Macrofauna bentónica, a nivel de Clase, en una pradera marina tropical expuesta al mar abierto: relación con las variables ambientales

Antecedentes: Las praderas de pastos marinos son ecosistemas altamente productivos que albergan comunidades densas y diversas de macrofauna bentónica. Estos ecosistemas están siendo diezmados drásticamente a nivel mundial, afectando la densidad y diversidad de su macrofauna bentónica. Objetivo: Se investigó si la estructura de la comunidad de macrofauna bentónica, de una pradera marina tropical expuesta a mar abierto, está relacionada con el gradiente de variables ambientales y biológicas generado por la distancia de la costa. Métodos: El estudio se realizó en la pradera de pastos marinos de la Reserva de la Biosfera Los Petenes. Las muestras biológicas y las variables ambientales fueron obtenidas por triplicado en 12 sitios, en tres transectos localizados a 0.5, 9.0 y 17.0 km desde la costa. Resultados: La densidad de la macrofauna bentónica varió de 933 a 2550 ind. m-2. Los ejemplares recolectados pertenecieron a 10 clases taxonómicas: Asteroidea, Bivalvia, Echinoidea, Gastropoda, Holoturoidea, Malacostraca, Ophiuroidea, Polychaeta, Polyplacophora y Sipunculidea. La composición taxonómica en los transectos alejados de la costa fue homogénea dentro de transectos, pero diferente entre transectos. La composición del transecto cercano a la costa fue heterogenea, principalmente influenciada por la baja diversidad del sitio cercano a la ciudad de Campeche. Conclusiones: En esta pradera marina tropical, la composición de la macrofauna bentónica está modulada principalmente por un set de variables ambientales que cambian gradualmente desde la costa hacia mar abierto: biomasa del pasto marino Thalassia testudinum, biomasa de algas, profundidad y concentración de fosfato en el sedimento. En contraste, la densidad máxima de la macrofauna bentónica está limitada a una biomasa óptima del pasto marino dominante T. testudinum. Esta relación no es lineal, sino que se ajusta a una distribución Log Normal.Background: Seagrass meadows are highly productive marine ecosystems that harbor dense and diverse benthic macrofauna communities. These, seagrass ecosystems are being drastically decimated worldwide, which, in turn, affects the density and diversity of the associated macrofauna. Goals: We investigated if the benthic macrofaunal community structure in a tropical seagrass meadow exposed to the open sea is related to the gradient of environmental and biological factors generated by the distance from the coast. Methods: The study was conducted in the seagrass meadow from Los Petenes Biosphere Reserve. Biological samples and environmental variables were obtained by triplicate at twelve sampling sites divided into three transects located at 0.5, 9.0, and 17.0 km from the coast. Results: Benthic macrofaunal density varied from 933 to 2550 indv. m-2. The collected specimens belonged to ten taxonomic classes: Asteroidea, Bivalvia, Echinoidea, Gastropoda, Holothuroidea, Malacostraca, Ophiuroidea, Polychaeta, Polyplacophora, and Sipunculidea. Taxonomic composition from far from the coast transects was homogeneous within transects but different between transects. Taxonomic composition of near to the coast transect was heterogeneous, mainly influenced by the low diversity of classes from the site closest to the Campeche city. Conclusions: In this tropical seagrass meadow, the composition of the benthic macrofauna is mainly modulated by a set of environmental variables that gradually change from the coast to the open sea: Thalassia testudinum biomass, algae biomass, depth, and phosphate levels in sediment. In contrast, the maximum density of the benthic macrofauna is limited to an optimal biomass of the dominant seagrass species T. testudinum. This relationship is not lineal, but it follows a Log-Normal distribution pattern

Measurement of the cross-section of high transverse momentum vector bosons reconstructed as single jets and studies of jet substructure in pp collisions at √s = 7 TeV with the ATLAS detector

This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of √s = 7 TeV;{\rm Te}{\rm V}$and correspond to an integrated luminosity of$4.6\;{\rm f}{{{\rm b}}^{-1}}$. The measurement is performed by reconstructing the boosted W or Z bosons in single jets. The reconstructed jet mass is used to identify the W and Z bosons, and a jet substructure method based on energy cluster information in the jet centre-of-mass frame is used to suppress the large multi-jet background. The cross-section for events with a hadronically decaying W or Z boson, with transverse momentum${{p}_{{\rm T}}}\gt 320\;{\rm Ge}{\rm V}$and pseudorapidity$|\eta |\lt 1.9$, is measured to be${{\sigma }_{W+Z}}=8.5\pm 1.7$ pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson