2004 Vol. 28, No. 05
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Light particle emission at around 107°and 128°in the reaction induced by 25MeV/u 6He from 9Be target were clearly observed. The shape of the energy spectra obtained is consistent with an equilibrium evaporation from a source with a temperature of 5.6MeV or 5.2MeV for complete fusion or for incomplete fusion, respectively. A large number of tritons were detected compared to the number of protons, which may be related to the widely studied exotic cluster structure and the isospin effect of 6He.
On the basis of the study of inclusive hadronic events, two methods are adopted to determine the number of produced ψ(2S) events collected by BES in 2001—2002 run, which is 14.0×106 with the uncertainty of 4%.
The mass splitting of K*(892)± and K*(892)0 is studied through J/ψ→K±K*(892) and J/ψ→K0*892)0 at EBPCⅡ/BESⅢ. The Geant3-based Monte-Carlo simulation shows that the K*(892) mass splitting can be precisely measured at BESⅢ. If the mass splitting is 600MeV, then BESⅢ can give ΔM=5.79±0.16±0.13MeV, where the first error is statistical error and the second is systemic error.
The 3-jet events from hadronic Z0 decay is studied using Monte-Carlo simulation. Quark and Gluon jets are identified through the b-tag method. A new physical quantity——hardness is defined, and the hardness distributions of quark and gluon jets are calculated. The dependence of the average multiplicity and average transverse momentum on hardness as well as the multiplicity and transverse momentum distributions in a certain hardness range in the quark and gluon jets are calculated respectively, and compared. It is found that the properties of quark and gluon jets are considerably different in these respects. The properties of quark jets are almost independent on hardness, while those of gluon jets have strong correlation with hardness. When Hd>10GeV the average multiplicity and average tranverse momentum of gluon jets are higher than those of quark jets; but when H-d<6GeV the results are reversed. This indicates that the conclusion on gluon jets being “fatter” than quark jets is valid only for hard gluons.
We study the lepton flavor violating (LFV) processes l-i→l-jν-l-l in the context of the topcolor-assisted technicolor (TC2) models. We find that the branching ratios Br(τ→l-jν-τ-τ) are larger than the branching ratios Br(τ→l-jν-l-l) in all of the parameter space. Over a wide range of parameter space, we have Br(τ→l-jν-τ-τ)～10-6 and Br(τ→l-jν-l-l)～10-9(l=μ or e). Taking into account the bounds given by the experimental upper limit Brexp(μ→3e)≤1×10-12 on the free parameters of TC2 models, we further give the upper limits of the LFV processes l-i→l-jν-l-l. We hope that the results may be useful to partly explain the data of the neutrino oscillations and the future neutrino experimental data might be used to test TC2 models.
With helicity partial wave analysis formalism, we discuss how one can distinguish f-0 resonance from f2 resonance in the process of J/ψ→fJ(θ1,1) with fJ→ππ(θ2, 2) and →K(θ3, 3) by various projections of angular distributions. We find that f-0 and f2 can give the same one-dimensional angular distributions for I(θ1)∪I(1)∪I(θ2)∪I( 2), but cannot give the same I(θ1)∪I(1)∪I(θ2)∪I(2)∪I( 3). So it is necessary to consider all three decay vertices in order to distinguish f0 from f2 by one-dimensional projections of angular distributions.
The coupled cluster method is improved with the random phase approximation (RPA) to calculate vacuum wave function and vacuum energy of 2+1-D SU(2) lattice gauge theory. In this calculating, the trial wave function composes of single-hollow graphs. The calculated results of vacuum wave functions show very good scaling behaviors at weak coupling region 1/g2〉1.2 from the third order to the sixth order, and the vacuum energy obtained with RPA method is lower than the vacuum energy obtained without RPA method, which means that this method is a more efficient one.
High-spin states of 126Cs have been populated via the 116Cd(14N,4n) 126Cs reaction. The experiment was performed at Niels Bohr Institute in Denmark in 1991. After careful data analysis, most of the previously-known bands have been pushed up to much higher spins and 3 new rotational sequences have been identified. Spin, parity and configuration assignments are tentatively proposed for all of the observed bands.
High spin states of 135La have been experimentally studied by using 128Te(10B, 3n) 135La reaction at 46 MeV beam energy. Based on the γ-γ coincidence relationships, relative intensities and ADO ratios, a level scheme of 135La has been established. Both signature components of the πh11/2 negative-parity band and a band crossing at ω≈0.40MeV were observed. In view of the systematics of the N=78 isotones, this backbending is proposed to be caused by the alignment of a pair of πh11/2 protons. The πh11/2 protons drive the nuclear core towards γ≈0°, the collective prolate shape. In addition, a ΔI=1 negative-parity band with strong M1 transitions and a very small signature splitting was observed. Comparing with the systematic features of ΔI=1 bands in neighboring odd-proton nuclei in this mass region, the πh11/2(νh11/2)2 configuration was assigned to the ΔI=1 bands of 135La. The alignment of the h11/2 neutron pair drives the nuclear core towards γ≈-60°, the collective oblate shape.
The α-cluster model is extended to study the unfavored α-decay lifetimes around a closed shell. The newly discovered α-decay of 209Bi [Marcillac et al., Nature (London) 422, 2003: 876] and a odd-A N=127 isotones are investigated by the α-cluster model. The experimental decay lifetimes can be reproduced satisfactorily. The application of the α-cluster model to research unfavored α-decays has been proved reliable. The theoretical calculations also reflect the measured α particle preformation factor near magic number (N=126). The α-cluster model is improved by introducing a Z-dependent preformation factor.
It is introduced briefly to calculate normalization factor for absolute intensities of gamma-rays arrising from β－ decay. The examples are given to illustrate their application. The intensity balance check and some discussion are also given in text.
Based on experimental data of total, nonelastic, elastic cross section and elastic scattering angular distribu-tions for n+Cr reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 1 to 250 MeV. The cross sections, angular distributions and double differential cross sections are calculated and analyzed by optical model, distorted wave Born approximation theory, the unified Hauser-Feshbach theory, and exciton model. The results indicate that the cross sections can be given for n+52Cr reactions which are all in good agreement with experimental data.
The variation of the quadrupole deformations β of the ground state even-even nuclei with A≥100 are investigated systematically. The studied nuclei are classified into different groups not only by their mass numbers but also by if the valence nucleons are particles or holes. Smooth behaviors of the β values against (NpNn)1/2 are found with different slopes and trends in different groups of nuclei. This is explained as that the contribution to the quadrupole deformation from valence particles and that from valence holes are different. The behavior of the β values against (NpNn)1/2 are also investigated for the nuclei near the drip lines. This seems to imply that the universal correlations under the NpNn scheme is still valid for nuclei far from stability.
It was studied to calibrate a lead scintillating fiber sandwiched electromagnetic calorimeter using proton and electron beams. The calibration constants from proton and muon were compared. After attenuation correction, the proton constants were used to reconstruct single electron events at different beam energies, excellent linearity was obtained. The results show that the non-shower proton can be used to calibrate such shower counter.
The research and development of a new type detector for solar neutrino detection is introduced. The detector uses two types of scintillators: one is the gadolinium(Gd) loaded liquid scintillator with the concentration of 5%, for which the light attenuation length is ≥150cm and the energy resolution is 21%(standard deviation) for 60keV Gamma-ray; the other is a 1cm×3cm GSO:Ce crystal, which has the light yield 20% with respect to the NaI:Tl, the light decay time 60ns and the energy resolution 9.2%(standard deviation) for 662keV Gamma-ray. The characters of the detector composed by both scintillators for solar neutrino detector and the methods to suppress the backgroud are discussed. A simulation for such detector with the size 10cm×50cm shows the light collection efficiency can reach 20%.
A simple cosmic ray stand for testing sampling scintillating fiber calorimeter module has been constructed. The measurement and analyses method is reported. A module of sampling scintillating fiber calorimeter from KLOE (INFN, Italy) is tested by using cosmic ray and the preliminary results for time resolution (252ps) and spacial resolution (4.1cm) are obtained.
In order to get a beam spot with limited dimension and symmetrical distribution on the target, the required parameters of the beam transport system are discussed. The related formulas to determine these parameters for different initial conditions are given also.
In electron storage rings, interactions by beams with residual gas produce the bremsstrahlung and it is one of the main sources of the beam loss. We analyze the bremsstrahlung and calculate the dose rate in the linear section of the storage rings. The result may help to understand it and shield it properly.
In this paper, the turn-by-turn system of Hefei Light Source (HLS), and the log-ratio electronics circuit with working frequence 408MHz (2*RF of HLS) are described. They are used to monitor the injection effectiveness, damping rate, β oscillation and v variation for research the instability of beam. The Log-ratio signal processor has low noise, high bandwidth and wide dynamic range, as well as linear response. The calibration of the system and its application in commissioning of the upgraded injection system of HLS is emphases. The practice proves the turn-by-turn BPM system is quite useful for the beam-injection adjusting and indispensable for machine research.
The BEPCⅡ future pre-injector consists of a thermionic gun followed by two subharmonic bunchers (SHB), a travelling wave prebuncher and a travelling wave buncher. All components downstream of the gun are immersed in a solenoid field for transverse focusing. Beam dynamics simulation and optimization have been carried out with programs PARMELA and EGUN. SHBs' bunching voltage and bunching drift distance, prebuncher and buncher's phase and acceleration gradient, and solenoid field profile have been studied. The bunch charge limitation for 10ps bunch length at the buncher exit is also investigated.
When the bunch goes through a chicane, the energy will be redistributed within the bunch due to CSR (coherent synchrotron radiation), which would cause nonlinearity. Present theory states that this nonlinearity would add a huge amount to emittance growth. Based on simulation results, this paper would point out that the theory is only valid under an ideal condition that the bunch initially has no nonlinerity and under some given parameters there could be a cancellation between the nonlinearity caused by CSR and the initial nonlinearity. So under these circumstances we can expect CSR to improve the beam quality. This paper provides a brief information about CSR and a full estimation of effects of CSR on beam qualities.
A slow positron beam with intensity of 106e+/s produced by the Beijing Electron-Positron Collider (BEPC) is transported by the 100 Gauss magnetic field system with the oscillation less than 10. In this paper, the distributions of magnetic field at target chamber, sample chamber and Penning-Trap storage are calculated systematically, and the parameters of solenoidal coils and steering coils are calculated respectively. The correction coils are designed to compensate the affect induced by the geomagnetic field and the bent tube. Results of electron beam experiment show that the positron beams are transported to sample chamber with the beam spot size basically unchanged, and the magnetic field distributions satisfy to the requirement of the slow positron beam system.
The radiation destructive appeatance caused by intensive electron beam current with 12MeV energy reveals different mechanism of fracture from those caused by lower energy electron or X-ray due to the strong penetrating ability of the electron. In the paper, the fracture profiles of the 1.2mm Ta target, which is destructed by 12MeV electron beam, are studied using microscope and scanning electron microscope. The result indicates mechanical tear is the major reason, and moreover, the tear fracture is almost symmetrical. In order to understand this, the energy deposit of electron beam along the depth of the target is given out by Monte-Carlo simulation, which is also symmetrical and higher in center, lower in sides. A preliminary conclusion on the major destructing mechanism of the target is drawn out: 12MeV electron beam, which has strong penetration ability, can heat the whole target almost at the same time. The expansion of the center part of the target is constrained by the boundary which results in two shock waves with most destructive power produced in the two sides of center. After the shock waves reach the free surfaces of the target, by wave reflection, two rarefaction waves will propagate inward, then symmetric tearing happens when the two waves meet at the center region of the target.
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