分类: 物理学 >> 核物理学 提交时间: 2016-08-25
摘要: The branching fractions of the Υ(1S) inclusive decays into final states with a J/ψ or a ψ(2S) are measured with improved precision to be $\BR(\Upsilon(1S)\to J/\psi + {\rm anything})=(5.25\pm 0.13(\mathrm{stat.})\pm 0.25(\mathrm{syst.}))\times 10^{-4}$ and $\BR(\Upsilon(1S)\to \psi(2S) + {\rm anything})=(1.23\pm 0.17(\mathrm{stat.})\pm 0.11(\mathrm{syst.}))\times 10^{-4}$. The first search for Υ(1S) decays into XYZ states that decay into a J/ψ or a ψ(2S) plus one or two charged tracks yields no significant signals for XYZ states in any of the examined decay modes, and upper limits on their production rates in Υ(1S) inclusive decays are determined.
分类: 物理学 >> 核物理学 提交时间: 2016-08-24
摘要: The process γγ→pp¯K+K− and its intermediate processes are measured for the first time using a 980~fb−1 data sample collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. The production of pp¯K+K− and a Λ(1520)0 (Λ¯(1520)0) signal in the pK−~(p¯K+) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540~MeV/c2, denoted as Θ(1540)0~(Θ¯ (1540)0) or Θ(1540)++~(Θ(1540)−−), is seen in the pK−~(p¯K+) or pK+~(p¯K−) invariant mass spectra. Cross sections for γγ→pp¯K+K−, Λ(1520)0p¯K++c.c. and the products $\sigma(\gamma \gamma \to \Theta(1540)^0 \bar{p} K^+ +c.c.)\BR(\Theta(1540)^0 \to p K^{-})$ and$\sigma(\gamma \gamma \to \Theta(1540)^{++} \bar{p} K^- +c.c.)\BR(\Theta(1540)^{++}\to p K^{+})$ are measured. We also determine upper limits on the products of the χc0 and χc2 two-photon decay widths and their branching fractions to pp¯K+K− at the 90\% credibility level.
分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We discuss the prospects of a very long baseline neutrino oscillation experiment from HIPA to Beijing. The current understanding of neutrino oscillations, both theoretically and experimentally, are summarized. The figure of merits for interested physics m
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A lithium-assisted approach has been developed for the exfoliation of pristine graphite, which allows the large-scale preparation of few-layer graphene nanosheets. The process involves an unexpected physical insertion and exfoliation, and the graphene nanosheets prepared by this method reveal undisturbed sp2-hybridized structures. A possible two-step mechanism, which involves the negative charge being trapped around the edges of the graphite layers and a subsequent lithiation process, is proposed to explain the insertion of lithium inside the graphite interlayers. If necessary, the present exfoliation can be repeated and thinner (single or 2–3 layer) graphene can be achieved on a large scale. This simple process provides an efficient process for the exfoliation of pristine graphite, which might promote the future applications of graphene.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A surface protective structure to efficiently improve the cyclic stability and lifetime of the lithium metal electrode is investigated. By volu- metrically confining plated lithium metal in the inter-space of a ceramic porous layer and isolating the confined lithium via a rein- forced skin-layer from attack by electrolyte solvents, the coulombic efficiency of the protected lithium metal electrode reaches very high values of $97–99%.