2002 Vol. 26, No. S1
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Our studies on the meson Bc are briefly reviewed. The decays of the meson Bc to a P-wave charmonium χc or hc are reported comparatively precisely because they are fresh results obtained recently.
The problem of chirally enhanced corrections for B decays into two light pseudos- calars in QCD factorization scheme is discussed. We find that the infrared divergences of the vertex corrections cancel only if the twist-3 wave functions are symmetric. In that case chirally enhanced corrections can be included consistently. The divergences appeared in the hard spectator scattering are also discussed briefly.
We study the production of the neutral top-pion predicted by topcolor-assisted Technicolor (TC2) theory in high energy e+e－ collider (LC) experiments. Our results show that the production cross section is very large and the signatures of πt0 can be detected in LC experiments via the processes e+e－→tc, e+e－→γtc and e+e－→Ztc.
Based on factorization theorem, we develop a theory called perturbative QCD approach to deal with non-leptonic two body B decays. We apply the Sudakov resummation to transverse momentum distribution of quarks. Using the light cone wave function, we calculate many decays of B meson. Our result of branching ratios agrees with the B factory experiment. Our prediction of CP asymmetry will be tested soon by experiments.
In this talk we briefly summarise our recent study (hep-ph/0007165) on searching for top squark at hadron colliders. The light top-squark (stop) if produced in hadron colliders in the form of the pair and decaying through the likely decay chain followed by , can mimic closely a top quark event when the mass of the stop is close to that of the top quark. Because of the much lower production rate, the stop event can be buried under the top quark event sample. In order to uncover the stop event, specific selection cuts need to be applied. Through Monte Carlo simulation with suitable kinematic cuts, we found that such stop event can be extracted from the top quark sample and detected by the top counting experiments in the upcoming upgraded Tevatron and LHC. However, because of the small statistics of the Run 1 of the Tevatron, the stop signal remains hidden at Run 1.
Motivated by recent CELO measurements and the progress of the theory of B decays, B→PV(P=π, K; V= K*,ρ,ω) decay modes are studied in the framework of QCD factorization. All the measured branching ratios are well accommodated in the reasonable parameter space and predictions for other decay modes are well below the experimental upper limits.
With an upgraded Beijing Spectrometer (BESII) at the Beijing Electron Positron Collider (BEPC), the BES collaboration finished two runs of R scan in the energy region from 2 to 5 GeV. R values for all 6+85 scanned energy points are presented, with an average undertainty of 6.6%,which represents an improvement by a factor of 2—3. These measurements make an important contribution to the precision determination of a(M2Z), the QED coupling constant evaluated at the Z pole. The results also contribute to the interpretation of muon g－2 measurement.
The supersymmetric sinh-Gordon model on a half-line with integrable boundary conditions is considered perturbatively to verify conjectured exact reflection factors to one loop order. Propagators for the boson and fermion fields restricted to a half-line contain several novel features and are developed as prerequisites for the calculations.
The quark exchange effect in the two baryon systems is studied. The results show that the quark effect becomes obvious only when the two baryon clusters are closed together, and it also depends the spin-flavor quantum number of the system. The expectation value of the permutation operator of the spin-flavor-color space is a very important quantity to measure the quark exchange effect.some binding energies of the dibaryons are calculated, which are cardinal in examining the quark effect.
Based on an isospin-dependent quantum molecular dynamics model,the role of the momentum dependent interaction(MDI) on the isopspin effects of fragmentations and dissipations in the intermediate energy heavy ion collisions are studied.It was found that the values of the nuclear stopping,the number of nucleon emissions and the multiplicity of the intermediate mass fragments with MDI are larger than those without MDI. Especially the differences between those quantities with isospin dependent in-medium nucleon-nucleon cross section and those without the isospin independent in-medium nucleon-nucleon cross section (i.e., the isospin effect of in-medium nucleon-nucleon cross section) under MDI are also larger than those differences without MDI in the relative high energy region, which means that the momentum dependent interaction enhances the sensitivities of those quantities to the isospin effect of in-medium nucleon-nucleon cross section at the relative high beam energies.
We discuss the symmetry relations among Green’s functions, i.e., the transverse and the normal (longitudinal) Ward-Takahashi relations. Solving consistently this set of WT relations, we obtain the nonperturbative fermion-boson vertex function, which leads to consistently truncated and closed Dyson-Schwinger equations for the propagators up to the quantum anomaly, thus providing the consistent nonperturbative approach of studying hadronic physics.
The kaon flow in heavy-ion collisions at intermediate energy is studied in the QMD model. The calculated results show that the experimental data are only consistent with the ones that include the kaon mean-field potential from the chiral Lagrangian.This indicates that the sideflow pattern of positive charged kaons is an useful probe of the kaon potential in nuclear medium.
The data of multi-particle production in 158 A GeV Pb+Pb collisions and s=130 A GeV Au+Au collisions are analyzed by two-source statistical model. It is found that in 158 A GeV Pb+Pb collisions the source is composed of a hot, small inner part and a large, cool outer part. The outer part characterizes the projectile-like and target-like, and the inner part characterizes the central reaction zone. In s=130 A GeV Au+Au collisions, there is a much hotter and larger inner source. The temperature is at least 15MeV higher than that in the inner source in 158 A GeV Pb+Pb collisions. The volume is at least two times of that in the later collision. The reason is that the s=130 A GeV Au+Au collision has large rapidity region [－4.9,4.9], while the experimental data are taken from a small pseudo-rapidity region, |η|<0.5 in which the particles are uniformly distributed as a single source. For a source formed with uniformly-distributed particles, both the single-source statistical model and the two-source statistical model are available, while for a source formed with non-uniformly-distributed particles, only the two-source statistical model is available. The RHIC can provide a hot and large inner source that may be formed in the early stage of hadronization from QGP and may have important physical content behind. We suggest to make synchronous measurement in the outer region, e.g. 3<|y|<4, so as to make comparison.
A New relativistic and singularity free baryon form factor for crossing channel study is proposed. This new form factor satisfies the crossing symmetry law of strongly interacting particle scattering amplitudes transfered from t-channel to s-channel or the inverse.
Theoretical Formalism for N* study via J/ψ→ppω decay process is given. By analyzing 58M J/ψ events collected at BES, possible existing lower-lying N* states can be explored.
A more rational scheme of time reversal transformation is provided in the paper. In the new scheme, the transition probabilities are invariable under time reversal in the electromagnetic interaction processes of pure sates. But the evolutions of macro-processes can’t keep unchanged under time reversal owing to the interference effects of probability amplitudes between non-pure state processes. In this way, the so-called reversibility paradox, i.e. time reversal is reversible in micro-processes but irreversible in the macro-processes, can eliminated completely.
The origin and signature of ultra high-energy cosmic rays are still somewhat mysterious. In this paper, we present an effective acceleration mechanism for such ultra high-energy events based on supermassive stellar objects with saturation of magnetic monopoles of ‘t Hooft-Polyakov type in the universe. Catalyzed by magnetic monopoles, nucleons may decay to energetic charged particles and radiation, and can travel to great distance from their source because of the absence of horizon and central singularity of these supermassive stellar objects, due to Rubakov-Callan effect. These rapid rotating collapsed objects have radial magnetic fields in the local co-rotating frame. The induced electromagnetic fields in the rest frame are quite different from that of the usual dipole fields. The strength of such induced fields are very strong and decrease with the square of distance. As a result, the energetic charged particles released during nucleon decay may be further accelerated for a rather long period and the resulting energy of such cosmic rays may be far beyond 1021 eV.
Experimental equipments for spectroscopic studies of highly ionized atoms by means of beam-foil technique has been set up at the terminal voltage 13MV tandem accelerator in China Institute of Atomic Energy (CIAE), and measurements of spectra have been carried out for elements S,Br,Ge,Ni,Cu and Ti.
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