493 research outputs found

    Evidence for the positive-strangeness pentaquark Θ+\Theta^+ in photoproduction with the SAPHIR detector at ELSA

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    The positive--strangeness baryon resonance Θ+\Theta^+ is observed in photoproduction of the nK+Ks0\rm nK^+K^0_s final state with the SAPHIR detector at the Bonn ELectron Stretcher Accelerator ELSA. It is seen as a peak in the nK+\rm nK^+ invariant mass distribution with a 4.8σ4.8\sigma confidence level. We find a mass MΘ+=1540±4±2\rm M_{\Theta^+} = 1540\pm 4\pm 2 MeV and an upper limit of the width ΓΘ+<25\rm \Gamma_{\Theta^+} < 25 MeV at 90% c.l. From the absence of a signal in the pK+\rm pK^+ invariant mass distribution in γppK+K\rm\gamma p\to pK^+K^- at the expected strength we conclude that the Θ+\Theta^+ must be isoscalar.Comment: 9 pages, 4 figure

    Comparison of some Reduced Representation Approximations

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    In the field of numerical approximation, specialists considering highly complex problems have recently proposed various ways to simplify their underlying problems. In this field, depending on the problem they were tackling and the community that are at work, different approaches have been developed with some success and have even gained some maturity, the applications can now be applied to information analysis or for numerical simulation of PDE's. At this point, a crossed analysis and effort for understanding the similarities and the differences between these approaches that found their starting points in different backgrounds is of interest. It is the purpose of this paper to contribute to this effort by comparing some constructive reduced representations of complex functions. We present here in full details the Adaptive Cross Approximation (ACA) and the Empirical Interpolation Method (EIM) together with other approaches that enter in the same category

    The unexpected resurgence of Weyl geometry in late 20-th century physics

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    Weyl's original scale geometry of 1918 ("purely infinitesimal geometry") was withdrawn by its author from physical theorizing in the early 1920s. It had a comeback in the last third of the 20th century in different contexts: scalar tensor theories of gravity, foundations of gravity, foundations of quantum mechanics, elementary particle physics, and cosmology. It seems that Weyl geometry continues to offer an open research potential for the foundations of physics even after the turn to the new millennium.Comment: Completely rewritten conference paper 'Beyond Einstein', Mainz Sep 2008. Preprint ELHC (Epistemology of the LHC) 2017-02, 92 pages, 1 figur

    The PHENIX Experiment at RHIC

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    The physics emphases of the PHENIX collaboration and the design and current status of the PHENIX detector are discussed. The plan of the collaboration for making the most effective use of the available luminosity in the first years of RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program available at http://www.rhic.bnl.gov/phenix

    Ductile-Phase Toughening of Brazed Joints

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    A heat treatment is presented that uses ductile-phase toughening to mitigate the effect of brittle intermetallics in a Ni-based braze alloy. The fracture resistance has been enhanced by creating a microstructure containing elongated ductile γ-(Ni) domains that align, preferentially, across the joint. The development of this beneficial microstructure is based on an understanding of the transient dissolution, isothermal solidification, and coarsening phenomena. Due to slow kinetics, the elimination of intermetallics by diffusion is avoided in favor of ductile domain formation through solidification control. The toughening has been attributed to a combination of bridging and process zone dissipation, enabled by the ductile phase
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