7 research outputs found

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

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    Event-shape observables measured using charged particles in inclusive ZZ-boson events are presented, using the electron and muon decay modes of the ZZ bosons. The measurements are based on an integrated luminosity of 1.1fb11.1 {\rm fb}^{-1} of proton--proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy s=7\sqrt{s}=7 TeV. Charged-particle distributions, excluding the lepton--antilepton pair from the ZZ-boson decay, are measured in different ranges of transverse momentum of the ZZ boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and F\mathcal{F}-parameter, which are in particular sensitive to properties of the underlying event at small values of the ZZ-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 ZZ-boson transverse momenta than at low ZZ-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

    Performance of the ATLAS muon trigger in pp collisions at root s=8 TeV

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    We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; ISF, MINERVA, GIF, ICORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW and NCN, Poland; GRICES and FCT, Portugal; MNE/IFA, Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America

    Aspects of neutron-spin echo spectroscopy at pulsed sources

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    The integrated elliptic flow of charged particles produced in Pb+Pb collisions at (Formula presented.)\ua0TeV\ua0has been measured with the ATLAS detector using data collected at the Large Hadron Collider. The anisotropy parameter, v2, was measured in the pseudorapidity range |\u3b7| 642.5 with the event-plane method. In order to include tracks with very low transverse momentum pT, thus reducing the uncertainty in v2 integrated over pT, a 1 \u3bcb-1 data sample recorded without a magnetic field in the tracking detectors is used. The centrality dependence of the integrated v2 is compared to other measurements obtained with higher pT thresholds. The integrated elliptic flow is weakly decreasing with |\u3b7|. The integrated v2 transformed to the rest frame of one of the colliding nuclei is compared to the lower-energy RHIC data

    Electron and photon energy calibration with the ATLAS detector using LHC Run 1 data

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    This paper presents the electron and photon energy calibration achieved with the ATLAS detector using about 25 fb1^{-1} of LHC proton--proton collision data taken at centre-of-mass energies of s\sqrt{s} = 7 and 8 TeV. The reconstruction of electron and photon energies is optimised using multivariate algorithms. The response of the calorimeter layers is equalised in data and simulation, and the longitudinal profile of the electromagnetic showers is exploited to estimate the passive material in front of the calorimeter and reoptimise the detector simulation. After all corrections, the ZZ resonance is used to set the absolute energy scale. For electrons from ZZ decays, the achieved calibration is typically accurate to 0.05% in most of the detector acceptance, rising to 0.2% in regions with large amounts of passive material. The remaining inaccuracy is less than 0.2-1% for electrons with a transverse energy of 10 GeV, and is on average 0.3% for photons. The detector resolution is determined with a relative inaccuracy of less than 10% for electrons and photons up to 60 GeV transverse energy, rising to 40% for transverse energies above 500 GeV.Comment: 39 pages plus author list + cover pages (51 pages total), 42 figures, 8 tables, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/PERF-2013-05

    Physical activity during pregnancy through postpartum: A study of predictive and explanatory factors in a multi-ethnic population

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    The study objectives were to (a) describe steps and moderate-to-vigorous intensity physical activity (MVPA) from pregnancy and postpartum across ethnic groups, (b) test prognostic factors for early identification of pregnant women at risk of non-compliance with the guideline (=150 MVPA minutes/week), and (c) to explore the association between access to recreational areas and MVPA. Data originated from the Stork-Groruddalen Cohort Study (n=823). MVPA was monitored with a multi-sensor device in gestational week (GW) 15 and 28 and three months postpartum. Country of birth defined ethnicity. Data on access to recreational areas was obtained by geographic information systems and self-report. MVPA declined between GW 15 and 28, by which only 25% complied with the guideline. Four factors predicted guideline non-compliance (ethnic minority background, high body fat percentage, at least two previous births and few physically active friends). MVPA increased significantly for Western women between GW 28 and postpartum, while the increase was modest for ethnic minority women. Women with good access to recreational areas accumulated more MVPA minutes/day than women with limited access
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