1,168 research outputs found

    Study of Inclusive J/psi Production in Two-Photon Collisions at LEP II with the DELPHI Detector

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    Inclusive J/psi production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction gamma gamma -> J/psi+X is seen. The number of observed N(J/psi -> mu+mu-) events is 36 +/- 7 for an integrated luminosity of 617 pb^{-1}, yielding a cross-section of sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the event shapes of different types of gamma gamma processes in the PYTHIA program, we conclude that (74 +/- 22)% of the observed J/psi events are due to `resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon.Comment: 13 pages, 8 figures, Accepted by Phys. Lett.

    Measurement of the relative rate of prompt Ōác0, Ōác1 and Ōác2 production at ‚ąös=7TeV

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    Prompt production of charmonium Ōác0, Ōác1 and Ōác2 mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of ‚ąös=7TeV. The Ōác mesons are identified through their decay to J/Ōąő≥, with J/Ōą‚Üíőľ+mu‚ąí using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of 1.0fb‚ąí1 collected by the LHCb detector, is used to measure the relative prompt production rate of Ōác1 and Ōác2 in the rapidity range 2.0<y<4.5 as a function of the J/Ōą transverse momentum from 3 to 20 GeV/c. First evidence for Ōác0 meson production at a hadron collider is also presented

    Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV