2002 Vol. 26, No. 3
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We argue that a small or large CP-violating asymmetry AψKS in B0d vs B0d→J/ψKS decays,which seems to be favored by the recent BaBar or Belle data,might hint at the existence of new physics in B0d-B0d mixing. We present a model-independent framework to show how new physics modifies the standard-model CP-violating asymmetry A SM ψKS. We particularly emphasize that an experimental confirmation of AψKS≈A SM ψKS must not imply the absence of new physics in B0d-B0d mixing.
The structure and working principle of a six-gap resistive plate chamber is discussed. A π-beam with a momentum of 7GeV/c is used to test this detector,and a time resolution between 60 and 70ps is obtained. The detection efficiency is greater than 97%. In the test with a 3GeV/c beam of positive particles,this detector got a clear separation between p/π particles.
A method of combined D0 and D+ single and double tags to measure their branching fractions is reported. With this method, we can measure the inclusive and exclusive branching fractions of D0 and D+ based on the data taken at s=4.03GeV using BES detector at BEPC collider. As well known, it is very difficult to study D physics with the data taken at s=4.03GeV. Compared with the data taken at s=3.77GeV, where it is just at the threshold of the pure pairs of D+D－ and D0D0 productions. While at s=4.03 GeV D* and D*D* can also be produced and then the so-called contaminated final states D+D0 and D－D0 can be produced via the cascade decays of the D*+ to charged and neutral D. This makes some trouble for the study. The key to solve this problem is how to determine the ratios β, which denotes the recoil D0 production agaist the tagged D+, and η, which denotes the recoil D－ production agaist the tagged D0. We developed the double tag method and single tag method to determine these two parameters, and compared them with cross section method developed by us before. They are consistent with each other within errors, so that the validity of this method was proved. As an example of its application, we set the upper limit for D+→e+ν decay to be Br(D+→e+ν)<1.6% at 90% C. L.. This value is consistent with that BES Collaboration published.
The event-space moments Cp,q(M) have been calculated using the method of single-event factorial moments. Comparing this with the calculated results for the pure statistical fluctuations Monte-Carlo event sample, the variations of the moments Cp,q(M) with M are caused dominantly by the statistical fluctuation. The erraticity analysis of the pseudorapidity gaps is performed for the NA27 data. The entropy-like quantities Sq and Σq are calculated. It is found that Sq and Σq deviate significantly from 1. Sq and ∑q versus q have exponential behavior. FRITIOF simulation can reproduce the scaling behavior, but the deviations of the values from the experimental data are rather large.
We develop a new approach to constructing the lattice operators for the calculation of the glueball mass, which is based on the connection between the continuum limit of the chosen operator and the quantum number JPC of the state. The spin of the state is then determined uniquely and directly in numerical simulation. Furthermore, the approach can be applied to the calculation of the mass of glueball states with any spin. J. Under the quenched approximation, we present our preliminary results in SU(3) pure gauge theory for the mass of 0++ state and 2++ state, which are 1754(85)(86) MeV and 2417(56)(117) MeV, respectively.
Based on the phase-space generating functional of Green function, the canonical Noether identities under the local transformation at the quantum level have been derived. For the gauge-invariant system, the quantal Noether identities in configuration space have been also deduced. It is pointed out that in certain cases the quantal Noether identities may be converted to quantal conservation laws of the system. This method for obtaining the quantal conservation laws is significantly different from the first Noether theorem at the quantum level. The application to non-Abelian CS theories is studied, the quantal conserved BRS and PBRS charges are obtained, and these two conserved charges are totally different.
The Angular distribution and excitation function of the disspative products have been measured in the reaction 19F+93Nb. The reaction time of the dissipative products is extracted from the angular distribution and compared with that extracted from their energy auto-correlation function. A great difference exists between the reaction times extracted from these two methods. The results obtained from analyzing these two methods in different symmetrical reaction systems show that the reaction time extracted in the more symmetrical system by analyzing the slope of the angular distribution demonstrates the characteristic times of both direct and dissipative products, while the reaction times extracted in the more asymmetrical system only reflects the character of the direct products. But the method of the energy auto-correlation function can give the characteristic time for dissipative products in both symmetrical and asymmetrical system. In addition, the damping rotation feature of the dinuclear system formed in the dissipative reaction can be described by analyzing the energy auto-correlation function.
The action among nucleons is simplified as the bond of nuclear force from which the formula of volume energy and the formula of surface energy are inferred. And the two parameters are worked out by the binding energy of 21H, and then two parameters are reduced. The formula of binding energy is given by using both the experimental data and the theory value, which is obtained from the semi-rational formula and Zeng′s formula of binding energy. Then basing on this formula of binding energy, we get the D-value of odd-even mass of nuclei and β stable line. In correspondence with the empirical formula of β stable line, the value of parameter is modified, so the final formula of binding energy is obtained. The calculation values of new formula are good agreement with experimental data, especially for heavy nuclei, further supporting the utility of the formula to describe nuclear structure.
Based on the systematic investigation of the data available, a Z 1/3 law for nuclear charge radii is shown to be superior than the generally accepted A1/3 law. The Z1/3 law describes data very well for the nuclei close to the β-stability line, while an approximate linear dependence of isospin must be added when it is applied to the nuclei far from the β-stability line. A new isospin dependence Z1/3 formula thus obtained is proved to be more effective to describe the charge radii data. The collective behavior of the light and heavy nuclei has been discussed.
In this article, we have modified the r2 correlated kernel. Under this modification, the kernel remains V30 r2δ(τ) at small r and when r is large enough, it tends to be Aδ(τ), where A is a constant. Thus, the kernel no longer corresponds to a complete confinement potential. By solving the Gap equation, we found that the contribution of the modification to quark-antiquqrk condensation is obvious, though the main results of vacuum condensation remain.
The configuration-dependent cranked Nilsson-Strutinsky model is used to study the band structures in 131La. Shape coexistence and band termination are investigated for several configurations. The calculations indicate that 131La is a γ-soft nucleus. The theoretical results are compared with experimental data. The calculated π(h11/2)2⊙ν(h11/2)8 configuration with (π,α)=(+,－1/2) shows very good agreement with the experimental band observed to highest spin. The termination of this band is not favored, i.e. a relatively large energy is required to build the highest spin states in the band.
The characters of a kind of new detector, "CaF2(Eu)+liquid scintillator" mixed WIMP detector, which is proposed by Beijing Group, are introduced. The preliminary design of the structure of this detector has been made, by studying its optical collection efficiency with simulation. In addition, it shows that the mixed detector would be good at excluding the backgrounds, which are produced by the decays of the radioactive contamination inside the detector.
The positron yield is a very important parameter for positron source,and directly symbolizes the quality of an e+ accelerator. Now BEPC is planned to be upgraded into BEPCⅡ,many parameters of positron source should be greatly improved to meet the requirements of intense e+ beam injection. We will optimize each section of the positron source to get the highest yield. EGS4 and PARMELA codes are used for positron source design. We use EGS4 code to simulate the electron-gamma shower of high-energy electrons in a medium,optimize target thickness,and analyze positron distributions in phase space. We discuss the positron yield's dependence on some system parameters. Then we use PARMELA code to track and simulate particle motion in the matching,focusing and accelerating systems,discuss how to choose capture section RF phase. Finally we get a reasonable positron yield at the end of positron source.
We present a beam dynamics simulation study on 1.6 cell,high gradient W-Band photocathode RF gun which is capable of generating and accelerating 300pC electron bunch. The design system is made up of 91.392GHz photocathode RF gun and 91.392GHz travelling wave linac cells. Based on the numerical simulation using SUPERFISH and PARMELA and the conventional RF linac scaling law,the design will produce 300pC at 1.74MeV with bunch length 0.72ps and normalized tranverse emittance 0.55mm mrad. We study the beam dynamics in high frequency and high gradient;due to the high gradient,the ponderomotive effect plays an important role in beam dynamics;we found the ponderomotive effect still exist with only the fundamental space harmonics (synchrotron mode) due to the coupling of the transverse and longitudinal motion.
The target system design is one of the key problems in the ISOL facility for RIB generation. In this paper,the diffusion and adsorption processes in the target materials are simulated so as to investigate the release time of radioactive species from the uniform or Gaussian distribution,cylindrical,spherical or planar target materials operated at different temperatures based on the idea of using ion implantation at HRIBF for the selection of RIB targets. The effusion process from the surface of the target material to the ionization chamber of the online ion source is also investigated in this paper. The Monte-Carlo techniques are used for the numerical simulation based on the measurement data of surface physics from ZFK,Germany. The empirical formulas and the tables of characteristic effusive-flow times for various particles through tubes of different dimension and material are extracted from the simulation. One can design the dimension of the effusion tube and determine the material for the tube by using the formulas and the tables.
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