10,995,908 research outputs found

    Mass splittings and matrix elements of mesons and baryons containing a single heavy quark

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    We present a study in the quenched approximation of the BB parameter BBB_B and the decay constant fBf_B using heavy-quark propagators implemented in the static approximation, and light-quark propagators computed using an O(a)O(a)-improved fermion action. We find a value of \Bbstat close unity, and discuss the systematic errors entering into the calculation. \fbstat is extracted using a variational fitting technique in order to obtain a reliable estimate of the ground state. In the second part of the talk, we describe an exploratory study of baryons containing a single heavy quark, computed using the O(a)O(a)-improved fermion action. We obtain masses generally in good agreement with experiment in both the charm and beauty sectors. We also report preliminary results for the form factor G1G_1 in the semi-leptonic Λb→Λc\Lambda_b \rightarrow \Lambda_c transition.Comment: 6 pages, uuencoded compressed postscript file, to be published in the Proceedings of Lattice 9

    Results from Lattice QCD for baryons containing a heavy quark

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    We present the calculation of the spectrum of baryons containing one heavy quark. Heavy baryon and meson mass splittings are computed and compared with experiment. We give preliminary results for the form factor G1G_1 for the semileptonic decay Λb→Λclνˉ \Lambda_b \rightarrow \Lambda_c l \bar{\nu} and investigate its flavour symmetry.Comment: 3 pages, uuencoded, Proceedings of the EPS/HEP95 conferenc

    Charmed Meson Spectroscopy and Matrix Elements with an O(a)-Improved Clover Fermion Action

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    We present preliminary results for the spectrum and decay matrix elements for heavy-light and heavy-heavy mesons, obtained on the 64-node Meiko Computing Surface at the University of Edinburgh. Quark propagators are computed with an O(a)-improved fermion action on 24^3x48 lattices at beta = 6.2, using three values of the quark mass up to around the strange quark mass, and four values of the quark mass in the region of the charm quark mass. We compare results for the hyperfine splitting in charmonium with those obtained using the conventional Wilson fermion action and find that the splitting is 1.83(15) times larger with the improved action. Our measurements of f_B indicate non-scaling corrections of the order of 20% to the Heavy Quark Effective Theory expectation. A comparison is made with results obtained on 16^3x48 lattices at beta = 6.0.Comment: at Lattice '92, 4 pages latex + 3 postscript figures, Edinburgh Preprint 92/51

    Measurement of the hadronic cross section at KLOE using the radiative return

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    We report on the measurement of the hadronic cross section below 1GeV at the electron-positron-collider DAPHNE, using the multiple purpose detector KLOE. The radiative return, which is due to initial state radiation (e+ e- \to gamma + hadrons), allows us to obtain the cross section for variable center-of-mass-energies of the hadronic system from the 2m_pi threshold up to 1.02GeV. This measurement can be performed while DAPHNE is running with a fixed accelerator energy on the phi mass (1.02 GeV). For the exclusive process e+ e- \to pi+ pi- gamma, the status of the analysis and first preliminary results of the invariant mass spectrum of the two-pion-state are presented.Comment: Invited talk at the workshop "e+e- Physics at Intermediate Energies", SLAC, April 30 - May 2, 2001 (T07

    Study of Gamma-Ray Bursts of energy E>10 GeV with the ARGO-YBJ detector

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    The study of high energy gamma-ray bursts can be performed by large area air shower arrays operating at very high mountain altitudes. ARGO-YBJ is a detector optimized to observe small size air showers, to be constructed at the Yangbajing Laboratory (Tibet, P.R. China) at an altitude of 4300 m. One of the goals of the experiment is the study of Gamma-Ray Bursts of energies E > 10 GeV. This can be achieved using the "single particle" technique, more profitable in the energy region E < 50 GeV, and the "low multiplicity" technique, suitable to observe GRBs at higher energies. The sensitiviy of ARGO-YBJ allows the detection of GRBs with energy fluences in the range 1--100 GeV as low as F~10^{-6} -- 10^{-5} erg cm^{-2}, depending on the spectral characteristics of the burst.Comment: 4 pages, 2 figures, to appear in the proceedings of 26th International Cosmic Ray Conference (Salt Lake City, 1999

    Quenched Light Hadron Spectroscopy: Comparing the Wilson and O(a)-Improved Fermion Actions

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    We have studied the light hadron spectrum and decay constants for quenched QCD at beta=6.2 on a 24^3x48 lattice. We compare the results obtained using a nearest-neighbour O(a)-improved ("clover") fermion action with those obtained using the standard Wilson fermion action on the same gauge configurations. For pseudoscalar meson masses in the range 330-800 MeV, we find no significant difference between the results for the two actions. The scales obtained from the string tension and mesonic sector are consistent, but higher than those derived from baryon masses. The ratio of the pseudoscalar decay constant to the vector meson mass is roughly independent of quark mass as observed experimentally.Comment: at Lattice '92, 4 pages, Edinburgh Preprint: 92/51

    Gamma-Hadron Discrimination with a Neural Network in the ARGO-YBJ Experiment

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    The structure of a neural network developed for the gamma hadron separation in the ARGO-YBJ detector is presented. The discrimination power in the full ARGO-YBJ energy range is shown in detail and the improvement in the detector sensitivity is also discussed.Comment: 4 pages, 4 figures, to appear in the proceedings of the 26th International Cosmic Ray Conference (Salt Lake City, 1999

    Performance of RPCs operated at the YangBaJing Laboratory

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    The ARGO-YBJ experiment will be installed at YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China), 4300 m a.s.l. . It consists of a full coverage of about 10^4 m^2 realized with RPC chambers. A small carpet of about 50 m^2 has been operated at YangBaJing in order to check the RPC performance in these high altitude conditions. Results concerning efficiency and time resolution are reported.Comment: 4 pages, 4 figures, to appear in the proceedings of 26th International Cosmic Ray Conference (Salt Lake City, 1999

    Underground Muons in Super-KAMIOKANDE

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    The largest underground neutrino observatory, Super-Kamiokande, located near Kamioka, Japan has been collecting data since April 1996. It is located at a depth of roughly 2.7 kmwe in a zinc mine under a mountain, and has an effective area for detecting entering-stopping and through-going muons of about 1238m21238 m^2 for muons of >1.7GeV>1.7 GeV. These events are collected at a rate of 1.5 per day from the lower hemisphere of arrival directions, with 2.5 muons per second in the downgoing direction. We report preliminary results from 229 live days analyzed so far with respect to zenith angle variation of the upcoming muons. These results do not yet have enough statistical weight to discriminate between the favored hypothesis for muon neutrino oscillations and no-oscillations. We report on the search for astrophysical sources of neutrinos and high energy neutrino fluxes from the sun and earth center, as might arise from WIMP annihilations. None are found. We also present a topographical map of the overburden made from the downgoing muons. The detector is performing well, and with several years of data we should be able to make significant progress in this area.Comment: 4pages, 6 figure

    Compactly presented groups

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    This survey purports to be an elementary introduction to compactly presented groups, which are the analogue of finitely presented groups in the broader realm of locally compact groups. In particular, compact presentation is interpreted as a coarse simple connectedness condition on the Cayley graph, and in particular is a quasi-isometry invariant. In the appendix, an example of a Lie group, not quasi-isometric to any homogeneous graph, is given; the short argument relies on results of Trofimov and Pansu, anterior to~1990.Comment: Preliminary version (13 pages). Comments welcome
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