Search for non-resonant Higgs boson pair production in final states with leptons, taus, and photons in pp collisions at √s = 13 TeV with the ATLAS detector

A search is presented for non-resonant Higgs boson pair production, targeting the bbZZ, 4V (V = W or Z), V V τ τ , 4τ , γγV V and γγτ τ decay channels. Events are categorised based on the multiplicity of light charged leptons (electrons or muons), hadronically decaying tau leptons, and photons. The search is based on a data sample of proton-proton collisions at √s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1. No evidence of the signal is found and the observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 17 (11) times the Standard Model predicted cross-section at 95% confidence level under the background-only hypothesis. The observed (expected) constraints on the HHH coupling modifier, κλ, are determined to be −6.2 < κλ < 11.6 (−4.5 < κλ < 9.6) at 95% confidence level, assuming the Standard Model for the expected limits and that new physics would only affect κλ

Beam-induced backgrounds measured in the ATLAS detector during local gas injection into the LHC beam vacuum

Inelastic beam-gas collisions at the Large Hadron Collider (LHC), within a few hundred metres of the ATLAS experiment, are known to give the dominant contribution to beam backgrounds. These are monitored by ATLAS with a dedicated Beam Conditions Monitor (BCM) and with the rate of fake jets in the calorimeters. These two methods are complementary since the BCM probes backgrounds just around the beam pipe while fake jets are observed at radii of up to several metres. In order to quantify the correlation between the residual gas density in the LHC beam vacuum and the experimental backgrounds recorded by ATLAS, several dedicated tests were performed during LHC Run 2. Local pressure bumps, with a gas density several orders of magnitude higher than during normal operation, were introduced at different locations. The changes of beam-related backgrounds, seen in ATLAS, are correlated with the local pressure variation. In addition the rates of beam-gas events are estimated from the pressure measurements and pressure bump profiles obtained from calculations. Using these rates, the efficiency of the ATLAS beam background monitors to detect beam-gas events is derived as a function of distance from the interaction point. These efficiencies and characteristic distributions of fake jets from the beam backgrounds are found to be in good agreement with results of beam-gas simulations performed with theFluka Monte Carlo programme

Search for heavy Majorana neutrinos in e±e± and e±μ± final states via WW scattering in pp collisions at √s = 13 TeV with the ATLAS detector

A search for heavy Majorana neutrinos in scattering of same-sign W boson pairs in proton–proton collisions at √s = 13 TeV at the LHC is reported. The dataset used corresponds to an integrated luminosity of 140 fb−1, collected with the ATLAS detector during 2015–2018. The search is performed in final states including a same-sign ee or eμ pair and at least two jets with large invariant mass and a large rapidity difference. No significant excess of events with respect to the Standard Model background predictions is observed. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. New constraints are set on the values of the |VeN|2 and |VeN V*μN| parameters for heavy Majorana neutrino masses between 50 GeV and 20 TeV, where VℓN is the matrix element describing the mixing of the heavy Majorana neutrino mass eigenstate with the Standard Model neutrino of flavour ℓ = e, μ. The sensitivity to the Weinberg operator is investigated and constraints on the effective ee and eμ Majorana neutrino masses are reported. The statistical combination of the ee and eμ channels with the previously published μμ channel is performed

Search for dark mesons decaying to top and bottom quarks in proton-proton collisions at √s = 13 TeV with the ATLAS detector

A search for dark mesons originating from strongly-coupled, SU(2) dark favor symmetry conserving models and decaying gaugephobically to pure Standard Model final states containing top and bottom quarks is presented. The search targets fully hadronic final states and final states with exactly one electron or muon and multiple jets. The analyzed data sample corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions collected at √s = 13 TeV with the ATLAS detector at the Large Hadron Collider. No significant excess over the Standard Model background expectation is observed and the results are used to set the first direct constraints on this type of model. The two-dimensional signal space of dark pion masses mπD and dark rho-meson masses mρD is scanned. For mπD /mρD = 0.45, dark pions with masses mπD < 940 GeV are excluded at the 95% CL, while for mπD /mρD = 0.25 masses mπD < 740 GeV are excluded

Combination of searches for Higgs boson decays into a photon and a massless dark photon using pp collisions at √s = 13 TeV with the ATLAS detector

A combination of searches for Higgs boson decays into a visible photon and a massless dark photon (H → γγd) is presented using 139 fb−1 of proton-proton collision data at a centre-of-mass energy of √s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The observed (expected) 95% confidence level upper limit on the Standard Model Higgs boson decay branching ratio is determined to be B(H → γγd) < 1.3% (1.5)%. The search is also sensitive to higher-mass Higgs bosons decaying into the same final state. The observed (expected) 95% confidence level limit on the cross-section times branching ratio ranges from 16 fb (20 fb) for mH = 400 GeV to 1.0 fb (1.5 fb) for mH = 3 TeV. Results are also interpreted in the context of a minimal simplified model

4200 New Shell Mound Sites in the Southern Red Sea

This article presents evidence for over 4200 prehistoric shell midden sites distributed on opposite sides of the southern Red Sea. These sites were primarily discovered using survey methods and site location models developed for locating shell midden sites on the Farasan Islands, where over 3000 have been found during previous research. These sites have been extensively excavated in the field and dated. Combining predictive models with remote sensing, an additional 1200 sites have been detected on the opposite side of the Red Sea, centred on the Dahlak Islands in Eritrea. Before these discoveries on the Farasan and Dahlak Archipelagos, the number of published prehistoric shell midden sites in the southern Red Sea was less than twenty. Combined, these sites represent a significant addition to the prehistoric coastal archaeology of the region. These new shell midden sites, and their apparent similarities on the two opposing coastlines, may indicate evidence of cultural contacts across the Red Sea during the Holocene Red Sea

Coupled model-data approach to terrestrial methane cycling during Paleogene greenhouse climates

Although methane is a critical greenhouse gas (GHG), there are no proxy methods for reconstructing its ancient atmospheric concentration. This is especially important because biogenic methane emissions are controlled by environmental conditions, such as temperature and precipitation, such that methane could be a significant positive or negative feedback on global climate. Understanding how methane emissions and cycling acted in the high pCO2 greenhouse worlds of the Paleogene potentially bridges the gap between our understanding of other, better (although arguably still poorly-) constrained GHGs and global temperature. We apply an advanced three dimensional global modelling strategy to the problem of Eocene trace GHG concentrations and show how important these may be in high-CO2 worlds, with as much as 2.7 ºC of global warming contributed by increased trace GHGs. We compare the model results to an indirect proxy for Paleogene methane cycling afforded by the distributions and carbon isotopic compositions of hopanoid lipid biomarkers with 13C-depleted isotopic compositions indicative of enhanced methane cycling. Examination of literature-derived and new hopanoid carbon isotopic analyses supports the spatial relationships between temperature, precipitation and methane cycling observed in the biogeochemical model. Together, the biogeochemical model and organic proxy data apply new constraints on ancient methane emissions in high-CO2 worlds

A large handaxe from Wadi Dabsa and early hominin adaptations within the Arabian Peninsula

The role played by the Arabian Peninsula in hominin dispersals out of Africa has long been debated. The DISPERSE Project has focused on south-western Arabia as a possible centre of hominin settlement and a primary stepping-stone for such dispersals. This work has led to the recent discovery, at Wadi Dabsa, of an exceptional assemblage of over 1000 lithic artefacts, including the first known giant handaxe from the Arabian Peninsula. The site and its associated artefacts provide important new evidence for hominin dispersals out of Africa, and give further insight into the giant handaxe phenomenon present within the Acheulean stone tool industry

The potential of biomarker proxies to trace climate, vegetation, and biogeochemical processes in peat: A review

Molecular fossils (biomarkers) are abundant in organic rich natural archives such as peats and lignites (fossilized peat), where their distribution is governed by their biological source, environmental factors, such as temperature and pH, and diagenetic reactions. As a result, biomarkers in peat have become an important tool to study past variations in vegetation, environment and climate in terrestrial settings, as well as biogeochemistry on time-scales of hundreds to millions of years ago. In recent years, significant progress has been made in understanding the controls on biomarker distributions, especially those derived from microorganisms and peat-forming plants, allowing for example, the quantification of past temperature and vegetation history during peat formation. Herein, we provide a review of a range of commonly applied biomarker proxies in peats, discuss the latest proxy developments, and explore the potential of using biomarkers in peat and lignite as paleoenvironmental proxies. We provide a framework for biomarker analyses in peat and identify possible future research directions