2011 Vol. 35, No. 8
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With the recent investigations of the g*g*-η(') transition form factor and η-η' mixing scheme, we present an updated study of the radiative decays J/ψ → η(')γ in perturbative QCD. The decays are taken as a test ground for the g*g*-η(') transition form factors and the η-η' mixing scheme. The form factors are found to be working for glunic η' production and the mixing angle is constrained to be φ=35.1°±0.8°.
With two-body unitarity equations, we demonstrate the relation between the data of Dalitz analysis of a D+ → K-π+π+ decay experiment and that of Kπ scattering, and point out that there might be some underestimated ambiguity in the existing data sets, if the I=1/2 component of the Kπ system is dominant in this decay process. It is suggested that the unitarity constraints should be built in to deal with the raw data to obtain an improved result from the Dalitz analysis.
The transverse charge density of pions is calculated based on relativistic quantum mechanics, where the pion is regarded as a quark-antiquark bound state. Corrections from the two spin-1/2 constituents and from the wave function of a quark and antiquark inside the bound system are discussed. The calculated results are compared to the results with a realistic effective Lagrangian approach as well as to that with a simple covariant model where the pion is regarded as a composite system with two scalar particles.
In this paper, we calculate the production of a charged top pion in association with a W boson via gg fusion at CERN's Large Hadron Collider in the context of the topcolor assisted technicolor model. We find that the total cross section of pp → gg → W±πt is several dozen femtobarns with reasonable values of the parameters, and the total cross section of pp → W±πt can reach a few hundred femtobarns when we consider the sum of the contributions of these two parton subprocesses, gg → W±πt and bb → W±πt.
Based on Bose-Einstein condensation at minimized momentum state, we get the expressions for the critical temperature and condensed fraction of Bose-Einstein condensation (BEC) in an external potential in the three-dimensional (3D) case. For the 1D and 2D cases, we present not only the critical temperature and corresponding particles but also the condition of BEC occurrence.
Monochromatic γ-rays are thought to be the smoking gun signal for identifying dark matter annihilation. However, the flux of monochromatic γ-rays is usually suppressed by virtual quantum effects since dark matter should be neutral and does not couple with γ-rays directly. In this work, we study the detection strategy of the monochromatic γ-rays in a future space-based detector. The flux of monochromatic γ-rays between 50 GeV and several TeV is calculated by assuming the supersymmetric neutralino as a typical dark matter candidate. The detection both by focusing on the Galactic center and in a scan mode that detects γ-rays from the whole Galactic halo are compared. The detector performance for the purpose of monochromatic γ-ray detection, with different energy and angular resolution, field of view, and background rejection efficiencies, is carefully studied with both analytical and fast Monte-Carlo methods.
The neutron leakage fluxes from the lunar surface are calculated by Monte Carlo transport code based on Geant4. The integral fluxes of fast neutrons, epi-thermal neutrons and thermal neutrons are analyzed. Numerical results for 20 kinds of lunar soils and 7 minerals show that the fast neutron fluxes are linearly related to the average atomic mass numbers of the lunar materials used in simulations. Meanwhile, the average atomic mass numbers are strongly modulated by the abundances of iron (Fe) and titanium (Ti), and a linear relationship between the average atomic mass numbers and the abundances of Fe and Ti is found. Furthermore, the results show that the ratios of epi-thermal to thermal fluxes for lunar soils are linearly related to the macroscopic absorption cross sections of lunar materials, and that the macroscopic absorption cross sections monotonically increase with the abundances of Fe and Ti by a simple function. Then we reach the conclusion that the neutron fluxes can provide the information about the Fe and Ti contents.
High-energy heavy-ion collisions produce abundant hyperons and nucleons. A dynamical coalescence model coupled with the ART model is employed to study the production probabilities of light clusters, deuteron (d), triton (t), helion (3He), and hypertriton (Λ3H) at subthreshold energy of Λ production (≈ 1 GeV per nucleon). We study the dependence on the reaction system size of the coalescence penalty factor per additional nucleon and entropy per nucleon. The Strangeness Population Factor (S3 / (3He × (Λ/p))) shows an extra suppression of hypertriton comparing to light clusters of the same mass number. This model predicts a hypertriton production cross-section of a few μb in 36Ar+36Ar, 40Ca+40Ca and 56Ni+56Ni in 1 A GeV reactions. The production rate is as high as a few hypertritons per million collisions, which shows that the fixed-target heavy-ion collisions at CSR (Lanzhou/China) at Λ subthreshold energy are suitable for breaking new ground in hypernuclear physics.
The Nilsson mean-field plus the extended pairing model for well-deformed nuclei is applied to some representative rare earth examples. The binding energies, some low-lying pair-excited states and even-odd mass differences of Er, Yb and Hf isotopes are calculated systematically within the proton frozen-pair excitation limit. A comparison with experimental data for these nuclei shows that the results of the extended pairing model are better than those for the standard pairing model with the BCS approximation and the nearest-orbit pairing model.
The realistic shell model Hamiltonians, USD and GXPF1A, have been transformed from the particle-particle (normal) representation to the particle-hole representation (multipole-multipole) by using the known formulation in Ref. . The obtained multipole-multipole terms were compared with the known spherical tensor forces, including the coupled ones. It is the first time the contributions of the coupled tensor forces to the shell model Hamiltonian have been investigated. It has been shown that some coupled-tensor forces, such as r2Y2σ]1, also give important contributions to the shell model Hamiltonian.
Two couples of low pressure multi-wire proportional chambers (MWPC) were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory (Jlab). In the experiment, a continuous wave (CW) electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy (1.853 GeV) and high intensity (500 nA) primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4.
In this paper, we studied the development of hadronic shower in an electromagnetic calorimeter of Alpha Magnetic Spectrometer Ⅱ. Two parametrized empirical formulae were proposed to describe the hadronic shower shape in calorimeter. Using 100 GeV proton beam incident on the center of the ECAL, detailed plots of lateral and longitudinal hadronic shower behavior were given and we found the formulae can describe the development of the hadronic shower with the test beam data. The possible application of the parametrized formulae including e±-π± discrimination and tau jet reconstruction was discussed.
The evolution of inter-device leakage current with total ionizing dose in transistors in 180 nm generation technologies is studied with an N-type poly-gate field device (PFD) that uses the shallow trench isolation as an effective gate oxide. The overall radiation response of these structures is determined by the trapped charge in the oxide. The impacts of different bias conditions during irradiation on the inter-device leakage current are studied for the first time in this work, which demonstrates that the worst condition is the same as traditional NMOS transistors. Moreover, the two-dimensional technology computer-aided design simulation is used to understand the bias dependence.
The particle acceptance instead of the G-factors has been introduced for a particle telescope. The particle acceptance of a telescope module TEST is simulated by using the GEANT4 Monte-Carlo package. The results are presented and explained.
The injecton pulsed bending bump magnets of Rapid Cycling Synchrotron (RCS) in China Spallation Neutron Source (CSNS) consist of four horizontal bending (BH) magnets and four vertical bending (BV) magnets. The BH magnets are operated at a repetition rate of 25 Hz and are excited with a trapezoid rectangle waveform with about 1.6 milliseconds duration. The eddy current is induced in BH magnets and in the end plates it is expected to be large, so the heat generation is of our great concern. In this paper, the eddy current loss of the BH magnet has been investigated and calculated by using a coupling method of 3D electromagnetic and thermal analysis. The accuracy of the analysis is confirmed by testing the prototype BH magnet. The end plate temperature of the BH magnet provided with slit cuts has been decreased obviously and met the requirements.
We try to design the lattice with 2 super periods and 4-DBA structure in order to provide more drifts for the future development of the TTX source. Due to the space limitation in the lab, the 4-DBA lattice is suitable.In the paper,we present the lattice design with a 4-DBA structure mainly for the pulse mode of the compact laser-electron storage ring (LESR). Element parameters of the lattice are optimized with the help of the professional software and beam dynamics such as intra-beam scattering (IBS) and Compton scattering (CS) are calculated. Besides, the fringe field effect is analyzed with the numerical method.
The construction of China Spallation Neutron Source (CSNS) has been initiated in Dongguan, Guangdong, China. Thus a detailed radiation transport analysis of the shutter neutron beam stop is of vital importance. The analyses are performed using the coupled Monte Carlo and multi-dimensional discrete ordinates method. The target of calculations is to optimize the neutron beamline shielding design to guarantee personal safety and minimize cost. Successful elimination of the primary ray effects via the two-dimensional uncollided flux and the first collision source methodology is also illustrated. Two-dimensional dose distribution is calculated. The dose at the end of the neutron beam line is less than 2.5 μSv/h. The models have ensured that the doses received by the hall staff members are below the standard limit required.
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