Combination of searches for heavy spin-1 resonances using 139 fb−1 of proton-proton collision data at s = 13 TeV with the ATLAS detector

A combination of searches for new heavy spin-1 resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons or quarks, is presented. The data sample used corresponds to 139 fb−1 of proton-proton collisions at = 13 TeV collected during 2015–2018 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting quark pairs (qq, bb, , and tb) or third-generation leptons (τν and ττ) are included in this kind of combination for the first time. A simplified model predicting a spin-1 heavy vector-boson triplet is used. Cross-section limits are set at the 95% confidence level and are compared with predictions for the benchmark model. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The complementarity of the various analyses increases the sensitivity to new physics, and the resulting constraints are stronger than those from any individual analysis considered. The data exclude a heavy vector-boson triplet with mass below 5.8 TeV in a weakly coupled scenario, below 4.4 TeV in a strongly coupled scenario, and up to 1.5 TeV in the case of production via vector-boson fusion

Search for dark photons in rare Z boson decays with the ATLAS detector

A search for events with a dark photon produced in association with a dark Higgs boson via rare decays of the standard model Z boson is presented, using 139     fb − 1 of √ s = 13     TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. The dark boson decays into a pair of dark photons, and at least two of the three dark photons must each decay into a pair of electrons or muons, resulting in at least two same-flavor opposite-charge lepton pairs in the final state. The data are found to be consistent with the background prediction, and upper limits are set on the dark photon’s coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, α D ϵ 2 , in the dark photon mass range of [5, 40] GeV except for the Υ mass window [8.8, 11.1] GeV. This search explores new parameter space not previously excluded by other experiments

Trade-offs and synergies in the structural and functional characteristics of leaves photosynthesizing in aquatic environments

Aquatic plants, comprising different divisions of embryophytes, derive from terrestrial ancestors. They have evolved to live in water, both fresh and salty, an environment that presents unique challenges and opportunities for photosynthesis and growth. These include, compared to air, a low water stress, a greater density, and attenuation of light, and a more variable supply of inorganic carbon, both in concentration and chemical species, but overall a lower carbon availability, and the opportunity to take up nutrients from the water. The leaves of many aquatic plants are linear, dissected, whorled, or cylindrical with a large volume of air spaces. They tend to have a high specific leaf area, thin cuticles, and usually lack functional stomata. Exploiting the availability of chemicals in their environment, freshwater macrophytes may incorporate silica in their cell wall, while seagrasses contain sulphated polysaccharides, similar to those of marine macroalgae; both groups have low lignin content. This altered cell wall composition produces plants that are more flexible and therefore more resistant to hydraulic forces (mechanical stress arising from water movement). Aquatic plants may have enhanced light harvesting complexes conferring shade adaptation, but also have mechanisms to cope with high light. Aquatic plants have evolved numerous strategies to overcome potential carbon-limitation in water. These include growing in micro-environments where CO2 is high, producing leaves and roots that exploit CO2 from the air or sediment and operating concentrating mechanisms that increase CO2 (CCM) around the primary carboxylating enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase. These comprise C4 metabolism, crassulacean acid metabolism, and the ability to exploit the often high concentrations of HCO3−, and ~50% of freshwater macrophytes and ~85% of seagrasses have one or more CCM. Many of these adaptations involve trade-offs between conflictin constraints and opportunities while others represent ‘synergies’ that help to maximize the productivity of this important group of plants