301 research outputs found

    Neutrino Clustering in the Galaxy with a Global Monopole

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    In spherically symmetric, static spacetime, we show that only j=1/2 fermions can satisfy both Einstein's field equation and Dirac's equation. It is also shown that neutrinos are able to have effective masses and cluster in the galactic halo when they are coupled to a global monopole situated at the galactic core. Astronomical implications of the results are discussed.Comment: 8 pages, Revtex

    Observation of Two New N* Peaks in J/psi -> ppi−nˉp pi^- \bar n and pˉπ+n\bar p\pi^+n Decays

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    The πN\pi N system in decays of J/ψ→NˉNπJ/\psi\to\bar NN\pi is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying N∗→πNN^*\to \pi N compared with πN\pi N and ÎłN\gamma N experiments which mix isospin 1/2 and 3/2 for the πN\pi N system. Using 58 million J/ψJ/\psi decays collected with the Beijing Electron Positron Collider, more than 100 thousand J/ψ→pπ−nˉ+c.c.J/\psi \to p \pi^- \bar n + c.c. events are obtained. Besides two well known N∗N^* peaks at 1500 MeV and 1670 MeV, there are two new, clear N∗N^* peaks in the pπp\pi invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the N∗(1440)N^*(1440) peak and a long-sought "missing" N∗N^* peak above 2 GeV in the πN\pi N invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the N∗(1440)N^*(1440) peak as 1358±6±161358\pm 6 \pm 16 MeV and 179±26±50179\pm 26\pm 50 MeV, and for the new N∗N^* peak above 2 GeV as 2068±3−40+152068\pm 3^{+15}_{-40} MeV and 165±14±40165\pm 14\pm 40 MeV, respectively

    Three-Particle Correlations from Parton Cascades in Au+Au Collisions

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    We present a study of three-particle correlations among a trigger particle and two associated particles in Au + Au collisions at sNN\sqrt{s_{NN}} = 200 GeV using a multi-phase transport model (AMPT) with both partonic and hadronic interactions. We found that three-particle correlation densities in different angular directions with respect to the triggered particle (`center', `cone', `deflected', `near' and `near-away') increase with the number of participants. The ratio of `deflected' to `cone' density approaches to 1.0 with the increasing of number of participants, which indicates that partonic Mach-like shock waves can be produced by strong parton cascades in central Au+Au collisions.Comment: 9 pages, 6 figures; Final version to appear in Physics Letters

    Search for Invisible Decays of η\eta and ηâ€Č\eta^\prime in J/ψ→ϕηJ/\psi \to \phi\eta and ϕηâ€Č\phi \eta^\prime

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    Using a data sample of 58×10658\times 10^6 J/ψJ/\psi decays collected with the BES II detector at the BEPC, searches for invisible decays of η\eta and ηâ€Č\eta^\prime in J/ψJ/\psi to ϕη\phi\eta and ϕηâ€Č\phi\eta^\prime are performed. The ϕ\phi signals, which are reconstructed in K+K−K^+K^- final states, are used to tag the η\eta and ηâ€Č\eta^\prime decays. No signals are found for the invisible decays of either η\eta or ηâ€Č\eta^\prime, and upper limits at the 90% confidence level are determined to be 1.65×10−31.65 \times 10^{-3} for the ratio B(η→invisible)B(η→γγ)\frac{B(\eta\to \text{invisible})}{B(\eta\to\gamma\gamma)} and 6.69×10−26.69\times 10^{-2} for B(ηâ€Č→invisible)B(ηâ€Č→γγ)\frac{B(\eta^\prime\to \text{invisible})}{B(\eta^\prime\to\gamma\gamma)}. These are the first searches for η\eta and ηâ€Č\eta^\prime decays into invisible final states.Comment: 5 pages, 4 figures; Added references, Corrected typo

    Scaling of anisotropy flows in intermediate energy heavy ion collisions

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    Anisotropic flows (v1v_1, v2v_2 and v4v_4) of light nuclear clusters are studied by a nucleonic transport model in intermediate energy heavy ion collisions. The number-of-nucleon scalings of the directed flow (v1v_1) and elliptic flow (v2v_2) are demonstrated for light nuclear clusters. Moreover, the ratios of v4/v22v_4/v_2^2 of nuclear clusters show a constant value of 1/2 regardless of the transverse momentum. The above phenomena can be understood by the coalescence mechanism in nucleonic level and are worthy to be explored in experiments.Comment: Invited talk at "IX International Conference on Nucleus-Nucleus Collisions", Rio de Janeiro, Aug 28- Sept 1, 2006; to appear on the proceeding issue in Nuclear Physics

    Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model

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    In the framework of a multi-phase transport model (AMPT) with both partonic and hadronic interactions, azimuthal correlations between trigger particles and associated scattering particles have been studied by the mixing-event technique. The momentum ranges of these particles are 3<pTtrig<63< p^{trig}_T< 6 GeV/cc and 0.15<pTassoc<30.15< p_{T}^{assoc} < 3 GeV/cc (soft), or 2.5<pTtrig<2.5<p^{trig}_T< 4 GeV/cc and 1<pTassoc<2.51< p_{T}^{assoc} < 2.5 GeV/cc (hard) in Au + Au collisions at sNN\sqrt{s_{NN}} = 200 GeV. A Mach-like structure has been observed in correlation functions for central collisions. By comparing scenarios with and without parton cascade and hadronic rescattering, we show that both partonic and hadronic dynamical mechanisms contribute to the Mach-like structure of the associated particle azimuthal correlations. The contribution of hadronic dynamical process can not be ignored in the emergence of Mach-like correlations of the soft scattered associated hadrons. However, hadronic rescattering alone cannot reproduce experimental amplitude of Mach-like cone on away-side, and the parton cascade process is essential to describe experimental amplitude of Mach-like cone on away-side. In addition, both the associated multiplicity and the sum of pTp_{T} decrease, whileas the increases, with the impact parameter in the AMPT model including partonic dynamics from string melting scenario.Comment: 9 pages, 5 figures; Physics Letters B 641, 362-367 (2006

    Scaling of Anisotropic Flow and Momentum-Space Densities for Light Particles in Intermediate Energy Heavy Ion Collisions

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    Anisotropic flows (v2v_2 and v4v_4) of light nuclear clusters are studied by Isospin-Dependent Quantum Molecular Dynamics model for the system of 86^{86}Kr + 124^{124}Sn at intermediate energy and large impact parameters. Number-of-nucleon scaling of the elliptic flow (v2v_2) are demonstrated for the light fragments up to AA = 4, and the ratio of v4/v22v_4/v_2^2 shows a constant value of 1/2. In addition, the momentum-space densities of different clusters are also surveyed as functions of transverse momentum, in-plane transverse momentum and azimuth angle relative to the reaction plane. The results can be essentially described by momentum-space power law. All the above phenomena indicate that there exists a number-of-nucleon scaling for both anisotropic flow and momentum-space densities for light clusters, which can be understood by the coalescence mechanism in nucleonic degree of freedom for the cluster formation.Comment: 8 pages, 3 figures; to be published in Physics Letters

    Kaluza-Klein Cosmology With Modified Holographic Dark Energy

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    We investigate the compact Kaluza-Klein cosmology in which modified holographic dark energy is interacting with dark matter. Using this scenario, we evaluate equation of state parameter as well as equation of evolution of the modified holographic dark energy. Further, it is shown that the generalized second law of thermodynamics holds without any constraint.Comment: 13 pages, accepted for publication in Gen. Relativ. Gravi
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