28 research outputs found

    Measurement of the correlation between the polar angles of leptons from top quark decays in the helicity basis at √s = 7 TeV using the ATLAS detector

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    A measurement of the correlations between the polar angles of leptons from the decay of pair-produced t and t̄ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 4.6  fb−¹ at a center-of-mass energy of √s = 7  TeV collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles θ1 and θ2 between the charged leptons and the direction of motion of the parent quarks in the tt̄ rest frame are sensitive to the spin information, and the distribution of cosθ1 ⋅ cosθ2 is sensitive to the spin correlation between the t and t̄ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed

    Search for massive, long-lived particles using multitrack displaced vertices or displaced lepton pairs in pp collisions at √s = 8 TeV with the ATLAS detector

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    Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of proton-proton collisions at √s=8  TeV corresponding to an integrated luminosity of 20.3  fb−1 collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R-parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios

    Measurement of the CP-violating phase ϕs and the Bs0 meson decay width difference with Bs0 → J/ψϕ decays in ATLAS

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    A measurement of the Bs0 decay parameters in the Bs0 → J/ψϕ channel using an integrated luminosity of 14.3 fb−1 collected by the ATLAS detector from 8 TeV pp collisions at the LHC is presented. The measured parameters include the CP -violating phase ϕs, the decay width Γs and the width difference between the mass eigenstates ΔΓs. The values measured for the physical parameters are statistically combined with those from 4.9 fb−1 of 7 TeV data, leading to the following: ϕ s =−0.090±0.078(stat.)±0.041(syst.)rad ΔΓ s =0.085±0.011(stat.)±0.007(syst.)ps −1 Γ s =0.675±0.003(stat.)±0.003(syst.)ps −1 In the analysis the parameter ΔΓs is constrained to be positive. Results for ϕs and ΔΓs are also presented as 68% and 95% likelihood contours in the ϕs-ΔΓs plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions

    Measurement of the differential cross-section of highly boosted top quarks as a function of their transverse momentum in s =8 TeV proton-proton collisions using the ATLAS detector

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    The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3  fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for tt¯ events in the lepton+jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum for values above 300 GeV. The hadronically decaying top quark is reconstructed as an anti-kt jet with radius parameter R=1.0 and identified with jet substructure techniques. The observed yield is corrected for detector effects to obtain a cross-section at particle level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of a majority of next-to-leading-order and leading-order matrix-element Monte Carlo generators are found to agree with the measured cross-sections.- We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. 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; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, FP7, Horizon 2020 and Marie Sklodowska-Curie Actions, European Union; Investissements d'Avenir Labex and Idex, ANR, Region Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; the Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) an

    Measurement of the production cross-section of a single top quark in association with a W boson at 8 TeV with the ATLAS experiment

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    The cross-section for the production of a single top quark in association with a W boson in proton-proton collisions at s√=8TeV is measured. The dataset corresponds to an integrated luminosity of 20.3 fb−1, collected by the ATLAS detector in 2012 at the Large Hadron Collider at CERN. Events containing two leptons and one central b-jet are selected. The W t signal is separated from the backgrounds using boosted decision trees, each of which combines a number of discriminating variables into one classifier. Production of W t events is observed with a significance of 7.7σ. The cross-section is extracted in a profile likelihood fit to the classifier output distributions. The W t cross-section, inclusive of decay modes, is measured to be 23.0 ± 1.3(stat.)− 3.5+ 3.2(syst.)±1.1(lumi.) pb. The measured cross-section is used to extract a value for the CKM matrix element |Vtb| of 1.01 ± 0.10 and a lower limit of 0.80 at the 95% confidence level. The cross-section for the production of a top quark and a W boson is also measured in a fiducial acceptance requiring two leptons with pT> 25 GeV and |η| 20 GeV and |η|  20 GeV, including both W t and top-quark pair events as signal. The measured value of the fiducial cross-section is 0.85 ± 0.01(stat.)− 0.07+ 0.07(syst.)±0.03(lumi.) pb

    Measurement of the total cross section from elastic scattering in pp collisions at s√ = 7 TeV with the ATLAS detector

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    A measurement of the total pp cross section at the LHC at √s = 7 TeV is presented. In a special run with high-β beam optics, an integrated luminosity of 80 µb−1 was accumulated in order to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the |t| range from 0.01 GeV2 to 0.1 GeV2 to extrapolate to |t| → 0, the total cross section, σtot(pp → X), is measured via the optical theorem to be: σtot(pp → X) = 95.35 ± 0.38 (stat.) ± 1.25 (exp.) ± 0.37 (extr.) mb, where the first error is statistical, the second accounts for all experimental systematic uncertainties and the\ud last is related to uncertainties in the extrapolation to |t| → 0. In addition, the slope of the elastic cross section at small |t| is determined to be B = 19.73 ± 0.14 (stat.) ± 0.26 (syst.) GeV−2

    Search for the b¯b decay of the Standard Model Higgs boson in associated (W/Z)H production with the ATLAS detector

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    A search for the bb¯ decay of the Standard Model Higgs boson is performed with the ATLAS experiment using the full dataset recorded at the LHC in Run 1. The integrated luminosities used are 4.7 and 20.3 fb−1 from pp collisions at s√=7 and 8 TeV, respectively. The processes considered are associated (W/Z)H production, where W → eν/μν, Z → ee/μμ and Z → νν. The observed (expected) deviation from the background-only hypothesis corresponds to a significance of 1.4 (2.6) standard deviations and the ratio of the measured signal yield to the Standard Model expectation is found to be μ = 0.52 ± 0.32 (stat.) ± 0.24 (syst.) for a Higgs boson mass of 125.36 GeV. The analysis procedure is validated by a measurement of the yield of (W/Z)Z production with Z→bb¯ in the same final states as for the Higgs boson search, from which the ratio of the observed signal yield to the Standard Model expectation is found to be 0.74 ± 0.09 (stat.) ± 0.14 (syst.)

    Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks in pp collisions at root s=8 TeV with the ATLAS detector

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    This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb−1 of pp collisions at a center-of-mass energy of 8 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum bb¯ system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected Standard Model backgrounds. Model-independent upper limits are placed on the visible cross sections for events with a Higgs boson decaying into bb¯ and large missing transverse momentum with thresholds ranging from 150 to 400 GeV. Results are interpreted using a simplified model with a Z0 gauge boson decaying into different Higgs bosons predicted in a two-Higgs-doublet model, of which the heavy pseudoscalar Higgs decays into a pair of dark matter particles. Exclusion limits are also presented for the mass scales of various effective field theory operators that describe the interaction between dark matter particles and the Higgs boson

    The SAPHO syndrome revisited with an emphasis on spinal manifestations

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    The synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome includes a group of chronic, relapsing, inflammatory musculoskeletal disorders with similar manifestations, in particular synovitis, hyperostosis, and osteitis, which may or may not be associated with neutrophilic skin eruptions such as palmoplantar pustulosis and acne conglobata. The syndrome occurs at any age, can involve any skeletal site, and its imaging appearances are variable, depending on the stage/age of the lesion and imaging method. The diagnosis is difficult if there is no skin disease. Awareness of the imaging appearances, especially in the spine, may help the radiologist in avoiding misdiagnosis (e.g., infection, tumor) and unnecessary invasive procedures, while facilitating early diagnosis and selection of an effective treatment. In this article, we provide an overview of the radiological appearances of SAPHO syndrome, focusing on the magnetic resonance imaging findings of vertebral involvement, and present relevant clinical and pathological features that assist early diagnosis

    Henkilöstön osaamisen kehittäminen:Casino Helsinki

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    Opinnäytetyön tarkoituksena oli tutkia Casino Helsingin henkilöstön osaamisen kehit-tämistä. Osatavoitteena oli saada tietoa henkilöstön mielipiteistä, heidän osaamisensa kehittämisen nykytilasta ja arvio tulevaisuuden näkymistä. Tarkoituksena oli selvittää miten hospitality- ja kassaosastojen yhdistyminen ja sen seurauksena tapahtunut osaa-misen kehittämisprosessi sujui, missä onnistuttiin ja missä epäonnistuttiin. Opinnäytetyön teoriaosuuden aiheina olivat osaamisen kehittäminen ja sen mittaaminen ja arviointi. Teoriaosuudessa tutkittiin kyseisiä aiheita ja niiden pohjalta muodostettiin tutkimuksen empiiriseen osaan kuuluvat kysymykset. Empiirinen osuus toteutettiin kvalitatiivisella eli laadullisella tutkimusmenetelmällä. Aineisto kerättiin maalis- ja huhtikuun 2013 välisenä aikana haastatteluiden avulla. Ky-symykset osoitettiin kahden osaston työntekijöille ja esimiehille. Tutkimus osoitti, että henkilöstön osaamisen kehittämisen kannalta sen jatkuva koulutus ja uuden oppiminen ei ole trendi ja se on tullut jäädäkseen, ja pysyäkseen tämän päivän kehityksessä ja kil-pailussa mukana, organisaatioiden on hyväksyttävä se. Haastateltavat ymmärsivät osaamisen kehittämisen hyödyt työnantajan näkökulmasta. Henkilöstö kokee olevansa paremmin selvillä omasta osaamisestaan ja sen tuomasta hyödystä organisaation menestyksen kannalta. Osa haastateltavista antoi ristiriitaisen kuvan osaamisensa hyödyllisyydestä, mutta katsovat sen auttaneen työyhteisöä siirtymään eteenpäin yt-neuvotteluiden jälkeen.The aim of the thesis was to find out how Casino Helsinki developed the know-how of their personnel. Part of the aim was to find out the personnel´s view on their current state of knowhow and thoughts on developing their know how after the training pro-cess, and how uniting Hospitality and Cash desk departments went and how it pro-gressed, where it succeeded and where it failed to succeed. The theory of the thesis is based on literature and publications dealing with develop-ment of personal training which can be viewed as one of the key points of human re-source management. The empirical part of the thesis was implemented by using the qualitative research method. The research material was gathered March and April of 2013 by interviews. The questions were presented to 5 members of the personnel of Casino Helsinki. The research showed that developing personnel and constantly learn-ing more about their know-how will benefit the personnel in the long run. Therefore it shouldn’t be viewed as a current trend, but as something that is here to stay and com-panies have to adapt to it in order to stay current with today’s ever changing competi-tion. The interviewees understood the importance of an effective personnel for the key success of the compan
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