2003 Vol. 27, No. 11
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This paper develops a method of Vector Projection (VP) , which is based on investigations and a mathematical abstraction of many methods of Pulse Shape Discrimination (PSD) used in particle identification. VP is a universal method and its optimum parameter selection is discussed in detail. Optimized PSD effect by using VP with appropriate parameters is verified utilizing the data obtained from the FADC measurement system.
The Structure of BES Ⅱ μ Detector and its original offline calibration method is introduced, The calibration method is improved after careful study of the basic principle of various offline calibration method and the main reasons which caused the z position resolution of the μ Detector worsened. Using the improved offline calibration method, the z position resolution of the μ Detector is improved about 20 % compared with the previous method.
The pion fragmentation functions are studied in the Field-Feynman recursive model with distinction of Duπ+,Ddπ+ and Dsπ+ , by taking into account the flavor structure in the excitation of the sea quark-antiquark pairs by the initial quarks. The analytical results obtained are compatible with the available empirical results with only three parameters. The framework is also extended to predict the kaon fragmentation functions with distinction of DsK+(z) , DuK+ (z) ,DsK+(z)and DdK+ (z) . This work gives a significant modification to the original model, and the predictions can be tested by further experimental results on kaon fragmentation functions.
Photon radiation and dilepton production induced by mutiple parton rescattering are investigated when a hard parton jet produced in relativistic high energy heavy ion collision pass through strong interaction medium. We derive the transverse momentum spectrum and parton energy loss for the radiated photon, the invariant mass spectrum of dilepton. The numerical results turn out: the photon yield decreases as increasing transverse momentum, the dilepton yield decreases as increasing invariant mass. Parton energy loss due to photon radiation depends linearly on thickness of medium targets.
Generalized q-deformation coherent states of a non-harmonic oscillator in a finite-dimensional Hilbert Space are constructed. Their amplitude-squared squeezing are discussed. The result shows that there are squeezing effects in these quantum states. The relationship between condition of squeezing and parameters S, r, q is found.
The time-space structure of particles for individual air showers induced by primary γ-rays and protons at the observation level is analysed by Monte Carlo simulation. It is shown that air showers induced by the primary γ-rays can be effectively separated from the air showers induced by protons (background) using the combination cuts on the arrival time fluctuation and the lateral distribution width of secondary particles in air showers. This method can be used for reducing the background of hadrons in searching for γ-ray point sources for ARGO experiment coorperated by China and Italy at Yangbajing. The effect of this method on the significance of γ-ray signals is also estimated.
Very high energy gamma rays from gamma ray bursts are explained by the expanding fireball model. The high energy gamma ray generation efficiency, the relativistic effect, and the absorption in cosmic background radiation are taken into account. It is shown that the ejection of gamma rays with the energies higher than 10GeV may happen at the very beginning of the fireball expansion～10－5s with a fluence up to 10－4—10－6cm－2 arriving at the earth.
By re-analyzing the results of the theoretical abundance of AGB stellar models and the observed abundances of 51 AGB samples, we find that the abundance distribution of heavy elements belonging to the main-component of slow neutron capture process (SMH elements) of any AGB star is similar to that of the scaled s-process main component of the solar system. It means that superposition of the SMH element abundance distributions of AGB stars should be similar to that of the scaled solar s-main component. As a conclusion, the heavy element abundance pattern of the solar s-main component is a typical one and can be used as a standard in the investigation of heavy element abundances in single star.
High-spin states in 169Re were studied and resulted in the identification of a strongly coupled band based on the 9/2－ Nilsson state and a decoupled band built on the h9/2 intruder proton orbital (nominally 1/2－). The cranked shell nodel calculations present configuration-dependent deformations that can explain the different band crossing frecpiencies. The experimental 9/2－ band in Re shows the largest signature splitting at low spin among the known odd mass Re isotopes. After the alignment of a pair of the i13/2 neutrons, the phase of the splitting is inverted with a significantly reduced amplitude. Additionally, a three-quasipariticle band was observed and assigned to be built likely on the π9/2－⊙AE configuration.
The dependence of He and intermediate mass fragments (IMF) production rates in the reactions 55MeV/u 40Ar+58,64Ni on the isospin, impact parameter and primary excitation energy of the reaction system was studied by using the 4:v charged particle multidetector array system ( MUDAL) . For the mentioned two reaction systems, the measured He particle contribution in the total charged particle multiplicity increases with increasing the total charged particle multiplicity but for the contribution of IMFs in the total charged particle multiplicity increases with increasing the total charged particle multiplicity at lower total charged particle multiplicities, and latter on it drops down with further increaseg of the total charged particle multiplicities. The experimental results of these two reaction systems with the same nuclear charge indicate that the contributions of He and IMFs in the total charged particle multiplicities are obviously isospin dependent.
Using different ratioes of ρs to ρb , we have calculated the in-medium kaon and antikaon effective masses which are not only dependent on the nuclear vector density ρs but also on the scalar density ρs . Based on the Walecka model and in the relativistic mean field approximation, the relation between the two nuclear densities is also discussed and then the dependence of in-medium kaon and antikaon effective masses are improved.
Within the spin-dependent Brueckner-Hatree-Fock framework, the equation of state of the spin-polarized neutron matter has been investigated by adopting the realistic nucleon-nucleon interaction AV18 supplemented with a microscopic three-body force. The related physical quantities such as spin-symmetry energy, magnetic susceptibility and the Landau parameter G0 in spin channel, have been extracted. The three-body force effects have been studied and discussed with a special attention. It is shown that in the whole range of spin-polarization, the energy per particle of spin-polarized neutron matter fulfills a quadratic relation versus the spin-polarization parameter δ= (p-p )/p . The predicted spin-symmetry energy is positive in the density region up to ρ = 0.8fm-3 and increase monotonically as increasing density so that no any evidence is found for a spontaneous transition to a ferromagnetic state in neutron matter. The three-body force effect is to strongly increase the spin-symmetry energy and reduce the magnetic susceptibility at high densities, as a consequence , to make neutron matter become more stable against spin fluctuation. The obtained Landau parameter G0 and its density dependence may serve as a constraint on the spin-spin parts of the phenomenological Skyrme and Skyrme-like interactions .
The radial equation in its standard form, which can be solved by using the threepoint central difference method from central two points towards outside point by point, is reduced from Schrodinger equation or from the low energy approximation of Dirac equation. In this paper, a method for solving the radial equation of the bound state to get the binding energy and the radial wave function is given, and the binding energies of the ground state (GS) of several Ξ－ hypernuclei are calculated.
A semiempirical expression for the excitation function for (n,p) reaction were obtained on the basis of evaporation and exciton models with the energies range up to 20 MeV. Within the nuclide of 12≤A≤209, the adjusted parameter of the semiempirical expression was investigated, the parameter is dependent on the atomic number, mass number of the target nuclide, and the energy of the incident neutron. The predictions of the excitation function for (n,p) reaction are good agreement with the experimental data.
This paper describes the structure of the water tank of the Cerenkov calorimeter for neutrino detection. Based on the GEANT4 Monte Carlo package, the detailed optical processes for the Cerenkov light in the water tank are simulated . Results show that the design of the water tank is appropriate and they are useful for the detector optimization.
Plenty of experimental studies on the effects of performances of RFC operated with different gas mixtures have been carried out. The curves of signal amplitude, multi-counting, efficiency, single counting rate and dark current versus the high voltage were measured using cosmic rays, based on the gas mixtures of Argon, Iso-butane and F134A with different fractions. The measured results show the plateau length could be prolonged, the detection efficiency increased and the dark current decreased in the plateau region of RFC, if the Argon ratio was reduced and the ratios of Iso-butane and F134A increased correspondingly, at the cost of increasing the working high voltage.
A low pressure two dimensional position sensitive multiwire proportional chamber (LPMWPC) has been developed for measurements of low Z charged particles from the nuclear reaction induced by radioactive ion beam. The detector has a 50mm×50mm sensitive area and consists of three grids (X-position cathode Y-position) . The position is determined through delay line readout mode. The detector has good beam transparency and is also adequate to be used in vacuum . The LPMWPC has been tested at a pressure of 800Pa of n-heptane and a bias Voltage of 720V. The test results indicate that the position resolution of the chamber is Δx = Δy = 1mm and detection efficiency is larger than 80% for the low Z particle at intermediate energies. This kind of chamber has be used to determine the direction of the incident particle.
RF Pulse stretcher is an antiphrasis of RF pulse compressor. It is used to convert short high power RF pulse to long low power RF pulse. The Power Extraction and Transfer Structure (PETS) in CTFⅡ(Compact Linear Collider Test Facility Phase two) can provide 280MW 16ns pulse. It is desirable to use it to get longer pulse to study the pulse length dependence of maximum achievable surface gradient in one of the 30GHz copper accelerating structures. The 30GHz RF pulse stretcher was designed, manufactured, tuned, installed and successfully operated in CTFⅡ .
This paper presents the development of a 1kW S-Band RF Solid State Amplifier (SSA) for the BEPC Linac. IkW peak power with a pulse width of 2-10μs under low voltage operation is achieved by combining eight 160W high power Solid State Amplifiers using a low-loss(0.3dB) combiner. Other key performance parameters are: RF phase drift during pulse ≤±1 degree, RF rise time/fall time is 88ns/40ns, RF pulse flatness is 0.7 % , and RF power stability is 0.1dB.
The structural parameters in a semicrystalline polymer three-phase system have been evaluated using small angle X-ray scattering technique. The crystallinity and the lamellar thickness are not consistent with those in two-phase system. The analysis of some semicrystalline polymer samples indicates that the Bragg long period approaches to the sum of the correlation function long period and the thickness of the transition layer. It is also consistent with the conclusion that the interphase layers exist in semicrystalline polymers.
Longgang volcanic swarm belongs to one of volcanic areas which have been active since modern times. In view of multiple eruptions during histories, it is very important to determine age of every eruption for evaluating volcanic hazards. The alkaline basalt samples taken from Dayizishan and Diaoshuihu are analyzed by U-series component method, after magnetic separation. The ages of the two samples are (71±9)ka, (106±13)ka before presence, respectively. These data indicate that there exist intensively eruptive activities during late Pleistocene.
New measurements of R value in the energy range of 2-5GeV were completed by Beijing Spectrometer Collaboration (BES) at Beijing Electron Positron Collider (BEPC) and caused a strong impact on the search for new physics and Higgs particle in the international high energy physics community. The newest progress and future prospect for the experimental measurement of R value and some relative physics, such as the anomalous magnetic moment of muon αμ, the running QED coupling constant a (Mz2), the muonium hyperfine splitting (HFS) VHFS, and the determination of strong coupling constant αs and heavy quark masses, in both experimental and theoretical aspects, were introduced.
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