1993 Vol. 17, No. 10
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The application of dE/dx method for e/π identification to the measurement of the mass of τ heavy lepton by Beijing Spectrometer(BES) operated at Beijing Electron Positron Collider (BEPC) is described.With this method,the efficiency of selecting the eμ events from decaying from τ+τ－ is increased by a factor of more than 3 compared with using traditional e/π identification by electromagnetic shower measurement.It results in not only that the loss of the eμ events in off-line selection is reduced,but also that the amount of the time needed to run the BES/BEPC for data collection and computer CPU time for data off-line processing is reduced by ～75% for selecting the same number of τ+τ－ events.
The formation cross sections of iodine isotopes from the intereamtion of 47MeV/u 12C with 133Cs have been measured radio-chemically.The isotopic yield distribution curve has been costructed.It is found that the peak of the curve is in the vicinity of 124I and the curve has a FWHM of 6.5 mass units.The mass loss of the most probable product is 9.2 mass units.The cross section of 131I which is produced by striping of two protons from the target nuclei is 0.47—0.87mb.The activities of 132I was not observed.
The motion of charged particle beams in a beam optical system can be described by means of the transformations of the phase space contours and particle distribution functions.These transformations compose several groups—the beam transport group (BT group),contour preserving group (CP group),distribution preserving group (DP group) and so on.The principal problems of beam optics can be reduced to two:the determination of the eigen phase space contour of a transformation and the determination of the transformation can preserve the shape of a phase space contour.
Up to now,no model can reproduce the baryon rates measured by ARGUS collaboration in direct Υ decays,except a qualitative explanation given by Lund model.Instead of the string fragmentation model in Lund picture,we apply the quark production rule and combination rule for qq fragmentation to the colour string for Υ→3g.The results agree well with ARGUS data without extra parameter.
In order to reduce the influence of the geometrical acceptance and improve the precision we introduce the pseudoscalar meson angular distribution of the moment HJ(jm,θ).It is more sensitive than the usual projective pseudoscalar meson angular distribution WJ(θ) for determining that the spin of the ξ(2220) is 2 or 4.We also give some moments which are needed for the moment analysis and some relations of moments to represent the helicity amplitude ratios xJ and yJ directly.
In this paper the general forms of the polarization tensors of Z→3γ decay and γ→γ scattering at one-loop level are discussed.The constrained equations for the tensors are deduced from the S3 symmetry and gauge invariance.We give the procedures of our method and compare the results of W-boson-loop with those of fermion-loop.
Through boson expansion and the modified Jancovici-Schiff substitution a 1-to-1 corre-spondence between fermion collective pair space and the interacting boson space is obtained.The boson mappings of fermion operators are uniquely determined and the IBM Hamiltonian takes a non-Hermitian form.The calculation of fermion matrix elements and spurious problem are also discussed.
A method of n-particle transverse correlation function for the study of collective flow is proposed,which extends both the study of n-particle azimuthal correlations and the estimation of collectivity to the study including the magnitudes as well as the azimuthal angles for all the n-particle transverse momentum vectors.This method is more sensitive to the collectivity of collective flow than the method based on multi-particle azimuthal correlations.Using the new method,n-particle transverse correlations are analyzed for collisions of 1.2A GeV Ar+KC1 in the Bevalac streamer chamber,and the results have been compared with a Monte-Carlo simulation,which show that the collectivity for this experiment is between 85% and 95%.
The parmeterized full amplitudes for proton 4He scattering at energies 200,350,500,560,800,1030,1240,and 1730MeV are obtained.These amplitudes are useful as input for studing the α-particle structure of nuclei by means of intermediate energy proton.
The high energy α-particle elastic scattering on 4He is studied applying the Glauber formalism.The results show that the theory provides a satisfactory description of the data in the middle momentum transfer range.
In this work the cross sections and angular distributions for pp→π+π－ and K+K－ reactions are calculated on the basis of the 3S1 model by adopting relativistic transition potentials and quark (antiquark)spinor.
The relation between average transverse momentum and multiplicity in hadron-hadron Collisions is calculated using the Three Fire Ball Model.Starting from the change of contribution from the two side-fireballs,the raising of slope of average transverse momentum versus multiplicity as the energy increases is successfully explained.
The dynamics of the N-Y system with S=－1 is re-solved,and the spurious resonances in the former calculation are removed.By using the double Fourier transformation,the GCM kernels are transformed into RGM kernels,and then,the effective local N-Y potentials with S=－1 is calculated.It is shown that these potentials are similar to that of Yamamoto's obtained by using the OBE model with phenomenological hard cores.With these potentials,the phase shifts and cross sections of the system can be re-produced.
In order to take the influence of the average distribution of particles into account in the intermittent behavior,the weighted distribution is proposed.The weight factors are determined and calculated by the average distribution of particles.The calculations show that the ln
Briefly described are the calculation methods of the multipolarity mixing ratio δ,the internal conversion coefficients αK,αL,αM,and αN+O of K,L,M,N and O shell,and the total internal conversion coefficient α for a γ transition from measured internal conversion coefficient for one of shells.
New neutron-rich heavy isotope 237Th was produced in the 238U(n,2p)237Th reaction by 14MeV neutron irradiation of (NH4)2U2O7 powder and separated by radiochemical methods.The new activity was first identified by following the time sequence spectra of the γ-rays of its daughter 237pa.A radioactive series decay analyzing program was applied resulting in the halflife of 5.0±0.9min for 237Th.In addition,a new 35.1±0.3keV γ-ray with T1/2=5.0±1.1min was found and assigned to 237Th.
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