2007 Vol. 31, No. 3
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In measuring the ψ(2S) radiative decays at BESⅡ, contribution of the background is serious in most of the final states. To extract the number of signal events, a fit to the χ2 distribution of kinematic fit using signal and background components is proposed. Extensive Monte-Carlo simulations (MCS) are performed, and the results show that the shape of χ2 distribution of the signal channel looks different from those of the background channels, thus it provides us by fitting the χ2 distribution of the data to extract the number of signal events. An input-output test is performed using MCS, and the uncertainty of the fit method is found to be less than 2%.
In the framework of the topcolor-assisted Technicolor(TC2) model, the neutral top-pion (Π0t) production processes at hadron colliders(Tevatron and LHC), pp(pp)→Π0tΠ0t and pp(pp)→bΠ0t, are studied. The results show that the cross sections of these two processes at Tevatron are too small to observe Π0t. The cross sections can be significantly enhanced at LHC, but Π0t is also not observable via Π0tΠ0t production at LHC. The cross section of bΠ0t production reaches the level of a few hundred fb even a few pb at LHC and 104—105 events can be produced each year. Furthermore, Due to the existence of the flavor-changing coupling Π0t tc, Π0t can be experimentally detected via the decay mode Π0t tc with the clean background. Therefore, the enough distinguished Π0t events would be obtained via the bΠ0t production at LHC future experiments. Our study can provide the valuable theoretical information for probing neutral top-pion and testing TC2 model at LHC.
Due to the presence of extra top quark T in the little Higgs model, the CKM matrix is not unitary and the flavor changing neutral currents may exist at the tree level. We discuss the possibility of detecting the flavor changing signals of the Littlest Higgs(LH) model at the high-energy linear e+e－ collider (ILC) via the processes e+e－→tc+tc and e+e－→WWνeνe→(tc+tc) νeνe. We find that the resonance production cross section for the process e+e－→tc+tc is significantly large, which can be detected in the future ILC experiment.
The dispersion relation is included into the optical potential. Compared with the common coupled-channel optical model, the number of potential parameters is greatly reduced. The coupled-channel method based on the soft rotator model is used to analyze the nucleon scattering by a deformed 28Si nucleus. A set of the optical potential parameters is obtained, and the numerical results show a good agreement with the available experimental data of neutron total cross sections, neutron/proton elastic and inelastic angular distributions.
The high-spin states in 187Pt have been studied experimentally by means of in-beam γ-ray spectroscopy techniques via the 173Yb(18O, 4n) fusion-evaporation reaction. The high-spin level scheme of 187Pt has been established, including three rotational bands. Based on the systematics of level structure in neighboring nuclei and by comparing the experimental and theoretical B(M1)/B(E2) ratios, configurations of 11/2+, 7/2－ and 1/2－ have been proposed for the three rotational bands, respectively. Band properties of band crossing frequency, alignment gain and signature splitting have been discussed.
Pseudospin symmetry and spin symmetry in the relativistic harmonic oscillator are investigated systematically by solving the Dirac equation with scalar and vector potentials and are found to be a good approximation in realistic nuclei such as 208Pb. The pseudospin breaking and spin breaking are shown in correlation with nuclear mean field. The harmonic oscillator frequency and the distance of well-bottom deviation from the center of the potential play an important role in the splittings of energy and wavefunction. The energy-level crossing are found for all the pseudospin partners. The dependence of splittings with quantum numbers is also analyzed.
The aim of this paper is to study the influence of the curvature and the compressibility energies on prescission neutron emission of four neutron-deficient systems: 188Pt,200Pb, 213Fr and 224Th within a modified version of the combined dynamical statistical model. The calculated results show that prescission neutron multiplicities from the modified model are closer to the data compared with the underestimate of the original one. The physics that the compressibility energy needs to be considered in this work is discussed.
We systematically analyze the formula of the mass difference between the odd and even nuclei and its connection to the energy gap parameter. By calculating the mass difference of ten isotope chains near Sn and Pb, we find that all the shell structure, the pairing interaction and the nuclear deformation affect the value of Δ(3)n considerably. A modified formula of mass difference is proposed.
Properties of color-flavor locked (CFL) strange quark matter have been studied in a mass-density-dependent model, and compared with the results in the conventional bag model. In both models, the CFL phase is more stable than the normal nuclear matter for reasonable parameters. However, the lower density behavior of the sound velocity in this model is completely opposite to that in the bag model, which makes the maximum mass of CFL quark stars in the mass-density-dependent model larger than that in the bag model.
We examine the two-pion and three-pion correlation functions for a granular source model of coherent droplets under the assumption that the pions emitted from the same droplet are coherent. The chaoticity of the source increases with the number of droplets in the granular source. By comparing the normalized pure three-pion correlations of the granular source and a partially coherent Gaussian source, we find that the difference of the nomalized pure three-pion correlations between the two sources is distinct in small Q3 regine, when the chaoticity parameter of two-pion correlation is smaller than 0.8.
Multi-hit 3-layer delay-line anode (Hexanode) has an increased ability to detect multi-hit events in a collision experiment. Coupled with a pair of micro-channel plates, it can provide position information of the particles even if the particles arrive at the same time or within small time dwell. But it suffers from some ambiguous outputs and signal losses due to timing order and triggering thresholds etc. We have developed a signal reconstruction program to correct those events. After the program correction, the dead time only exists when 2 particles arrive at the same time and the same position within a much smaller range. With the combination of Hexanode and the program, the experimental efficiencies will be greatly improved in near threshold double ionization on He collisions.
RADFET multi-channel detector will be used to measure the integrated dose near the BESⅢ crystal calorimeter. In the design of this detector, it is significant to know the detailed features of 400nm IMPL RADFET dosimeter. By using 60Co source, we made experiments and studied the features of this kind of RADFET dosimeter, including the consistency between different channels, the radiation intensity dependence to the integrated dose measurement and the annealing phenomena of RADFET dosimeter. The study results are very useful for the design of RADFET multi-channel detector and the application of RADFET dosimeter in other fields.
The operation of a repetitively pulsed relativistic klystron amplifier at 100Hz has been reported. The electron beam was reproducibly modulated to >74%. Using a 700kV, 6.5kA, 25ns electron beam and a 500kW Magnetron as inputs, we extracted 1.2GW radiation power in 20ns FWHM pulses at 2.95GHz. The average power is 2.4kW. The efficiency is 24%, and the gain is about 34dB. Limitations attributing directly to the repetitive pulsing at these levels have not been observed.
The beam extracted from cyclotron is of Gaussian distribution, but in many applications the uniformly distributed beam is needed. There are some methods to achieve uniform beam, but the uniformity is less than expected. This paper introduces the process of the wobbling magnet design which can get the high uniform beam. On the base of the design theory and the measurement to the wobbling magnet, we can confirm that there has high uniform beam on the target under the wobbling magnet effect. It is the first time to design and manufacture the wobbling magnet by ourselves in our country, and the measurement results show that the magnetic field in the wobbling magnet are satisfied the requirement of the storage wobbling magnet.
The paper reports the preliminary study of an electron gun based on the field emission of carbon nanotubes. The result of the field emission experiment shows that the carbon nanotubes are excellent field emitters, yielding current densities higher than 0.5mA/cm2 with operating field about 2.7MV/m.
The improved design of the higher order modes(HOMs) couplers with TESLA style has been discussed, and the experiment study on the improved coupler has been done. Comparison of the experimental result with the simulation result shows that the improvement of the HOMs Coupler is successful in HOMs damping.
The beam phase measurement system in the HIRFL is introduced. Based on the double-balanced mixer principle using rf-signal mixing and filtering techniques, a stable and sensitive phase measurement system has been developed. The phase history of the ion beam is detected by using a set of capacitive pick-up probes installed in the cyclotron. The phase information of the measurement is necessary for tuning to obtain a optimized isochronous magnetic field which induces to maximize the beam intensity and to optimize the beam quality. The result of the phase measurement is reliable and the accurancy reaches ±0.5°.
In this paper, we introduce the phase space reconstruction method based on Hilbert transform to comprehensively analyse the Bunch-by-bunch measurement record. The analyzing results include one beam position monitor (BPM) phase space reconstruction, bunch oscillation's phase information, mode diagnosing, tune evolvement regressed from phase space and the damping rate of the mode and bunch oscillation. The new method to calculate the tune evolvement exhibits a very high resolution both in time domain and frequency domain without any time domain average. The exponential fit to the mode and bunch oscillation damping curve are also exhibited in this paper.
Following the widespread application of ion beam biological technology, more experimental researches on low energy ion impletation into plant seeds has been conducted. In the studies of the physical mechanism, the emphasis are put on the depth and concentration distribution of the ions implanted into the seeds at low energy. The calculations directly using the LSS theory and the TRIM program for the distribution of ions implanted into seeds at low energy are not in agreement with the experimental results. With considering targets and correctting LSS theory according to the distinguishing texture of plant seeds, we calculated the penetration range distribution for vanadium ions implanted into peanut seed at 200keV and for titanium ions energy implanted into the cotton seed at 20keV in two dimension approximation by using the Monte-Carlo method. The calculation results are in agreemante with experiments. After implated into the peanut seed or the cotton seed, the nitrogen ion range distribution, whith coold not be measured so far, was also calculated with the same initial condition and theory model. This could be a preliminary method for calculation of the range distribution of nitrogen implated into seeds at low energy.
A novel X-ray source based on tiny target Bremsstrahlung and tabletop synchrotron was introduced in this paper. It is advantageous in the simple size and low price, perfect in high brilliance and flat spectrum, and it can be used as quasi-point X-ray source. With the help of Poisson Superfish and electron trace program, this paper describes the design method and presents the essential design work for its storage ring and perturbator. The designed magnet satisfies the performance specification, and realizes an effective injection by use of the perturbator.
The interaction of non-channeling particles with superlattice and the problem of transitional radiation are discussed. By comparing the transitional radiation with the channeling radiation, one finds that the background of the channeling radiation is enhanced in the long wave region by the transitional radiation, and the transitional radiation of the superlattice is strong, because the superlattice is constituted with multi-layer films which are alternately grown up with two materials with different dielectric properties. Thus, particles with ultra-high energy might be identified by using the property of the transitional radiation of superlattice.
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