2003 Vol. 27, No. 12
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The BES experiment at Beijing electron-position collider provides an excellent laboratory for the research of Baryon spectroscopy. Some difficulties arise due to the oftenappeared low-momentum of final state particles in such research. Using Ξ * spectrum study from the decay J/ψ→+ΛK- as an example, we analyzed and compared the effects on the results with different versions of MC simulation, as well as the experimental data of low momentum particles, and derived the detection limit for this channel.
Based on the Monte Carlo simulation and J/ψ data of BES Ⅱ, the performance of p and in BES detector is studied, which includes the criteria for removing the secondary charged tracks and fake photons produced by the annihilation of with the materials, the energy loss and deposited energy of p and in BSC, as well as the minimum p and momentum which can be reconstructed correctly, The combined TOF and dE/dxinformation is suggested to be used for p and identification.
The rare decay B+→D+sK*0 can occur only via annihilation diagrams in the Standard Model. We calculate the branching ratio in perturbative QCD approach based on k T factorization theorem. We find that the branching ratio of this decay is about of order 10－8, which may be sensitive to new physics.
We study the branching ratio of the inclusive b→sτ+τ－ decay in two Higgs doublet model Ⅲ, including leading order QCD corrections. We find that neutral Higss bosons mediated tree level diagrams dominate the decay within reasonable parameter space and thus the process might be observed in future B mesons experiments.
In the context of flavor-universal topcolor-assisted technicolor (TC2) models, we study the lepton flavor violating (LFV) processes Z→lilj. We find that the extra U(1) gauge boson Z′ can give significantly contributions to these LFV processes. With reasonable values of the parameters, the branching ratios of the processes Z→τμ and Z→τe can approach the experimental upper limits. The indirect bound on the process Z→μe can give a severe constraint on the flavor-universal TC2 models.
Inflation plays a significant role in interpreting current observations. Despite the success of inflation theory, the reheating energy scale ρreh is largely uncertain today. This consequently induces uncertainty to the primordial spectrum when achieving primordial spectra from inflation models. In this paper, we study the effects of this uncertainty on the primordial spectrum and cosmic microwave background (CMB) radiation. For the primordial spectra with small running indices, our result shows that the effect is negligible if the inflation parameter V0 can be normalized freely. But for models with large running indices, we find that ρreh can be highly restricted by the CMB observations.
Two independent measurements with different target foils of nominally the same thickness have been performed for the 19F+93Nb dissipative heavy ion collision. The beam 19F8+ energies were from 102 MeV to 108 MeV in steps of 250keV. The probability distribution of the differences of the cross sections in the two measurements and the probability distribution of the measured cross section relative deviations from the energy smooth background are analyzed. These distributions indicate that the non-reproducibility of the cross sections is of a statistical significance but not resulted from the insufficient statistics counting rates.
The proton and neutron 1S0 pairing gaps in β-stable neutron star matter have been studied by using the isospin dependent Brueckner-Hartree-Fock approach and the BCS theory. We have concentrated on investigating and discussing the effect of three-body force. The calculated results indicate that the three-body force has only a small effect on the neutron 1S0 superfluidity in β-stable neutron matter, i.e., it leads to a small reduction of the neutron 1S 0 paring gap. However the three-body force not only suppresses strongly the strength of the proton1S0 superfluidity in β-stable neutron star matter but also reduces largely the density domain for the proton 1S0 superfluidity phase from ρ B<0.45fm－3 to ρB<0.3fm－3. It is also shown that the three-body force enhances largely the proton fraction in β-stable neutron star matter at high densities.
The α-decay lifetimes of the newly synthesized superheavy elements are calculated using the α-cluster model and the results are in good agreement with experimental data. This indicates the reliability of the α-cluster model. The theoretical lifetimes based on the Hartree-Fock nuclear mass table are also calculated, which are useful for further theoretical and experimental researches on superheavy nuclei. We have also analyzed the α-decay energies, the separation energies of the last two neutrons and the separation energies of the last two protons of the superheavy nuclei. The shell effect at Z=114 and N=184 is discussed.
Based on Schrdinger equation, the method of analytical continuation in the coupling constant (ACCC) is employed to investigate the energy and width of single-particle resonance in spherically symmetric square well, harmonic oscillator potential and Woods-Saxon potential. The influences of the interval for the coupling constant values and the order of Pade polynomial are analyzed. It has been shown that, by properly chosen interval for the coupling constant values and the order of Pad polynomial, stable and convergent energy and width of single-particle resonance can be obtained.
The inversion of 2s1/2 and 1p1/2 levels occurred in the one-neutron halo nucleus,11Be, is studied in detail. It is pointed out that, for neutron halo nuclei, such as 11Be, the one neutron separation energy, Sn, and the depth of the last neutron in the potential well, Dg, should have quite different values. After the failure of the Woods-Saxon potential, we construct a new potential, called as Double modified-Woods-Saxon (DMWS) potential, to describe the mean field of 11Be, which has been able perfectly to reproduce this level inversion phenomenon without the help of configuration mixing. It has been shown that the level inversion in the 11Be may indicate that the halo nuclei have a quite different mean field in contrast to the stable ones.
YBJ-ARGO experiment is designed to detect small size air showers at an energy threshold of～100GeV using a full coverage RPC array. Its data acquisition system is based on a high speed event driven architecture with multi-level high speed buffers. Both Data acquisition and event building are controlled by hardware, without software penalties and CPU overheads, thus meeting the request of high event rate and data rate.
Based on GEANT4, we simulated single TOF scintillation counter and got its intrinsic time resolution. By comparing two kinds of plastic scintillator material—BC404 and BC408 and different modes of coupling between the scintillator and PMT, we got their. respective intrinsic time resolations and pulse heights Our simulation results will be an important reference for BESⅢ TOF design.
In the process of design and research of BESⅢ crystal calorimeter we study its performance by Monte Carlo simulation and then optimize the scheme. Those results show that the the following scheme is optimized. CsI crystals typically have a front face of about 5×5cm2 and a rear face of about 6.5×6.5cm2, and the length of all crystals is 28cm. The crystals are supported by four iron screws fixed at the rear end. All crystals point to the collision point with a small tilt of 1°—3° in the θand 1.5° in theφ. Then we obtain that the energy resolution is about 2.1% and the position resolution about 6mm for 1GeV photon.
Longitudinal focusing is of great importance in space-charge-dominated bunched beams such as heavy ion fusion. The bunches lengthen rapidly due to the strong space-charge forces during transportation. The electron ring at University of Maryland (UMD) is designed to operate with bunches having rectangular and parabolic profiles. Three induction cavities along the ring will be employed for longitudinal focusing. In this paper, we first briefly review the longitudinal dynamics of parabolic and rectangular bunches. The design of the induction cavities with their high repetition rate modulators is then presented. The preliminary test results of lower voltage and repetition rate version of two different modulators and the PSPICE simulation results show that modulators work well.
Complementary chaos and spin polarization stability in cyclotrons are studied from the nonautonomous SU(2) dynamical system by the algebraic dynamical method. The results are as follows:for the case of initially low polarization,the magnetically induced polarization is sensitive to the irregular perturbation,while for the case of initially high polarization,the magnetically induced polarization is stable with respect to the irregular perturbation. The fluctuations of the transverse and longitudinal components of the spin polarization are complementary to each other due to the existence of an invariant of the SU(2) dynamical system,which can be used as a feedback signal to control the spin polarization stability.
Impedance modelling in an accelerator is reviewed in this paper,cutoff effects is discussed both from electrodynamics and beam dynamics points of view. From Vlasov-Maxwell equation,the general solution is derived for stationary distribution with space charge and arbitrary external fields and arbitrary distribution models,which can be applied in stability analysis and simulation. The stationary distributions of two example models are solved under high current paramet-ers of heavy-ion ring-accelerators. Longitudinal“dispersion”functions are also calculated from the solved stationary distributions,which are very important for Landau damping and stability in bunched beam.
The upgrading project of the HLS (Hefei Light Source) klystron modulators was firstly introduced. Constant-current, switch-mode,PFN charging power supplies were adopted in the new design. Charging parameters were calculated. Simulation model of main discharging circuit was established. An emphasis of analysis was put on the reversal voltage problem. A protection circuit was designed based on the simulation results and reversal voltage study. Major waveforms measured from daily operation were presented. Finally new control system of the modulators was described.
Longitudinal beam feedback system is widely used to damp coupling bunch instability. Kicker is one of the key components of the longitudinal feedback system. A prototype cavity of longitudinal feedback kicker is developed according to the parameter of BEPCⅡ. The usage of nose cone in the kicker design increased the shunt impedance. In order to avoid the extra tapper in the storage ring, the racetrack shape beam pipe is applied in the kicker. The impedance and the bandwidth of the kicker is measured by the coaxial line impedance measurement platform and the result achieved the design goals.
Experimental results of x-rays dose enhancement effects are given for SRAM with different integration from 16k to 4M irradiated by 20—100keV X rays in Beijing Synchrotron Radiation Facility and by cobalt source γ rays. The ratio of radiation damage to the SRAMs irradiated with two sources are measured. The relationship of radiation hardness of SRAM versus different integration for γ-rays irradiation and the damage threshold values of X-rays for SRAM with different integration are presented.
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