802 research outputs found
La recherche du boson de Higgs dans l'expérience ALEPH au LEP
No full textThe Iliggs boson is an important missing part in the standard model of particle physics. It could be produced at the LEP collidervia the process ete- -+ Zo + HoZ*. A search for a signal in the Zo + Houü,, Zo + Hoete- and Zo + Ho p+ tt- channels can be performed using either sets of cuts or neural networks. The two methods give similar results. No signal of the Higgs boson is seen in the data, and the mass domain 0.07 < rnno 3 a8.8 GeV/c2 is excluded at 95% confidence level
Search for the standard Higgs boson in the H^o nu nu bar channel using a neutral network
No full textS-shape correction using a neural network
No full textA neural network can be used to fit the S-shape corrections in the measurement of eta in the ATLAS electromagnetic calorimeter. Various learning methods are compared
Measurements of mean lifetime and branching fractions of b hadrons decaying to J / psi
No full textFrom a data sample of 450 000 hadronic events recorded with the ALEPH detector at LEP, 92±10 events are observed containing a J/ψ meson decaying to μ+μ− or e+e−. From these data the measured inclusive branching fraction for a b flavoured hadron to decay to a J/ψ is BR(b→ J/ψX) = (1.21±0.13 (stat.)±0.08 (syst.))%, and the average b hadron lifetime in the events tagged with a J/ψ is τb = 1.35+0.19−0.17±0.05 ps. Five events are observed consistent with the exclusive decay B± → J/ψK± and from these events the exclusive branching fraction is measured to be BR(B± → J/ψK±) = (0.22±0.10±0.02)%. Upper limits for other exclusive branching ratios are given
Study of the B+c → J/ψD+s and B+c → J/ψD*s+ decays with the ATLAS detector
No full textThe 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.ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-015-3743-8</p
Measurement of differential production cross-sections and forward-backward ratio in p+Pb collisions with the ATLAS detector
No full textSee paper for full list of authors - 13 pages plus author list + cover pages (26 pages total), 8 figures, 8 tables, submitted to Phys. Rev. C. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2013-07/International audienceMeasurements of differential cross-sections for production in p+Pb collisions at = 5.02 TeV at the LHC with the ATLAS detector are presented. The data set used corresponds to an integrated luminosity of 28.1 nb. The mesons are reconstructed in the dimuon decay channel over the transverse momentum range GeV and over the center-of-mass rapidity range . Prompt are separated from resulting from -hadron decays through an analysis of the distance between the decay vertex and the event primary vertex. The differential cross-section for production of nonprompt is compared to a FONLL calculation that does not include nuclear effects. Forward-backward production ratios are presented and compared to theoretical predictions. These results constrain the kinematic dependence of nuclear modifications of charmonium and -quark production in p+Pb collisions
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