821 research outputs found

    Search for dark matter in events with heavy quarks and missing transverse momentum in pp collisions with the ATLAS detector

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    This article reports on a search for dark matterpair production in association with bottom or top quarks in20.3fb−1ofppcollisions collected at√s=8TeVbytheATLAS detector at the LHC. Events with large missing trans-verse momentum are selected when produced in associationwith high-momentum jets of which one or more are identifiedas jets containingb-quarks. Final states with top quarks areselected by requiring a high jet multiplicity and in some casesa single lepton. The data are found to be consistent with theStandard Model expectations and limits are set on the massscale of effective field theories that describe scalar and tensorinteractions between dark matter and Standard Model par-ticles. Limits on the dark-matter–nucleon cross-section forspin-independent and spin-dependent interactions are alsoprovided. These limits are particularly strong for low-massdark matter. Using a simplified model, constraints are set onthe mass of dark matter and of a coloured mediator suitableto explain a possible signal of annihilating dark matter

    The global cardiovascular magnetic resonance registry (GCMR) of the society for cardiovascular magnetic resonance (SCMR): its goals, rationale, data infrastructure, and current developments

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    BACKGROUND: With multifaceted imaging capabilities, cardiovascular magnetic resonance (CMR) is playing a progressively increasing role in the management of various cardiac conditions. A global registry that harmonizes data from international centers, with participation policies that aim to be open and inclusive of all CMR programs, can support future evidence-based growth in CMR. METHODS: The Global CMR Registry (GCMR) was established in 2013 under the auspices of the Society for Cardiovascular Magnetic Resonance (SCMR). The GCMR team has developed a web-based data infrastructure, data use policy and participation agreement, data-harmonizing methods, and site-training tools based on results from an international survey of CMR programs. RESULTS: At present, 17 CMR programs have established a legal agreement to participate in GCMR, amongst them 10 have contributed CMR data, totaling 62,456 studies. There is currently a predominance of CMR centers with more than 10 years of experience (65%), and the majority are located in the United States (63%). The most common clinical indications for CMR have included assessment of cardiomyopathy (21%), myocardial viability (16%), stress CMR perfusion for chest pain syndromes (16%), and evaluation of etiology of arrhythmias or planning of electrophysiological studies (15%) with assessment of cardiomyopathy representing the most rapidly growing indication in the past decade. Most CMR studies involved the use of gadolinium-based contrast media (95%). CONCLUSION: We present the goals, mission and vision, infrastructure, preliminary results, and challenges of the GCMR. TRIAL REGISTRATION: Identification number on ClinicalTrials.gov: NCT02806193. Registered 17 June 2016

    Measurements of time-dependent CP asymmetries in BDπ±B \to D^{*\mp} \pi^{\pm} decays using a partial reconstruction technique

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    We report results on time-dependent CP asymmetries in BDπ±B \to D^{*\mp}\pi^{\pm} decays based on a data sample containing 657 {\times} 10610^6 BBˉB\bar{B} pairs collected with the Belle detector at the KEKB asymmetric-energy e+ee^+ e^- collider at the Υ(4S)\Upsilon(4S) resonance. We use a partial reconstruction technique, wherein signal BDπ±B \to D^{*\mp}\pi^{\pm} events are identified using information only from the fast pion from the B decay and the slow pion from the subsequent decay of the DD^{*\mp}, where the former (latter) corresponds to D+(D)D^{*+} (D^{*-}) final states. We obtain CP violation parameters S+=+0.061±0.018(stat)±0.012(syst)S^+ = +0.061 \pm 0.018(\mathrm{stat}) \pm 0.012(\mathrm{syst}) and S=+0.031±0.019(stat)±0.015(syst)S^- = +0.031 \pm 0.019(\mathrm{stat}) \pm 0.015(\mathrm{syst}).Comment: 8 pages, 5 figures, 2 tables, submitted to Physical Review D (RC

    Observation of D+K+η()D^+ \rightarrow K^{+} \eta^{(\prime)} and Search for CP Violation in D+π+η()D^+ \rightarrow \pi^+ \eta^{(\prime)} Decays

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    We report the first observation of the doubly Cabibbo-suppressed decays D+K+η()D^+ \rightarrow K^+ \eta^{(\prime)} using a 791 fb1^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e+ee^+e^- collider. The ratio of the branching fractions of doubly Cabibbo-suppressed relative to singly Cabibbo-suppressed D+π+η()D^+ \rightarrow \pi^+ \eta^{(\prime)} decays are B(D+K+η)/B(D+π+η)\mathcal{B}(D^+ \rightarrow K^+ \eta)/\mathcal{B}(D^+ \rightarrow \pi^+ \eta) = (3.06 ±\pm 0.43 ±\pm 0.14)% and B(D+K+η)/B(D+π+η)\mathcal{B}(D^+ \rightarrow K^+ \eta')/\mathcal{B}(D^+ \rightarrow \pi^+ \eta') = (3.77 ±\pm 0.39 ±\pm 0.10)%. From these, we find that the relative final-state phase difference between the tree and annihilation amplitudes in D+D^+ decays, δTA\delta_{TA}, is (72 ±\pm 9)^\circ or (288 ±\pm 9)^\circ. We also report the most precise measurements of CP asymmetries to date: ACPD+π+ηA_{CP}^{D^+ \rightarrow \pi^+ \eta} = (+1.74 ±\pm 1.13 ±\pm 0.19)% and ACPD+π+ηA_{CP}^{D^+ \rightarrow \pi^+ \eta'} = (-0.12 ±\pm 1.12 ±\pm 0.17)%.Comment: 6 pages, 2 figures, 3 tables. Published in PR

    Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 8 TeV pp collisions with the ATLAS detector

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    A search for the direct production of charginos and neutralinos in final states with three leptons and missing transverse momentum is presented. The analysis is based on 20.3 fb−1 of s√ = 8 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations and limits are set in R-parity-conserving phenomenological Minimal Supersymmetric Standard Models and in simplified supersymmetric models, significantly extending previous results. For simplified supersymmetric models of direct chargino (χ˜±1) and next-to-lightest neutralino (χ˜02) production with decays to lightest neutralino (χ˜01) via either all three generations of sleptons, staus only, gauge bosons, or Higgs bosons, (χ˜±1) and (χ˜02) masses are excluded up to 700 GeV, 380 GeV, 345 GeV, or 148 GeV respectively, for a massless (χ˜01

    Muon reconstruction performance of the ATLAS detector in proton–proton collision data at √s = 13 TeV

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    This article documents the performance of the ATLAS muon identification and reconstruction using the LHC dataset recorded at √s = 13 TeV in 2015. Using a large sample of J/ψ→μμ and Z→μμ decays from 3.2 fb−1 of pp collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to 99% over most of the covered phase space (|η| 2.2, the pT resolution for muons from Z→μμ decays is 2.9 % while the precision of the momentum scale for low-pT muons from J/ψ→μμ decays is about 0.2%

    Search for W′→tb→qqbb decays in pp collisions at √s=8 TeV with the ATLAS detector

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    A search for a massive W′ gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in pp collisions at the LHC. The dataset was taken at a centre-of-mass energy of √s=8 TeV and corresponds to 20.3 fb−1 of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass W′ bosons in the range 1.5–3.0 TeV. b-tagging is used to identify jets originating from b-quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the W′→tb cross section times branching ratio ranging from 0.16pb to 0.33pb for left-handed W′ bosons, and ranging from 0.10pb to 0.21pb for W′ bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the W′-boson coupling to tb as a function of the W′ mass using an effective field theory approach, which is independent of details of particular models predicting a W′boson

    Search for vectorlike B quarks in events with one isolated lepton, missing transverse momentum, and jets at √s = 8 TeV with the ATLAS detector

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    A search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of pp collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb −1 . No significant excess of events is observed above the expected background. Limits are set on vectorlike B production, as a function of the B branching ratios, assuming the allowable decay modes are B → Wt/Zb/Hb. In the chiral limit with a branching ratio of 100% for the decay B → Wt, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 810 GeV (760 GeV). In the case where the vectorlike B quark has branching ratio values corresponding to those of an SU(2) singlet state, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 640 GeV (505 GeV). The same analysis, when used to investigate pair production of a colored, charge 5/3 exotic fermion T 5/3 , with subsequent decay T 5/3 → Wt, sets an observed (expected) 95% C.L. lower limit on the T 5/3 mass of 840 GeV (780 GeV)
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