2000 Vol. 24, No. 5
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Two new methods are introduced for the first time at BES to measure the integrated luminosity from events in large angle produced by QED dimuon and two-gamma production processes. With these methods,the integrated luminosities of the 6 energy points at 2.6,3.2,3.4,3.55,4.6 and 5.0 GeV scanned for the measurement of R are determined. The measured integrated luminosities are consistent with that determined using large angle Bhabha events.
The Effective Chiral Lagrangian (ECL) for the Pseudoscaler Goldstone Bosons is derived from QCD without making approximations. The coefficients up to p4 order in the ECL are expressed in terms of certain Green's function in QCD.
In this paper,the nonperturbative corrections to the one-gluon exchange potentential is studied. The results show that it is essential to adopt covariant gauges for the QCD vacuum gluon fields in order to obtain a gauge-invariant nonperturbative corrections.The new forms of the nonperturbative corrections to the one-gluon exchange potential are presented.
By a different way, we particularized the action of the diffeomorphism constraint (D-constraint) on the abstract wave function in the extended loop representation to the action in the loop representation. Using the two-point propagator of Chern-Simons theory as the basic blocks of quantum gravity states, we constructed the extended knot invariant gravity states (*φG)n that which satisfied with the homogeneous D-constraint. For the states of n=1,2, we demonstrated a detailed proof, To the states of n>2, we gave a general identification.
The radiative correction of self-energy of an electron moving with momentum p and emitting-absorbing the virtual photon is calculated by the noncovariant quantum perturbation theory to have the form being b2p4. After adding modifications arising from the vacuum polarization and finite nucleus size,we find the Lamb shift (LS) of 2S1/2-2P1/2 states in Hydrogen atom being 1056.522 MHz,smaller than the experimental value 1057.845 MHz by 0.13%. Taking the relativistic modification by Dirac equation into account,the energy differences of 4D5/24S1/2 states, the so-called Hyper LS and absolute LS of 1S state in Hydrogen are also calculated with maximum discrepancy up to 6.7%. The reasons are analyzed.For dealing with the divergence,we propose a simple but effective regularization renormalization method,showing that we have to reconfirm the reduced mass first before bringing a finite and fixed modification to it via radiative corrections.
The high spin states of 143Nd have been studied in 130Te(18O,5n) reaction at a beam energy of 80MeV. Based on delayed γ-γ coincidence,γ ray angular distribution,and γ ray linear polarization measurements,a high-spin isomer in 143Nd was identified for the first time with a measured half-life of (35±8) ns and Jπ=49/2+. The characteristic of the high-spin isomer in 143Nd was stressed with a deformed independent particle model. The model assigned a stretched configuration of [ν(f7/2h9/2i13/2)π(h2 11/2)] to the 49/2+ isomer in 143Nd As the isomers in the N=83 heavier isotones,the occurrence of the 49/2+ isomer in 143Nd can be interpreted to be caused by the sudden change in nuclear shape along the yrast line.
A complex straggling algorithm is presented to calculate depth dose distribution of intermediate energy heavy-ion beam. Relative dose Bragg curves of carbon and oxygen ion beams with intermediate energies were computed according to the algorithm above. Comparisons between the relative doses predicted and measured were taken up. The Bragg curves predicted by the complex straggling algorithm show a good agreement with the experimental data. So the reasonableness of this algorithm and its reliability for calculating depth doses were verified. Hence the principle and method to deduce the depth dose distribution of therapeutic beam was integrated after this algorithm was developed.
The level schemes with high spin states in neutron-rich145,147La nuclei have been established from the study of prompt γ-rays emitted in the spontaneous fission of 252Cf. Many new levels and γ transitions have been idenfified. The highest spin states in both nuclei were expanded up to(41/2+)and (43/2－)respectively. The alternating parity band structures and strong E1 transitions between negative-and positive-parity bands show strong octupole deformation. The collective bands observed in 145La give evidence for co-existence and competition between symmetric and asymmetric shapes. From the systematic comparison with the neighboring isotones, the s=+i bands in both nuclei most probably originate from the single particle πh11/2 orbital coupling with the neighboring even-even cores, respectively. Band crossing of the πh11/2 bands was found aroundω≈0.26—0.30MeV and these backbends are related to the alignment of two i13/2 neutrons from cranked shell model calculations.
We have used the isospin dependent quantum molecular dynamics to investigate the probable observable for probing isospin dependent nucleon-nucleon cross section in multifragmentation process of intermediate energy heavy ion collisions. The calculation results show that the correlation between the intermediate mass fragment multiplicity Nimf and the total number of charged particles Nc is a sensitive observable for probing in medium isospin dependent nucleon-nucleon cross section in the chosen energy region. Because we apply the reversible reaction effect of heavy mass projectile on light mass target in the chosen energy region, which result in more intermediate mass products emitted towards forward angles, it is convenient to extract in medium isospin dependent nucleon-nucleon cross sections by combining theory simulations and experimental observations under the conditions of limited detectors.
Radiation hardness of a particle detector, double metal contact GaAs semiconductors has been investigated in 14 MeV neutron exposure. The leak current, the charge collection efficiency and the spectrum of MIPs are measured after 1012n/cm2 dose. The results are compared with 60Co 1.25MeV γ photons radiation. The mechanism of radiation damage and the effect on time performances of GaAs detectors are discussed. A hypothesis of the active layer distribution of the GaAs detectors based on experiment data is given. The computation agrees with test results.
The process of ion generation and trapping, trapped ion′s influence on the beam, the DC clearing electrodes mechanism and clearing effect were investigated in HLS ring. Theoretical and experimental basis was provided for the efficient performance of the light source.
The interpretation of new particle search results involves a confidence level calculation on either the discovery hypothesis or the background-only(“null”)hypothesis. A typical approach uses toy Monte Carlo experiments to build an expected experiment estimator distribution against which an observed experiment's estimator may be compared. In this note, a new approach is presented which calculates analytically the experiment estimator distribution via a Fourier transform, using the likelihood ratio as an ordering estimator. The analytic approach enjoys an enormous speed advantage over the toy Monte Carlo method, making it possible to quickly and precisely calculate confidence level results.
Assuming the spin parity JPC of the ξ(2230) is 2++, the mixing of the neutral tensor mesons f2(1270), f′2(1525) and the glueball candidate ξ(2230) are investigated. The glueball quarkonia content of the f2(1270),f′2(1525) and ξ(2230) is obtained from a detailed fit to the available decay data of these three states. Several predictions for the decays of the ξ(2230) are presented.
We studied the medium effects on ρ meson mass by taking account of the vacuum effects with the effective Lagrangian approach. We show that the ρ meson mass decreases with both temperature and chemical potential. Then we checked the validity of Brown-Rho scaling law in different conditions.
Based on thermodynamic relations, the initial values of the quark gluon system from relativistic nucleus-nucleus collisions are obtained. Using these initial values we have studied the dilepton production on the basis of the relativistic hydrodynamic model, and found that with increasing incident energy a characteristic plateau indicating the formation of the quark-gluon plasma appears in the total yield, which may be tested in future experiments in CERN and Brookhaven.
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