1996 Vol. 20, No. 7
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The method for particle identification using dE/dx in the BES large cylindrical drift chamber has been briefly described. The performance of the particle identification using dE/dx has been given. After applying systematic effect corrections and absolute energy calibration to the dE/dx raw data, the dE/dx energy rssolution of 7.5% has been obtained for minimum ionization particles (0.4-0.5GeV /c π) in a case corresponding to more than 30 dE/dx samples per track.This results in 3σK/π separation for momentum up to 0.65GeV /c and 3σe /π separation in a momentum range of 0.2≤p≤4GeV/c.
The threefold fragmentation in hot nuclei with medium mass number has been measured in 25MeV/u 40Ar+115In, 103Rh,93Nb reactions. The fragments emitted at angles larger than 32°were detected by ten parallel plate position-sensitive avalanche counters (PPAC) with area of 25×20cm2 for each. The quantities of total kinetic energy (TKE), the yield ratio of threefold over fission P32, the distributions of fragment mass, velocity and relative angle etc. were obtained. From the mass ratio of the fragment, a simple empirical expression could be deduced. By analyzing their angular correlation function with a simple space-time model, the time difference between the two scission points in threefold process for Ar+In system were derived. A systematics of P32 versus Z2/A for hot nuclei was observed.
Particle-particle correlation function and emission time of light particles detected in coincidence with fission fragments have been measured for the 40Ar+197Au collisions at E/A=25MeV. A mean emission time of 200-300fm/c suggests that the prescission emission of light particles dominates. The emission time changes slightly for particles of in-plane emission and out-of-plane emission, but varies dramatically with the energy of particles. It decreases from about 300fm/c for mid-rapidity particles to about 30-100fm/c for projectile-like particles.
Numerical reasults are presented for the photoproduction of twojets via resolved quasi-real photons at HERA in next-to-leading order(NLO) QCD. It shows that the NLO contribution is about a factor of 0.5 to 1 of the LO contribution. This may provide an explanation to the ZEUS results: "the LO QCD results is below data a factor of 1.5 to 2". When the invariant mass of two-jet system is not too large, say less than 30GeV, the cross section is dominated by the photon gluon distributionin.This may be used to measure the gluon structure of photon. When the invariant mass of two-jet system is larger, say than 30GeV, the cross section is dominated by the photon quark distributionin. This may be used to measure the quark structure of photon.
The one-loop contributions of pseudo Goldstone bosons to the flavorchanging decay Z→bs(bs) in the one generation technicolor models(OGTM) and the technicolor model with a massless scalar doublet are calculated. We find that the contributions can strongly cnhance the branching ratio B(Z→bs+bs). So, a more stringent limit on the parameters h. λ can be obtained.
The relations between L± operators and the generators in the quantum enveloping algebras are studied.The L±operators for UqAN and UqG2 algebras are explicitly expressed by the generators as examples.
In this paper, one-dimensional projection of two-dimensional self-affine phase space which has three kinds self-affine fractal are analytically studied. A one-dimensional projection α-model corresponding to different fractal is obtained.Using this model, the one-dimensional 2, 3 moments of normalized probability and correlation moments are calculated analytically. The results are cosistent with the experimental results. The dependence of the moments of normalized probability and correlation moments on fractal forms of phase space is obtained simultaneously.
Assuming that both the soft component and the hard component obey KNO scaling in the multiplicity distribution of high energy hadron-hadron collision but their respective parameters are different, the multiplicity distriblltion of the charged particle in pp collision at √S =1800GeV is calculated. We find that <n>=47.0 which can be tested. by experiments.
Properties of negative-parity πh11/2 bands in odd-A 117—125Cs nuclei are investigated by using the triaxial rotor plus particle model with the variable moment of inertia (VMI) of the core. The good agreement between theory and experiment shows that this model can be used to describe the properties of odd-A transitional nuclei with soft core.
The fusion-fragmentation model is used to analysis the ALADIN data of the multifragmentation of projectile remnant in reaction of 600 MeV/u Au bombarding Cu target. Since the fusion-fragmentation model includes both the dynamical formation and the statistical disassembly of hot nucleus, all the ALADIN data can be reproduced very well if the model parameter concerning excitation energy is somewhat adjusted.
By means of the thermo field dynamics, the change of nucleon effective mass in nuclear matter with density is discussed. Based on the x-rescaling model, the ratios R(x) of the structure function for different nuclei are calculated from the shift of nucleon mass in nuclear matter. Our result is in agreement with the experiment.The relation between Brown-Rho conjecture and EMC effeCt is explored.
In this paper, The N,Δ spectra are recalculated in the N≤6 configuration space,and the effects of high configuration space mixing are emphasized. The calculations converge and show that under a right form of confinement potential, the results for some spectra can be improved definitely with the inclusion of the N≤6 configuration space.
This paper describes the measurement principle and methods of RF superconducting Nb cavity according to the energy conservation. It suggests that there are differences in measuring methods between high power and low power cavities due to electron field emission(FE) existing in superconducting Nb cavities. A set of exact formulae and equations on physics parameters of superconducting Nb cavities has been systematically derived, such as quality factor Q0 without loads, the maximum of the surface electrical field intensity Esp, the maximum of the accelerating gradient Eacc, etc.
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