2005 Vol. 29, No. 09
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Q value, the ratio of charmless hadronic decays between ψ'and J/ψ, is evaluated to be (26.0±3.5).In the evaluation of Q value, the correlations due to measured variable transformation and experimental common error have been taken into account carefully, and several approaches are adopted to find out the correlation coefficient or covariance between different measurements.
In the context of the littlest Higgs(LH) model, we study the contributions of the new particles to the branching ratio Rb of the Z→bb process. We find that the contributions mainly come from the vector-like quark Tand the gauge boson ZH,BH and depend on the free parameters f, c'and xL. The precisely measured value of Rb can give severe constraints on these free parameters.
The problem about cosmological constant is a difficult and important problem,people even don't know what it is really originated from. In this letter, we show up a kind of origin of the cosmological constant from the viewpoint of some extra dimensional spaces, obtain different values of the cosmological constant under different circumstances, acquire the evolution function with time t. And we achieve a cosmological constant that may be fitted with modern astronomic observation.
Four different reconstruction methods are used to prove that the existence of a narrow baryon state in the quasi-real photo-production on a deuterium target through the decay channel pK0s→pπ+π－ is independent of the reconstruction method, in which a peak is found around 1530MeV.
The ψ'→J/ψ π+π- decay process provides a new way to extract the ππ S wave phase shifts up to 0.59GeV. In this paper we derive the formulae for extracting the ππS wave phase shifts from the invariant mass spectrum of ππ in the ψ'→J/ψ π+π- decay.
The Pomeron-nucleon coupling vertex is theoretically derived from the fundamental theory of strong interaction, QCD. The empirical vertex βγμF1(t) used commonly in diffractive processes with a coupling strength β=6.0GeV—1 is initially obtained. Our study not only reproduces the Pomeron-nucleon coupling from QCD but also clearly shows the gluonic origin and glueball nature of Pomeron. From this investigation together with the results of our previous study, we may claim that the Pomeron could be regarded as a Reggeized tensor glueball ξ(2230) with quantum numbers of IGJPC=0+2++which lies on the Pomeron rajectory αP(t=Mξ2)=2. Consequently, longstanding puzzle that no physical particle lies on the Pomeron trajectory seems to be solved.
The off-diagonal components of Hamiltonian was considered in the Feshbach-Kerman-Koonin multi-step compound theory (FKK-MSC) of the pre-equilibrium reaction to induce the coupling between P and Q spaces in addition to the direct and the multi-step direct reactions. The transition from P to Q chain was introduced in an improved FKK-MSC formula, which can give a unified expression for FKK-MSC theory of pre-equilibrium reaction and Hauser-Feshbach model of the compound nucleus reaction (CN). The FKK-MSC theory was further refined. The calculated results shows that after considered the transition from P to Q chain, the FKK-MSC cross sections become smaller and the CN cross sections become greater than former analyses and they give a good agreement with the experimental results.
By fitting the experimental data of total, innelastic and elastic scattering angular distributions for n+Cu reactions, a set of neutron optical model potential parameters is obtained. The inelastic scattering angular distributions of discrete levels and double differential cross sections are calculated and analyzed by using the distorted wave Born approximation theory, the unified Hauser-Feshbach model and the exciton model. By fitting data the neutron level deduced deformation parameters are obtained. The results indicate that the calculated results of the inelastic scattering angular distributions and the total outing neutron double-differential cross sections for n+63,65Cu can be obtained, which are all in good agreement with the experimental data.
Using the particle-number conservation method for treating the cranked shell model with pairing interaction, we systematically investigate the variations of the moments of inertia, the angular moment alignment and the signature splitting with rotational frequencies for superdeformed bands in the A～190 mass region. According to our calculated results, we provide a global description of the configuration structure of superdeformed bands in the A～190 mass region. Most superdeformed bands are located at the strong-coupling orbits, such as neutron 5/2, 9/2. A few superdeformed bands lie on high j orbits, i.e., neutron 3/2, 5/2. Our calculated configuration assignments give a satisfactorily explanation to the general behavior, the anomalous change and the band crossing of superdeformed bands in the A～190 mass region.
The three dimensional Total Routhian Surface (TRS) calculations are carried out for 64 nuclei in the 70≤A≤90 region to find triaxial superdeformed nuclei. A total of 12 nuclei are predicted to have triaxial superdeformation in which the neutron rotational energy plays a key role and the neutron shell energy plays additional role in the formation of triaxial superdeformed nuclei.
Within the isospin dependent Brueckner-Hartree-Fock framework, the proton and neutron single particle potentials in isospin asymmetric nuclear matter as well as their isospin denpendence have been investigated. The symmetry potential is extracted from the proton and neutron single nucleon potentials. The symmetry potential turns out to depend strongly on both momentum and density, while it is almost independent of the isospin asymmetry. The density and momentum dependence of the predicted symmetry potential has been compared with the phenomenological parameterizations adopted in the BUU simulations of the heavy ion collisions induced by neutron-rich nuclei. It is found that the microscopic symmetry potential shows a completely different momentum and density dependence from the phenomenological ones and thus the present results are useful for putting a strict constraint on the phenomenological models for the symmetry potential.
The properties of the nuclei belonging to the newly discovered alpha-decay chain starting from Bh have been studied. The axially deformed relativistic mean field (RMF) calculation with the force TMA and NL-Z2 has been performed in the blocked BCS approximation. Some ground state properties such as the binding energies, deformations, spins and parities, as well as Q-values of the alpha decay for this decay chain have been calculated and compared with known experimental data. Good agreement is observed. The single-particle spectrum of the nucleus Bh has been studied.
The experimental observation on the multiplicity dependence of event-by-event transverse momentum fluctuation in relativistic heavy ion collisions is studied using Monte Carlo simulation. It is found that the Monte Carlo generator HIJING is unable to describe the experimental phenomenon well. A simple Monte Carlo model is proposed, which can recover the data and thus shed some light on the dynamical origin of the multiplicity dependence of event-by-event transverse momentum fluctuation.
Using coincidence method, transit time spread (TTS) is measured with Cherenkov light produced by cascade γ radioactive source, 60Co on photocathode window of photomultiplier tube (PMT). Transit time distributions with single and multi-photon electrons are fitted to Poisson convoluted with Gaussian, and TTS are obtained. The study to XP2020 and XP2020Q PMTs shows that TTS is consistent with data supplied by Philips. TTS is inversely proportional to the square root of number of photoelectrons. The method is feasible when single and multi-photon electrons can be distinguished.
In the design of the linear accelerating structure, the coupling factor between cavities is a crucial parameter. The error of coupling factor accounts for the electric or magnetic field error mainly. To accurately design the coupling iris, the accurate calculation of coupling factor is essential. The numerical simulation is widely used to calculate the coupling factor now. By using MAFIA code, two methods have been applied to calculate the dispersion characteristics of the single-period structure, one method is to simulate the traveling wave mode by the period boundary condition; another method is to simulate the standing wave mode by the electrical boundary condition. In this work, we develop the two methods to calculate the coupling factor of double-period accelerating structure. Compared to experiment, the results for both methods are very similar, and in agreement with measurement within 15% deviation.
Generally, the design of the target used in the medical electron accelerator follows the thick-target rule, that is, using a target thicker than the electron range to make almost no electrons penetrating out of the target. In this article, a new rule of target design is proposed. The target and the relevant components (primary collimator and flattening filter) are considered as a whole system when designing the target, that is, using a thinner target to increase the dose rate and using the primary collimator and the flattening filter to reduce the contaminated electrons. To improve the dose rate in the treatment, an optimization is given to the target design of BJ-6, a 6MV medical linear electron accelerator, by using Monte Carlo method. By using MC codes of MCNP and BEAMnrc, simulations are given to calculate the percent depth dose profiles in the 10cm×10cm field and the 30cm×30cm field respectively. The surface dose satisfies the national standards and the dose rate in treatment increases 10 percent of that of the present thick-target. The feasibility of this method has been tested by experiment.
High charge state metal ion beam is quite effective and essential for new investigations on atomic physics and surface physics. Recently, The high intensity high charge state lead ion beams have been produced with IMP 14.5GHz LECR3, we investigated experimentally influences of some key parameters, such as magnetic field, electrical power on oven, gas mixing etc.,on lead ion beam production. Through optimization of the ion source conditions, stable 207Pb30+ beam of 18eμa and 207Pb37+ beam of 6.7eμa have been obtained with oven method at 20kV extraction voltage.
Usually, the RF electro-magnetic field can affect the resonant cavity in two ways. One is the heat loading to the cavity due to the RF power dissipation, and another is the Lorenz force due to the high RF surface field. In this paper, the RF electro-magnetic field effects on the Sub-harmonic Buncher 2 (SHB2) are described and some results presented and discussed. The analyses of the RF electro-magnetic field effects were performed by coupled simulations with finite difference method software-Superfish and finite element method software--ANSYS. In addition, the RF electro-magnetic field effects on the Sub-harmonic Buncher 1 (SHB1) are also described.
The Q-slope at high gradient affects the performance of superconducting cavity greatly. Recent researches show that low temperature (100—150)°C heat treatment (bake) has positive effects on the performance of superconducting cavities. A lot of cavity tests are analyzed based on bake treatment. The average gradient Eacc, max and Eacc at Q=1×1010 are increased by more than 3.5MV/m. Q at Eacc, max is increased and the Q-slope is improved. Analysis on bake temperature shows that higher bake temperature leads to higher Q value. Comparison of BCP and EP cavities shows that at least 60—80μm EP is needed for BCP surface. More than 10—15μm removal of the surface by BCP will degrade the performance of an EP cavity. Oxygen diffusion model is used to illustrate bake effect.
A new method is proposed for measurement of the length of pico-second electron bunch. For an electron bunch from MPG(Micro Pulse Gun), a numerical model using computing codes such as MAFIA has been constructed. And according to our own experimental condition, the model is discussed and its resolution is about 2ps. It is proved that the method is feasible for the measurement of the length of pico-second electron bunch.
Monte Carlo Hamiltonian method is a new algorithm for numerical simulation of quantum theories.The advantage is its ability to study spectrum and wave functions beyond the ground state.The previous approach needs information on free particles and is difficult to be used for lattice gauge theory. In this paper, we propose a new approach to MCH, which may overcome the difficulty. We describe the basic ideas, and use a 1-dimensional quantum mechanical model V(x)=μ2x2+λx4(其中μ2< 0,λ>0) as an example.
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