• Weak decays of doubly heavy baryons: “decay constants”
    Inspired by the recent observation of the Ξcc++ by the LHCb Collaboration, we explore the "decay constants" of doubly heavy baryons in the framework of QCD sum rules. With the Ξcc, Ξbc, Ξbb, and Ωcc, Ωbc, Ωbb baryons interpolated by three-quark operators, we calculate the correlation functions using the operator product expansion and include the contributions from operators up to dimension six. On the hadron side, we consider both contributions from the lowest-lying states with JP=1/2+ and from negative parity baryons with JP=1/2-. We find that the results are stable and the contaminations from negative parity baryons are not severe. These results are ingredients for the QCD study of weak decays and other properties of doubly-heavy baryons.
  • Double differential cross sections of light charged particle production for the n+238U reaction
    Production of light complex particles from the n+238U reaction is analyzed with the exciton model including the improved Iwamoto-Harada pickup mechanism for the preequilibrium process. It is allowed that some of the nucleons forming the complex ejectile come from levels below the Fermi energy, and the intrinsic structure of the emitted particle is taken into account. The equilibrium-state emissions are also considered by using Hauser-Feshbach theory with the width fluctuation correction and the evaporation model. Moreover, all cross sections, angular distributions, energy spectra and double differential cross sections of neutron, proton, deuteron, triton and alpha emissions for the n+238U reaction are consistently calculated and analyzed with nuclear theoretical models in the energy range En ≤ 150 MeV. ENDF-formatted nuclear data including information about the production of light charged particles are obtained.
  • Analysis of Forbush decreases observed using a muon telescope in Antarctica starting on 21 June 2015
    A cosmic-ray muon telescope has been collecting data since the end of 2014, which was shortly after the telescope was built in the Zhongshan Station of Antarctica. The telescope is the first observation device to be built by Chinese scientists in Antarctica. The pressure change is very strong in Zhongshan station. The count rate of the pressure correction results shows that the large variations in the count rate are likely caused by pressure fluctuations. During the period from 18 June to 22 June 2015, four halo coronal mass ejections (CMEs) were ejected from the Sun. These CMEs initiated a series of Forbush decreases (FD) when they reached the Earth. We conducted a comprehensive study of the intensity fluctuations of galactic cosmic rays recorded during FDs. The intensity fluctuations used in this study were collected by cosmic ray detectors of multiple stations (Zhongshan, McMurdo, South Polar, and Nagoya), and the solar wind measurements were collected by ACE and WIND. The profile of the FD of 22 June demonstrated a four-step decrease. The traditional one- or two-step FD classification method does not adequately explain the FD profile results. The interaction between the faster CME that occurred on 21 June 2015 and the two slow CMEs of the earlier few days should be considered. The cosmic ray intensities of the South Pole, McMurdo, and Zhongshan stations have similar hourly variations, whereas the galactic cosmic rays recorded between polar and non-polar locations are distinct. The FD pre-increase of 22 June 2015 for the Nagoya muon telescope (non-polar location) lags those of the McMurdo and Zhongshan stations (polar locations) by 1 h. The FD onset of 22 June 2015 for the Nagoya muon telescope lags those of the polar locations by 1 h.
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