455,524 research outputs found

    Fair Pi

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    International audienceIn this paper, we define fair computations in the pi-calculus. We follow Costa and Stirling's approach for CCS-like languages but exploit a more natural labeling method of process actions to filter out unfair process executions. The new labeling allows us to prove all the significant properties of the original one, such as unicity, persistence and disappearance of labels. It also turns out that the labeled pi-calculus is a conservative extension of the standard one. We contrast the existing fair testing with those that naturally arise by imposing weak and strong fairness as defined by Costa and Stirling. This comparison provides the expressiveness of the various fair testing-based semantics and emphasizes the discriminating power of the one already proposed in the literature

    Explicit fairness in testing semantics

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    In this paper we investigate fair computations in the pi-calculus. Following Costa and Stirling's approach for CCS-like languages, we consider a method to label process actions in order to filter out unfair computations. We contrast the existing fair-testing notion with those that naturally arise by imposing weak and strong fairness. This comparison provides insight about the expressiveness of the various `fair' testing semantics and about their discriminating power.Comment: 27 pages, 1 figure, appeared in LMC

    Theoretical description of the J/ψη(η)h1(1380)\boldsymbol{J/\psi \to \eta (\eta') h_1(1380)}, J/ψη(η)h1(1170)\boldsymbol{J/\psi \to \eta (\eta') h_1(1170)} and J/ψπ0b1(1235)0\boldsymbol{J/\psi \to \pi^0 b_1(1235)^0} reactions

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    We have made a study of the J/ψηh1,ηh1J/\psi \to \eta' h_1, \eta h_1 (with h1h_1 being h1(1170)h_1(1170) and h1(1380)h_1(1380)) and J/ψπ0b1(1235)0J/\psi \to \pi^0 b_1(1235)^0 assuming the axial vector mesons to be dynamically generated from the pseudoscalar-vector meson interaction. We have taken the needed input from previous studies of the J/ψϕππ,ωππJ/\psi \to \phi \pi \pi, \omega \pi \pi reactions. We obtain fair agreement with experimental data and provide an explanation on why the recent experiment on J/ψηh1(1380),h1(1380)K+K+c.c.J/\psi \to \eta' h_1(1380), h_1(1380) \to K^{*+} K^- +c.c. observed in the K+Kπ0K^+ K^- \pi^0 mode observes the peak of the h1(1380)h_1(1380) at a higher energy than its nominal mass.Comment: 21 pages, 6 figure

    Regge description of two pseudoscalar meson production in antiproton-proton annihilation

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    A Regge-inspired model is used to discuss the hard exclusive two-body hadronic reactions (pbar p ----> pi+ pi-, pi0 pi0, K+ K-, Kbar0 K0) for the FAIR facility project at GSI with the Panda detector. The comparison between the differential cross sections predictions and the available data is shown to determine the values of the few parameters of the model.Comment: 9 pages, 13 figure

    Direct Photons in Nuclear Collisions at FAIR Energies

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    Using the extrapolation of existing data estimations of prompt photon production at FAIR energies have been made. At y=yc.m.y=y_{c.m.} the rapidity density of prompt photons with pt>p_{t}> 1.5 GeV/c per central Au+Au event at 25 AGeV is estimated as 104\sim 10^{-4} . With the planed beam intensity 10910^{9} per second and 1% interaction probability, for 10% of most central events one can expect the prompt photon rate 102\sim 10^{2} photons per second. Direct photons from the hadron scenario of ion collisions generated by the Hadron-String-Dynamics (HSD) transport approach with implemented meson scatterings πρπγ,ππργ\pi\rho\to\pi\gamma, \pi\pi\to\rho\gamma have been analyzed. Photons from short-living resonances (e.g. ωπ0γ\omega \to \pi^{0} \gamma) decaying during the dense phase of the collision should be considered as direct photons. They contribute significantly in the direct photon spectrum at pt=0.51p_{t}=0.5 - 1 GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions the HSD generator predicts, as a lower estimate, γdirect/γπ0\gamma_{direct}/\gamma_{\pi^{0}} \simeq 0.5% in the region pt=0.51p_{t}=0.5 - 1 GeV/c. At pt=1.52p_{t}=1.5 - 2 GeV/c γprompt/γπ0\gamma_{prompt}/\gamma_{\pi^{0}} \simeq 2%. Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics (BHD) model. The BHD spectra differ strongly from the HSD predictions. The direct photon spectrum is very sensitive to the initial temperature parameter T0T_{0} of the model. The 10 MeV increase in the T0T_{0} value leads to \sim 2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of Sciences, ITEP, Moscow, 26 - 30 November 200

    Double pion production in NNNN and NˉN\bar{N}N collisions

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    With an effective Lagrangian approach, we give a full analysis on the NNNNππNN \to NN\pi\pi and NˉNNˉNππ\bar{N}N\to \bar{N}N\pi\pi reactions by exploring the roles of various resonances with mass up to 1.72 GeV. We find large contributions from Δ\Delta, N(1440)N^*(1440), Δ(1600)\Delta(1600) and Δ(1620)\Delta(1620) resonances. Our calculations also indicate sizeable contributions from nucleon poles for the energies close to the threshold. A good description to the existing data of different isospin channels of NNNNππNN\to NN\pi\pi and NˉNNˉNππ\bar{N}N\to \bar{N}N\pi\pi for beam energies up to 2.2 GeV is reached. Our results provide important implications to the ABC effect and guildlines to the future experimental projects at COSY, HADES and HIRFL-CSR. We point out that the \={P}ANDA at FAIR could be an essential place for studying the properties of baryon resonances and the data with baryon and anti-baryon in final states are worth analyzing.Comment: Invited plenary talk at the 11th International Workshop on Meson Production, Properties and Interaction (MESON2010), 10-15 June, 2010, Krakow, Polan
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