2008 Vol. 32, No. 9
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The experimental high-K 2- and 3-quasiparticle bands of well deformed rare-earth nuclei are analyzed. It is found that there exists significant nonadditivity in moments of inertia (MOIs) for these bands. The microscopic mechanism of the rotational bands is investigated by the particle number conserving (PNC) method in the frame of cranked shell model with pairing, in which the blocking effects are taken care of exactly. The experimental rotational frequency dependence of these bands is well reproduced in PNC calculations. The nonadditivity in MOIs originates from the destructive interference between Pauli blocking effects.
A new gravitational model for dark energy is presented based on the model of de Sitter gauge theory of gravity. In the model, in addition to the cosmological constant, the homogeneous and isotropic torsion and its coupling with curvature play an important role for dark energy. The model may supply the universe with a natural transit from decelerating expansion to accelerating expansion.
The helicity amplitudes for J/ψ→ΛΛ and the relevant background decays are presented for measuring the Λ decay parameter α+(Λ→pπ+) in J/ψ→ΛΛ . The Monte Carlo (MC) simulations based on the helicity amplitudes information are carried out. The likelihood fit method to determine the Λ decay parameter is presented. Based on the MC generated sample, the sensitivity of the measurement for α+ has been estimated, which shows that the J/ψ→ΛΛ channel can be used to measure the Λ decay parameter α+(Λ→pπ+) well.
The topcolor-assisted technicolor (TC2) model predicts a number of neutral scalars like the top-pion (π0t) and the top-Higgs (h0t). These scalars have flavor-changing neutral-current (FCNC) top quark couplings, among which the top-charm transition couplings may be sizable. Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider (LHC) through the parton processes cg→t π0t and cg→t h0t. In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space. Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC, these rare processes will serve as a good probe for the TC2 model.
Because the nucleon may be excited and transformed into a virtual Δ resonance easily, we consider the decuplet contribution to the parity-violating (PV) nucleon-nucleon interaction in the chiral effective field theory. The effective PV nucleon-nucleon potential is derived without introducing any unknown coupling constants.
Working in the physics of Wilson factor and Aharonov-Bohm effect, we find in the fluxtube-quark system the topology of a baryon consisting of three heavy flavor quarks resembles that of the fractional quantum Hall effect (FQHE) in condensed matter. This similarity yields the result that the constituent quarks of baryon have the ``filling factor'' 1/3, thus the previous conjecture that quark confinement is a correlation effect is confirmed. Moreover, by deriving a Hamiltonian of the system analogous to that of FQHE, we predict an energy gap for the ground state of a heavy three-quark system.
We investigate quantum teleportation as a tool to study the thermally entangled state of a two-qubit Heisenberg XXZ chain. Our work is mainly to investigate the characteristics of a Heisenberg XXZ chain and get some analytical results of the fully entangled fraction. We also consider the entanglement teleportation via a two-qubit Heisenberg XXZ chain.
An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented.
The nuclear shadowing and antishadowing effects are explained by a unitarized BFKL equation. The Q2- and x-variations of the nuclear parton distributions are detailed based on the level of the unintegrated gluon distribution. In particular, the asymptotical behavior of the unintegrated gluon distribution near the saturation limit in nuclear targets is studied. Our results in the nuclear targets are insensitive to the input distributions if the parameters are fixed by the data of a free proton.
We calculate the unpolarized cross sections for dissociation reactions of charmonia in collisions with π, ρ and K in a potential that is derived from QCD. The reactions are governed by the quark-interchange processes. The mesonic quark-antiquark relative-motion wave functions are determined by the central spin-independent terms of the potential. The numerical wave functions and cross sections are parametrized. The difference of transition amplitudes in the prior form and in the post form is explored by deriving and examining the transition amplitudes of the one-gluon-exchange spin-spin term of the potential in the two forms. We find that the post-prior discrepancy in meson-meson elastic scattering that is governed by quark-interchange processes depends on the difference of quark or antiquark masses and of quark-antiquark spatial distributions of the two mesons.
The final state particle multiplicity distributions in high-energy nucleus-nucleus collisions are described by two different sub-distributions contributed by a single nucleon. The Monte Carlo calculated results from the two sub-distributions and the participant-spectator model are compared and found to be in agreement with the experimental data of Au-Au collisions at s=130 AGeV and Pb-Pb collisions at 158 AGeV.
The principle of the method for the BESⅢ event start time determination and the code construction are described. The investigation of influence of the noise, the method of rejecting noise and the performance checking by the Monte Carlo physics data sample are also presented. The preliminary results got from the Monte Carlo simulation are presented, the reconstruction efficiency of J/ψ→ anything events at noise level 0~60% can achieve above 99%, and the error rate is below 1%.
A code LEADS based on the Lie algebraic analysis for the continuous beam dynamics with space charge effect in beam transport has been developed. The program is used for the simulations of axial-symmetric and unsymmetrical intense continuous beam in the channels including drift spaces, electrostatic lenses and DC electrostatic accelerating tubes. In order to get the accuracy required, all elements are divided into many small segments, and the electric field in the segments is regarded as uniform field, and the dividing points are treated as thin lenses. Iteration procedures are adopted in the program to obtain self-consistent solutions. The code can be used in the designs of low energy beam transport systems, electrostatic accelerators and ion implantation machines.
The charge stripping injection method has been adopted for the accumulation of light heavy ions in HIRFL-CSR. This method has some special requirements for the accelerating particles, and at the same time the structure of the injection orbit has to be changed. In this paper, the design of the orbit has been presented, as well as the calculation of the beam line matching. According to the result of commissioning, stripping injection can accumulate the beam to a higher current.
This paper describes a field programming gate array (FPGA) based low level radio frequency (LLRF) prototype for the SSRF storage ring RF system. This prototype includes the local oscillator (LO), analog front end, digital front end, RF out, clock distributing, digital signal processing and communication functions. All feedback algorithms are performed in FPGA. The long term of the test prototype with high power shows that the variations of the RF amplitude and the phase in the accelerating cavity are less than 1% and 1° respectively, and the variation of the cavity resonance frequency is controlled within ±10 Hz.
In the upgrade project of the Beijing Electron Positron Collider (BEPCⅡ), three superconducting magnets are employed to realize the goal of two orders of magnitude higher luminosity. A cryogenic system with a total capacity of 0.5~kW at 4.5~K was built at the Institute of High Energy Physics (IHEP) to support the operations of these superconducting devices. For preparing the commissioning of the system, the refrigeration process was simulated and analyzed numerically. The numerical model was based on the latest engineering progress and focused on the normal operation mode. The pressure and temperature profiles of the cryogenic system are achieved with the simulation. The influence of the helium mass flow rates to cool superconducting magnets on the thermodynamic parameters of their normal operation is also studied and discussed in this paper.
High power conditioning of the input coupler for BEPCII superconducting cavity has been performed. After room temperature conditioning, the RF power of 150 kW with continuous wave at standing wave mode passed through the coupler without any problem. Meanwhile, a series of methods have also been studied to improve the performance of the coupler during the beam operation. Up to now, the input coupler can feed a RF power up to 100 kW stably with high current of 250 mA at 2.5 GeV.
Thin silicon phthalocyanine dichloride films on HOPG were prepared and the
sample was heated in the vacuum with laser. The thickness of the thin sample
on HOPG was checked by X-ray photoemission spectroscopy. The orientation of
the molecules in respect to the substrate plane was investigated by measuring the silicon K-edge near edge X-ray absorption fine structure (NEXAFS). In the NEXAFS spectra of the thin sample, two clear peaks which were assigned to 1s→σSi-N* and 1s→σSi-Cl* appeared around 1847.2 eV and 1843.1 eV respectively. The intensities of the resonance peaks showed strong polarization dependence. A quantitative analysis of the polarization dependence revealed that the Si-N bond tended to lie down while the Si-Cl bond was out of the molecular plane.
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