2001 Vol. 25, No. 06
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Measurement of the production cross section of the D+s D- s in e+e- annihilation at the Center-of-Mass Energy of s=4.03 GeV is reported in the paper. The cross section for the D+s D- s production has been measured using a data sample of 22.3 pb－1 collected with BES detector at BEPC e+e- collider. The D+ s measons are reconstructed in the π+,K*0 K+ and K0K+ decay modes. A total number of 94±13 singly tagged D+ s events is obtained from the three modes. This yelds the cross section value σ prod D+s D－ s=(451±63±118)pb for D+ s D－ s production. Based on the numbers of singly tagged D+ s events for each of the three decay modes,the decay branching fractions for D+ s→K *0 K+ and K0K+ have been determined to be (3.02±0.94±0.91)% and (3.28±1.22±0.94)%,respectively.
We show that measuring the polarization of hyperon in the lepton induced reactions is an ideal way to study the spin transfer in high energy hadronization processes. After a brief summary of the polarization of the initial quark or antiquark in these reactions,we give the calculation method of the polarization of hyperon. As an example,we calculate polarizations of different hyperons in e+e－ annihilation at LEP energys and compare these results with the available data. The results show that measurements of such polarizations should provide important information about the question of which picture of spin structure of baryon is more suitable in describing the spin effects in the high energy fragmentation processes.
Using the Hamiltonian of symmetrical one dimersional infinitely deep square well potential and natural operators,we obtain its nonlinear spectrum and generating algebra,and get a class of new nonlinear coherent states on the basis of the nonlinear algebra obfained. These coherent states are of temporal stability,and can be regarded as the eigenstates of the lower operator with the eigenvalues in an operator field and as the rotational states of the generalized minimal uncertainly states as well.
Isotope ratios,defined as the yield ratio of two isotopes with the same charge,were analyzed as a function of kinetic energy of outgoing particles at 20° in the reactions of 40Ar+112,124Sn and 5°in36Ar+112,124Sn at incident energy of 35MeV/u. Isotope ratios between the neutron-deficient isotopes and stable isotope increase with kinetic energy,while those between the neutron rich isotopes and stable isotope decrease. This different behavior was observed similar for both 112Sn and 124Sn targets. The isotope ratios show rather obvious target dependence at 20° and little target dependence at 5°. As the outgoing energy getting down,the N/Z ratio of the fragmentation products at 5° diverts gradually from the N/Z ratio of the projectile to that of the system. These observations indicate that the isospin degree of freedom does not reach complete equilibrium in the peripheral or semi-peripheral collision at this bombarding energy.
The excitation functions of the dissipative fragments emitted from the reaction of 27Al+27Al have been measured in the energy region from 114MeV to 127MeV in steps of 200keV. The detection system covered continuous angles from 10° to 57° in laboratory system. The energy autocorrelation functions of the dissipative fragments have been analyzed by using different approaches,especially using the statistical nuclear reaction model with memory. The results indicate that the intermediate dinuclear system formed in the dissipative process is set in a damped coherent nuclear rotation which causes the nonself averaging oscillation structure in the excitation functions and originates from a typical quantum chaotic motion.
We introduced an extended Glauber theory for a halo nucleus scattering, where the halo nucleons and the nuclear core were treated separately. Expressions of reaction and interaction cross sections of the halo nucleus scattering were derived. We took the halo structure of the projectile nucleus into account and adopted an improved optical limit approximation. In the framework of the extended Glauber theory, we studied the reaction cross section for the halo nucleus 14Be scattering on a target 12C. For comparison, the reaction cross sections of 12Be+12C were calculated as well. The density distribution of target 12C is taken from experiments, and those of the projectiles 12Be and 14Be were obtained by two methods. One is that the harmonic oscillator wave functions for 12Be and 14Be are used. The length of harmonic oscillator is adjusted to reproduce the reaction cross section of 12Be+12C at the high energy E=790MeV/u . The density distribution of 14Be was also calculated self-consistently in the relativistic mean field (RMF) theory, with a long tail wave functions for the two neutrons in 14Be. It was found that the calculated reaction cross sections for 12Be+12C at E=790MeV/u and E=56.5MeV/u were in good agreement with the experimental data no matter harmonic oscillator or RMF wave functions were used. In contrast, the experiments of the reaction cross sections for 14Be+ 12C could only be reproduced when the wave functions of two 2s1/2 neutrons spreaded over with a long tail. It comes to a conclusion that two outside neutrons in 14Be form a halo structure.
The 27 superdeformed bands, whose spin determinations aren't in agreement with two-parameter, three-parameter and four-parameter I(I+1) expansions, are analyzed. The results show that the angular momenta of 18 superdeformed bands can be determined by comparison with the variation of the kinematic and dynamic moments of inertia with rotational frequency and their mutual relation. The angular momenta of superdeformed bands like 192Hg(2), which have bands cross, can also determined by analyzing the spectra before bands cross and by comparison with the variation of the kinematic and dynamic moments of inertia with rotational frequency and their mutual relation.
The η photon production reaction on nuclei is studied by employing N*(1535) resonance model. The parameters of the model are extracted by using experimental data of N* decay channels and fitting γp→ηp reaction cross section. The result shows that the theoretical values are in good agreement with experimental data if MN*=1550MeV. The total cross section of the η photoproduction on 12C is calculated. We find that the width of N*(1535) in nuclei increases because of corrections of many-body effects, and the interaction between N* and nuclei has the feature of repulsion.
The microscopic mechanism of the identical odd-and even-mass number nuclear bands in normally deformed rare-earth nuclei was investigated using the particle-number conserving (PNC) method for treating nuclear pairing correlation. It was found that the odd particle of an odd-A identical band always occupied a cranked low j and high Ω Nilsson orbital (e.g. proton 7/2, 5/2). On the contrary, if the odd particle occupies an intruder high j orbital (e.g. neutron 7/2, proton 9/2), the moment of inertia of the odd-A band was much larger than that of neighboring even-even ground state band. The observed variation of moment of inertia (below bandcrossing) was reproduced quite well by the PNC calculation, in which no free parameter was involved. The strengths of monopole and Y20 quadrupole interactions were determined by the experimental odd even differences in binding energy and bandhead moment of inertia.
We presented a Q2-rescaling parameters′empiric formula of the Q2-rescaling model, in which we established the connection between the Q2-rescaling parameters ξi(i=V,S,G) and the mean binding energy in nucleus. By using the formula, we can get the Q2-rescaling parameters for various nuclei with A>12, and thus further calculate the relevant nuclear process and make out prediction.
Within the framework of Hartree-Fock theory with extended Skyrme effective interaction, the excitation energy as a function of temperature and density was investigated and used to analyse the ALADIN calaric curve. Our work began on the assumption that the temperature plateau of ALADIN calaric curve was resulted from the compression excitation energy. The theoretical calculations with this assumption were in good agreement with the ALADIN caloric curve, which indicates that our assumption is reasonable, i.e., the temperature plateau of ALADIN calaric curve is resulted from the compression excitation energy, and liquid-gas phase transition isn’t the only interpretation for the ALADIN caloric curve. Therefore, we provided a new interpretation for the ALADIN caloric curve.
The enlarged new absorption cross sections of J/ψ by π and ρ were put into the hadron and string cascade model, JPCIAE, and the J/ψ suppression factors in P-A, O-U, S-U and Pb-Pb minimum bias collisions at 200A GeV/c were calculated with nuclear absorption mechanism only. The results seem to indicate that, with new enlarged cross section it is still hard to change the aspect that nuclear absorption mechanism itself could not easily account for the J/ψ anomalous suppression in Pb-Pb collisions.
By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems 40Ca+58Ni and 40Ca+58Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.
This paper presents the measurement on the light output non uniformity of full size PbWO4 crystal, which will be used in the electromagnetic calorimeter (ECAL) of CMS detector. It makes use of the 22Na radiactive source and the coincident method. With the help of convolution fitting method, it is possible to make fine measurement on the light output non uniformity of the crystal. The effect of depolishing one of the lateral faces of the crystal on the non-uniformity has been studied. The slope of the non uniformity curve decreases with the increasing of the roughness. When the roughness reaches Rz=(1.49±0.27)μm the non uniformity curve meets the requirement of CMS ECAL.
The equations of motion of particles in an AVF cyclotron in a curvilinear coordinate system are derived for the cases with and without space charge forces. Assuming a set of the parameter values in the equations, numerical calculations are carried out by using Lunge-Kutta methods in the case with space charge forces. The results show that the formation of the beam halo is also a main reason of the beam losses, but the mechanism here is different from that in a linear accelerator. It is not given rise by resonance and chaos but the outward repellent motion and the vortex motion of the particles in the bunch.
The experiment study on self-amplified high-power klystron is carried out in the microwave system of BFEL. The performance of the self amplified klystron including output power, frequency, frequency stability, buildup time etc. is measured by modalating its feedback parameters. The experiment results show that the self amplified klystron can be used as one of the microwave sources in electron LINAC for the industrial application.
FEM amplifier with a novel groove waveguide and helical wiggler is proposed and researched both in three-dimensional nonlinear theory and numerical computation in this paper. A set of equations about this model is derived. Efficiency and bandwidth of the FEM are studied including the electron beam emittance effect on it.
Superconducting resonator is the important component of a superconducting accelerator. The best choice of the acceleration cavity for heavy ion superconducting accelerator is quarter wave resonator (QWR). By sputtering a layer of niobium films of several microns on the OFHC copper substrate, good superconducting properties and acceleration properties of the cavity can be obtained. However, it is very difficult to get uniform niobium films by sputtering because the inner surface of the QWR is complicated. To deal with this problem, we developed a multiparameter adjusting method to control the sputtering process of different parts of the QWR. A layer of uniform niobium film with nice superconducting performance is obtained. The low temperature experiments with liquid helium show that the Cu Nb QWR has good superconducting characters. The Q value of the cavity is about 5×108.
The X ray standing wave experiment method is established with the double-crystal monochromator and precision 2-circle goniometer at Beijing Synchrotron Radiation Facility. It is used combined with the X-ray diffraction, to investigate the heterostructure of super thin Ge atomic layer within Si crystals. The results show that the Ge x Si1－x alloy layer with average x=0.13 was formed in the Si crystal sample due to the segregation of Ge atoms during the preparation. Due to the diffusion of Ge atoms to the crystal surface, the Gex Si1－x alloy layer was disappeared and nearly pure Ge layer was formed on the Si crystal surface after annealing at 650℃.
The HF microwave leak in the gallery of klystron of NSRL affects microwave communication greatly. In order to reduce electromagnetic radiation field and to restrain electromagnetic noise, it is necessary to locate the noise source. But for the complicated leaked field, it is difficult to locate the noise source. We can measure the leaked field and calculate it, so as to locate the radiant noise source and study the method of reduction the electromagnetic noise. This article gives the method and formulas of calculating of electromagnetic field, and also On-the-spot contrast test.
An Isotope of element 105 with mass number 259 has been produced via the reaction 241Am(22Ne,4n)259Db at Elab=120MeV. The reaction products were transported and collected using the helium-jet technique and rotating wheel apparatus. The α decays of the products and their daughter nuclides were detected by a series of Si(Au) detectors. The Z and A of the nuclide have been unambiguously identified by the genetic relationship between the new activity and the known nuclide 255Lr. The new nuclide 259Db has a half life of (0.51±0.16)s and decay by alpha particle emission with energy of 9.47MeV. The Qα value for new isotope 259Db is in good coincidence with the predicted result.
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