Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of event-shape observables in Z→ℓ+ℓ− events in pp collisions at √ s=7 TeV with the ATLAS detector at the LHC

Event-shape observables measured using charged particles in inclusive $Z$-boson events are presented, using the electron and muon decay modes of the $Z$ bosons. The measurements are based on an integrated luminosity of $1.1 {\rm fb}^{-1}$ of proton--proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy $\sqrt{s}=7$ TeV. Charged-particle distributions, excluding the lepton--antilepton pair from the $Z$-boson decay, are measured in different ranges of transverse momentum of the $Z$ boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and $\mathcal{F}$-parameter, which are in particular sensitive to properties of the underlying event at small values of the $Z$-boson transverse momentum. The Sherpa event generator shows larger deviations from the measured observables than Pythia8 and Herwig7. Typically, all three Monte Carlo generators provide predictions that are in better agreement with the data at high $Z$-boson transverse momenta than at low $Z$-boson transverse momenta and for the observables that are less sensitive to the number of charged particles in the event.Comment: 36 pages plus author list + cover page (54 pages total), 14 figures, 4 tables, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2014-0

Morfologia do fruto, da semente e morfo-anatomia da pl\ue2ntula de Vitex megapotamica (Spreng.) Moldenke (Lamiaceae)

Vitex megapotamica (tarumã) é espécie arbórea, decídua, com ocorrência, no Brasil, desde Minas Gerais até o Rio Grande do Sul. Visando à caracterização morfológica do fruto, da semente e morfo-anatômica da plântula, frutos desta espécie foram coletados e as sementes postas para germinar em laboratório. As plântulas foram coletadas desde a protrusão da raiz até o desenvolvimento do primeiro par de eofilo. Foram realizadas medições e pesagem de frutos, e contagem do número de sementes por frutos. As características morfológicas do fruto e da semente são aqui descritas e ilustradas, assim como a morfo-anatomia da plântula. O fruto é drupóide, nuculânio, tetralocular, contendo apenas uma ou duas sementes com fina camada de endosperma e embrião axial, foliáceo. O diásporo (pirênio) é constituído pelo endocarpo mais a semente. O endocarpo lenhoso parece exercer restrição sobre a germinação das sementes desta espécie. A plântula é epigea, fanerocotiledonar, com paracotilédones elípticos, com margem inteira, e eofilos opostos, simples, elípticos, com margem serreada, apresentando tricomas tectores. Tanto o paracotilédone quanto o eofilo apresentam mesofilo heterogêneo, dorsiventral, feixe colateral em forma de arco e estômatos anomocíticos. A raiz é poliarca, com córtex parênquimático; o hipocótilo possui tricomas glandulares e não-glandulares, colo distinto, e com cerca de 20 dias encontra-se em início de crescimento secundário. Diversas das características da plântula de Vitex megapotamica estão relacionadas à sua condição de espécie heliófila

Evidence for the associated production of a W boson and a top quark in ATLAS at √s = 7 TeV

Contains fulltext : 103353.pdf (preprint version ) (Open Access

Search for supersymmetry in events with photons, bottom quarks, and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS detector

Contains fulltext : 111247.pdf (preprint version ) (Open Access

Charged-particle multiplicities in <i>pp</i> interactions at &#8730;s = 900 GeV measured with the ATLAS detector at the LHC

The first measurements from proton–proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |η|&#60;2.5 and pT&#62;500 MeV. The measurements are compared to Monte Carlo models of proton–proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at η=0 is measured to be1.333&#177;0.003(stat.)&#177;0.040(syst.), which is 5–15% higher than the Monte Carlo models predict

Search for displaced muonic lepton jets from light Higgs boson decay in proton-proton collisions at s=7\sqrt{s}=7 TeV with the ATLAS detector

A search is performed for collimated muon pairs displaced from the primary vertex produced in the decay of long-lived neutral particles in proton-proton collisions at sqrt(s) = 7 TeV centre-of-mass energy, with the ATLAS detector at the LHC. In a 1.9 fb-1 event sample collected during 2011, the observed data are consistent with the Standard Model background expectations. Limits on the product of the production cross section and the branching ratio of a Higgs boson decaying to hidden-sector neutral long-lived particles are derived as a function of the particles' mean lifetime