist, das Wahrscheinlichkeitskalkül zu vermitteln und andererseits ein Verständnis von Wahrscheinlichkeiten durch die Präsentation von absoluten Häufigkeiten unterstützt werden kann (Gigerenzer & Hoffrage, 1995; Binder et al., 2015). Überdies können Knoten-Ast-Strukturen „curricular mitwachsen“, indem mit entsprechenden Visualisierungen gearbeitet wird, die zunächst nur absolute Häufigkeiten in den Knoten enthalten, in der Sekundarstufe I können dann relative Häufigkeiten an den Ästen ergänzt werden und in höheren Klassen schließlich auch entsprechende Wahrscheinlichkeiten

W/Z Bremsstrahlung as the Dominant Annihilation Channel for Dark Matter, Revisited

We revisit the calculation of electroweak bremsstrahlung contributions to dark matter annihilation. Dark matter annihilation to leptons is necessarily accompanied by electroweak radiative corrections, in which a $W$ or $Z$ boson is also radiated. Significantly, while many dark matter models feature a helicity suppressed annihilation rate to fermions, bremsstrahlung process can remove this helicity suppression such that the branching ratios Br($\ell \nu W$), Br($\ell^+\ell^-Z$), and Br($\bar\nu \nu Z$) dominate over Br($\ell^+\ell^-$) and Br($\bar\nu \nu$). We find this is most significant in the limit where the dark matter mass is nearly degenerate with the mass of the boson which mediates the annihilation process. Electroweak bremsstrahlung has important phenomenological consequences both for the magnitude of the total dark matter annihilation cross section and for the character of the astrophysical signals for indirect detection. Given that the $W$ and $Z$ gauge bosons decay dominantly via hadronic channels, it is impossible to produce final state leptons without accompanying protons, antiprotons, and gamma rays.Comment: 8 pages, 6 figures; replaced to match published versio

Processes Contributing to Resilience of Coastal Wetlands to Sea-Level Rise

The objectives of this study were to identify processes that contribute to resilience of coastal wetlands subject to rising sea levels and to determine whether the relative contribution of these processes varies across different wetland community types. We assessed the resilience of wetlands to sea-level rise along a transitional gradient from tidal freshwater forested wetland (TFFW) to marsh by measuring processes controlling wetland elevation. We found that, over 5 years of measurement, TFFWs were resilient, although some marginally, and oligohaline marshes exhibited robust resilience to sea-level rise. We identified fundamental differences in how resilience is maintained across wetland community types, which have important implications for management activities that aim to restore or conserve resilient systems. We showed that the relative importance of surface and subsurface processes in controlling wetland surface elevation change differed between TFFWs and oligohaline marshes. The marshes had significantly higher rates of surface accretion than the TFFWs, and in the marshes, surface accretion was the primary contributor to elevation change. In contrast, elevation change in TFFWs was more heavily influenced by subsurface processes, such as root zone expansion or compaction, which played an important role in determining resilience of TFFWs to rising sea level. When root zone contributions were removed statistically from comparisons between relative sea-level rise and surface elevation change, sites that previously had elevation rate deficits showed a surplus. Therefore, assessments of wetland resilience that do not include subsurface processes will likely misjudge vulnerability to sea-level rise

Processes Contributing to Resilience of Coastal Wetlands to Sea-Level Rise

The objectives of this study were to identify processes that contribute to resilience of coastal wetlands subject to rising sea levels and to determine whether the relative contribution of these processes varies across different wetland community types. We assessed the resilience of wetlands to sea-level rise along a transitional gradient from tidal freshwater forested wetland (TFFW) to marsh by measuring processes controlling wetland elevation. We found that, over 5 years of measurement, TFFWs were resilient, although some marginally, and oligohaline marshes exhibited robust resilience to sea-level rise. We identified fundamental differences in how resilience is maintained across wetland community types, which have important implications for management activities that aim to restore or conserve resilient systems. We showed that the relative importance of surface and subsurface processes in controlling wetland surface elevation change differed between TFFWs and oligohaline marshes. The marshes had significantly higher rates of surface accretion than the TFFWs, and in the marshes, surface accretion was the primary contributor to elevation change. In contrast, elevation change in TFFWs was more heavily influenced by subsurface processes, such as root zone expansion or compaction, which played an important role in determining resilience of TFFWs to rising sea level. When root zone contributions were removed statistically from comparisons between relative sea-level rise and surface elevation change, sites that previously had elevation rate deficits showed a surplus. Therefore, assessments of wetland resilience that do not include subsurface processes will likely misjudge vulnerability to sea-level rise

Primary pollinator exclusion has divergent consequences for pollen dispersal and mating in different populations of a bird-pollinated tree

Pollination by nectarivorous birds is predicted to result in different patterns of pollen dispersal and plant mating compared to pollination by insects. We tested the prediction that paternal genetic diversity, outcrossing rate and realized pollen dispersal will be reduced when the primary pollinator group is excluded from bird-pollinated plants. Pollinator exclusion experiments in conjunction with paternity analysis of progeny were applied to Eucalyptus caesia Benth. (Myrtaceae), a predominantly honeyeater-pollinated tree that is visited by native insects and the introduced Apis mellifera (Apidae). Microsatellite genotyping at 14 loci of all adult E. caesia at two populations (n = 580 and 315), followed by paternity analysis of 705 progeny, revealed contrasting results between populations. Honeyeater exclusion did not significantly impact pollen dispersal or plant mating at Mount Caroline. In contrast, at the Chiddarcooping site, the exclusion of honeyeaters led to lower outcrossing rates, a threefold reduction in the average number of sires per fruit, a decrease in intermediate-distance mating and an increase in near-neighbour mating. The results from Chiddarcooping suggest that bird pollination may increase paternal genetic diversity, potentially leading to higher fitness of progeny and favouring the evolution of this strategy. However, further experimentation involving additional trees and study sites is required to test this hypothesis. Alternatively, insects may be effective pollinators in some populations of bird-adapted plants, but ineffective in others.Jack family trust; Australian Research Council, Grant/Award Number: DP140103357; University of Western Australia; Great Southern Development Commission; Holsworth Wildlife Research Endowment—Equity Trustees Charitable Foundation; Wiley Fundamental Ecology Award, Ecological Society of Australia Student Research Awar