1999 Vol. 23, No. 1
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Using hadronic events sample collected around 3.55 GeV with Beijing Spectrometer (BES) at Beijing Electron Positron Collider (BEPC) and the published data, we studied distributions characterizing the hadronic events produced from the e+e－ annihilation and the most sensitive parameters in the LUND model and found that the characterizing distributions of the hadronic events of the BEPC data agree well with that predicted by the LUND model with tuned parameters.
The structure function of τ→π±2π0v is measured by model independent method. The result is compared with Kuhn-Santamaria model, Isgur-Morningstar-Reader model and Feindt model. Good consistency between data and the three models is shown within the experimental error range. The comparison with the structure function of τ→3π±v measured by OPAL Collaboration also shows there is no obvious difference within 0.5
The production mechanism of ring-like events has been investigated by using the data of pseudorapidity distribution of charged particles produced in pp collisions at 400GeV/c. The results show that the model of coherent gluon emission within a finite region of space-time is a possible production mechanism of ring-like events, but certainly not dominant.
A search for 10Tev γ-ray continuous emission from 58 Supernova Remnants which include Crab Nebula and 25 Active Galactic Nuclei which include Mrk421 and Mrk501 with the data of Tibet I air shower array from 1990 June to 1993 October is executed by the method of equi-zenith angle to estimate the bacdground events. The significance of DC excess is calculated according to the Li and Ma prescription. No significant DC excess is observed from these candidates. The integral distribution of significances is checked by the Kolmogorov-Smirnov test which examines the divergence from a standard normal distribution. No significant deviation is found. Flux upper limit is obtained for each source at 95% C.L.
Data taken with ACT2 and ACT3 betWeen 1995 and 1997 are used to search for 0.1 second bursts of TeV gamma Rays from evaporating Primordial Black Holes (PBHs). There is no evidence for such bursts in the dataset. Using the result,the upper limit of 3 ×108pc－3yr－1 on the rate-density of evaporating PBHs is set in the vicinity of the solar system at a 99% confidence level.
Interaction time ～4.3×10－21s of the dissipative products in the collision 27Al+27Al is extracted from the measurement of excitation functions by using the developed Ericson statistical theory.
The multiparticle Bose-Einstein correlations for formation of quark-gloun plasma (QGP) in high energy heavy ion collisions are analysed. Investigating the average correlation intensities of multipions as a function of pion multiplicity indicats that they have obvious enhancements in the high multiplicity region. This signature can be used to detect the existence of QGP in rare high-pion-multiplicity events sensitively in high energy heavy ion collisions.
Splitting of a hot nucleus into three comparable pieces in the 40Ar+159Tb reaction at 30MeV/u was measured. For the splitting there are two modes: one is a successive binary process, such as sequential fission or a cascade fission, another is a prompt threefold fragmentation (3F). The paper presents the identification between the two modes of the threefold fragmentation by the experimental results, such as the mass distribution of the fragments, the orientation of the fragmentation plane, etc.. In the two modes, the prompt one with collective deformation is emphasized.Furthermore fitting the mass distribution and finding a scaling law about the most-probable mass ratio in the 3F are given. In addition, the orientation of the fragmentation plane could also be used to measure the impact parameters, there for to distinguish 3F events associated with cental collision from the sequential fission after a quasi-elastic scattering or deep-inelastic collision.
Within the O(6) limit of s-d IBM1, the effective three-body potential between the interactions of d-bosons is introduced with the consideration of octupole states, which are produced by a f-boson plus (N-1) s-d-bosons. Then the analytic expressions of positive and negative parity energy spectrum formula are obtained. Also the energy spectra of even-even nuclei 118Xe and 120Xe are calculated. Good fits with the experimental data are obtained, and Staggering phenomena is quantitatively analyzed with Staggering index formula.
In this paper, we study the behavior of high intense beams in the periodic filed by using thin lens approximation for the space-charge forces. The main chaotic behavior and halo formation can be shown through simple calculations. Meanwhile, it is very easy for us to study the behavior of high intense beams with more complicated realistic distributions than K-V distribution by this approximation, which is rather difficult by other ways.
The operation of colliders are often limited by the nonlinear effects of beam-beam interaction, especially for the strong current machines, such as BEPCⅡ (BEPC multibunch collision scheme). The beam-beam interaction in BEPCⅡ is very complicated. The bunch will collide with another bunch head on at the south interaction point and interact with another bunches due to the long distance beam-beam force at other eleven points along the ring. This paper has studied the tune shift and tune spread due to the long distance beam-beam interaction effects. The long distance beam-beam effects of BEPCⅡ injection mode have also been studied.
We consider the mass dependence on the mixing between a pure glueball and a normal qq meson in QCD sum rules. In the normal correlation functions, the gluonic current and qq current are assumed to couple to both glueball and qq states. By using the low-energy theorem, we construct a sum rule for the mixing correlation function (the gluonic current and the qq current). Through these relationships and based on the assumption of two states (one glueball and one qq meson) dominance, we find the masses of the 0++ lowest-lying glueball and qq meson.
The oscillatory behavior of H moments obtained from the experimental data in pp and pp collisions is studied in the Three-Fireball Model (TFM). It is found that similar to that in the negtive binomial distribution (NBD), the H moment in the full TFM distribution is a monotonic function of q, but oscillates when the distribution is truncated by a not too large value of ncut. This shows that H moment oscillation is not a special property of pQCD or NBD, but is common for many truncated multiplicity distributions.
A new nuclide 238Th has been produced via multinucleon transfer reaction induced by 60MeV/u 18O ion irradiation of natural uranium. The thorium was radiochemically separated from the mixture of uranium and its reaction products. The activity of thorium was measured by using a HPGe detector and a planar HPGe detector. The 238Th has been identified for the first time by measuring the growth and decay of the γ-rays from its daughter 238Pa. The half-life of 238Th was determined to be (9.4±2.0)min. In addition,a new (89.0±0.3)keV γ-ray with T1/2=(8.9±1.5)min was observed and assigned to 238Th decay based on the measurement of transition energy and half life.
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