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

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

Climate change and water quality responses in agricultural catchments with high legacy storages of nutrients

International audienceThe effects of climate change on the quality of freshwaters remains poorly investigated while these effects are likely to be ambiguous. Indeed, such effects are partly direct such as temperature control on reaction rates, and partly indirect such as decrease of dilution processes with drier low flows. How the fate of a given pollutant responds to climate change can differ depending on its sources, reactivity and mobilization processes. Therefore, investigating the hydrochemical response of streams to climate change requires considering several elements that differ in their sources and pathways, and in their sensitivity to local and global forcings.A cross-analysis of hydro-climatic variables and the dynamics of three solutes - carbon (C), nitrogen (N) and phosphorus (P) - was conducted at multiple temporal scales using the long-term data sets from a Critical Zone Observatory in Western France (AgrHyS). We identified trends on climatic variables (air temperature increased, winters became wetter and summers drier) and stream concentrations (NO3 concentrations decreased, DOC concentrations increased). However, no effect of air temperature and radiation was observed on stream-water concentrations for the three solutes and there was no clear response of seasonal water-quality signals to increased contrast among hydrological seasons. Therefore, despite observed inter and intra-annual effects of climate on water quality, long-term changes of stream-water concentrations seemed to be more related to agricultural changes than to climate variations. In such a temperate and humid region, the seasonal amplitude of climatic variables is higher than the magnitude of their long-term changes. In addition, agricultural catchments of Western Europe have received high inputs of nutrients since the 1960s that led to create legacy storages in particular N and P in the soil, the vadose zone and/or the groundwater. The damped response of water quality may then be related to legacy storage, leading to lower sensitivity to climatic than to agricultural drivers. Disentangling the respective effects of climate and human activities on stream water quality is particularly challenging, even more in such contexts dealing with legacy storages. As a perspective, we show how using ratios of elements with contrasted properties or origin can help addressing this challenge