Application of the zero-range potential model to positron annihilation on molecules

In this paper we use a zero-range potential (ZRP) method to model positron interaction with molecules. This allows us to investigate the effect of molecular vibrations on positron-molecule annihilation using the van der Waals dimer Kr2 as an example. We also use the ZRP to explore positron binding to polyatomics and examine the dependence of the binding energy on the size of the molecule for alkanes. We find that a second bound state appears for a molecule with ten carbons, similar to recent experimental evidence for such a state emerging in alkanes with twelve carbons.Comment: 14 pages, 6 figures, to be published in Nuclear Instruments and Methods

Intra-regional transportation of a tugboat fouling community between the ports of recife and natal, northeast Brazil

This study aimed to identify the incrusting and sedentary animals associated with the hull of a tugboat active in the ports of Pernambuco and later loaned to the port of Natal, Rio Grande do Norte. Thus, areas with dense biofouling were scraped and the species then classified in terms of their bioinvasive status for the Brazilian coast. Six were native to Brazil, two were cryptogenic and 16 nonindigenous; nine of the latter were classified as established (Musculus lateralis, Sphenia fragilis, Balanus trigonus, Biflustra savartii, Botrylloides nigrum, Didemnum psammatodes, Herdmania pallida, Microscosmus exasperatus, and Symplegma rubra) and three as invasive (Mytilopsis leucophaeta, Amphibalanus reticulatus, and Striatobalanus amaryllis). The presence of M. leucophaeata, Amphibalanus eburneus and A. reticulatus on the boat's hull propitiated their introduction onto the Natal coast. The occurrence of a great number of tunicate species in Natal reflected the port area's benthic diversity and facilitated the inclusion of two bivalves - Musculus lateralis and Sphenia fragilis - found in their siphons and in the interstices between colonies or individuals, respectively. The results show the role of biofouling on boat hulls in the introduction of nonindigenous species and that the port of Recife acts as a source of some species.Este trabalho objetivou identificar os animais incrustantes e sedentários associados ao casco de um rebocador que atuava nos Portos de Pernambuco e foi cedido para o Porto de Natal, Rio Grande do Norte. Áreas com densa bioincrustação foram raspadas e as espécies foram posteriormente classificadas em relação ao status de bioinvasão no litoral brasileiro. Dentre as espécies identificadas, seis eram nativas do Brasil, duas criptogênicas e 16 exóticas. Destas, oito foram classificadas como estabelecidas (Musculus lateralis, Sphenia fragilis, Balanus trigonus, Biflustra savartii, Botrylloides nigrum, Didemnum psammatodes, Herdmania pallida, Microscosmus exasperatus, Symplegma rubra) e três como invasoras (Mytilopsis leucophaeta, Amphibalanus reticulatus e Striatobalanus amaryllis). A presença de M. leucophaeata, Amphibalanus eburneus e A. reticulatus no casco da embarcação, propiciou sua introdução na costa de Natal. A ocorrência de grande número de espécies de tunicados em Natal refletiu a biodiversidade bêntica da área portuária e facilitou a inclusão de dois bivalves, Musculus lateralis e Sphenia fragilis, encontrados em seus sifões e nos interstícios entre colônias ou indivíduos, respectivamente. Os dados obtidos indicam que a incrustação em cascos de embarcações tem um papel preponderante na introdução de espécies exóticas, e que o Porto do Recife atuou como fonte de algumas destas espécies

Study of Z → llγ decays at √s = 8 TeV with the ATLAS detector

This paper presents a study of Z → llγ decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton–proton data sample corresponding to an integrated luminosity of 20.2 fb−1 collected at a centre-ofmass energy √s = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with stateof-the-art predictions for final-state QED radiation. First measurements of Z → llγ γ decays are also reported

Search for leptoquark pair production decaying into te−te¯ + or tμ−t¯μ+ in multi-lepton final states in pp collisions at √s = 13 TeV with the ATLAS detector

A search for leptoquark pair production decaying into te−te¯ + or tμ−t¯μ+ in final states with multiple leptons is presented. The search is based on a dataset of pp collisions at √s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. Four signal regions, with the requirement of at least three light leptons (electron or muon) and at least two jets out of which at least one jet is identified as coming from a b-hadron, are considered based on the number of leptons of a given flavour. The main background processes are estimated using dedicated control regions in a simultaneous fit with the signal regions to data. No excess above the Standard Model background prediction is observed and 95% confidence level limits on the production cross section times branching ratio are derived as a function of the leptoquark mass. Under the assumption of exclusive decays into te− (tμ−), the corresponding lower limit on the scalar mixed-generation leptoquark mass mLQd mix is at 1.58 (1.59) TeV and on the vector leptoquark mass mU˜1 at 1.67 (1.67) TeV in the minimal coupling scenario and at 1.95 (1.95) TeV in the Yang–Mills scenario

Constraints on spin-0 dark matter mediators and invisible Higgs decays using ATLAS 13 TeV pp collision data with two top quarks and missing transverse momentum in the final state

This paper presents a statistical combination of searches targeting final states with two top quarks and invisible particles, characterised by the presence of zero, one or two leptons, at least one jet originating from a b-quark and missing transverse momentum. The analyses are searches for phenomena beyond the Standard Model consistent with the direct production of dark matter in pp collisions at the LHC, using 139 fb−1 of data collected with the ATLAS detector at a centre-of-mass energy of 13 TeV. The results are interpreted in terms of simplified dark matter models with a spin-0 scalar or pseudoscalar mediator particle. In addition, the results are interpreted in terms of upper limits on the Higgs boson invisible branching ratio, where the Higgs boson is produced according to the Standard Model in association with a pair of top quarks. For scalar (pseudoscalar) dark matter models, with all couplings set to unity, the statistical combination extends the mass range excluded by the best of the individual channels by 50 (25) GeV, excluding mediator masses up to 370 GeV. In addition, the statistical combination improves the expected coupling exclusion reach by 14% (24%), assuming a scalar (pseudoscalar) mediator mass of 10 GeV. An upper limit on the Higgs boson invisible branching ratio of 0.38 (0.30+0.13−0.09) is observed (expected) at 95% confidence level

Search for doubly charged Higgs boson production in multi-lepton final states using 139 fb−1 of proton–proton collisions at s√ = 13 TeV with the ATLAS detector

A search for pair production of doubly charged Higgs bosons (H±± ), each decaying into a pair of prompt, isolated, and highly energetic leptons with the same electric charge, is presented. The search uses a proton–proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb−1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider (LHC). This analysis focuses on same-charge leptonic decays, H±±→ℓ±ℓ′± where ℓ,ℓ′=e,μ,τ, in two-, three-, and four-lepton channels, but only considers final states which include electrons or muons. No evidence of a signal is observed. Corresponding upper limits on the production cross-section of a doubly charged Higgs boson are derived, as a function of its mass m(H±±), at 95% confidence level. Assuming that the branching ratios to each of the possible leptonic final states are equal, B(H±±→e±e±)=B(H±±→e±μ±)=B(H±±→μ±μ±)=B(H±±→e±τ±)=B(H±±→μ±τ±)=B(H±±→τ±τ±)=1/6, the observed (expected) lower limit on the mass of a doubly charged Higgs boson is 1080 GeV (1065 GeV) within the left-right symmetric type-II seesaw model, which is the strongest limit to date produced by the ATLAS Collaboration. Additionally, this paper provides the first direct test of the Zee–Babu neutrino mass model at the LHC, yielding an observed (expected) lower limit of m(H±±) = 900 GeV (880 GeV)