50 research outputs found

    A rosa na vida dos povos

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    Textos en portugués y españolCatalogación basada en las portadas de cada parteEl nombre y mención de la serie aparece en port. como tít. del volume

    Study of the B-c(+) -> J/psi D-s(+) and Bc(+) -> J/psi D-s*(+) decays with the ATLAS detector

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    The decays B-c(+) -> J/psi D-s(+) and B-c(+) -> J/psi D-s*(+) are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb(-1) of pp collisions collected at centre-of-mass energies root s = 7 TeV and 8 TeV, respectively. Signal candidates are identified through J/psi -> mu(+)mu(-) and D-s(()*()+) -> phi pi(+)(gamma/pi(0)) decays. With a two-dimensional likelihood fit involving the B-c(+) reconstructed invariant mass and an angle between the mu(+) and D-s(+) candidate momenta in the muon pair rest frame, the yields of B-c(+) -> J/psi D-s(+) and B-c(+) -> J/psi D-s*(+), and the transverse polarisation fraction in B-c(+) -> J/psi D-s*(+) decay are measured. The transverse polarisation fraction is determined to be Gamma +/-+/-(B-c(+) -> J/psi D-s*(+))/Gamma(B-c(+) -> J/psi D-s*(+)) = 0.38 +/- 0.23 +/- 0.07, and the derived ratio of the branching fractions of the two modes is B-Bc+ -> J/psi D-s*+/B-Bc+ -> J/psi D-s(+) = 2.8(-0.8)(+1.2) +/- 0.3, where the first error is statistical and the second is systematic. Finally, a sample of B-c(+) -> J/psi pi(+) decays is used to derive the ratios of branching fractions B-Bc+ -> J/psi D-s*+/B-Bc+ -> J/psi pi(+) = 3.8 +/- 1.1 +/- 0.4 +/- 0.2 and B-Bc+ -> J/psi D-s*+/B-Bc+ -> J/psi pi(+) = 10.4 +/- 3.1 +/- 1.5 +/- 0.6, where the third error corresponds to the uncertainty of the branching fraction of D-s(+) -> phi(K+ K-)pi(+) decay. The available theoretical predictions are generally consistent with the measurement

    A search for an excited muon decaying to a muon and two jets in pp collisions at √s = 8 TeV with the ATLAS detector

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    A new search signature for excited leptons is explored. Excited muons are sought in the channel ppμμμμ jet jetpp \to \mu\mu^* \to \mu \mu\textrm{ jet jet}, assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb1^{-1} of pppp collision data at a centre-of-mass energy of s\sqrt{s} = 8 TeV taken with the ATLAS detector at the Large Hadron Collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass mμm_{\mu^*}. For mμm_{\mu^*} between 1.3 TeV and 3.0 TeV, the upper limit on σB(μμqqˉ\sigma B(\mu^* \to \mu q \bar{q}) is between 0.6 and 1 fb. Limits on σB\sigma B are converted to lower bounds on the compositeness scale Λ\Lambda. In the limiting case Λ=mμ\Lambda = m_{\mu^*}, excited muons with a mass below 2.9 TeV are excluded. With the same model assumptions, these limits at larger μ\mu^* masses improve upon previous limits from traditional searches based on the gauge-mediated decay μμγ\mu^* \to \mu \gamma.Comment: 33 pages in total, author list starting page 16, 4 figures, 5 tables, final version published by New Journal of Physics including corrections in Erratum https://dx.doi.org/10.1088/1367-2630/ab46ed. All figures including auxiliary are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2015-0

    Search for anomalous electroweak production of WW/WZ in association with a high-mass dijet system in pp collisions at √s=8  TeV with the ATLAS detector

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    A search is presented for anomalous quartic gauge boson couplings in vector-boson scattering. The data for the analysis correspond to 20.220.2 fb1^{-1} of s=8\sqrt{s}=8 TeV pppp collisions, and were collected in 2012 by the ATLAS experiment at the Large Hadron Collider. The search looks for the production of WWWW or WZWZ boson pairs accompanied by a high-mass dijet system, with one WW decaying leptonically, and a WW or ZZ decaying hadronically. The hadronically decaying W/ZW/Z is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. Constraints on the anomalous quartic gauge boson coupling parameters α4\alpha_4 and α5\alpha_5 are set by fitting the transverse mass of the diboson system, and the resulting 95% confidence intervals are 0.024<α4<0.030-0.024<\alpha_4<0.030 and 0.028<α5<0.033-0.028<\alpha_5<0.033.Comment: 38 pages in total, author list starting page 22, 5 figures, 2 tables, published in Phys. Rev. D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2015-09

    Antonio Machado y Álvarez an Hugo Schuchardt (17-06765)

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    Antonio Machado y Álvarez an Hugo Schuchardt (04-06752)

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    Antonio Machado y Álvarez an Hugo Schuchardt (20-06768)

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    Antonio Machado y Álvarez an Hugo Schuchardt (05-06753)

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    Antonio Machado y Álvarez an Hugo Schuchardt (18-06766)

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    Antonio Machado y Álvarez an Hugo Schuchardt (12-06760)

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