502 research outputs found

    Measurement of the Omega_c Lifetime

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    We present the measurement of the lifetime of the Omega_c we have performed using three independent data samples from two different decay modes. Using a Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts normally used in charm analysis. The short but measurable lifetime of the Omega_c is demonstrated by a clear enhancement of the signals at short but finite decay lengths. Using a continuous maximum likelihood method we determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs. This makes the Omega_c the shortest living weakly decaying particle observed so far. The short value of the lifetime confirms the predicted pattern of the charmed baryon lifetimes and demonstrates that the strong interaction plays a vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip

    Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu

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    We measure the magnetic susceptibility of ultrathin Co films with an in-plane uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie temperature the influence of the magnetic anisotropy can be investigated by means of the parallel and transverse susceptibilities along the easy and hard axes. By comparison with a theoretical analysis of the susceptibilities we determine the isotropic exchange interaction and the magnetic anisotropy. These calculations are performed in the framework of a Heisenberg model by means of a many-body Green's function method, since collective magnetic excitations are very important in two-dimensional magnets.Comment: 7 pages, 3 figure

    Transverse Momentum Spectra of J/ψJ/\psi and ψ\psi^{\prime} Mesons from Quark Gluon Plasma Hadronization at CERN SPS

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    A popular derivation of the apparent temperature of the particle transverse momentum spectra and its inconsistency are considered. An improved formula for the apparent temperature is discussed. It is shown that recent results on transverse mass spectra of J/ψJ/\psi and ψ\psi^{\prime} mesons support a hypothesis of statistical production of charmonia at hadronization and suggest the early thermal freeze-out of these mesons. Using the apparent temperature formula the collective transverse velocity of the hadronizing quark gluon plasma is extracted to be 0.2 \approx 0.2. Predictions for transverse mass spectra of hidden and open charm mesons along with bottomonium at SPS and RHIC energies are discussed.Comment: Talk given at the Conference ``Strange Quarks in Matter 2001'', Frankfurt, September 24-29, 200

    A study of the centrally produced baryon-antibaryon systems in pp interactions at 450 GeV/c

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    A study of the centrally produced ppbar, ppbarpi, ppbarpipi and lambda lambda channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. No significant new structures are observed in the mass spectra, however, important new information on the production dynamics is obtained. A systematic study of the production properties of these systems has been performed and it is found that these systems are not produced dominantly by double Pomeron exchange.Comment: 13 pages, Latex, 4 Figure

    A study of pseudoscalar states produced centrally in pp interactions at 450 GeV/c

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    A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.Comment: 11 pages, Latex, 3 Figure

    Search for the exotic Ξ(1860)\Xi^{--}(1860) Resonance in 340GeV/c Σ\Sigma^--Nucleus Interactions

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    We report on a high statistics search for the Ξ(1860)\Xi^{--}(1860) resonance in Σ\Sigma^--nucleus collisions at 340GeV/c. No evidence for this resonance is found in our data sample which contains 676000 Ξ\Xi^- candidates above background. For the decay channel Ξ(1860)Ξπ\Xi^{--}(1860) \to \Xi^-\pi^- and the kinematic range 0.15<xF<<x_F<0.9 we find a 3σ\sigma upper limit for the production cross section of 3.1 and 3.5 μ\mub per nucleon for reactions with carbon and copper, respectively.Comment: 5 pages, 4 figures, modification of ref. 43 and 4
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